Showing papers in "Journal of Plant Ecology in 2018"

Water availability drives gradients of tree diversity, structure and functional traits in the Atlantic-Cerrado-Caatinga transition, Brazil

Abstract: Aims Climate and soil are among the most important factors determining variation in tree communities, but their effects have not been thoroughly elucidated to date for many vegetation features. In this study, we evaluate how climate and soil gradients affect gradients of vegetation composition, species diversity and dominance, structure and functional traits (seed mass and wood density) using over 327 000 trees in 158 sites distributed along environmental gradients in the transitions among the Atlantic forest, Cerrado and Caatinga in Minas Gerais State (MG), Brazil (nearly 600 000 km 2). Methods Gradients in species, genus and family abundance in addition to basal area, stem density, species diversity (Fisher's alpha), dominance percentage, seed mass and wood density were correlated using multiple regressions with environmental variables, as summarized in four principal component analysis axes (two climatic - precipitation seasonality and temperature range - and two edaphic - soil fertility and soil moisture). Additionally, ordinary kriging maps were used to better illustrate the gradients. Important Findings Multiple regression models indicate that all variables but dominance percentage were affected by one or more of the environmental gradients, but the average R 2 was low (26.25%). Kriging maps reinforced the patterns observed in the regression models. Precipitation seasonality and soil moisture gradients were the most important gradients affecting vegetation features. This finding suggests that water availability is an important determinant of vegetation features in these vegetation transitions.

Constraints on treeline advance in a warming climate: a test of the reproduction limitation hypothesis

Abstract: Several mechanistic hypotheses have been developed to explain the existence of alpine treelines worldwide. The reproduction limitation hypothesis (RLH) postulates that reproductive processes such as seed production and dispersal are restricted in treeline environments, thereby limiting the establishment of new individuals in advance of extant treelines. Despite its popularity, no study has tested this hypothesis in a comprehensive fashion. In this experiment, we attempted to answer whether there are enough viable seeds being dispersed beyond treeline for sexually mediated treeline advance, and what the implications of climate change might be on these processes. We established 30 plots across two aspects (north vs. south) and three elevational habitats (forest, treeline and tundra) in a white spruce (Picea glauca) boreal forest-alpine tundra ecotone in southwest Yukon, Canada. In each plot, tree characteristics, seed production and predispersal damage were measured. Additionally, eight dispersal trays were positioned in each plot to measure seed rain, and germination trials with and without predation exclosures were constructed in a subset of plots to quantify dispersal and germination success. Results were highly variable both temporally and spatially. In 2014, a mast year, 69% of adult trees produced cones compared to 0.4% in the following year. Higher density of trees in forest plots compared to treeline and tundra resulted in greater seed production at lower elevations. Across all plots, 88% of seeds were damaged before dispersal or were not viable. Treeline plots had significantly greater predispersal damage. Seed rain was greater in south-facing plots than north-facing plots. Less than 2% of seeds produced on the landscape were dispersed into Tundra plots, located 50 m above treeline. There was a net movement of seeds from the north-facing slope to the south at our study site, likely due to prevailing winds during the dispersal period. Germination counts were more than double on north-facing slopes and one-third higher inside exclosures. Cumulatively, the results provide some evidence for the RLH. Collectively, the high amount of predispersal damage and non-viable seeds, variability associated with dispersal and significant seed predation can functionally influence treeline dynamics. These findings suggest that global treeline distribution models, which rely largely on temperature, may not be entirely accurate for predicting treeline advance—at least at finer temporal scales. Many stochastic factors need to align temporally for successful advance, which is likely to result in a lag of many decades between the period of temperature amelioration and an increased number of trees beyond extant treelines.

Understanding plant drought resistance in a Mediterranean coastal sand dune ecosystem: differences between native and exotic invasive species

Abstract: Mediterranean coastal dunes are habitats of great conservation interest, with a distinctive and rich flora. In the last century, Acacia spp., native from Australia, have been introduced in Portugal, with the objective of stabilizing sand dunes, and since have become dominant in numerous sand dune habitats. This invasion process led to the reduction of native plant species richness, changed soil characteristics and modified habitat’s microclimatic characteristics. The aim of this research was to typify and compare, in Mediterranean sand dune ecosystems, the ecophysiological responses to drought of Helichrysum italicum and Corema album, two native species, and Acacia longifolia, an exotic invasive species. We addressed the following specific objectives: (i) to compare water relations and water use efficiencies, (ii) to evaluate water stress, (iii) to assess water use strategies and water sources used by plants and (iv) to evaluate the morphological adaptations at leaf and phyllode level. In order to obtain an integrative view of ecophysiological patterns, water relations and performance measuring methods have been applied: predawn (ψPD) and midday (ψMD) water potential, chlorophyll a fluorescence, oxygen isotopic composition of xylem, rain and groundwater (δ¹⁸O) and leaf carbon isotopic discrimination (Δ¹³C). The leaf characteristics of the three species, as well as the histochemistry of non-glandular trichome cell walls, were also studied to identify morpho-traits related to drought resistance. The results support our initial hypothesis: although A. longifolia clearly possesses a degree of resistance to water stress, such ability is provided by a different water strategy, when compared to native species. Natives relied on morphological adaptations to restrict water loss, whereas the invasive species adjusted the water uptake as a way to balance their limited ability of restricting water loss. We corroborate that woody native species (i) have a conservative water-saving strategy and minor seasonal variations relative to invasive species, (ii) use enriched water sources during drought periods, indicating different water sources and root systems comparing with invasive species and (iii) present drought leaf morpho-functional adaptations related with limiting water loss. Comparing the physiological performance of invasive and native species can offer causal explanations for the relative success of alien plant invasions on sand dunes ecosystems.

Plant responses to simulated warming and drought: a comparative study of functional plasticity between congeneric mid and high elevation species

Abstract: Aims: Effects of climate change, especially changes in temperatures and precipitation patterns, are particularly pronounced in alpine regions. In response, plants may exhibit phenotypic plasticity in key functional traits allowing short-term adjustment to novel conditions. However, little is known about the degree of phenotypic plasticity of high elevation species relative to mid elevation congeners. Methods: We transplanted 14 herbaceous perennial species from high elevation into two common gardens (1050 and 2000 m.a.s.l.) in the Swiss Alps, and we examined plastic responses in key functional traits to changes in temperature and soil water availability. This design was replicated with 14 congeneric species from mid elevation to assess if the degree of phenotypic plasticity differs between mid and high elevation species. Survival was assessed across two growing seasons, while aboveground biomass and specific leaf area (SLA) were measured after the first growing season, and biomass allocation to belowground and reproductive structures after the second. Moreover, a phenotypic plasticity index was calculated for the functional traits to compare the degree of plasticity between mid and high elevation species. Important Findings: Aboveground biomass was higher in mid elevation species relative to high elevation congeners in all treatments, yet decreased for both with elevation and drought. Similarly, SLA decreased with elevation and drought. Root mass fraction (RMF) was generally higher in high elevation species, and decreased with drought at the lower site. Drought increased the allocation to reproductive structures, especially when plants were grown at their elevation of origin. Interestingly, no difference was found in the degree of phenotypic plasticity averaged across mid and high elevation species for any of the studied functional traits. These results indicate that phenotypic plasticity in the focal traits did not depend on the elevation of origin of the species. Plasticity was not related to environmental heterogeneity, nor constrained by selective pressures at high elevation. However, both species groups showed a remarkable capacity for short-term acclimation to a prospective climate through rapid adjustments in key functional traits.

Climatic correlates of phylogenetic relatedness of woody angiosperms in forest communities along a tropical elevational gradient in South America

Abstract: Aims This study assesses the relationship between phylogenetic relatedness of angiosperm tree species and climatic variables in local forests distributed along a tropical elevational gradient in South America. In particular, this paper addresses two questions: Is phylogenetic relatedness of plant species in communities related to temperature variables more strongly than to water variables for tropical elevational gradients? Is phylogenetic relatedness of plant species in communities driven by extreme climatic conditions (e.g. minimum temperature (MT) and water deficit) more strongly than by climatic seasonal variability (e.g. temperature seasonality and precipitation seasonality)? Methods I used a set of 34 angiosperm woody plant assemblages along an elevational gradient in the Andes within less than 5 degrees of the equator. Phylogenetic relatedness was quantified as net relatedness index (NRI) and nearest taxon index (NTI) and was related to major climatic variables. Correlation analysis and structure equation modeling approach were used to assess the relationships between phylogenetic relatedness and climatic variables. Important Findings Phylogenetic relatedness of angiosperm woody species in the local forest communities is more strongly associated with temperature‐related variables than with water‐related variables, is positively correlated with mean annual temperature (MAT) and MT, and is related with extreme cold temperature more strongly than with seasonal temperature variability. NTI was related with elevation, MAT and MT more strongly than was NRI. Niche convergence, rather than niche conservatism, has played a primary role in driving community assembly in local forests along the tropical elevational gradient examined. Negative correlations of phylogenetic relatedness with elevation and higher correlations of phylogenetic relatedness with elevation and temperature for NTI than for NRI indicate that evolution of cold tolerance at high elevations in tropical regions primarily occurred at recent (terminal) phylogenetic nodes widely distributed among major clades.

Does higher ploidy level increase the risk of invasion? A case study with two geo-cytotypes of Solidago gigantea Aiton (Asteraceae)

Abstract: Understanding the role of genetics in biological invasions has become an important aspect for modern plant ecology. Many studies suggest that increased ploidy level benefits the success of an invasive species, but the basis for this phenomenon is not fully understood. In its native, North American range, Solidago gigantea has three geo-cytotypes comprising di-, tetra- and hexaploid populations, while in Europe, where it is highly invasive, S. gigantea stands are composed primarily of tetraploid individuals. Our study investigates whether North American hexaploids can induce a greater risk of invasion, due to their higher performance in a non-native range, as compared to the existing tetraploids of that range. We performed greenhouse and common garden experiments along with microsatellite analyses to test whether differences in chromosome number and origin of the species mean superior fitness in the introduced range. Genetic diversity was significantly higher in the native hexaploid populations (AR = 6.04; Hₑ = 0.7794), rather than the non-native tetraploid populations (AR = 4.83; Hₑ = 0.6869). Furthermore, differentiation between geo-cytotypes was moderate (ρST = 0.1838), which was also confirmed by their clear segregation in principal component analysis and structure analyses, proving their different genetic structure. In contrast to genetic diversity, the non-native tetraploid geo-cytotype performed better in the common garden experiment, implying that higher genetic diversity does not always mean better success. Our results suggest that native hexaploids do not present a greater risk, as assessed by their performance in the introduced range, when compared to the non-native tetraploids, as was suggested by previous studies. Nevertheless, their introduction is still undesirable due to their different genetic structure, which, through hybridization, could give a new drive to the invasion of S. gigantea.

Variation of carbon and nitrogen stoichiometry along a chronosequence of natural temperate forest in northeastern China

Abstract: Aims Carbon (C) and nitrogen (N) stoichiometry contributes to understanding elemental compositions and coupled biogeochemical cycles in ecosystems. However, we know little about the temporal patterns of C:N stoichiometry during forest development. The goal of this study is to explore the temporal patterns of intraspecific and ecosystem components' variations in C:N stoichiometry and the scaling relationships between C and N at different successional stages. Methods Along forest development in a natural temperate forest, northeastern China, four age gradients were categorized into ca. 10‐, 30‐, 70‐ and 200‐year old, respectively, and three 20 m × 20 m plots were set up for each age class. Leaves, branches, fine roots and fresh litter of seven dominant species as well as mineral soil at depth of 0–10 cm were sampled. A Universal CHN Elemental Analyzer was used to determine the C and N concentrations in all samples. Important Findings Intraspecific leaf C, N and C:N ratios remained stable along forest development regardless of tree species; while C, N concentrations and C:N ratios changed significantly either in branches or in fine roots, and they varied with tree species except Populus davidiana (P < 0.05). For ecosystem components, we discovered that leaf C:N ratios remained stable when stand age was below ca. 70 years and dominant tree species were light‐demanding pioneers such as Betula platyphylla and Populus davidiana, while increased significantly at the age of ca. 200 years with Pinus koraiensis as the dominant species. C:N ratios in branches and fresh litter did not changed significantly along forest development stages. C concentrations scaled isometrically with respect to N concentrations in mineral soil but not in other ecosystem components. Our results indicate that, leaf has a higher intraspecific C:N stoichiometric stability compared to branch and fine root, whereas for ecosystem components, shifts in species composition mainly affect C:N ratios in leaves rather than other components. This study also demonstrated that C and N remain coupled in mineral soils but not in plant organs or fresh litter during forest development.

Arbuscular mycorrhizal fungi differ in affecting the flowering of a host plant under two soil phosphorus conditions

Abstract: Studies have showed that arbuscular mycorrhizal fungi (AMF) can greatly promote the growth of host plants, but how AMF affect flowering phenology of host plants is not well known. Here, we conducted a pot experiment to test whether life cycle and flowering phenology traits of host plant Medicago truncatula Gaertn can be altered by AMF under low and high soil phosphorus (P) levels. The experiment was conducted in a greenhouse at Zhejiang University in China (120°19′E, 30°26′N) and had a completely randomized design with two factors: AMF treatments and soil P levels. Six AMF species (Acaulospora scrobiculata, As; Gigaspora margarita, Gma; Funneliformis geosporum, Fg; Rhizophagus intraradices, Ri; Funneliformis mosseae, Fmo and Glomus tortuosum, Gt.) were used, and two soil P levels (24.0 and 5.7 mg kg⁻¹ Olsen-soluble P) were designed. The six AMF species were separately inoculated or in a mixture (Mix), and a non-AMF control (NAMF) was included. When plants began to flower, the number of flowers in each pot was recorded daily. During fruit ripening, the number of mature fruits was also recorded daily. After ~4 months, the biomass, biomass P content and AMF colonization of host plant were measured. Correlation between root colonization and first flowering time, or P content and first flowering time was analyzed. Under the low P level, first flowering time negatively correlated with root colonization and biomass P. Only host plants with AMF species As, Fg, Ri, or Mix were able to complete their life cycle within 112 days after sowing. And treatment with AMF species Fg, Gt, or As resulted in two periods of rapid flower production while other fungi treatments resulted in only one within 112 days after sowing. The cumulative number of flowers produced and biomass P content were highest with species Fg. Host biomass allocation significantly differed depending on the species of AMF. Under both soil P levels, the host plant tended to allocate more biomass to fruits in the Mix treatment than in the other treatments. These results indicated that the effects of AMF on host flowering phenology and biomass allocation differed depending on AMF species and soil P levels.

Effects of nitrogen addition on plant biomass and tissue elemental content in different degradation stages of temperate Steppe in northern China.

Abstract: Aims Grassland degradation has become a common problem worldwide. Several studies have analyzed the effects of nitrogen (N) addition on plant growth in grasslands, but few have considered its effects on plant growth in degraded grasslands. The aim of this study was to evaluate the effects of N addition on plant growth in grasslands with different levels of degradation in Inner Mongolia, China. Methods A 2-year field experiment was conducted to evaluate plant growth response to N addition in degraded grasslands on the Inner Mongolian Steppe. Grasslands with four levels of degradation were selected for N-addition treatments (0, 10, 20, 30, 40, 50 g N m−2 year−1). Important Findings Aboveground biomass was increased by N fertilization in degraded grasslands, and N addition was significantly related to increased biomass in grasslands with severe degradation. However, N fertilization did not significantly affect belowground biomass. The effects of N addition on foliar nutrient concentrations in the same species differed among grasslands with different degradation levels. There was an inconsistent response to N addition between Sanguisorba officinalis and Vicia sepium in non-degraded grassland. There was a significant positive correlation between foliar N content and aboveground biomass in grasslands with different levels of degradation. Our results indicate that the effects of N addition on plant growth in grasslands differ according to the severity of degradation. We conclude that N fertilization may be an effective management technique for degraded grasslands in this area and may improve forage productivity in the short term.

Species abundance distributions as a proxy for the niche–neutrality continuum

Abstract: © The Author(s) 2017. Aims Species abundance distributions (SADs) are often used to verify mechanistic theories underlying community assembly. However, it is now accepted that SADs alone are not sufficient to reveal biological mechanisms. Recent attention focuses on the relative importance of stochastic dispersal processes versus deterministic processes such as interspecific competition and environmental filtering. Here, we combine a study of the commonness and rarity of species (i.e. the SAD) with mechanistic processes underlying community composition. By comparing the occurrence frequencies of each and every species with its abundance, we quantify the relative contributions of common and rare species to the maintenance of community structure. Essentially, we relate the continuum between commonness and rarity with that of niches and neutrality. Methods An individual-based, spatially explicit model was used to simulate local communities in niche spaces with the same parameters. We generated sets of assemblages from which species were eliminated in opposing sequences: from common to rare and from rare to common, and investigated the relationship between the abundance and frequency of species. We tested the predictions of our model with empirical data from a field experiment in the environmentally homogeneous alpine meadows of the Qinghai- Tibetan plateau. Important Findings Our simulations support the widespread notion that common species maintain community structure, while rare species maintain species diversity, in both local and regional communities. Our results, both from theoretical simulations and from empirical observations, revealed positive correlations between the abundance of a particular species and its occurrence frequency. SAD curves describe a continuum between commonness and rarity. Removing species from the 'rare' end of this continuum has little effect on the similarity of communities, but removing species from the 'common' end of the continuum causes significant increases in beta diversity, or species turnover, between communities. In local communities distributed in a homogenous habitat, species located at the 'common' end of the continuum should be selected by environmental filtering, with niche space partitioning governed by interspecific competition. Conversely, species located at the 'rare' end of the continuum are most likely subject to stochastic dispersal processes. Species situated at intermediate locations on this continuum are therefore determined by niche and neutral processes acting together. Our results suggest that, in homogeneous habitats, SAD curves describing the common-rare continuum may also be used to describe the continuum between niches and neutrality.

Emergent interactions influence functional traits and success of dune building ecosystem engineers

Abstract: Dune building processes are affected by interactions between the growth of ecosystem engineering dune grasses and environmental factors associated with disturbance such as sand burial and sea spray. Research investigating how species interactions influence dune community structure and functional trait responses in high abiotic stress environments is minimal. We investigated how species interactions influence the functional trait responses of three dominant dune grasses to common abiotic stressors. We performed a multi-factorial greenhouse experiment by planting three common dune grasses (Ammophila breviligulata Fern., Uniola paniculata L. and Spartina patens Muhl.) in different interspecific combinations, using sand burial and sea spray as abiotic stressors. Sand burial was applied once at the beginning of the study. Sea spray was applied three times per week using a calibrated spray bottle. Morphological functional trait measurements (leaf elongation, maximum root length, aboveground biomass and belowground biomass) were collected at the end of the study. The experiment continued from May 2015 to August 2015. Species interactions between A. breviligulata and U. paniculata negatively affected dune building function traits of A. breviligulata, indicating that interactions with U. paniculata could alter dune community structure. Furthermore, A. breviligulata had a negative interaction with S. patens, which decreased S. patens functional trait responses to abiotic stress. When all species occurred together, the interactions among species brought about coexistence of all three species. Our data suggest that species interactions can change traditional functional trait responses of dominant species to abiotic stress.

Using resistance distance from circuit theory to model dispersal through habitat corridors

Abstract: Resistance distance (RD), based on circuit theory, is a promising metric for modelling effects of landscape configuration on dispersal of organisms and the resulting population and community patterns. The values of RD reflect the likelihood of a random walker to reach from a source to a certain destination in the landscape. Although it has successfully been used to model genetic structures of animal populations, where it most often outperforms other isolation metrics, there are hardly any applications to plants and, in particular, to plant community data. Our aims were to test if RD was a suitable metric for studying dispersal processes of plants in narrow habitat corridors (linear landscape elements [LLE]). This would be the case, if dispersal processes (seed dispersal and migration) resembled random walks. Further, we compared the model performance of RD against least-cost distance (LCD) and Euclidean distance (ED). Finally, we tested the suitability of different cost surfaces for calculations of LCD and RD. We used data from 50 vegetation plots located on semi-natural LLE (field margins, ditches, road verges) in eight agricultural landscapes of Northwest Germany. We mapped LLE, including hedges and tree rows, from aerial images in a Geographic Information System, converted the maps into raster layers, and assigned resistance values to the raster cells, where all cells outside of LLE received infinite resistance and, thus, represented barriers to dispersal. For all pairs of plots within study areas, we calculated Jaccard similarity assuming that it was a proxy (or correlate) of dispersal events between plots. Further, we calculated RD and LCD of the network of LLE and ED between the plots. We modelled the effects of distance metrics on community similarity using binomial generalized linear mixed models. ED was clearly the least suitable isolation metrics. Further, we found that RD performed better than LCD at modelling Jaccard similarity. Predictions varied markedly between the two distance metrics suggesting that RD comprises additional information about the landscape beyond spatial distance, such as the possible presence of multiple pathways between plots. Cost surfaces with equal cell-level resistances for all types of LLE performed better than more complex ones with habitat-specific resistances. We conclude that RD is a highly suitable measure of isolation or, inversely, connectivity for studying dispersal processes of plants within habitat corridors. It is likely also suitable for assessing landscape permeability in other landscape types with areal habitats instead of narrow corridors. RD holds the potential to improve assessments of isolation (or connectivity) for models of regional population and meta-community dynamics.

Broussonetia papyrifera controls nutrient return to soil to facilitate its invasion in a tropical forest of Ghana

Abstract: Aims Non-native invasive plants can alter soil chemistry through litter production and decomposition to facilitate their invasion. However, the important roles of these underlying processes in plant invasion remain poorly understood, particularly in tropical forest ecosystems. Here, we compared litter production, quality and decomposition of two invasive species (Broussonetia papyrifera and Cedrela odorata) and two co-occurring native species (Celtis mildbraedii and Funtumia elastica), and soil properties under them to elucidate their roles in the invasion of a tropical forest in Ghana. Methods Leaf litter production rates were determined using 36 mesh traps installed in the study area, while litter quality and soil physicochemical properties were determined using standard protocols. A 6-month decomposition experiment using the litterbag technique was conducted to compare the decomposition rates of the species. Important Findings Litter production varied among the species and over time, with B. papyrifera producing 0.35–4.27 tons ha−1 y−1 from October to January; the other species produced 0.03–1.74 tons ha−1 y−1 over the same period. In the litterbag experiment, B. papyrifera recorded the lowest mass remaining (11–36%), followed by C. odorata (17– 51%), F. elastica (31–55%) and C. mildbraedii (48–62%) in that order. Broussonetia papyrifera had the highest nitrogen (3.91%) and phosphorus (0.24%) but lowest lignin (12.20%) concentrations and the lowest C:N (10.87) ratio, indicating higher litter quality compared to the other species. Soil under B. paprifera was richest in phosphorus and nitrogen compared to the other species. Overall, our results indicate that the production of more nutrient-rich and rapidly decomposing leaf litter by B. papyrifera may constitute an important positive feedback mechanism driving its invasion and impacts in this tropical forest.

Responses of nighttime sap flow to atmospheric and soil dryness and its potential roles for shrubs on the Loess Plateau of China

Abstract: Aims Nocturnal sap flow (Enight) has been observed in a variety of plant species and environmental conditions. In water-limited environments, Enight is important in the regulation of plant water’s physiology. This study was designed to evaluate the way in which Enight (defined as sap flow from 20:30 to 06:00) responded to changes in the atmospheric vapor pressure deficit (VPD) and the soil water content (SWC), and explored its potential physiological significance for different plant species in a semi-arid area. Methods We selected three shrub species: Vitex negundo L. (VN), Hippophae rhamnoides L. (HR) and Spiraea pubescens Turcz (SP) in the semi-arid Loess Plateau of China. The plots of the three communities dominated by each of three species were on the same hill slope. Half-hourly sap flow density was measured in six to seven sample stems for each species during the main growing season (June to August 2015). VPD, SWC, leaf water potential (Ψleaf) and stomatal conductance (Gs) were measured at the same time. Regression analyses were conducted to determine the relationships between Enight, Eday, Enight/Edaily, VPD and SWC at halfhourly and daily time scales, as well as between Enight, Eday and Ψleaf. Important Findings The mean values of Enight and Eday were higher, but Enight/Edaily values were lower for VN compared to HR and SP. The responses of sap flow density to VPD and SWC varied at different temporal scales. VPD was the dominant factor that affected Enight and Eday at the half-hourly scale for all three species. In contrast, SWC was the key factor that influenced Eday at the daily time scale. The values of Eday and Enight/Edaily correlated negatively with SWC because the effect of SWC was stronger on Eday than on Enight. Although the low fraction of Enight/Edaily (4%–7%) may indicate a minor shortterm effect of Enight on the standing water balance, Enight had ecophysiologically significance to the plants. The discrepancy in Ψleaf between sunset and the following day’s predawn (ΔΨ) indicated that stem refilling occurred during this period. SP had the higher fraction of recharge water among the three species, as it had the relatively higher value of ΔΨ/Enight. Enight had positive relationship with predawn Gs. The increased Gs facilitated rapid onset of photosynthesis in the early morning. In addition, the positive correlation between Enight and Eday from 06:00 to 10:30 suggested that Enight was beneficial for transpiration in the following morning. The responses of Enight to VPD and SWC indicated differences in plant adaptation to drought stress, which provides important information for our understanding of the reactions to climate changes among species in semi-arid areas.

Pollinators exert positive selection on flower size on urban, but not on rural Scotch broom (Cytisus scoparius L. Link).

Abstract: Adaptive evolution of invasive species is both particularly exciting for the evolutionary biologist and worrisome for those interested in controlling or halting spread. Invasive species often have a distinct timeline and well-recorded population expansion. As invaders encounter new environments, they undergo rapid adaptive evolution. Our aim in this study was to measure variation of floral size in the invasive shrub Cytisus scoparius (Scotch broom) and measure natural selection by pollinators on that trait. Past research has found that this invasive plant is pollinator limited in Washington State and that declines in pollinator populations can contribute to local extinction in another invaded range (New Zealand). This plant is pollinated by both native and introduced species of bees, representing a broad range of pollinator sizes. Cytisus scoparius has a flower structure that is highly conducive to studies on pollinator choice, even in the absence of direct pollinator observations. We surveyed urban and rural sites in and around the city of Olympia in Washington State. Measuring banner width, we were able to show that flower size varies substantially between plants but minimally within plants. By measuring the proportion of flowers that were ‘tripped’, we could determine pollinator visitation rates and thus determine the level of selection due to pollinator choice alone. We found that C. scoparius is under natural selection by pollinators for increased flower size. However, such positive natural selection was only seen in urban populations although it was consistent across two flowering seasons. Rural populations of Scotch broom do not appear to be under selection on flower size. The natural selection by pollinators on broom flowers could result in adaptive evolution into a new pollination niche by an invading species. A higher level of variation in broom flowers seen here than seen in previous works in native regions suggests that C. scoparius may be highly diverse and primed for adaptive evolution.

Soil attributes structure plant assemblages across an Atlantic forest mosaic

Abstract: Community assembly persists as a key topic in ecology due to the complex variation in the relative importance of assembly forces and mechanisms across spatio-temporal scales and ecosystems. Here we address a forest–savanna vegetation mosaic in the Brazilian Atlantic forest to examine the role played by soil attributes as determinants of community assembly and organization at a landscape spatial scale. We examined soil and plant assemblage attributes across 23 plots of forest and savanna in a 1600 km² landscape exposed to the same climatic conditions in the Atlantic forest region of northeast Brazil. Assemblage attributes included species richness, taxonomic and functional composition (community weighted mean, CWM) and functional diversity (quadratic diversity; Rao’s quadratic entropy index) relative to plant leaf area, specific leaf area, leaf dry matter content, thickness and succulence. Our results suggest that forest and savanna patches exposed to the same climatic conditions clearly differ in terms of soil attributes, plant assemblage structure, taxonomic and functional composition. By selecting particular plant strategies relative to resource economy, soil potentially affects community structure, with forest assemblages bearing more acquisitive resource-use strategies, while conservative plant strategies are more frequent in savannas. Accordingly, savanna–forest mosaics in the Atlantic forest region represent spatially organized plant assemblages in terms of taxonomic and functional features, with a signal of trait convergence in both vegetation types. Soil-mediated filtering thus emerges as a potential deterministic assembly force affecting the spatial organization of savanna–forest boundaries and mosaics.

Aboveground resilience to species loss but belowground resistance to nitrogen addition in a montane plant community

Abstract: Decades of empirical work have demonstrated how dominant plant species and nitrogen fertilization can influence the structure and function of plant communities. More recent studies have examined the interplay between these factors, but few such studies use an explicit trait-based framework. In this study, we use an explicit trait-based approach to identify potential mechanisms for community-level responses and to test ecological niche theory. We experimentally manipulated plant communities (control, −dominant species, −random biomass) and nitrogen (N) inputs (control, +organic N, +inorganic N) in a fully factorial design. We predicted that traits related to plants’ ability to take up different forms of soil N would differ between dominant and subordinate species, resulting in interactive effects of dominant species loss and N fertilization on plant community structure and function. The study took place in a montane meadow in the Rocky Mountains, Colorado, USA. After four years, the plant community in removal plots converged toward a species composition whose leaf and root functional traits resembled those of the previously removed dominant species. Ecosystem productivity generally increased with N addition: soil carbon efflux was ~50% greater when either form of N was added, while inorganic N addition increased aboveground biomass production by ~60% relative to controls. The increase in production was mediated by increased average height, leaf mass:area ratio and leaf dry matter content in plant communities to which we added inorganic N. Contrary to our predictions, there were no interactive effects of N fertilization and dominant species loss on plant community structure or ecosystem function. The plant community composition in this study exhibited resistance to soil N addition and, given the functional convergence we observed, was resilient to species loss. Together, our results indicate that the ability of species to compensate functionally for species loss confers resilience and maintains diversity in montane meadow communities.

Simulated N and S deposition affected soil chemistry and understory plant communities in a boreal forest in western Canada

Abstract: Aims We conducted a simulated nitrogen (N) and sulfur (S) deposition experiment from 2006 to 2012 to answer the following questions: (i) does chronic N and S deposition decrease cation concentrations in the soil and foliage of understory plant species, and (ii) does chronic N and S deposition decrease plant diversity and alter species composition of the understory plant community in a boreal forest in western Canada where intensifying industrial activities are increasing N and S deposition? Methods Our field site was a mixedwood boreal forest stand located ~100 km southeast of Fort McMurray, Alberta, Canada. the experiment involved a 2 × 2 factorial design, with two levels each of N (0 and 30 kg N ha−1 yr−1; applied as NH4NO3) and S addition (0 and 30 kg S ha−1 yr−1; applied as Na2SO4). Four blocks were established in July 2006, each with four plots of 20 × 20 m randomly assigned to the treatments. Soil and understory vegetation were sampled and cover (%) of individual species of herb (height ≤ 0.5 m) and shrub (height 0.5–1 m) layers was determined in August 2012. Important Findings Seven years after the treatments began, N addition increased dissolved organic carbon and N in the mineral soil (P < 0.05), whereas S addition decreased exchangeable cations (P < 0.05) in the forest floor. In the shrub layer, species evenness, and overall diversity were decreased by N addition (P < 0.05) due to increases in abundance of nitrophilous species and S addition (P < 0.01) due to decreased cation concentrations in soils. total shrub cover decreased with S addition (P < 0.10). Nitrogen and S addition affected neither species richness nor evenness in the herb layer. However, permutational multivariate analysis of variance and non-metric multidimensional scaling analyses (based on plant cover) indicated that the effect of N and S addition on understory plant species composition in the both shrub and herb layers was species-specific. Addition of N decreased foliar phosphorus and potassium concentrations in some species, suggesting potential risk of N-meditated nutrient imbalance in those species. Our results indicate that long-term elevated levels of N and S deposition can negatively impact plant nutrition and decrease the diversity of the understory plant community in boreal forests in northern Alberta, Canada. However, considering that the current N and S deposition rates in northern Alberta are much lower than the rates used in this study, N and S deposition should not negatively affect plant diversity in the near future.

Discovering the type of seed dormancy and temperature requirements for seed germination of Gentiana lutea L. subsp. lutea (Gentianaceae)

Abstract: Aims There are a number of mechanisms that regulate germination; among these, seed dormancy, one of the most important, is an adaptative mechanism in plants to promote survival by dispersing germination in space and time until environmental conditions are favourable for germination. The main goals of this study were to determine the temperature requirements for seed dormancy release and germination of Gentiana lutea subsp. lutea, to identify the class and level of seed dormancy and to suggest an optimal germination protocol. Methods Seeds belonging to two different localities were subjected to various pre-treatments, including cold stratification (0 and 5°C), warm stratification (25/10°C) and different combinations of these, and then incubated at a range of constant temperatures (5–25°C) and 25/10°C. Embryo growth during pre-treatments and incubation conditions were assessed at different times by measuring the embryo to seed length ratio (E:S ratio). The final germination percentage (FGP) and the germination rate (t50) were calculated. Important Findings Fleshy mature seeds of G. lutea subsp. lutea have linear underdeveloped embryos. Cold stratification at 0°C was effective in overcoming the physiological dormancy (PD) and promoted embryo growth and subsequent germination. After cold stratification at 0°C, both the root and the shoot emerged readily under a wide range of temperatures. G. lutea subsp. lutea seeds showed an intermediate complex morphophysiological dormancy (MPD). As regards the optimal germination protocol for this taxon, we suggest a period of cold stratification at ca. 0°C followed by seed incubation at 10–20°C. The optimal germination temperatures found for seeds of this taxon, as well as its pre-chilling requirement at 0°C, suggest that it is well adapted to a temperate climate; this behavior highlights an increasing threat from global warming for G. lutea, which could reduce the level of natural emergence in the field, prejudicing also the long-term persistence of the natural populations in Sardinia.

Distinct edaphic habitats are occupied by discrete legume assemblages with unique indicator species in the Cape Peninsula of South Africa

Abstract: Aims the Cape Peninsula is a small area (471 km2) situated on the south-westernmost tip of the Core Cape Subregion (CCR) of South Africa. Within the Cape Peninsula, Fabaceae are the third most species-rich plant family (162 species) and they have the second highest number of endemic species after the Ericaceae. However, legumes are not the dominant taxa in the vegetation. they tend to show patchy distributions within the landscape and different species assemblages usually occupy particular niches at any given locality. the present study undertook to establish if edaphic factors influence legume species distribution in the Cape Peninsula and to determine the key indicator species for the different assemblages. Methods Soils from 27 legume sites, spanning all major geological substrates of the Cape Peninsula, were analysed for 31 chemical and physical properties. Legume species present at each site were recorded and a presence/absence matrix was generated. Cluster analysis and discriminant function analysis (DFA) were run to group the sites based on overall similarity in edaphic characteristics and to identify the soil parameters contributing towards discriminating the groups. Canonical correspondence analysis (CCA) was used to test for a correlation between legume species compositions and edaphic factors. the strength of the association between legume species and site groupings based on edaphic properties was assessed using indicator species analysis. Important findings Based on similarity in overall soil characteristics, the sites formed three clusters: one comprising sites of sandstone geology, one with dune sand sites and the third cluster comprising sites of both shale and granite geologies (hereafter referred to as soil types). the DFA confirmed the distinctness of these clusters and the CCA showed a significant correlation between legume species composition and edaphic factors. the key edaphic parameters were clay content, iron (Fe), potassium (K), sulphur (S) and zinc (Zn). these findings reveal that the Cape Peninsula is edaphically heterogeneous and edaphically distinct habitats contain discrete legume species assemblages that can be distinguished by unique indicator species. Furthermore, multiple soil parameters, rather than a single parameter, are involved. therefore, edaphic factors play a significant role in driving the distribution of legume species in the Cape Peninsula and discrete legume species assemblages occupy distinct habitats.

Effects of the frequency and the rate of N enrichment on community structure in a temperate grassland.

Abstract: Nitrogen (N) enrichment caused by human activities threatens biodiversity and alters plant community composition and structure. It has been found that heavy and infrequent N inputs may over-estimate species extinction, but it remains unclear whether plant community structure will equally respond to frequent reactive N enriched conditions. We independently manipulated the rates and the frequencies of N addition in a temperate steppe, northern China, between 2008 and 2013. We found that plant community structure changes, measured by ‘Euclidean distance’ involving species richness, composition and productivity, were significantly positively related to increasing N enrichment rates rather than frequencies. Changes in aboveground net primary productivity (ANPP), plant species richness and shifts in dominant species were observed. Community ANPP increased with N enrichment, whereas species richness reduced. The frequency of N enrichment increased species richness but had no impacts on community ANPP and the relative ANPP of the two dominant species, C₃ perennial bunchgrass Stipa grandis and C₃ perennial rhizome grass Leymus chinensis. The ANPP and relative ANPP of the two dominant species were significantly negatively correlated with each other. Moreover, changes in the relative ANPP of S. grandis was negatively associated with the changes in community structure. After 5 years’ treatment, direct influence of the frequency of N enrichment on plant community structure was not observed, but the effects of the rate of N enrichment were apparent. Our results suggested that further study in various ecosystems and with long-term and well-controlled comparisons the frequency vs. the rate of N enrichment may still be needed.

Solutes in native plants in the Arabian Gulf region and the role of microorganisms: future research

Abstract: Aims One of the outstanding challenges facing humankind is increasing crop production under various types of severe environmental conditions. Many measures have been taken to adopt molecular and biotechnological approaches that lead to the development of transgenic plants able to deal with such harsh and polluted environments. However, such solutions could be very expensive and require considerable efforts and time to achieve these objectives. The main objective of this review is to discuss the new biological solutions that have emerged in the last decade, as environmentally friendly approaches, perhaps to support and/or replace the present efforts. These solutions based on plant–microbe interactions could be a lifeline and promising alternative strategy to create plants with a high resistance to the extreme environments. Methods During the last two decades research projects have been conducted to study the ecology, identify the features, and the ecophysiology of native plants and the associated microorganisms in the Arabian Gulf region and particularly in Qatar. Many physiological and biochemical parameters have been determined, including organic solutes (amino acids like proline, glycinebetaine, soluble sugars, etc.), photosynthetic pigments, organic acids and inorganic ions especially heavy metals, along with the physical and chemical properties of the soil in various locations of the State of Qatar. Also, the microorganisms adjacent to and associated with these native plants were identified to elucidate the possible roles in the soil biota in supporting these plants against extreme environmental conditions. Important Findings Investigations of native plants in the Arabian Gulf states during the last decade have shown that wild plants exhibit different abilities to accumulate organic solutes to cope with the harsh natural environments. Pollution is a major factor stressing wildlife in this region due to the expansion of urban sectors and industrial activities of oil and gas. Compatible osmolytes, like proline, accumulate in wild plants in response to severe environmental conditions and heavy metal contaminated soil. Accumulation of these solutes in plant tissues could provide some level of adaptation and resistance against all these types of environmental stresses. We present some promising efforts in the Arabian Gulf region to remediate desert soil and water polluted with heavy metals and petroleum hydrocarbons. Substantial evidence is introduced about the roles of microorganisms associated with wild plants in natural habitats, such association may help them cope with the extreme stresses. Possible mechanisms adopted by microorganisms in alleviating the harsh abiotic stresses facing the wild life are discussed, one of which is the promotion of biosynthesis and transport of organic solutes to the plants. Also, the main possibilities of the origin of activities of the accumulation of compatible organic solutes are suggested and the objectives of the future research are discussed.

Effect of invasion by Hyptis suaveolens on plant diversity and selected soil properties of a constructed tropical grassland

Abstract: Aims Hyptis suaveolens (L.) Poit is an important invader of the tropical and sub-tropical regions of the world. In our study, it has been investigated that how does the H. suaveolens invasion regulate plant species diversity across the seasons in the dry tropical grassland. We hypothesized that a shift in soil inorganic-N availability is caused by invasion, and this shift is integral to access the invasion effect on plant diversity. Methods The study was performed in experimental plots at the Botanical Garden of the Banaras Hindu University (25°16′3.3′′ N and 82°59′22.7′′ E), Varanasi, Uttar Pradesh, India. Five replicates (each, 2 × 2m) of non-invaded grassland plots (NIG) and five grassland plots invaded with H. suaveolens (IG) were established. These plots were constructed by transplanting indigenous grassland patches from an adjacent native grassland. In the invaded plots, 20 individuals of H. suaveolens were transplanted per plot. After 1 year of establishment, diversity attributes and soil properties were recorded from these plots in three seasons as per standard protocol. Important Findings The results indicated that Hyptis invasion negatively affects plant diversity, with relatively higher impact in rainy season as compared to the winter season. IG exhibited lower soil moisture content and temperature than NIG in rainy season, whereas soil ammonium-N, nitrate-N, total inorganic-N, N mineralization registered higher values for IG than NIG in both rainy and winter season. Diversity indices were negatively correlated with soil inorganic-N pool and N mineralization. However, these indices were positively correlated with microbial biomass carbon (MBC), and the correlation coefficient for this relationship was higher for rainy season as compared to winter. Species richness (r = 0.65) and Shannon diversity (r = 0.757) were significantly correlated with the ratio of ammonium-N to nitrate-N. The negative effect of invasion by H. suaveolens on the plant diversity is possibly mediated by the effect of invasion on N mineralization processes (mainly nitrification) and the availability of soil inorganic-N pools. The study indicates that Hyptis invasion has an enormous potential to change the structure and composition of plant communities in the dry tropical grasslands.

Breeding system and pollination ecology of a potentially invasive alien Clematis vitalba L. in Ireland

Abstract: Invasive alien plants can greatly affect native communities and ecosystem processes but only a small fraction of alien plant species become invasive. Barriers to establishment and invasion include reproductive limitations. Clematis vitalba L. has been a popular horticultural species for the past century and is widely distributed and can be highly invasive. In Ireland, it is considered naturalized and potentially invasive. Despite this, little is known about its reproductive biology. We carried out manipulative field experiments in Ireland and compared fruit and seed set from a number of pollination treatments, namely cross-pollination, geitonogamy, autogamy and natural pollination. We also recorded floral visitation to C. vitalba through a series of timed observations. We found that C. vitalba is capable of uniparental reproduction via geitonogamy and autonomous selfing, albeit at a reduced rate compared with outcrossing treatments. Clematis vitalba was visited by at least 10 native pollinator taxa, with hoverflies dominating visitation. Neither fruit set nor seed set in our study population was pollen limited. Given the lack of reproductive constraint, C. vitalba may easily spread in suitable habitats. This is of concern in Ireland, given its prevalence in some of the country’s most floristically diverse regions.

N and P resorption as functions of the needle age class in two conifer trees

Abstract: Aims Given the importance of resorption in nutrient conservations, nutrient resorption should change with leaf age if resorption depends on nutrient content, and if nutrient content changes with leaf age. However, no study has addressed this issue. Methods Here, we measured N and P concentrations of needles of different ages in two woody evergreen conifer species—white spruce (Picea glauca Voss.) and balsam fir (Abies balsamea Mill.)—to determine the effects of needle aging on nutrient resorption. Important Findings For both species, N and P concentrations were higher in newer needles than in older needles. Nutrient resorption efficiency, i.e. percentage of nutrients resorbed during senescence, also declined significantly with needle age from 73 to 22% in these two evergreen conifer species. The difference in nutrient resorption between old and young needles may be attributed to the size of N and P sink tissues, which is likely to decrease with needle age. These results suggest that needle age affects the extent of N and P resorption in these two evergreen conifer species.

Lignin characteristics in soil profiles in different plant communities in a subtropical mixed forest

Abstract: Aims Lignin is generally considered as an important indicator of soil organic carbon (SOC) storage and dynamics. to evaluate the effects of plant communities and soil depth on soil lignin is critical to better understand forest carbon cycling. Methods We compared lignin content and chemical signature in three soil depths of four major plant communities in a subtropical forest, which located in the north part of Wuling Mountains, China. Lignin was measured using CuO oxidation method. Important Findings Both lignin content and its biochemical signature in plant litter varied among communities. However, these differences were mostly no longer exist in the upper soil layers. Lignin chemistry in soils inherited some of the biochemical signature of lignin in litter, but in a diminished magnitude. these results suggest that different plant communities had similar decomposition process with varying rates, caused diminished differences in lignin content and its biochemical signature. Lignin content decreased with soil depth, but the biochemical signature of lignin was not significantly different among soil layers for all communities, which suggests that vertical movement of lignin within the soil profile is very likely a key process causing this similar biochemical signature. these results emphasized the important roles of lignin inputs and soil eluviation in shaping lignin characteristics and distribution in forest soils, which pinpoint the urgent need to consider hydrological processes in studying forest soil carbon cycling.

Plant responses to variable timing of aboveground clipping and belowground herbivory depend on plant age

Abstract: Aims Plants use different types of responses such as tolerance and induced defense to mitigate the effects of herbivores. The direction and magnitude of both these plant responses can vary with plant age. However, most studies have focused on aboveground herbivory, whereas important feeding occurs belowground. Here, we tested the hypothesis that plant tolerance and defense following shoot damage or root herbivory depends on plant age. Methods In order to test our hypothesis, we exposed the perennial grass species Holcus lanatus to defoliation and root nematode inoculation at three growth stages (young, intermediate and old plants), and examined responses of plant traits related to tolerance (regrowth following defoliation) and defense (leaf and root nitrogen and phenolics). Important Findings Defoliation overall reduced plant shoot and root biomass as well as foliar concentrations of phenolics regardless of plant age at defoliation. In contrast, defoliation increased foliar N concentrations, but only when defoliation occurred at intermediate and old plant age. Inoculation with root-feeding nematodes reduced root N concentrations after a prolonged period of growth, but only when nematodes had been inoculated when plants were young. The relative shoot regrowth rate of plants increased immediately after defoliation but this was independent of the plant age at which defoliation occurred, i.e. was not stronger in plants that were defoliated at a more advanced age, as hypothesized. Similarly, relative root growth rates increased shortly after defoliation, but this was only observed for plants defoliated when they were young. We conclude that plant responses to aboveground and belowground herbivory in traits related to both defense and tolerance are affected by plant age, but do not generally change with plant age.

Ecological role of physical dormancy in seeds of Oxytropis racemosa in a semiarid sandland with unpredictable rainfall

Abstract: Seed dormancy and the soil seed bank are crucial to plant regeneration strategy, especially in semiarid ecosystems with unpredictable precipitation. The aim of this study was to investigate how seed dormancy is controlled by environmental factors and how it is correlated with the soil seed bank and regeneration of the perennial legume Oxytropis racemosa, a dominant perennial herb in Mu Us Sandland of semiarid China. Germination and imbibition experiments on fresh intact and scarified seeds of O. racemosa were used to identify physical dormancy (PY) in seeds of this species. Soil seed bank dynamics, timing of seedling emergence and the fate of buried seeds in the natural habitat were investigated. PY was broken by mechanical scarification or wet heat/ice water cycles but not solely by dry heat or wet heat treatment. The soil seed bank exhibited seasonal changes in the number of seeds, which was highest in September and lowest in July. Seeds buried at different sand depths gradually lost dormancy; 20–42% of the seeds remained dormant after 20 months of burial. Dormancy break occurs gradually throughout the year. Our results indicate that O. racemosa exhibits hardcoatedness heterogeneity that spreads germination of a seed cohort between seasons and years in the semiarid environment, where the amount of precipitation during the growing season is highly variable.

Divergent biomass partitioning to aboveground and belowground across forests in China

Abstract: Aims Belowground to aboveground biomass (BGB/AGB) ratio is a highly valued parameter of the terrestrial carbon cycle and productivity. However, it remains far from clear whether plant biomass partitioning to aboveground and belowground is isometric (equal partitioning) or allometric (unequal partitioning) at community levels and what factors are necessary in order to regulate the partitioning. This study aimed to comprehensively find out the patterns of biomass partitioning and their regulatory factors across forests in China. Methods The data of AGB and BGB were compiled from 1542 samples for communities across forests in China. Standardized major axis regression was conducted to examine whether AGB and BGB were allocated isometrically or allometrically at a community level. Redundancy analysis was used to analyze the relationships of BGB/AGB ratio with climatic factors and soil properties. Important Findings We found that the slopes of the relationship between logAGB and logBGB were not always comparable to 1.0 (isometric allocation) at community levels, including primary forest, secondary forest, and planted forest. Meanwhile, samples in clay, loam, and sand soil types also presented the same phenomenon. Furthermore, the radically different allocations of AGB and BGB were found in northern and southern China. Environmental factors totally explained 3.86% of the variations in the BGB/AGB ratio at the community level, which include the mean annual precipitation, mean annual temperature, potential water deficit index, soil carbon content, soil nitrogen content, soil clay, soil loam, soil sand, soil pH, and soil bulk density. In addition, the environmental factors also have effects on the BGB/AGB ratio in other categories. The patterns revealed in this study are helpful for better understanding biomass partitioning and spreading the carbon circle models.