Showing papers in "Journal of Plant Ecology in 2010"

Soil microbial biomass carbon and nitrogen in forest ecosystems of Northeast China: a comparison between natural secondary forest and larch plantation

Abstract: Aims Natural secondary forest (NSF) and larch plantation are two of the predominant forest types in Northeast China. However, how the two types of forests compare in sustaining soil quality is not well understood. This study was conducted to determine how natural secondary forest and larch plantation would differ in soil microbial biomass and soil organic matter quality. Methods Microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), soil organic carbon (SOC) and total nitrogen (TN) in the 0- to 15-cm and 15- to 30-cm soil layers were investigated by making chemical and biological measurements in the montane region of eastern Liaoning Province, Northeast China, during the growing season of 2008 in stands of NSF and Larix olgensis plantation (LOP). Important Findings We found that soil MBC and MBN were significantly lower in the LOP than in the NSF. Both MBC and MBN declined significantly with increasing soil depth in the two types of stands. The ratios of MBC to SOC (MBC/SOC) and MBN to TN (MBN/TN) were also significantly lower in the LOP than in the NSF. Moreover, the values of MBC, MBC/SOC, and MBN/TN significantly varied with time and followed a similar pattern during the growing season, all with an apparent peak in summer. Our results indicate that NSF is better in sustaining soil microbial biomass and nutrients than larch plantation in the temperate Northeast China. This calls for cautions in large-scale conversions of the native forests to coniferous plantations as a forest management practice on concerns of sustaining soil productivity.

Effect of salinity on seed germination, ion content and photosynthesis of cotyledons in halophytes or xerophyte growing in Central Asia

Abstract: Aims We investigated the impact of salinity on seed germination, chlorophyll content, chloroplast structure and photosynthesis of the green embryos in desiccated seeds of the xerophyte Haloxylon persicum, xero-halophyte Haloxylon ammodendron and euhalophyte Suaeda physophora. Methods Seeds of H. persicum, H. ammodendron and S. physophora were collected from natural environment in Fukang, Xinjiang province. Pretreatment with 700 mM NaCl was carried out to stimulate the natural ‘seed priming’; we analyzed the joint effect of salinity and different species on germination physiology and cotyledonal structure and photosynthetic function changes during germination and recovery stage. Important Findings We found that seeds did not suffer ion toxicity for the two halophytes H. ammodendron and S. physophora, as evidenced by the high final germination after ungerminated seeds pretreated with 700 mM NaCl were transferred to distilled water, but the final germination of the xerophyteH. persicum was significantly lower than that of control. The Na + concentration in embryos increased under salinity for all species, while K + concentration decreased by salinity only for H. persicum and H. ammodendron, i.e. the concentration of K + in embryos of H. persicum and H. ammodendron decreased by 36% and 46%, respectively. For all species, whether dry intact seeds or cotyledons of dry seeds imbibed in deionized water and NaCl solution, had high chlorophyll content. Treatment with NaCl also caused chloroplast thylakoids to swell and chlorophyll content to decrease in seeds of H. persicum, but no significant change was observed in the more salt-tolerant species S. physophora and H. ammodendron. Fluorescence measurement showed that 700 mM NaCl decreased the Fv/Fm ratio of cotyledons in seeds for all species, especially for H. persicum and H. ammodendron .P hotosynthetic oxygen releasing was detected from the seeds that were moistened with distilled water and 700 mM NaCl for 6 or 24 h and from the seeds that were initially moistened with 700 mM NaCl in darkness for 10 days, then transferred to distilled water for another 6 and 24 h. The results indicated that the chlorophyll in cotyledon of desiccated seed had photosynthetic function in early germination stage, even under high-saline condition. In addition, the photosynthesis of chlorophyll in the embryonic cotyledons of desiccated seeds during germination was similar to that in leaves of young seedlings for all species. In conclusion, the chloroplasts of the two halophytes were more salt resistant compared with the xerophyte H. persicum. The photosynthetic function of chlorophyll in cotyledons of mature seeds may be ecologically important for seedling development in early stage for plants growing in extremely saline or arid environments.

Changes in soil microbial biomass and community structure with addition of contrasting types of plant litter in a semiarid grassland ecosystem

Abstract: Aims Elevated atmospheric CO2 has the potential to enhance the net primary productivity of terrestrial ecosystems. However, the role of soil microorganisms on soil C cycling following this increased available C remains ambiguous. This study was conducted to determine how quality and quantity of plant litter inputs would affect soil microorganisms and consequently C turnover. Methods Soil microbial biomass and community structure, bacterial community-level physiological profile, and CO2 emission caused by different substrate C decomposition were investigated using techniques of biological measurements, chemical and stable C isotope analysis, and BIOLOG-ECO microplates in a semiarid grassland ecosystem of northern China in 2006 and 2007 by mixing three contrasting types of plant materials, C3 shoot litter (SC3), C3 root litter (RC3), and C4 shoot litter (SC4), into the 10- to 20-cm soil layer at rates equivalent to 0 (C0), 60 (C60), 120 (C120 )a nd 240 g C m � 2 (C240). Important Findings Litter addition significantly enriched soil microbial biomass C and N and resulted in changes in microbial structure. Principal component analysis of microbial structure clearly differentiated among zero addition, C3-plant-derived litter, and C4-plant-derived litter and among shoot- and root-derived litter of C3 plants; soil microorganisms mainly utilized carbohydrates without litter addition, carboxylic acids with C3-plant-derived litter addition and amino acids with C4-plant-derived litter addition. We also detected stimulated decomposition of older substrate with C4-plant-derived litter inputs. Our results show that both quality and quantity of belowground litter are involved in affecting soil microbial community structure in semiarid grassland ecosystem.

Are some communities of the coastal dune zonation more susceptible to alien plant invasion

Abstract: Aims Coastal areas, and in particular coastal dunes, are ecosystems strongly affected by the invasion of alien plants. However, few attempts have ever been made to quantify alien species incidence in different communities along the coastal zonation. This work aims to analyze the distribution of alien plants along the coastal zonation of sandy shores on the Tyrrhenian coast, addressing specifically differences among plant communities in abundance of alien plants. Methods The study was performed on recent dunes (Holocene) of the central western coast of Italy. We selected dune landscapes where invasion processes were particularly evident. Vegetation plots were randomly sampled and through cluster analysis, we identified six plant communities corresponding to the typical zonation described for the Tyrrhenian sandy coast of Central Italy. We evaluated and compared frequency and abundance of invasion in these different communities. Further, we investigated how propagule pressure (measured using as proxy human structures) contributed to the observed invasion patterns. Important Findings We found a relatively low total number of aliens but also a differential distribution pattern and strong abundance of some of the aliens in specific sectors of the vegetation zonation. The perennial community of transition dunes appears most affected by invasion processes, related almost exclusively to the frequent and widespread Carpobrotus aff. acinaciformis. This alien species reaches high cover values, apparently lowering cover of native species of transition dune plant communities. Higher levels of invasion in the transition dune can be partially explained because of greater propagule pressure in this section of the dune profile. Our findings thus have important conservation and management implications since transition dune communities with Crucianella maritima are rare and protected (sensu Habitat 92/43/EEC Directive) along the entire Italian coast.

Drought tolerance in three hybrid poplar clones submitted to different watering regimes

Abstract: Aims Poplars grown in North China may experience water-deficient periods in their life cycle. The aim of the present paper was to quantify the response of three clones to different watering regimes and to determine which clone among the three is the best adapted to drought conditions. Methods Three hybrid poplar clones (clone DN-34, R-247 and OP-367) were used in the present experiment. The seedlings of the three clones were grown under four watering regimes: control (well watered, 100% field water capacity (FC)) and three drought treatments (drought stress I, 50% FC; drought stress II, 40% FC; drought stress III, 30% FC). Changes in morphological, physical and biochemical indicators of the three hybrid poplar clones were investigated. Important Findings Drought treatment (50%, 40% and 30% FC) decreased net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (gs), shoot height, total biomass and chlorophyll (Chl) content in all the three clones and it increased activities of antioxidant enzymes and free proline content. The highest values of the above-mentioned morphological and physiological parameters were recorded in clone OP-367 under 30% FC, followed by clone DN-34 and R-247. Relative leaf water content (RWC) and stem diameter (sd) markedly declined in clone R-247 and DN-34 under drought stress I, II and III, whereas RWC and sd declined in clone OP-367 only under drought stress II and III. Clone OP-367 had more RWC and sd than DN-34 and R-247. Only the 30% FC induced an increase in the root-to-shoot ratio (rs) and water use efficiency (WUE) in all the three clones. OP-367 was the most efficient clone in water absorption and use, for plants of the clone had the highest values of rs and WUE. Our data demonstrate that among the three clones, OP-367 was better able to maintain photosynthesis and growth and lower the damage caused by drought.

Effects of resource additions on species richness and ANPP in an alpine meadow community

Abstract: Aims Theories based on resourceadditions indicate that plant species richness is mainly determined by the number of limiting resources. However, the individual effects of various limiting resources on species richness and aboveground net primary productivity (ANPP) are less well understood. Here, we analyzed potential linkages between additions of limiting resources, species loss and ANPP increase and further explored the underlying mechanisms. Methods Resources (N, P, K and water) were added in a completely randomizedblockdesignto alpinemeadowplots in theQinghai-Tibetan Plateau. Plant aboveground biomass, species composition, mean plant height and light availability were measured in each plot. Regression and analysis of variance were used to analyze the responses of these measures to the different resource-addition treatments. Important Findings Species richness decreased with increasing number of added limiting resources, suggesting that plant diversity was apparently determined by the number of limiting resources. Nitrogen was the most important limiting resource affecting species richness, whereas PandK alonehad negligible effects.Thelargest reductioninspecies richness occurred when all three elements were added in combination. Water played a different role compared with the other limiting resources. Species richness increased when water was added to the treatments with N and P or with N, Pand K. The decreases in species richness after resource additions were paralleled by increases in ANPPand decreases in light penetration into the plant canopy,suggestingthatincreasedlightcompetitionwas responsible for the negative effects of resource additions on plant species richness.

The leaf size/number trade-off in herbaceous angiosperms

Abstract: Aims In this study, we examined the extent to which between-species leaf size variation relates to variation in the intensity of leaf production in herbaceous angiosperms. Leaf size variation has been most commonly interpreted in terms of biomechanical constraints (e.g. affected by plant size limitations) or in terms of direct adaptation associated with leaf size effects in optimizing important physiological functions of individual leaves along environmental gradients (e.g. involving temperature and moisture). An additional interpretation is explored here, where adaptation may be more directly associated with the number of leaves produced and where relatively small leaf size then results as a trade-off of high ‘leafing intensity’—i.e. number of leaves produced per unit plant body size. Methods The relationships between mean individual leaf mass, number of leaves and plant body size were examined for 127 species of herbaceous angiosperms collected from natural populations in southern Ontario, Canada. Important Findings In all, 88% of the variation in mean individual leaf mass across species, spanning four orders of magnitude, is accounted for by a negative isometric (proportional) trade-off relationship with leafing intensity. These results parallel those reported in recent studies of woody species. Because each leaf is normally associated with an axillary bud or meristem, having a high leafing intensity is equivalent to having a greater number of meristems per unit body size—i.e. a larger ‘bud bank’. According to the ‘leafing intensity premium’ hypothesis, because an axillary meristem represents the potential to produce either a new shoot or a reproductive structure, high leafing intensity should confer greater architectural and/or reproductive plasticity (with relatively small leaf size required as a trade-off). This greater plasticity, we suggest, should be especially important for smaller species since they are likely to suffer greater suppression of growth and reproduction from competition within multi-species vegetation. Accordingly, we tested and found support for the prediction that smaller species have not just smaller leaves generally but also higher leafing intensities, thus conferring larger bud banks, i.e. more meristems per unit plant body size.

A comparison of species composition and stand structure between planted and natural mangrove forests in Shenzhen Bay, South China

Abstract: Aims For assisting faster restoration of damaged or severely disturbed coastal ecosystems, selected mangrove species have been planted on previously mangrove-inhabited sites of the tropical and subtropical coasts of southern China. The objective of this study was to understand the stand dynamics of the planted mangroves and their functional traits in comparison with natural mangrove forests under similar site conditions. Methods Species composition, stand density, tree size distribution, and aboveground production were investigated along three transects in a 50year-old planted mangrove stand and three transects in an adjacent natural mangrove stand in Shenzhen Bay, South China. Measurements were made on tree distribution by species, stand structure, and aboveground biomass (AGB) distribution. Analyses were performed on the spatial patterns of tree size distribution and species association. Important Findings We found that the planted and natural mangrove stands did not differ in stand density, average diameter at breast height (DBH), species composition, and AGB. Spatial distribution of AGB and frequency at species level were also similar between the planted and natural stands. However, the traits in stand structure were more variable in the planted stand than in the natural stand, indicating higher spatiotemporal heterogeneity in the development and succession of planted mangroves. Geostatistical analyses show that both DBH and AGB were spatially auto-correlated within a specific range in the direction perpendicular to coastline. More than 60% of the variance in these attributes was due to spatial autocorrelation. The Ripley’s K-function analysis shows that the two dominant species, Kandelia obovata and Avicennia marina, clumped in broader scales in the natural stand than in the planted stand and displayed significant interspecific competition across the whole transect. It is suggested that interspecific competition interacts with spatial autocorrelation as the underlying mechanism shaping the mangrove structure. This study demonstrates that at age 50, mangrove plantations can perform similarly in stand structure, spatial arrangement of selected stand characteristics and species associations to the natural mangrove forests.

Using coloured roots to study root interaction and competition in intercropped legumes and non-legumes

Abstract: Aims Root interactions between neighbour plants represent a fundamental aspect of the competitive dynamics in pure stand and mixed cropping systems. The comprehension of such phenomena places big methodological challenges, and still needs clarification. The objectives of this work were (i) to test if a species with coloured roots can be used to examine the interaction in a legume-non-legume intercropping system; (ii) to verify the importance of initial root growth on the successive root development of mixture component plants; (iii) to test if the root interaction in the shallow layers has consequences for deep root growth and (iv) to compare the effect of intraspecific and interspecific competition on root development and biomass growth. Methods A detailed study on root growth and interaction was carried out using rhizotron tubes where two legume species were grown in pure stands or were intercropped with red beet, a variety of Beta vulgaris L. with clear red roots. Within the rhizotrons, the three species were grown either without competitors, with two plants of the same species to measure intraspecific competition or with one legume and one red beet plant to study interspecific competition. The use of mixtures where one component has clearly coloured roots, together with several scalar measurements of root depth and proliferation, allowed the measurement of the root system of each species when grown in the mixtures. Important findings The use of rhizotron tubes coupled with species with coloured roots represented a valuable method to study the belowground interaction in mixed cropping systems. The initial root growth was a very important feature for the subsequent dominance of a species and it was not related to seed dimension. Initial root growth was also important because the root interactions in the shallower soil layers were found to influence the root growth in deeper soil. The root system of the red beet showed much faster and deeper growth than that of the legumes, and made red beet the dominant component in the mixtures while the legume root system was confined to the shallower soil layer. Intraspecific competition was well tolerated by the legumes, but it was limiting for the highly competitive red beet. The outcome of root interaction between neighbour plants was confirmed to be speciesspecific as it changed according to the intensity of the competitive effect/response of each species of the mixture: both legumes were slightly affected by the intraspecific and highly affected by interspecific competition while red beet was more affected by intraspecific competition but strongly dominant when intercropped with legumes.

Effects of biological soil crusts on profile distribution of soil water, organic carbon and total nitrogen in Mu Us Sandland, China

Abstract: Aims Biological soil crusts (BSCs) can affect soil properties including water dynamics and cycling of soil carbon and nitrogen in dryland ecosystems. Previous research has mostly focused on effects of BSCs on soil water distribution or carbon and nitrogen fixation in the surface soil layer. Thus, little is known about effects of BSCs on properties throughout the soil profile. In the current study, we assessed the effects of BSCs on the distribution of soil water content (SW), soil organic carbon content (SOC) and soil total nitrogen content (STN) throughout the soil profile as well as the influence of water conditions on the effects of BSCs. Methods In a field investigation in Mu Us Sandland, North China, soil samples were taken from plots with and without BSCs on 13 and 28 September 2006, respectively. On the two sampling dates, average soil gravimetric water content was 3.83% (61.29%) and 5.08% (60.89%), respectively, which were regarded as low and high water conditions. Soil samples were collected every 5 cm to a depth of 60 cm, and SW, SOC and STN were measured in the laboratory. Important Findings (i) BSCs affected profile distribution of SW, SOC and STN. In addition, water conditions within the plots significantly modified BSCs’ effects on the profile distribution of SW, but marginally affected the effects on SOC and STN. (ii) Under high water conditions, SW in the surface soil layer (0–10 cm) was higher in soils with BSCs compared to those without BSCs, while the opposite was true in the deep soil layer (30–55 cm). (iii) Under low water conditions, SW was lower with BSCs compared with no BSCs in near-surface (5–20 cm) and deep (25–40 cm) soil layers. (iv) BSCs affected SOC and STN only in the surface soil layer (0–5 cm) and were modified by plot water conditions.

On the relationship between plant species diversity and genetic diversity of Plantago lanceolata (Plantaginaceae) within and between grassland communities

Abstract: Aims and Methods The relationship between genetic diversity and species diversity and the underlying mechanisms are of both fundamental and applied interest. We used amplified fragment length polymorphism (AFLP) and vegetation records to investigate the association between genetic diversity of Plantago lanceolata and plant species diversity using 15 grassland communities in central Germany. We used correlation and partial correlation analyses to examine whether relationships between genetic and species diversity were direct or mediated by environmental differences between habitats. Important Findings Both within- and between-population genetic diversity of P. lanceolata were significantly positively correlated with plant species diversity within and between sites. Simple and partial correlations revealed that the positive correlations indirectly resulted from the effects of abiotic habitat characteristics on plant species diversity and, via abundance, on genetic diversity of P. lanceolata. Thus, they did not reflect a direct causal relationship between plant species diversity and genetic diversity of P. lanceolata, as would have been expected based on the hypothesis of a positive relationship between plant species diversity and niche diversity.

Patterns of plant diversity at high altitudes on the Qinghai-Tibetan Plateau

Abstract: Aims To describe the biodiversity patterns of plants along an altitudinal gradient oil the Quighai-Tibetan Plateau and to clarify file bias in plant specimen records at high altitude Methods We conducted a large-scale investigation of vegetation at a wide range of altitudes, focusing oil a high-altitudinal range (3 200-5 200 m) at different locations on the Qinghai-Tibetan Plateau We then compared the altitudinal distribution of plant species obtained from our field investigation with that in plant specimen records from published sources and an online database Important Findings Our data provide evidence that altitude plays a large role in regulating species composition on the Qinghai-Tibetan Plateau WC Could not, however, detect a clear relationship between altitude and spe cies richness, although a weak monotonically increasing trend of richness was detected with increasing altitude According to specimen records, most species have been sampled at a wide range of altitudes, and the average range of 145 species is >2 000 m Despite this wide range, more than half of the species we observed were at higher altitudes than the specimen records indicate High-altitude areas have probably been so poorly sampled that Only a small fraction of the resident species has been recorded This' Study clearly shows the regional bias of specimen records in the Qinghai-Tibetan Plateau

Phylogeography of Potentilla fruticosa, an alpine shrub on the Qinghai-Tibetan Plateau

Abstract: Aims Our objectives were (i) to elucidate the phylogeography of chloroplast DNA (cpDNA) in Potentilla fruticosa in relation to Quaternary climate change and postglacial colonization, (ii) to infer historical population range expansion using mismatch distribution analyses and (iii) to locate the refugia of this alpine species on the QinghaiTibetan plateau during glacial–interglacial periods. Methods Potentilla fruticosa is a widespread species distributed on the Qinghai-Tibetan Plateau. We sampled leaves of P. fruticosa from 10 locations along a route of ;1 300 km from the northeastern plateau (Haibei, Qinghai) to the southern plateau (Dangxiong, Tibet). We examined the cpDNA of 15 haplotypes for 87 individuals from the 10 populations based on the sequence data from ;1 000 base pairs of the trnS–trnG and rpl20–rps12. Phylogenetic relationship of haplotypes was analyzed using the Phylip software package and the program TCS. The diversity of populations indices was obtained using the program ARLEQUIN. Important Findings With the limited samples, we found that (i) higher nucleotide diversity often occurs in high-altitude populations, (ii) the ancestral haplotypes distribute in the populations with higher nucleotide diversity than recent haplotypes, (iii) the expansion time of population in the high altitudes was estimated to be approximately at 52–25 ka BP (1000 years Before Present, where ‘‘Present’’ is AD 1950) and that in the low altitudes to be ;5.1–2.5 ka BPand (iv) the source location of P. fruticosa is at the high altitudes, which might provide refugia for the species during the interglacial warm periods. The species expanded from the high-elevated locations on the Tanggula Mountains during the Holocene.

CO2 enrichment accelerates successional development of an understory plant community

Abstract: Rising concentrations of atmospheric carbon dioxide ([CO{sub 2}]) may influence forest successional development and species composition of understory plant communities by altering biomass production of plant species of functional groups. Here, we describe how elevated [CO{sub 2}] (eCO{sub 2}) affects aboveground biomass within the understory community of a temperate deciduous forest at the Oak Ridge National Laboratory sweetgum (Liquidambar styraciflua) free-air carbon dioxide enrichment (FACE) facility in eastern Tennessee, USA. We asked if (i) CO{sub 2} enrichment affected total understory biomass and (ii) whether total biomass responses could be explained by changes in understory species composition or changes in relative abundance of functional groups through time. The FACE experiment started in 1998 with three rings receiving ambient [CO{sub 2}] (aCO{sub 2}) and two rings receiving eCO{sub 2}. From 2001 to 2003, we estimated species-specific, woody versus herbaceous and total aboveground biomass by harvesting four 1 x 0.5-m subplots within the established understory plant community in each FACE plot. In 2008, we estimated herbaceous biomass as previously but used allometric relationships to estimate woody biomass across two 5 x 5-m quadrats in each FACE plot. Across years, aboveground biomass of the understory community was on average 25% greater in eCO{sub 2} more » than in aCO{sub 2} plots. We could not detect differences in plant species composition between aCO{sub 2} and eCO{sub 2} treatments. However, we did observe shifts in the relative abundance of plant functional groups, which reflect important structural changes in the understory community. In 2001-03, little of the understory biomass was in woody species; herbaceous species made up 94% of the total understory biomass across [CO{sub 2}] treatments. Through time, woody species increased in importance, mostly in eCO{sub 2}, and in 2008, the contribution of herbaceous species to total understory biomass was 61% in aCO{sub 2} and only 33% in eCO{sub 2} treatments. Our results suggest that rising atmospheric [CO{sub 2}] could accelerate successional development and have longer term impact on forest dynamics. « less

Natural 15N abundance in soils and plants in relation to N cycling in a rangeland in Inner Mongolia

Abstract: Aims Natural N abundance provides integrated information about nitrogen (N) input, transformation and output, indirectly reflecting N cycling traits within terrestrial ecosystems. However, relationships between natural N abundance and N cycling processes are poorly understood in China. Here, our primary objectives were to (i) examine the effects of grazing at varying levels of intensity on dN of soils and plants in a semi-arid grassland; (ii) detect the relationships between dN of soils and four major N cycling processes (i.e. mineralization, nitrification, denitrification and ammonia volatilization); and (iii) determine whether dN of soils can be used as an indicator of N cycling in this semi-arid grassland. Methods The field experiment was conducted within the long-term (17-year) grazing enclosures in a semi-arid grassland in Inner Mongolia. Five grazing intensities (0.00, 1.33, 2.67, 4.00 and 5.33 sheep ha ) were designed. dN values of topsoils (0–10 cm), surface soils (0–2 cm) and plants were measured in 2006. Differences in dN of soils and plants between the five grazing intensities were examined. Rates of four soil N cycling processes were measured periodically during the 2005 and 2006 growing seasons. The dN values of topsoils were linked to the four N cycling processes to investigate their relationships. Important Findings The dN values of topsoils (5.20–5.96&) were substantially higher than the dN values of plants (2.51–2.93&) and surface soils (1.44–2.92&) regardless of grazing intensities. The N-depleted N losses during microbial decomposition of organic matter in concert with the downward movement of residual substrate over time are the possible causes of higher dN values in topsoils than in surface soils. In addition, the dN values of topsoils were positively correlated with the dN values of both plants and surface soils. Grazing, especially the high-intensity grazing (5.33 sheep ha ), resulted in a significant decrease in dN of surface soils. However, no statistically significant variations in dN of topsoils and plants were found in response to grazing. The dN values of topsoils exhibited significant dependence on the cumulative rates of NH3 volatilization, net nitrification and denitrification in 2005 but not in 2006.

Generalized food-deceptive orchid species flower earlier and occur at lower altitudes than rewarding ones

Abstract: Aims Food-deceptive pollination, in which plants do not offer any food reward to their pollinators, is common within the Orchidaceae. As food-deceptive orchids are poorer competitors for pollinator visitation than rewarding orchids, their occurrence in a given habitat may be more constrained than that of rewarding orchids. In particular, the success of deceptive orchids strongly relies on several biotic factors such as interactions with co-flowering rewarding species and pollinators, which may vary with altitude and over time. Our study compares generalized food-deceptive (i.e. excluding sexually deceptive) and rewarding orchids to test whether (i) deceptive orchids flower earlier compared to their rewarding counterparts and whether (ii) the relative occurrence of deceptive orchids decreases with increasing altitude. Methods To compare the flowering phenology of rewarding and deceptive orchids, we analysed data compiled from the literature at the species level over the occidental Palaearctic area. Since flowering phenology can be constrained by the latitudinal distribution of the species and by their phylogenetic relationships, we accounted for these factors in our analysis. To compare the altitudinal distribution of rewarding and deceptive orchids, we used field observations made over the entire Swiss territory and over two Swiss mountain ranges. Important Findings We found that deceptive orchid species start flowering earlier than rewarding orchids do, which is in accordance with the hypotheses of exploitation of naive pollinators and/or avoidance of competition with rewarding co-occurring species. Also, the relative frequency of deceptive orchids decreases with altitude, suggesting that deception may be less profitable at high compared to low altitude.

The role of shrub (Potentilla fruticosa) on ecosystem CO2 fluxes in an alpine shrub meadow

Abstract: Aims Recent studies have shown that alpine meadows on the Qinghai-Tibetan plateau act as significant CO2 sinks. On the plateau, alpine shrub meadow is one of typical grassland ecosystems. The major alpine shrub on the plateau is Potentilla fruticosa L. (Rosaceae), which is distributed widely from 3 200 to 4 000 m. Shrub species play an important role on carbon sequestration in grassland ecosystems. In addition, alpine shrubs are sensitive to climate change such as global warming. Considering global warming, the biomass and productivity of P. fruticosa will increase on Qinghai-Tibetan Plateau. Thus, understanding the carbon dynamics in alpine shrub meadow and the role of shrubs around the upper distribution limit at present is essential to predict the change in carbon sequestration on the plateau. However, the role of shrubs on the carbon dynamics in alpine shrub meadow remains unclear. The objectives of the present study were to evaluate the magnitude of CO2 exchange of P. fruticosa shrub patches around the upper distribution limit and to elucidate the role of P. fruticosa on ecosystem CO2 fluxes in an alpine meadow. Methods We used the static acrylic chamber technique to measure and estimate the net ecosystem productivity (NEP), ecosystem respiration (Re), and gross primary productivity (GPP) of P. fruticosa shrub patches at three elevations around the species' upper distribution limit. Ecosystem CO2 fluxes and environmental factors were measured from 17 to 20 July 2008 at 3 400, 3 600, and 3 800 m a.s.l. We examined the maximum GPP at infinite light (GPP(max)) and maximum R-e (R-emax) during the experimental time at each elevation in relation to aboveground biomass and environmental factors, including air and soil temperature, and soil water content. Important Findings Patches of P. fruticosa around the species' upper distribution limit absorbed CO2, at least during the daytime. Maximum NEP at infinite light (NEPmax) and GPP(max) of shrub patches in the alpine meadow varied among the three elevations, with the highest values at 3 400 m and the lowest at 3 800 m. GPP(max) was positively correlated with the green biomass of P. fruticosa more strongly than with total green biomass, suggesting that P. fruticosa is the major contributor to CO2 uptake in the alpine shrub meadow. Air temperature influenced the potential GPP at the shrub-patch scale. R-max was correlated with aboveground biomass and R-emax normalized by aboveground biomass was influenced by soil water content. Potentilla fruticosa height (biomass) and frequency increased clearly as elevation decreased, which promotes the large-scale spatial variation of carbon uptake and the strength of the carbon sink at lower elevations.

Mating system and pollination biology of a high-mountain perennial plant, Rhodiola dumulosa (Crassulaceae).

Abstract: Aims Rhodiola dumulosa is a perennial herb growing in a naturally fragmented habitat of high-mountain rocks. This research aims to (i) investigate the mating system characteristics and pollination biology of R. dumulosa, (ii) study the effects of ecological factors on the mating system and pollination biology of R. dumulosa and (iii) assess the relationship between its pollination and mating system. Methods Mating system parameters were analysed using allozyme markers. Growth of pollen tubes from artificial self- and cross-pollination was also examined. Field investigations were conducted on insect flower visitation during the blooming period of R. dumulosa. Relationships among mating system, insect flower visitation frequency and environmental factors were assessed.

Biodiversity and belowground interactions mediate community invasion resistance against a tall herb invader

Abstract: Aims Species-rich plant communities are hypothesized to be more resistant against plant invasions because they use resources in a more efficient way. However, the relative contributions of aboveground competition and belowground interactions for invasion resistance are still poorly understood. Methods We compared the performance of Knautia arvensis transplants growing in plots differing in plant diversity both under full competition and with shoots of neighbors tied back to determine the relative strength of aboveground competition in suppressing this test invader without the confounding effect of shading. In addition, we assessed the effects of belowground competition and soil-borne pathogens on transplant performance. Important Findings Both aboveground competition and plant species richness strongly and independently affected invader performance. Aboveground biomass, height, leaf mass per area and flowering of transplanted individuals of K. arvensis decreased with increasing species richness of the host community. Species-rich and species-poor communities both imposed equally strong aboveground competition on K. arvensis. However, belowground interactions (especially belowground root competition) had strong negative effects on transplant performance. In addition, the presence of grasses in a plant community further reduced the performance of K. arvensis. Our results suggest that belowground competition can render species-rich host communities more suppressive to newly arriving species, thus enhancing community invasion resistance.

Role of endogenous hormones, glumes, endosperm and temperature on germination of Leymus chinensis (Poaceae) seeds during development

Abstract: Aims Leymus chinensis is an original dominant plant in the Songnen grass- land, and it has great value for restoration of severely degraded land. However, seeds are dormant, and low germination percentage is a problem for restoringL.chinensis grassland. The mechanism of seed dormancy is not been well understood. The primary aims of the pres- ent study were to investigate the dormancy mechanism ofL.chinensis seeds (caryopses) with reference to the role of embryo-covering layers, endogenous hormones and temperature. Methods Changes in concentration of the endogenous hormones GA3, indole- acetic acid (IAA), zeatin riboside (ZR) and abscisic acid (ABA) inL.chi- nensis seeds from anthesis to maturity were measured by the enzyme- linked immunosorbent assay method. Germination at different stages of maturity were tested at 16/28C, 5/28C and 5/35C for intact seeds with glumes (control), intact seeds with glumes removed (naked- whole seeds) and intact seeds with glumes and one-half of the endo- sperm removed (naked-half seeds). Important Findings Of the four endogenous hormones monitored, only the concentra- tion of ZR differed significantly between the beginning and the end of seed development (increased); the GA3/ABA ratio also did not differ. Rank of germination percentage of control at the three tem- perature regimens was 5/28C > 16/28C > 5/35C. Germination per- centage of the naked-half seeds reached 100% under the three temperature regimens. We concluded that dormancy of L.chinensis seeds is not mainly controlled by endogenous hormones. Germina- tion temperature, mechanical resistance of glumes and inhibition of endosperm are the main factors controlling dormancy and germina- tion of L.chinensis seeds.

Effects of resource availability on the trade-off between seed and vegetative reproduction

Abstract: Aims To explore whether the trade-off between seed and vegetative reproductive modes is flexible in environments with different amounts of available resources to maintain optimal behaviors. Methods A transition matrix model was established to determine the optimal trade-off between seed and vegetative reproduction in resources– variable habitats. Important Findings The model predicts that plants allocate more resources to seed reproduction when available resources are scarce. With increasing resources, more vegetative propagules are produced. However, if resources keep increasing to a harmful level, plants would switch to seeds again.

Seasonal dynamics of foliar antioxidative enzymes and total anthocyanins in natural populations of Iris pumila L.

Abstract: Aims Plants in their natural habitats frequently cope with a multitude of abiotic stresses, such as high light intensity, extreme temperatures and water deficit, which often co-occur during periods of drought, especially in semi-arid and arid regions. Exposure of plants to stressful environmental conditions usually induce overproduction of reactive oxygen species (ROS) that, as highly toxic derivatives of O2, can assault all cell macromolecules, leading to the disruption of cellular homeostasis and, consequently, the uncoupling of major metabolic processes, the photosynthesis and photorespiration. In order to minimize ROS-mediated cellular damage, plants have evolved highly efficient antioxidative defense systems that include both enzymatic and non-enzymatic components. Since abiotic stress can also operate as a strong evolutionary force that shapes adaptations in natural plant populations, the aim of this study was to examine the seasonal variation patterns of two distinct antioxidative systems, ROS-scavenging enzymes and anthocyanin pigments, in the leaf tissue of a steppe plant, Iris pumila, as expressed under contrasting light conditions that the species regularly experiences in the wild. Methods We selected two natural populations of I.pumila inhabiting the alternative radiation environments in the Deliblato Sands, a sunexposed dune site and a woodland understory. The specific activity of three antioxidative enzymes, superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) and the content of total anthocyanins were examined in leaves of I.pumila plants collected from each of the 31 Iris clones (17 in the exposed population and 14 in the shaded population) once during each of the three seasons, spring, summer and autumn in 2004. Specifically, a fully expanded leaf was cut from each clonal plant between 15:00 and 16:00 h, immediately frozen in liquid nitrogen and stored at 70 C until preparation. Important Findings Generally, all three antioxidative enzymes were up-regulated in summer-harvested leaves compared to their spring or autumn counterparts, as was observed for the concentration of foliar anthocyanins, indicating that strengthening of antioxidant systems was the key mechanism for long-term acclimatization of I.pumila plants to stressful environmental conditions within their natural ecological niches. When plants from contrasting radiation environments were compared, SOD and CAT activities appeared to be greater in shade-exposed than in sun-exposed leaves. Conversely, POD activity and the content of foliar anthocyanins were notably higher in foliage experiencing full sunlight relative to those developed under vegetation canopy, suggesting the synergistic function of these two molecules in protecting leaf cells against photoinhibitory and photooxidative effects of strong light.

Experiment meets biogeography: plants of river corridor distribution are not more stress tolerant but benefit less from more benign conditions elsewhere

Abstract: Aims Factors limiting distributions of species are fundamental to ecology and evolution but have rarely been addressed experimentally for multiple species. The conspicuous linear distribution patterns of plant species confined to river corridors in the Central European lowlands constitute an especially long-standing distribution puzzle. We experimentally tested our novel hypothesis that the tolerance of species to river corridor conditions is independent of the degree of confinement to river corridor habitats, but that species not confined to river corridors are better able to take advantage of the more benign non-river corridor conditions. Methods We grew 42 herbaceous species differing in their confinement to river corridors in a common garden experiment on loamy soil typical for river corridor areas and sandy soil typical for non-river corridor areas, and with and without a flooding period. For a subset of species, we grew plants of both river corridor and non-river corridor origin to test for adaptation to river corridor conditions. Important findings Species more confined to river corridor areas benefited less from the more benign non-flooded and non-river corridor soil conditions than species of wider distributional range did. For subsets of 7 and 12 widespread species, the response to flooding and soil origin, respectively, did not differ between plants from river corridor sites and plants from other sites, suggesting that the habitat tolerance of widespread species is due to phenotypic plasticity rather than to local adaptation. Overall, we found clear support for our novel hypothesis that species not confined to river corridors are more able to take advantage of the more benign non-river corridor conditions. Our study provides a general hypothesis on differences between species confined to stressful habitats and widespread species out for test in further multispecies comparative experiments.

Time course of plant diversity effects on Centaurea jacea establishment and the role of competition and herbivory

Abstract: Aims Invasion resistance in experimental plant communities is known to increase with increasing diversity and further to depend on the presence of particular functional groups. To test whether these effects also hold true for the invader establishment phase beyond the seedling stage, we studied survival and performance ofCentaureajacea L. (brown knapweed) planted into experimental grassland communities of varying plant biodiversity over three consecutive years. Moreover, we analysed the role of insect herbivory and biomass of the recipient community for mediating diversity effects. Methods In 2005, seedlings of Centaurea were transplanted into experimental grassland communities (the Jena Experiment) covering a species richness (1–60) and functional group richness (1–4) gradient. Half of these transplants and the community surrounding them in each plot were sprayed with insecticide while the other half served as control. In 2006 and 2007 (during the second and third year after transplantation), we recorded survival, growth-related (e.g. transplant biomass, height) and reproduction-related traits (e.g. number of flower heads). Annual data on community aboveground biomass served as covariate to investigate mediating effects of aboveground competition with the recipient community. Important Findings Species richness was the most important factor responsible forCentaurea limitation. Higher levels of diversity decreased survival and all performance traits in both years. These diversity effects were partly driven by community biomass, but not fully explained by that covariate, suggesting the importance also of further processes. The influence of functional group richness was strong in the second year after transplantation and weaker in the third year. Among the particular functional groups, only the presence of legumes showed strong negative effects on Centaurea survival and weak negative effects on growth and reproduction, the latter two being mediated by biomass. Insect herbivore reduction considerably benefited Centaurea in sprayed monocultures, where it grew significantly larger than in all other diversity levels and than in the control subplots. We conclude that effects of plant community properties on invading individuals change in the course of establishment, that plant species richness effects are also important during later stages of establishment, and that biomass (especially at high diversity) and herbivory (especially at low diversity) of the recipient community are important in mediating community effects on invaders.

Influence of evenness on the litter-species richness–decomposition relationship in Mediterranean grasslands

Abstract: Aims Human impacts on natural ecosystems induce changes in their functioning through alterations in species richness, composition and evenness of plant communities. Most litter diversity–decomposition processes studies have only manipulated species richness, ignoring the role of evenness. Here, results from a field litterbag experiment are presented to test whether changes in evenness of species distribution in litter mixtures affected the strength of the litter-species richness–decomposition relationship. Methods Ten herbaceous species abundant in Mediterranean grassland communities and representative of different genera and functional groups were used. Species richness was directly manipulated to produce litter mixtures of three and six plant species, as well as litter of each individual species used. Each level of species richness was replicated several times such that each repeat had a different species composition. Three- and six-species litter mixtures were also treated to vary in evenness (three levels). Decomposition rate was assessed by percentage dry weight loss over the 90 days of the experiment. Important Findings Decomposition rate was positively related to the linear increase in litter-species richness and was affected by the composition of the litter-species mixture. Decomposition rates differed significantly between evenness treatments and moreover, the strength of the positive relationship between litter-species richness and decomposition rate decreased notably in the low-evenness treatment. The effects of evenness on decomposition rate, at different richness levels, were partially explained by the differences in the initial litter mixture’s carbon-to-nitrogen ratio within them. This study reveals that shortterm decomposition rate is positively affected by both components of Mediterranean grassland litter-species diversity.

N:P stoichiometry in Ficus racemosa and its mutualistic pollinator

Abstract: Aims Nitrogen (N) and phosphorus (P) are limiting nutrients to life across a variety of ecosystems. N:P stoichiometry, concerning the balance of these two elements, has recently received great attention. However, little is known about the nature of N:P stoichiometry in obligate mutualism. Methods N:P stoichiometry of Ficus racemosa and its pollinating wasp Ceratosolenfusciceps, an example of coevolving obligate mutualism, was investigated, and the N:P stoichiometric traits of male versus female wasps were compared. Important Findings Nutrient concentrations in C. fusciceps were much higher than in its host. N enrichment in fig wasp was evidently stronger than phosphorus. N concentrations of male fig wasps were significantly higher than those of females, while P concentrations of female fig wasps were remarkably higher than those of male ones. Therefore, N:P ratios in male fig wasps were significantly greater than in female fig wasps. N:P ratio in fig-pollinating wasp displayed linear functions to fig N contents, suggesting that N limitation in fig wasps may dominate the nutritional relationship between fig pollinator and its host. Fig wasp population size had significant influences on N concentrations in host fig and female wasp per se. Driven by the nutritional stress of pollinating and parasite insects, fig fruit preferred increasing its diameter first but not nutrient richness. Values for N and P contents of fig pollinators showed seasonal differences with greater N:P ratios in dry season than in rainy season. The observations suggest that tropical climate change would result in more severe N limitation to fig-pollinating wasp and may further influence the stability of fig–fig wasp mutualism.

Tornado effects on damage, resprouting and spatial heterogeneity in the Cross Timbers ecotone of Oklahoma, USA

Abstract: Aims In order to better understand how tornados structure the ecotone between eastern deciduous forest and tallgrass prairie, we sampled trees in a recent tornado blowdown area and in the adjacent undisturbed forest. Both are part of the Cross Timbers ecotone of Osage County, Northeastern Oklahoma, USA. Methods We set up a 1-ha square plot in each area and sampled all tree stems at least 50 cm tall where stems were identified to species and measured for size and spatial location in both plots. For the stems in the blowdown plot, we also scored damage and resprouting. We then used the spatial location data to compute the spatial heterogeneity and degree of clumping in both areas. Important Findings Significant clumping was observed in the control forest at the small spatial scale of 1–8 m and at the medium spatial scale of 30–36 m. The blowdown area: showed domination by post oak (Quercus stellata) with small stems, branch damage and stem resprouting above 1 m most common; had no trees that either lost their leaves without branch or stem damage or lived without some sort of resprouting, had a significant negative correlation between damage and resprouting and clumped only at small spatial scales for stems of medium size, for stems with branch damage and for stems that resprouted at or below 1 m height. We conclude that in addition to largely eliminating a forest’s spatial heterogeneity, tornados may also structure this ecotone by increasing tree persistence through resprouting.

Assessing frost hardiness of Pinus bungeana shoots and needles by electrical impedance spectroscopy with and without freezing tests

Abstract: Aims Nursery and forest operations require that frost hardiness results be produced faster than can be provided by controlled freezing tests. There is a great challenge to develop a rapid method for predicting frost hardiness that might not necessitate controlled freezing tests. The aim of this study was to examine the assessment of the frost hardiness of shoots and needles of Pinus bungeana by electrical impedance spectroscopy (EIS) with and without controlled exposure to freezing. Methods The frost hardiness of current-year shoots and needles of P. bungeana in an 8-year-old provenance field trial was measured at Shisanlin Nursery in Beijing, China, from September 2006 to January 2007 by means of EIS and conventional electrolyte leakage (EL). In the same plants, but without controlled freezing test, were monitored the EIS parameters in current-year shoots and needles. Important Findings The results showed that (i) after controlled freezing tests, the frost hardiness estimated by EIS parameters (extracellular resistance, re, and membrane time constant, sm) was significantly correlated with the frost hardiness assessed by EL method (r = 0.95) and (ii) for the samples not exposed to controlled freezing treatment, the relaxation time s1 for shoots and b for needles had greater correlations with the frost hardiness estimated by EL after controlled freezing tests relative to the other parameters (r = � 0.90 for shoots and r = 0.84 for needles, respectively). The parameters re of shoots and needles and sm of needles might be applied for measuring frost hardiness of samples after exposed to controlled freezing tests. The frost hardiness results can be obtained within 48 h. The parameters s1 of shoots and b of needles could be used for estimating the frost hardiness of samples without using a controlled freezing test. The frost hardiness results can be obtained within 24 h.

Compensatory effects between Pinus massoniana and broadleaved tree species

Abstract: Aims Evaluation of the interaction intensity between Masson pine (Pinus massoniana) and broadleaved trees will facilitate selecting tree combinations suitable for reforestation in abandoned sites in subtropical areas. Methods Pinus massoniana and seven broadleaved trees species were grown either in monoculture or in two-species mixture. Biomass of tree species was measured and inter-specific interactions were estimated using log response ratio. Test of homogeneity of variances was performed to compare the stability of biomass in the monoculture of the broadleaved trees with that in the mixture. Important Findings Our results showed that the direction and intensity of interactions between P. massoniana and the broadleaved trees varied from year to year and the identity of the broadleaved species. Facilitative interactions were found between Camellia oleifera, Rhus chinensis and P. massoniana. Pinus massoniana had competitive effects on Lithocarpus glaber, Cyclobalanopsis glauca and Elaeocarpus japonicus. Significantly negative relations were found between biomass of P. massoniana and the broadleaved trees in the third year of the experiment, and the compensatory effects between P. massoniana and the broadleaved trees may be involved in stability maintenance in the multi-species forests in the subtropical area. The results of homogeneity test of variances also showed that the biomass per pot in the mixture had significantly lower variances than that in the monoculture, suggesting that total biomass is more stable in the mixture than the monoculture.

UV light spectral response of photosynthetic photochemical efficiency in alpine mosses

Abstract: Aims Bryophytes play an important role in primary production in harsh alpine environment. As other alpine plants, the alpine bryophytes are often exposed to stronger UV radiation than lowland plants. Plants growing under high UV radiation may differ from those from low UV regimes in their physiological response to UV radiation. We were to (i) test the hypothesis and to address whether and/or how alpine bryophytes differ in photosynthetic photochemical characteristics in response to UV light and (ii) understand the potential effects of UV radiation on photosynthetic photochemical process in alpine bryophytes. Methods We examined the maximum quantum efficiency of photosystem II (PSII) photochemistry (Fv/Fm) for two alpine bryophyte species, Distichium inclinatum and Encalypta alpine, from a Kobresia humilis meadow and a Kobresia tibetica wetland, respectively, in Haibei, Qinghai (3729#N, 10112#E, altitude 3 250 m), and for a lowland bryophyte,Polytrichum juniperinum, under different spectrum of UV light. Biological spectral weighting function (BSWF) was obtained to evaluate the effect of UV light on the physiological response in these species. Important Findings 1) The maximum quantum efficiency of photosystem II photochemistry (Fv/Fm) declined linearly with the increase of radiation dose in wavelengths from 250 to 420 nm. The effect of UV radiation on Fv/Fm decreased with higher rate from 250 to 320 nm and from 400 to 420 nm than in UVA range. 2) The three species from different ecosystems contrasting in altitudes showed similar pattern of UV effectiveness. In comparison with other species reported so far, the moss BSWF was among those with the most modest decrease trend with spectrum effect of UV light 50 times higher at 250 than at 420 nm. 3) Under the scenario of 16% reduction of stratospheric ozone, the integrated effectiveness from 290 to 345 nm increased only 5%, suggesting that the photochemical activity of the bryophyte PSII is likely to insensitive to O3 depletion.