Showing papers in "Trees-structure and Function in 2018"

Quantifying branch architecture of tropical trees using terrestrial LiDAR and 3D modelling

Abstract: Tree architecture is the three-dimensional arrangement of above ground parts of a tree. Ecologists hypothesize that the topology of tree branches represents optimized adaptations to tree’s environment. Thus, an accurate description of tree architecture leads to a better understanding of how form is driven by function. Terrestrial laser scanning (TLS) has demonstrated its potential to characterize woody tree structure. However, most current TLS methods do not describe tree architecture. Here, we examined nine trees from a Guyanese tropical rainforest to evaluate the utility of TLS for measuring tree architecture. First, we scanned the trees and extracted individual tree point clouds. TreeQSM was used to reconstruct woody structure through 3D quantitative structure models (QSMs). From these QSMs, we calculated: (1) length and diameter of branches > 10 cm diameter, (2) branching order and (3) tree volume. To validate our method, we destructively harvested the trees and manually measured all branches over 10 cm (279). TreeQSM found and reconstructed 95% of the branches thicker than 30 cm. Comparing field and QSM data, QSM overestimated branch lengths thicker than 50 cm by 1% and underestimated diameter of branches between 20 and 60 cm by 8%. TreeQSM assigned the correct branching order in 99% of all cases and reconstructed 87% of branch lengths and 97% of tree volume. Although these results are based on nine trees, they validate a method that is an important step forward towards using tree architectural traits based on TLS and open up new possibilities to use QSMs for tree architecture.

Climate change and the regulation of wood formation in trees by temperature

Abstract: A better understanding of the influence of environmental conditions on wood formation should help to improve the radial growth of trees and to prepare for climate change. The cambial activity of trees is associated with seasonal cycles of activity and dormancy in temperate zones. The timing of cambial reactivation in early spring and dormancy in autumn plays an important role in determination of the cambial growth and the environmental adaptivity of temperate trees. This review focuses on the temperature regulation of the timing of cambial reactivation and xylem differentiation and highlights recent advances of bud growth in relation to cambial activity of temperate trees. In addition, we discuss relationships between the timing of cambial reactivation, start of xylem differentiation and changes in levels of storage materials to identify the source of the energy required for cell division and differentiation. We also present a summary of current understanding of the effects of rapid increases and decreases in temperature on cambial activity, by localized heating and cooling, respectively. Increases in temperature from late winter to early spring influence the physiological processes that are involved in the initiation of cambial reactivation and xylem differentiation both in localized heated stems and under natural conditions. Localized cooling has a direct effect on cell expansion, the thickening of walls of differentiating tracheids, and the rate of division of cambial cells. A rapid decrease in temperature of the stem might be the critical factor in the control of latewood formation and the cessation of cambial activity. Therefore, temperature is the main driver of cambial activity in temperate trees and trees are able to feel changes in temperature through the stem. The climate change might affect wood formation in trees.

Influence of arbuscular mycorrhizal fungi on the functional mechanisms associated with drought tolerance in carob (Ceratonia siliqua L.)

Abstract: Arbuscular mycorrhizal symbiosis strengthened the mechanisms developed by carob to withstand drought stress, including improved water relations, increased cell wall rigidity and osmolytes accumulation, and enhanced oxidative stress alleviation. The present investigation was carried out to provide more insight into the influence of arbuscular mycorrhizal fungi (Funneliformis mosseae, Rhizophagus fasciculatus, and Rhizophagus intraradices) on drought tolerance of carob. Non-mycorrhizal (NM) and arbuscular mycorrhizal (AM) carob plants were subjected to two watering regimes, 75% of field capacity (well water) or 25% of field capacity (water stress). Obtained results showed that stressed AM plants exhibited increased performance in terms of growth and biomass production, water and nutrient acquisition, and oxidative stress alleviation compared to NM plants. In fact, under limited water regime, AM plants maintained high stomatal conductance and high relative water content (over 94%) due to their high water and nutrient uptake efficiency. Moreover, AM plants especially those associated with F. mosseae maintained high membrane integrity (over 80%), high cell wall rigidity, and high leaf water potential and osmotic potential at full turgor and at turgor loss, while these parameters steeply decreased in NM plants. Furthermore, drought-stressed AM plants showed decreased hydrogen peroxide and malondialdehyde contents associated with increased activities of superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, and catalase compared to their relative NM plants. Thus, AMF strengthened the mechanisms involved in drought tolerance of carob by improving water relations, increasing cell wall rigidity, and enhancing oxidative stress alleviation. Funneliformis mosseae was the most effective in improving carob tolerance to drought stress.

Is embolism resistance in plant xylem associated with quantity and characteristics of lignin

Abstract: Key message We suggest, based on data available for lignin content and Ψ 50 , a limiting relationship between embolism resistance and lignin content across various groups of seed plants.

Are storage and tree growth related? Seasonal nutrient and carbohydrate dynamics in evergreen and deciduous Mediterranean oaks

Abstract: Seasonal dynamics of branch carbohydrates differed sharply between coexisting evergreen and deciduous Mediterranean oaks. Branch carbon storage was crucial in the evergreen, while it played a minor role in the deciduous oaks. The aim of this study was to describe the seasonal dynamics of nutrients and NSC in relation to the aboveground phenology of coexisting winter-deciduous (Quercus faginea) and evergreen (Quercus ilex subsp. ballota) oak species, and to analyse the relationship between the resource budget of branches and shoot growth. Monthly concentrations of nitrogen (N), phosphorus (P), potassium (K) and non-structural carbohydrates (NSC) plus the aboveground phenology of branches were measured over 2 years. We also analysed the correlation between the resource budget of branches prior to the growing season and the subsequent shoot and stem growth. Seasonal branch nutrient dynamics could be explained by shoot growth phenology, showing similar patterns across species. However, NSC dynamics varied between the two species, owing to the differences in leaf phenology and the contrasting role of branches as storage sites. NSC and N branch storage were crucial for the early stages of shoot growth in the evergreen trees. Accordingly, branch N and NSC storage pools in late winter correlated positively with spring growth, and NSC concentrations dropped during bud burst in all branch organs of Q. ilex. Contrastingly, branch NSC concentrations of the deciduous Q. faginea were only marginally affected by spring growth and no relationship was observed between branch N and NSC stores prior to bud burst. These results challenge previous assumptions on the lower relevance of branch NSC storage for the spring growth of evergreen trees and call for further studies where closely related pairs of coexisting evergreen and deciduous tree species are compared.

Solar radiation strongly influences the quantity of forest tree root exudates

Abstract: The quantity of root exudate carbon produced by Quercus crispula Blume was strongly influenced by the amount of solar radiation 1 day before collection. We aimed to investigate seasonality in the quantity of root exudate produced, and the factors affecting exudate quantity, in mature Quercus crispula Blume trees throughout the growing season. We also aimed to understand the timespan of exudation, from production of photosynthate to release as exudate. We measured the amount of root exudate C produced by Q. crispula, as well as environmental factors including solar radiation and soil and air temperature throughout the growing season. The model best explaining the amount of exudate C, based on the lowest Akaike’s information criterion, was selected to determine the environmental factors that affect exudation. The quantity of exudates did not show clear seasonality, and instead varied widely among sampling dates. A regression model with daily solar radiation for 1 day before sample collection as the sole factor affecting the quantity of exudates was selected as the best model. Solar radiation, which fluctuated greatly among days, more strongly affected the quantity of exudates produced than factors that fluctuated seasonally, such as average temperature. Furthermore, most root exudates from Q. crispula are released within 1 day of being generated by photosynthesis, rather than over several days.

Contact angle measurements and water drop behavior on leaf surface for several deciduous shrub and tree species from a temperate zone

Abstract: Leaf CA measurement should take into account angle variation during measurement time. Leaf wettability of common deciduous forest plants is characterized by wetting contact angles ranging from 60° to 140° with a significant variation between species of the same family. Leaf wettability is an important phenomenon that has an influence on several processes such as the hydrological cycle, plant pathogen growth, or pollutant and pesticide absorption/deposition. The main objective of this research was to investigate the leaf wettability differences of 19 species (16 trees and 3 shrubs) of deciduous plants commonly occurring in Polish forests (temperate climate). The measurements were gathered as follows: 20 undamaged leaves were selected for each species and the wettability was determined by contact angle measurements with an optical goniometer CAM 100 using the sessile drop method. The contact angle was measured with 1-s intervals during 2 min from droplet deposition on adaxial and abaxial leaf surface. Laboratory analyses were completed during the summer of 2016 during full vegetation growth. A general CA decrease with time was observed on both leaf sides. The contact angle values ranged from 60° to 140° depending on species and leaf side. Differences between contact angle values at the beginning and the end of measurement reached 23.6° and engendered changes of wetting classes for some species. In many cases, no wettability class change was observed despite a CA lowering of 20°. The abaxial side was found to be the more repellent for 14 out of 19 species. Altogether, the leaves were classified from highly wettable to highly non-wettable, probably depending on the plant-survival strategy.

Tree growth responses to changing temperatures across space and time: a fine-scale analysis at the treeline in the Swiss Alps

Abstract: Tree growth shows a non-linear response to temperature. Under climate change, this leads to a consistent increase of high basal area increments only at the highest elevations. Forest dynamics and particularly tree growth rates are considerably affected by temperature. Hence, global warming is expected to have large impacts on the growth and distribution of trees, especially at the cold distribution limit. While the influence of interannual temperature variability on tree growth has been described intensely, only few studies have analyzed how growth rates of trees decline along a fine-scale temperature gradient close to treeline. We compiled temporally and spatially highly resolved long-term air and soil temperature variables (degree-day sum, growing season length, and growing season mean temperature) at three study sites comprising nine elevation gradients in the Swiss Alps. These temperature variables were paired with basal area increment data of the four major treeline species growing along these transects. Close to treeline, basal area increment of all species depended primarily on degree-day sums or growing season length, rather than on growing season mean temperature. While basal area increment was best explained by combining air temperature of the current and previous growing seasons, the importance of soil temperature for tree growth was site-specific. When moving down from upper treeline, the temperature–growth relationship was strongly non-linear, showing a rapid decrease of temperature limitation and an increasing importance of factors other than temperature. Over the last 50 years, temperatures have increased substantially at all sites, with isotherms moving upward 160–260 m in elevation. The threshold dependence of growth to temperature that we identified has led to an increase of high basal area increments over time, which, however, was consistent throughout the population only at the highest elevations.

Genome-wide identification and characterization of novel lncRNAs in Ginkgo biloba

Abstract: We identified several novel lncRNAs that play important roles in Ginkgo biloba leaf development. A large number of long non-coding RNAs (lncRNAs) have emerged as important regulators of many biological processes in animals and plants. However, lncRNAs and their regulatory roles remain poorly characterized in woody plants, particularly in the gymnosperm G. biloba. We performed deep strand-specific RNA sequencing (ssRNA-seq), and obtained 27.44 GB raw data from all major developmental stages of G. biloba leaves. From these sequencing data, we identified 1323 novel lncRNAs. These lncRNAs were transcribed from 947 scaffolds of G. biloba, 57.6% of which came from intergenic regions. We also confirmed that Gb-lncRNAs were shorter and had fewer exons than protein-coding genes. Target prediction for 764 lncRNAs identified 1184 target genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation analysis revealed that these lncRNAs might be associated with photosynthesis, plant hormones, and secondary metabolism in leaves. Moreover, we constructed a network of regulatory interactions between lncRNAs and mRNAs; 89 lncRNAs were predicted as targets of 64 miRNAs and 33 lncRNAs functioned as miRNA precursors. Quantitative real-time PCR revealed that novel lncRNAs had stage- and tissue-specific expression patterns in G. biloba leaves. These results provide new insight into the function of lncRNAs in leaves and enhance our understanding of plant lncRNAs.

Relative influences of multiple sources of uncertainty on cumulative and incremental tree-ring-derived aboveground biomass estimates

Abstract: How forest growth responds to climate change will impact the global carbon cycle. The sensitivity of tree growth and thus forest productivity to climate can be inferred from tree-ring increments, but individual tree responses may differ from the overall forest response. Tree-ring data have also been used to estimate interannual variability in aboveground biomass, but a shortage of robust uncertainty estimates often limits comparisons with other measurements of the carbon cycle across variable ecological settings. Here we identify and quantify four important sources of uncertainty that affect tree-ring-based aboveground biomass estimates: subsampling, allometry, forest density (sampling), and mortality. In addition, we investigate whether transforming rings widths into biomass affects the underlying growth-climate relationships at two coniferous forests located in the Valles Caldera in northern New Mexico. Allometric and mortality sources of uncertainty contributed most (34–57 and 24–42%, respectively) and subsampling uncertainty least (7–8%) to the total uncertainty for cumulative biomass estimates. Subsampling uncertainty, however, was the largest source of uncertainty for year-to-year variations in biomass estimates, and its large contribution indicates that between-tree growth variability remains influential to changes in year-to-year biomass estimates for a stand. The effect of the large contribution of the subsampling uncertainty is reflected by the different climate responses of large and small trees. Yet, the average influence of climate on tree growth persisted through the biomass transformation, and the biomass growth-climate relationship is comparable to that found in traditional climate reconstruction-oriented tree-ring chronologies. Including the uncertainties in estimates of aboveground biomass will aid comparisons of biomass increment across disparate forests, as well as further the use of these data in vegetation modeling frameworks.

Is there a specific stage to rest? Morphological changes in flower primordia in relation to endodormancy in sweet cherry (Prunus avium L.)

Abstract: Comparison of five sweet cherry cultivars—over 3 years—shows an asynchronous early and late flower development, but a consistent, specific flower developmental stage for dormancy. In temperate woody deciduous perennials, dormancy is a survival strategy to persist winter temperatures; but chilling is also required for the release of flower bud dormancy and for the completion of flower development. This was noticed over 100 years ago, but the biological mechanisms underlying cold regulated dormancy and its release remain poorly understood. That chilling is required for the completion of flower development led us to hypothesize that a particular stage of flower development may be consistently associated with the dormant phase of flower bud development. Flower development of five sweet cherry cultivars was examined weekly under stereoscopic and optical microscopes over 3 years. Chilling requirements for each cultivar were determined by placing weekly shoots in forcing conditions. The establishment of a flower developmental scale showed that early and late flower development, in the autumn and spring, were asynchronous among cultivars and years. However, in all circumstances, dormancy occurred at the same stage of flower development, characterized by the presence of all flower whorls, with the anthers clearly differentiated in the four locules, and the pistil showing an incipient ovary, style and stigma. The length of time flower buds remained at this stage differed between cultivars and was related to their chilling requirements and date of flowering. The observation that a particular stage of flower development, common to the five cultivars examined, exists during the combined rest period provides a framework for further studies on the physiology and cellular biology of dormancy.

Micropropagation of axillary shoots of Salix viminalis using a temporary immersion system

Abstract: Culturing axillary shoot explants of willow in liquid medium in plantform™ and RITA ® vessels increased the multiplication coefficient relative to that obtained by culturing the explants in semisolid medium in jars. A protocol for micropropagating willow by multiplying axillary shoots in liquid medium was developed, and the effects of the type of explant, medium composition, bioreactor type and frequency of immersion were investigated. The type of explant influenced shoot quality and the multiplication coefficient, with basal segments showing a higher capacity for proliferation than apical and mid-shoot segments. Hyperhydricity was not observed in shoots cultured with Murashige and Skoog medium with half-strength nitrates and supplemented with 0.22 µM BA and 3% sucrose. The willow shoots cultured in plantform™ and RITA® vessels yielded higher multiplication coefficients than shoots grown in semisolid medium. High proliferation rates were obtained by immersion of shoots for 1 min three or six times a day, with additional aeration of 1 min per hour in the plantform™ bioreactors. Transfer to medium with 1% sucrose after 4 weeks of culture in medium with 3% sucrose increased the multiplication coefficient of basal segments cultured in RITA® vessels, suggesting that the species could be micropropagated under photoautotrophic conditions. The willow shoots rooted spontaneously and were successfully acclimatized to greenhouse conditions. This is the first report of the use of a temporary immersion system to culture Salix viminalis. The study findings indicate the feasibility of the system as a method for the large-scale propagation of this species.

Stoichiometric homeostasis, physiology, and growth responses of three tree species to nitrogen and phosphorus addition

Abstract: Homeostatic regulation coefficient (H) exists for trees and the tree species with higher H are more stable in physiological and growth responses to nutrient addition. Stoichiometric homeostasis, indicated by the homeostasis regulation coefficient (H), is closely related to evolutionary stage, and can reflect physiological and biochemical adaption of organisms to environmental changes. However, stoichiometric homeostasis is seldom studied in trees. In this case study, three tree species, two angiosperms (Quercus acutissima and Sapium sebiferum) and one gymnosperm (Metasequoia glyptostroboides), were chosen to calculate the H of nitrogen (HN), phosphorus (HP), and nitrogen:phosphorus (HN:P) after soil N and P addition. The responses of physiology, growth, and biomass to nutrients addition were also determined. The value of H ranged from 5.03 to 21.28 for all organs of the three tree species. H was significantly different among tree species (P = 0.010), and was all higher than that of herbs, which may result from phylogenetic differences (angiosperms:gymnosperms) and life form differences (trees:herbs). While having the largest H value, Q. acutissima had the smallest response ratio of physiology (effective quantum yield of PSII), growth (height, root collar diameter), and biomass to soil N and P addition, which indicated that species with stronger stoichiometric homeostasis showed better adaption to environment changes. Our results successfully expanded the stoichiometric homeostasis theory to trees, and provided a link between stoichiometric homeostasis and response of plant traits to environmental changes.

Relationships between leaf mass per area and nutrient concentrations in 98 Mediterranean woody species are determined by phylogeny, habitat and leaf habit

Abstract: This study reinforces the existence of the leaf economics spectrum in Mediterranean woody species, and demonstrates the strong influence of phylogeny, leaf habit and environmental context as main drivers of variability in structural and nutrient traits of leaves. Leaf structural and nutrient traits are key attributes of plant ecological strategies, as these traits are related to resource-use strategies and plant growth. However, leaf structure and nutrient composition can vary among different habitats, leaf habits or phylogenetic groups. In this study, we measured 13 leaf traits (one structural—leaf mass per area, LMA—and 12 nutrient traits) in 98 Mediterranean woody species growing over a wide range of environmental conditions, with the final aim of discerning the main causes of leaf trait variability. The variance decomposition results show that phylogeny, leaf habit and habitat type affected in several ways the structural and nutrient traits studied. Leaf nutrient concentrations are strongly positively correlated amongst themselves, and negatively correlated with LMA, in accordance with the “leaf economics spectrum”. We found that leaf habit and phylogeny were important causes of variation in LMA and in a broad number of leaf nutrients (i.e., C, N, Mg, S, K), while other micronutrients seemed to be more dependent on the environment (i.e., Cu and Mn). In summary, our study reinforces the existence of the leaf economics spectrum in a broad pool of Mediterranean woody species, and demonstrates the strong influence of phylogeny, leaf habit and environmental context as the main drivers of variability in some leaf structural and nutrient traits.

Blue light advances bud burst in branches of three deciduous tree species under short-day conditions

Abstract: An LED spectrum containing blue light advanced bud burst in branches of Betula pendula, Alnus glutinosa and Quercus robur compared with a spectrum without blue light in a controlled environment. During spring, utilising multiple cues allow tree species from temperate and boreal regions to coordinate their bud burst and leaf out, at the right moment to capitalise on favourable conditions for photosynthesis. Whilst the effect of blue light (400–500 nm) has been shown to increase percentage bud burst of axillary shoots of Rosa sp., the effects of blue light on spring-time bud burst of deciduous tree species have not previously been reported. We tested the hypotheses that blue light would advance spring bud burst in tree species, and that late-successional species would respond more than early-successional species, whose bud burst is primarily determined by temperature. The bud development of Alnus glutinosa, Betula pendula, and Quercus robur branches, cut from dormant trees, was monitored under two light treatments of equal photosynthetically active radiation (PAR, 400–700 nm) and temperature, either with or without blue light, under controlled environmental conditions. In the presence of blue light, the mean time required to reach 50% bud burst was reduced by 3.3 days in Betula pendula, 6 days in Alnus glutinosa, and 6.3 days in Quercus robur. This result highlights the potential of the blue region of the solar spectrum to be used as an extra cue that could help plants to regulate their spring phenology, alongside photoperiod and temperature. Understanding how plants combine photoreceptor-mediated cues with other environmental cues such as temperature to control phenology is essential if we are to accurately predict how tree species might respond to climate change.

Brassinosteroids mitigate iron deficiency improving nutritional status and photochemical efficiency in Eucalyptus urophylla plants

Abstract: Iron (Fe) is essential for the biosynthesis of constitutive proteins of chloroplasts, mitochondria and other organelles, and its deficiency triggers negative effects on photochemical efficiency and electron transport. Brassinosteroids are steroids that play beneficial roles related to chlorophyll fluorescence and plant nutrition. The aims of this research were to answer if epibrassinolide (EBR) can mitigate Fe deficiency in Eucalyptus urophylla plants and to evaluate the repercussions on nutritional status and physiological and biochemical behaviours. The experiment followed a completely randomized factorial design with two Fe conditions (Fe deficiency and control) and three levels of 24-epibrassinolide (0, 50 and 100 nM EBR). EBR application in E. urophylla plants exposed to Fe deficiency increased Fe contents in root, stem and leaf. EBR reduced the negative effects of Fe deficiency on chlorophyll fluorescence and gas exchange parameters. Fe deficiency caused reductions in Chl a, Chl b and total Chl, while plants sprayed with 100 nM EBR showed significant increases in these variables. Our results clearly reveal that EBR attenuated the negative effects caused by Fe deficiency on nutritional status and in the physiological and biochemical behaviours of E. urophylla plants, and these results were connected to increases in the contents of macronutrients and micronutrients, including Fe. EBR also improved the photochemical efficiency of PSII, gas exchange and photosynthetic pigments, inducing minor accumulations of oxidative compounds. Additionally, E. urophylla plants submitted to 100 nM of EBR had better nutritional, biochemical, physiological and morphological results.

Root-system characteristics of plantation-grown Populus tomentosa adapted to seasonal fluctuation in the groundwater table

Abstract: Populus tomentosa developed a deep root system, wide-spreading and dense lateral roots, and structural roots exploring both deep and shallow soil resources to adapt to intense seasonal groundwater table fluctuation. To elucidate the root-system characteristics of P. tomentosa adapting to seasonal fluctuation in the groundwater table, coarse-root architecture and fine-root morphology were investigated in a P. tomentosa plantation under groundwater table fluctuation with an average annual amplitude of 363 cm. Three stands of different ages and planting densities were selected for root sampling, comprising 34 structural roots for assessment of root architecture, ten stumps for measurement of rooting depth and spread distance, and 2106 soil blocks (to 150 cm depth) for analysis of fine-root distribution. The average rooting depth of these stands was 200 cm (maximum root depth 270 cm), indicating that P. tomentosa can be phreatophytic. In 4- and 7-year-old stands, the average lateral root spread distances were 437 and 535 cm, respectively. About 23% of the root area density was distributed in the top-most 20 cm soil, which might help P. tomentosa to intercept rainwater efficiently and absorb shallow soil water resources when the uptake function of deep roots was inhibited by flooding. Some horizontal, inclined, and vertical structural roots were capable of exploring both deep and shallow soil layers. In conclusion, a deep root system, wide-spreading and dense lateral roots in shallow soil layers, and development of some structural roots exploring both deep and shallow soil resources may be the three coordinate rooting adaption strategies that permit P. tomentosa to thrive in sites subject to large fluctuation in the groundwater table.

Somatic hybridization between diploid Poncirus and Citrus improves natural chilling and light stress tolerances compared with equivalent doubled-diploid genotypes

Abstract: The genome doubling of the allotetraploid somatic hybrid can confer greater tolerance to cold and light stress than the diploid parents and their respective tetraploid. Allopolyploids are generally known to display broader adaptation to abiotic stresses than their parental diploid species. In the Mediterranean area, Citrus species are subjected to abiotic constraints such as low temperature and high radiation. Tetraploids are known to resist these environmental constraints better, and so the use of new tetraploid rootstocks offers an alternative to overcome these threats to crop productivity. The objective of this study was to determine whether the use of an allotetraploid hybrid could provide greater tolerance to cold and light stresses than its diploid parents or respective doubled-diploid parents. We compared cold and light stress responses of the allotetraploid hybrid FlhorAG1 (FL-4x) with those of its diploid parents, the willow leaf mandarin (Citrus deliciosa Ten) (WLM-2x) and the Poncirus Pomeroy (Poncirus trifoliata (L.) Raf.) (POP-2x), and their respective doubled-diploids (WLM-4x and POP-4x, respectively) by measuring physiological and biochemical parameters. When subjected to cold and light stress, FL-4x showed lower photoinhibition (Fv/Fm) and less accumulation of oxidative markers (MDA and H2O2) than diploid and doubled-diploid WLM and POP genotypes. This was correlated with a greater increase for FL-4x in some antioxidant activities during cold stress (SOD, APX and GR) and light stress (SOD, APX and MDHAR mainly). Overall, our results suggest that greater antioxidant capability in FL-4x should make this allotetraploid hybrid more tolerant to low temperatures than the two WLM genotypes, and more tolerant to light stress than the two WLM and POP genotypes.

Intra-organismal variation in the structure of plant vascular transport tissues in poplar trees

Abstract: Phloem and xylem conduit structure vary greatly throughout the body of Populus trichocarpa trees, particularly between roots and shoots. This has implications for understanding organ and whole plant vascular function. Woody plant vascular transport occurs predominantly within secondary xylem and phloem, which are both produced by the vascular cambium during secondary growth. We examined how vessel and sieve tube structure varied throughout the plant body of P. trichocarpa trees and whether xylem and phloem conduit structure was correlated across different positions within the plant. We excavated entire juvenile P. trichocarpa trees and measured vessel and sieve tube structural traits of current-year growth in 1 m increments along the main root:shoot axis. Trees were > 4 m tall and had roots that extended 4–5 m at their longest length. We found that both sieve tube and vessel diameters greatly varied throughout the plant body and with organ diameter. Roots had wider diameter conduits than shoots. Sieve tube diameter was strongly correlated with vessel diameter, which may be related to their common developmental origin. Other structural traits, such as pit membrane area and pit density for xylem, and sieve plate area and number of sieve areas per plate for phloem, also varied and were correlated with changes in conduit diameter. The median air-seeding pressure of vessels (Pm) and vessel length did not differ between roots and shoots. Understanding plant vascular function will likely require increased knowledge of whole plant structure and function, since plant performance may be limited by any point along the transport pathway. Considering intra-organismal variation may be a way to evaluate structure–function hypotheses while controlling for confounding sources of variation that may impact inter-specific comparisons.

Site-specific climatic signals in stable isotope records from Swedish pine forests.

Abstract: Pinus sylvestris tree-ring delta C-13 and delta O-18 records from locally moist sites in central and northern Sweden contain consistently stronger climate signals than their dry site counterparts. ...

Analyzing key factors of roots and soil contributing to tree anchorage of Pinus species

Abstract: Tree anchorage is a primary function for plant survival which may reach its limit under extreme conditions such as windstorms. To better understand the processes and influential factors underlying tree anchorage, we analyzed the mechanical effects of root morphology and the material properties of roots and soil on the tree-overturning process with the recently developed finite element model RootAnchor. The root system was represented by a simplified 3D root pattern derived from an ensemble average of seven measured root systems of 19-year-old Pinus pinaster grown in sandy spodosol. Soil properties were measured by direct shear tests. Taguchi orthogonal arrays were used to examine the sensitivity of the geometric and material factors of roots and soil to tree anchorage. Tree anchorage was characterized by anchorage strength TMc and anchorage stiffness K0. Using a small number of numerical experiments, the sensitivity analysis prioritized only two key factors contributing to tree anchorage among the 34 factors considered. The results showed root morphological traits that played a dominant role in the material properties of roots and soil in tree anchorage. Taproot depth, the dimensions of the Zone of Rapid Taper (ZRT) and basal diameter of the windward shallow roots were the key factors contributing to TMc (variations > 8%). The dimensions of the taproot, root and soil stiffness, and the basal diameter of the leeward shallow roots were the most active factors for K0 (variations > 10%). These results provide insight into simplified tree anchorage expressions for the prediction of wind-induced uprooting.

Increasing tree diversity enhances microbial and enzyme activities in temperate Iranian forests

Abstract: Our findings show the differential impacts of tree types (hornbeam–ironwood natural forest and plantations of ash, maple, cypress and pine) on soil physical–chemical characteristics and how dominant tree species regulate the size and activity of soil microbial and enzymes. Soil microbial and enzyme activities have an important influence on nutrient cycling. The variation in soil carbon (C) and nitrogen (N) microbial indices as well as enzyme activities were determined under hornbeam–ironwood natural forest and 25-years old plantations of ash, maple, cypress and pine in northern Iran. Four soil profiles were dug along the four parallel transects in the central part of each forest stand, resulting in 16 soil samples for each stand at a depth of 0–15 cm. The results showed significant differences in most of studied soil physico-chemical properties among different land covers. Soil microbial basal respiration (MR) and substrate induced respiration (SIR) were found to be significantly higher under natural forest than in the plantation stands. Microbial biomass C (MBC) did not differ for the forest stands, whereas natural forest had significantly higher qCO2 (MR: MBC), microbial entropy (MBC: Corg) and C availability index (MR: SIR) values. The establishment of plantations reduced the values of soil microbial biomass N, mineral nitrogen (NH4–N and NO3–N) and N mineralization with the least under coniferous stands of cypress and pine, while greater amounts were observed under natural forest. With replacement in the type of tree species from natural forest to plantations, acid phosphatase, arylsulphatase and invertase enzyme activities decreased significantly in the topsoil, whereas like natural forest, ash plantation improved urease enzyme. This research recommends conservation of natural forests for increase of soil quality and plantation of suitable native broad-leaved species for rehabilitation of degraded natural forests.

Effects of nitrogen and phosphorus addition on leaf nutrient characteristics in a subtropical forest

Abstract: P deposition can alleviate P limitation in subtropical forests and P deposited in conjunction with high quantities of N does not enhance P limitation. Increasing nitrogen (N) and phosphorus (P) deposition could influence plant growth and survival to varying extents. N and P deposition is essential for subtropical forests where plant growth is limited by lower soil P availability in highly weathered soils. However, whether N and P deposition can increase leaf P concentration and alleviate P limitation is unclear. We investigated changes in N and P concentrations, N:P ratios, and resorption for six dominant species (two tree species and four understory species), following 2 years of N and P additions in a subtropical forest in southern China. P addition either alone or together with the addition of N increased green leaf P concentrations (except in Schima superba) and senesced leaf P and decreased N:P ratios (except in Pinus massoniana), but had no influence on P resorption. N addition had no apparent influence on leaf N concentrations, N:P ratios, or N resorption in all species. The considerable influence of P addition can be explained by rising soil P availability. Our results suggest that subtropical forests are P limited and that increasing P deposition can moderately alleviate the limitation of P. Furthermore, P deposited in conjunction with high quantities of N does not enhance P limitation, as it is insensitive to elevated N input.

An objective image analysis method for estimation of canopy attributes from digital cover photography

Abstract: A method was proposed to remove the subjectivity of gap size analyses approaches implemented by default in cover photography. The method yielded robust and replicable measurements of forest canopy attributes. Digital cover photography (DCP) is an increasingly popular method to estimate canopy attributes of forest canopies. Compared with other canopy photographic methods, DCP is fast, simple, and less sensitive to image acquisition and processing. However, the image processing steps used by default in DCP have a large substantial subjective component, particularly regarding the separation of canopy gaps into large gaps and small gaps. In this study, we proposed an objective procedure to analyse DCP based on the statistical distribution of gaps occurring in any image. The new method was tested in 11 deciduous forest stands in central Italy, with different tree composition, stand density, and structure, which is representative of the natural variation of these forest types. Results indicated that the new method removed the subjectivity of manual and semi-automated gap size classifications performed so far in cover photography. A comparison with direct LAI measurements demonstrated that the new method outperformed the previous approaches and increased the precision of LAI estimates. Results have important implications in forestry, because the simplicity of the method allowed objective, reliable, and highly reproducible estimates of canopy attributes, which are largely suitable in forest monitoring, where measures are routinely repeated. In addition, the use of a restricted field of view enables implementation of this photographic method in many devices, including smartphones, downward-looking cameras, and unmanned aerial vehicles.

The effect of temperature on the developmental rates of seedling emergence and leaf-unfolding in two dwarf bamboo species

Abstract: The mean and variance of developmental rates of bamboos at different temperatures follow a power law. The rate isomorphy hypothesis, demonstrated in insects and mites, does not hold in bamboos. The developmental time of plants and poikilotherms can be significantly affected by temperature. Developmental rate (i.e. the reciprocal of developmental time) of arthropods and germination rate of some plant seeds have been demonstrated to follow a linear function with temperature. The rate isomorphy hypothesis in entomology suggests a lower developmental threshold below which development of all life stages terminates. If this hypothesis also holds for plants, the estimated lower threshold for one development stage could be used for predicting thresholds of other stages. Here, we tested this hypothesis to compare the developmental time of seedling emergence and the time from seedling emergence to the unfolding of the third leaf in two bamboo species. We used five constant thermal environments from 18.5 to 28.5 °C with an increment of 2.5 °C. Both species showed a linear relationship between temperature and developmental rate, with the mean and variance of developmental rates following a power law. Using the bootstrap percentile method, we showed that the isomorphy hypothesis does not hold for both species. The effect of temperature on the survival rate at the time of seedling emergence differed significantly between the two species.

Stemflow in a neotropical forest remnant: vegetative determinants, spatial distribution and correlation with soil moisture

Abstract: Tree size and exposure is a key driver of stemflow; canopy heterogeneity leads to spatial randomness of stemflow; stemflow impacts soil moisture in superficial layers. Stemflow (SF) plays a relevant role in forest hydrology by delivering rain to the soil around trees. This study sought to explore the effects of tree traits on the amount of SF in an Atlantic Forest remnant in Southeast Brazil using stepwise regressions from April 2016 to March 2017. In addition, we evaluated the spatial association among trees in regard to SF using bivariate Ripley’s K as well as the impact of SF on soil water content (SWC) at five different layers (up to 1 m) using linear regression. We found that the diameter at breast height (DBH), percentage of mosses on the tree trunk, average leaf area, and relative position of the tree within the canopy were selected as explanatory variables in total and monthly average SF models. For the wet season SF models, crown area, percentage of mosses cover on the trunk, average leaf area, and relative position within the canopy were the selected variables, whereas for the dry period SF models, DBH and percentage of mosses were selected. A complete spatial randomness (CSR) between the SF classes was confirmed. We observed that SF impacted the SWC in the superficial layers. Therefore, tree size, exposure, and seasonal differences were the key drivers of SF amount due to the leaf losses during the dry period. Heterogeneity of the canopy is probably responsible for the CSR of SF in the study area. We expect that this study will contribute to the understanding of the hydrological processes in the Atlantic forest hotspot by clarifying the aspects of water capture by trees.

Downregulation of stress-associated protein 1 (PagSAP1) increases salt stress tolerance in poplar (Populus alba × P. glandulosa)

Abstract: Downregulating PagSAP1 expression increases salt tolerance in poplar and leads to the alterations in the regulation of genes involved in maintaining cellular ionic homeostasis. Plants have evolved defense mechanisms to cope with unfavorable climate conditions such as salinity, drought, and extreme temperatures. Such adaptive strategies include fine-tuning of stress-associated proteins (SAPs). Here, we investigated the molecular and physiological characteristics of the novel gene PagSAP1 from hybrid poplar (Populus alba × P. glandulosa) in response to salt stress. PagSAP1 encodes a putative protein containing an A20 and AN1 zinc-finger domain at its N- and C-terminus, respectively. Salt stress significantly downregulated the expression of PagSAP1 in roots, but not leaves, of poplar at the seven-leaf stage. Compared to control plants, knockdown (RNAi) transgenic poplar plants showed strong tolerance to salt stress, while overexpression (OX) of PagSAP1 increased salt sensitivity. Analysis of Ca2+, Na+, and K+ contents in roots and leaves following salt treatment (150 mM NaCl) revealed that RNAi plants accumulated more Ca2+ and K+, and less Na+ than PagSAP1 OX plants. The RNAi lines exhibited increased expression of genes involved in maintaining cellular ionic homeostasis across the plasma membrane, such as salt overly sensitive 3 (SOS3), SOS1, high-affinity K+ transporter 1 (HKT1), H+-ATPase, AAA-type ATPase, and Arabidopsis K+ channel 2 (AKT2). Taken together, these results indicate that PagSAP1 represents a promising candidate gene for engineering trees with improved salt tolerance, which would increase their suitability for planting in marginal lands, such as reclaimed areas.

A roadmap to disentangling ecogeographical patterns of spatial synchrony in dendrosciences

Abstract: A systematic assessment of spatial synchrony in tree growth, a fundamental feature of spatiotemporal forest dynamics, can provide valuable insights into complex tree reactions across species and environmental gradients. The concept of spatial synchrony in ecology refers to the presence of coordinated time fluctuations in certain characteristics that can be observed in plant and animal communities inhabiting an area. It is a well-known phenomenon common to virtually every taxon, but comparatively little attention has been given to the study of the temporal coherence of forest tree performance across biogeographical gradients. In forest ecosystems, tree growth dynamics is primarily driven by climatic variability (i.e., the Moran effect). Due to rapid climate change, trees are increasingly pushed to their physiological limits up to the level that many populations are facing immediate risk of extinction. The characterization of synchrony patterns in tree growth can provide clues on the relevance of emerging climatic threats on forests, as new combinations of precipitation and temperature are entraining tree performance worldwide. In this regard, comprehensive and systematic approaches to analyse spatiotemporal dynamics of tree growth are needed. Here, we present a methodology for disentangling and interpreting how the variability and common signal strength of tree growth (or other traits) are structured in tree-ring networks. It is grounded on mixed modelling principles and broadens well-known theoretical principles in dendrosciences. Based on this approach, we describe the essential properties of spatial synchrony in tree growth at multiple geographical scales. We also discuss the potential of this methodology to discern early warning signals of climate change impacts on forest ecosystems.

Silver-fir (Abies alba MILL.) neighbors improve water relations of European beech (Fagus sylvatica L.), but do not affect N nutrition.

Abstract: Water relations in the leaves of beech trees on sandstone-derived soil are supported by the presence of white fir neighbors. Climate extremes such as heat waves and prolonged periods of drought not only affect water relations of trees, but can also accelerate nitrogen (N) limitation under low soil N. To counteract these effects of climate change, it has been suggested to replace forest monocultures with mixed forest stands. In the present study, we tested, if water relations and N nutrition of shallow rooting and, hence, drought sensitive beech (Fagus sylvatica L.) could benefit from deep rooting and, hence, less drought sensitive silver-fir (Abies alba MILL.). Adult trees were analyzed on two forest sites stocking on different parent bedrock at different elevations. The sites differed in precipitation and total N contents in the soil, but revealed a similar soil water holding capacity. Surprisingly, analysis of root and leaf/needle bulk material revealed higher N contents in beech and fir tissues from the low compared to the high soil N site. Significant effects of silver-fir neighbors on N nutrition of beech were not observed. δ13C signatures of leaf/needle and root material served as indicators for water supply. In the leaves, but not in the roots of beech trees at the site with lower precipitation, δ13C signatures indicate improved water supply of beech in the presence of sufficient fir neighbors. Irrespective of this observation, water supply for both tree species appeared to be sufficient at both field sites despite low spring and early summer precipitation.

Improved germination conditions for Norway spruce somatic cotyledonary embryos increased survival and height growth of emblings

Abstract: Norway spruce is one of the most cultivated tree species in Nordic countries. However, intermittent shortages of improved seeds occur. As a powerful vegetative propagation technology, somatic embryogenesis (SE) could provide an alternative solution for this problem and also shorten the time required to obtain breeding gains. However, there are still large bottlenecks in SE, e.g. in the germination and acclimatization phases, which greatly affect the final outcome of somatic embryo plants (emblings). In this work, we examined the effects of in vitro embryo storage and germination treatments and ex vitro growing techniques on the survival and growth of emblings. The study comprised 32 genotypes from 18 full-sib families in four experiments, testing two different cold storage methods, three durations of in vitro germination, lower inorganic nitrogen content in the germination medium, and two plant-growing techniques. The best treatment combination—cold storage on filter paper, lower nitrogen content in the germination medium and one-week in vitro germination—resulted in an 88% higher survival and 28% higher growth compared to the poorest, reference treatment in the same test year. These emblings could be planted after a nursery period one year sooner than that of the control emblings. The results indicate that Norway spruce emblings germinated for one week in vitro can be transplanted and grown in nurseries without any additional treatments or environmental control differing from seedlings, which is a prerequisite to reach standards for forest regeneration material.