Optimal Community Assembly Related to Leaf Economic- Hydraulic-Anatomical Traits

Response of tree growth to nutrient addition is size dependent in a subtropical forest

Understanding how nutrient addition affects the tree growth is critical for assessing forest ecosystem function and processes, especially in the context of increased nitrogen (N) and phosphorus (P) deposition. Subtropical forests are often considered N-rich and P-poor ecosystems, but few existing studies follow the traditional "P limitation" paradigm, possibly due to differences in nutrient requirements among trees of different size classes. We conducted a three-year fertilization experiment with four treatments (Control, N-treatment, P-treatment, and NP-treatment). We measured soil nutrient availability, leaf stoichiometry, and relative growth rate (RGR) of trees across three size classes (small, medium and large) in 64 plots. We found that N and NP-treatments increased the RGR of large trees. P-treatment increased the RGR of small trees. RGR was mainly affected by N addition, the total effect of P addition was only 10 % of that of N addition. The effect of nutrient addition on RGR was mainly regulated by leaf stoichiometry. This study reveals that nutrient limitation is size dependent, indicating that continuous unbalanced N and P deposition will inhibit the growth of small trees and increase the instability of subtropical forest stand structure, but may improve the carbon sink function of large trees.

Soil water content and nitrogen differentially correlate with multidimensional leaf traits of two temperate broadleaf species

The variation and correlation of leaf economics and vein traits are crucial for predicting plant ecological strategies under different environmental changes. However, correlations between these two suites of traits and abiotic factors such as soil water and nitrogen content remain ambiguous. We measured leaf economics and vein traits as well as soil water and nitrogen content for two different shade-tolerant species (Betula platyphylla and Acer mono) in four mixed broadleaved-Korean pine (Pinus koraiensis) forests along a latitudinal gradient in Northeast China. We found that leaf economics traits and vein traits were decoupled in shade-intolerant species, Betula platphylla, but significantly coupled in a shade-tolerant species, A. mono. We found stronger correlations among leaf traits in the shade tolerant species than in the shade intolerant species. Furthermore, leaf economic traits were positively correlated with the soil water gradient for both species, whereas vein traits were positively correlated with soil water gradient for the shade intolerant species but negatively correlated in the shade tolerant species. Although economic traits were positively correlated with soil nitrogen gradient in shade intolerant species but not correlated in shade tolerant species, vein traits were negatively correlated with soil nitrogen gradient in shade tolerant species but not correlated in shade intolerant species. Our study provides evidence for distinct correlations between leaf economics and vein traits and local abiotic factors of species differing in light demands. We recommend that the ecological significance of shade tolerance be considered for species when evaluating ecosystem functions and predicting plant responses to environmental changes.

A dataset of functional traits for compound pinnate leaves of plants in the Huangshui River Valley of Qinghai Province, China

Background

Here, we present data collected from the Qinghai-Tibet Plateau that describes the variation of leaf functional traits across 32 plant species and could be used to investigate plant community functioning and predict the impact of climate change on biogeochemical cycles. The sampling area is located in Huangshui River Valley, in the southeast of Qinghai Province, China (36° 19' to 36° 53' N, 100° 59' to 102° 48' E). The area contains an alpine meadow typical of the Qinghai-Tibet Plateau.

New information

This dataset includes field survey data on the functional properties of compound leaves from herbaceous species in the Huangshui River Basin of Qinghai Province, China, at altitudes from 1800 m to 4000 m in the summer of 2021. Data were collected from 326 plots, including 646 data points of compound leaf plants, spanning 32 compound leaf plant species belonging to 14 genera and four families. The study species were chosen from 47 families, 165 genera and 336 species present in the plots and all compound leaf plants were chosen within each plot. We picked the parts containing leaves, petioles and rachis from the study plants and separated the leaves from the plants. The cut compound leaf part was a leaflet, while the petiole and rachis were linear elements. The dataset includes information about the leaflet trait variation (i.e. leaflet area, leaflet dry mass, specific leaflet area and leaflet nitrogen content per unit dry mass) and linear elements' biomass and nitrogen content per unit dry mass (i.e. both petiole and rachis) of 646 compound leaves. This dataset can be used to analyse the evolution of leaf traits and the basic functioning of ecosystems. Moreover, the dataset provides an important basis for studying the species distribution and protection of biodiversity of the Qinghai-Tibet Plateau and evaluating ecosystem services. These data also support the high-quality development of the Yellow River Basin and have empirical and practical value for alpine biodiversity protection and ecosystem management.

Leaf stomatal traits rather than anatomical traits regulate gross primary productivity of moso bamboo (Phyllostachys edulis) stands

Leaf stomatal and anatomical traits strongly influence plant productivity. Understanding the environmental adaptation mechanisms of leaf stomatal and anatomical traits and their relationship with ecosystem productivity is essential to better understand and predict the long-term adaptation strategies to climate change of moso bamboo forests. Here, we selected 6 sites within the moso bamboo distribution area, measured 3 leaf stomatal traits and 10 leaf anatomical traits of unmanaged moso bamboo stands. We explored the spatial variation characteristics of these traits and their response to environmental changes, assessed the relationships among these traits at regional scales through network analysis, and tested the direct and indirect effects of environmental, leaf stomatal and anatomical traits on gross primary productivity (GPP) of bamboo stands using structural equation modeling (SEM). The results showed that both climate and soil factors significantly affected leaf stomatal and anatomical traits of moso bamboo. Solar radiation (SR) and mean annual precipitation (MAP) out of the climatic factors were the key drivers of variation in leaf stomatal and anatomical traits, respectively. Soil moisture and nutrients out of the soil properties significantly affected both leaf stomatal and anatomical traits of moso bamboo. Network analysis further indicated that there was a significant correlation between leaf stomata and anatomical traits. Stomatal size (SS) showed the highest centrality value at the regional scale, indicating that it plays a key role in adjusting the adaptation of plants to external environmental conditions. SEM analysis showed that environment did not directly but indirectly affect GPP via stomatal performance. The environment explained 53.3% and 39.2% of the variation in leaf stomatal and anatomical traits, respectively, and leaf stomatal traits explained 20.8% of the regional variation in GPP. Our results demonstrate a direct effect of leaf stomatal traits rather than leaf anatomical traits on bamboo ecosystem productivity, which provides new insights into model predictions of bamboo forests under global climate change.

Variation in Leaf Pigment Complex Traits of Wetland Plants Is Related to Taxonomy and Life Forms

The leaf pigment complex traits of 44 wetland plant species from the Middle Urals (Russia) were studied to analyze their diversity in relation to taxonomy and life forms. The chlorophyll content per dry weight (ChlDW) and leaf area (ChlArea), the ratio of chlorophylls a and b, and CO2 uptake rates (ADW) were determined. ChlDW varied by 10-fold from 2.20 to 21.9 mg g−1 among the wetland plant species. The influence of taxonomy at the level of classes on the variation of the pigment complex traits was revealed. Dicots had greater ChlDW and had a greater proportion of chlorophylls in the light-harvesting complex (ChlLHC) than monocots. In dicots, ChlLHC was positively correlated with leaf area ratio (r = 0.63, p < 0.01), and the effect of life forms on the content and ratio of pigments was determined. In monocots, chlorophyll content was positively correlated with ADW (r = 0.75, p < 0.001) and plant height (r = 0.66, p < 0.001). In monocots, the effect of families on the pigment content was observed. The lack of differences in ChlArea between the different systematic groups and life forms indicates a similar ability of the leaf area unit to absorb a solar energy.

Divergent coupling mechanism of precipitation on plant community multifunction across alpine grassland on the Tibetan Plateau

INTRODUCTION

It is essential to understand plant adaptive strategies on plant stoichiometric traits at the species level rather than at the community level under various environmental conditions across the Tibetan Plateau (TP).

METHODS

Here, plant community function and edaphic and meteorological factors were collected at 111 sites along an extensive water-heat gradient during the peak growing season in 2015. Community-weighted mean trait (CWM) was introduced to illuminating dynamics of the functional trait at the community level.

RESULTS

Our results indicated that plant functional traits, including CWM-leaf total carbon (CWM_LTC), CWM-leaf total nitrogen (CWM_LTN), and CWM-leaf total phosphorus (CWM_LTP), showed similar and comparatively marked increases from alpine meadow (AM) to alpine steppe (AS). Moreover, since the tightly coordinated variation among each plant functional trait of AM was higher than that of AS, a more stable coupling mechanism of these plant functional traits could be observed in AM under a long-term evolutionary habit. Specifically, there was higher annual mean precipitation (AMP) in AM than that in AS significantly (P < 0.01), and AMP was significantly correlated with soil moisture and soil total phosphorus in AM. Generally, our findings suggest that precipitation determines divergent coupling plant community function in both AS and AM.

Contrasting adaptation and optimization of stomatal traits across communities at continental scale

Shifts in stomatal trait distributions across contrasting environments and their linkage with ecosystem productivity at large spatial scales have been unclear. Here, we measured the maximum stomatal conductance (g), stomatal area fraction (f), and stomatal space-use efficiency (e, the ratio of g to f) of 800 plant species ranging from tropical to cold-temperate forests, and determined their values for community-weighted mean, variance, skewness, and kurtosis. We found that the community-weighted means of g and f were higher in drier sites, and thus, that drought 'avoidance' by water availability-driven growth pulses was the dominant mode of adaptation for communities at sites with low water availability. Additionally, the variance of g and f was also higher at arid sites, indicating greater functional niche differentiation, whereas that for e was lower, indicating the convergence in efficiency. When all other stomatal trait distributions were held constant, increasing kurtosis or decreasing skewness of g would improve ecosystem productivity, whereas f showed the opposite patterns, suggesting that the distributions of inter-related traits can play contrasting roles in regulating ecosystem productivity. These findings demonstrate the climatic trends of stomatal trait distributions and their significance in the prediction of ecosystem productivity.

Leaf N:P ratio does not predict productivity trends across natural terrestrial ecosystems

Nitrogen (N) and phosphorus (P) are crucial nutrients for regulating plant growth. The classic growth rate hypothesis (GRH) proposes that fast-growing organisms have lower N:P ratios, and it is promising to predict net primary productivity (NPP) using the leaf N:P ratio at the community level (N:P_Com ). However, whether leaf N:P ratio can predict NPP in natural ecosystems on a large scale remains nebulous. Here, we systematically calculated leaf N:P_Com (community biomass-weighted mean and species-arithmetic mean) using the consistently measured data of 2,192 plant species-site combinations and productivity (biomass-based aboveground NPP and flux-based NPP) in 66 natural ecosystems in China. Unexpectedly, leaf N:P_Com hardly predicted productivity in natural ecosystems due to their weak correlation, although significantly negative or positive relationships across different ecosystems were observed. The ambiguous relationship between leaf N:P and species dominance reflected a luxury consumption of N and P in turnover and structure in natural communities, unlike what GRH suggests. Climate, soil, and leaf nutrients (rather than N:P) influenced productivity, which highlighted the importance of external environment and nutrient constrains. Our findings pose a major challenge for leaf N:P_Com as a direct parameter in productivity models and further question the direct application of classic hypotheses in short-term experiments or model species to long-term and complex natural ecosystems.

Divergent Abiotic Stressors Drive Grassland Community Assembly of Tibet and Mongolia Plateau

Multiple ecological processes simultaneously govern community assembly, but it remains unclear how abiotic stressors regulate the relative importance of these processes among different biogeographic regions. Therefore, we conducted a comprehensive study on the responses of community assembly to varying environmental gradients, using the mean, variance, skewness, and kurtosis of plant height (height), specific leaf area (SLA) and leaf dry matter content (LDMC) distributions on the Tibetan Plateau (TP) and the Mongolian Plateau (MP). Our results showed that the prevalence of trait convergence across all grasslands in both TP and MP seem to be the result of abiotic filtering or weaker competitive exclusion etc. These trait-convergence assembly processes decrease the functional dispersion but increase the evenness of the trait frequency distribution. The mean, variance, skewness, and kurtosis responses of grassland communities to abiotic stress varied between the TP and MP. On average, plant trait distribution was mainly driven by temperature on the TP, and low-temperature stress altered the community assembly rules. In contrast, water availability shaped plant trait frequency distributions on the MP, and drought stress mediated the balance between different assembly processes. Our results provide empirical evidence that divergent abiotic stressors regulate the grassland community assembly on the TP and MP. Together, our study speculates that different aspects of future climate change, such as climate warming and changing precipitation patterns, on community assembly are dependent on regional climatic regimes.

Effects of Water Availability on the Relationships Between Hydraulic and Economic Traits in the Quercus wutaishanica Forests

Water availability is a key environmental factor affecting plant species distribution, and the relationships between hydraulic and economic traits are important for understanding the species' distribution patterns. However, in the same community type but within different soil water availabilities, the relationships in congeneric species remain ambiguous. In northwest China, Quercus wutaishanica forests in the Qinling Mountains (QM, humid region) and Loess Plateau (LP, drought region) have different species composition owing to contrasting soil water availability, but with common species occurring in two regions. We analyzed eight hydraulic traits [stomatal density (SD), vein density (VD), wood specific gravity (WSG_branch), lower leaf area: sapwood area (Al: As), stomatal length (SL), turgor loss point (Ψ_Tlp), maximum vessel diameter (Vd_max) and height (Height)] and five economic traits [leaf dry matter content (LDMC), leaf tissue density (TD), leaf dry mass per area (LMA), Leaf thickness (LT) and maximum net photosynthetic rate (P_max)] of congeneric species (including common species and endemic species) in Q. wutaishanica forests of QM and LP. We explored whether the congeneric species have different economic and hydraulic traits across regions. And whether the relationship between hydraulic and economic traits was determined by soil water availability, and whether it was related to species distribution and congeneric endemic species composition of the same community. We found that LP species tended to have higher SD, VD, WSG_branch, Al: As, SL, Ψ_Tlp and Vd_max than QM species. There was a significant trade-off between hydraulic efficiency and safety across congeneric species. Also, the relationships between hydraulic and economic traits were closer in LP than in QM. These results suggested that relationships between hydraulic and economic traits, hydraulic efficiency and safety played the role in constraining species distribution across regions. Interestingly, some relationships between traits changed (from significant correlation to non-correlation) in common species across two regions (from LP to QM), but not in endemic species. The change of these seven pairs of relationships might be a reason for common species' wide occurrence in the two Q. wutaishanica forests with different soil water availability. In drought or humid conditions, congeneric species developed different types of adaptation mechanisms. The study helps to understand the environmental adaptive strategies of plant species, and the results improve our understanding of the role of both hydraulic and economic traits during community assembly.

C:N:P stoichiometry in terrestrial ecosystems in China

Ecological stoichiometry is an efficient tool for exploring the balance and cycling of coupled elements (e.g., carbon [C], nitrogen [N], and phosphorus [P]). Therefore, C:N:P ratios are essential input parameters in most ecological models of productivity or C cycling. However, previous C:N:P ratios estimated using the species arithmetic means exhibit high uncertainty when used as direct model parameters. In this study, we comprehensively calculated C:N:P ratios from organs to ecosystems for 66 typical natural ecosystems in China (e.g., forests, grasslands, and deserts) using the community biomass-weighted mean (CWM), with the consistently measured element data of 3229 site-species combination. The C:N:P ratios were 427:19:1, 885:13:1, 9549:33:1, and 797:18:1 in the leaves, branches, trunks, and roots of terrestrial ecosystems, respectively. Furthermore, the ratios were 91:4:1, 919:17:1, 1121:25:1, and 55:4:1 in ecosystems, plant communities, litter, and soils, respectively. Significant differences were observed in C:N:P ratios among different ecosystem types and biomes, with generally higher ratios in forests. Moreover, the latitudinal patterns of C:N ratios exhibited no obvious trends, whereas both C:P and N:P ratios decreased significantly with increasing latitude, especially in forests. Environmental conditions explained 15.4-86.6% of the spatial variation of C:N:P ratios from organs to ecosystems. In summary, this study systematically demonstrates the variations in biome-scale C:N:P stoichiometry in terrestrial ecosystems, as well as their influencing factors, using the CWM. More importantly, this study provides a systematic dataset of C:N:P ratios from plot to biome scale that can be used to improve relevant ecological models.

Variation Patterns of Functional Trait Moments Along Geographical Gradients and Their Environmental Determinants in the Subtropical Evergreen Broadleaved Forests

Understanding how environmental change alters the composition of plant assemblages is a major challenge in the face of global climate change. Researches accounting for site-specific trait values within forest communities help bridge plant economics theory and functional biogeography to better evaluate and predict relationships between environment and ecosystem functioning. Here, by measuring six functional traits (specific leaf area, leaf dry matter content, leaf nitrogen, and phosphorus concentration, leaf nitrogen/phosphorus, wood density) for 292 woody plant species (48,680 individuals) from 250 established permanent forest dynamics plots in five locations across the subtropical evergreen broadleaved forests (SEBLF) in China, we quantified functional compositions of communities by calculating four trait moments, i.e., community-weighted mean, variance, skewness, and kurtosis. The geographical (latitudinal, longitudinal, and elevational) patterns of functional trait moments and their environmental drivers were examined. Results showed that functional trait moments shifted significantly along the geographical gradients, and trait moments varied in different ways across different gradients. Plants generally showed coordinated trait shifts toward more conservative growth strategies (lower specific leaf area, leaf N and P concentration while higher leaf nitrogen/phosphorus and wood density) along increasing latitude and longitude. However, trends opposite to the latitudinal and longitudinal patterns appeared in trait mean values along elevation. The three sets of environmental variables (climate, soil and topography) explained 35.0-69.0%, 21.0-56.0%, 14.0-31.0%, and 16.0-30.0% of the variations in mean, variance, skewness, and kurtosis across the six functional traits, respectively. Patterns of shifts in functional trait moments along geographical gradients in the subtropical region were mainly determined by the joint effects of climatic and edaphic conditions. Climate regimes, especially climate variability, were the strongest driving force, followed by soil nutrients, while topography played the least role. Moreover, the relationship of variance, skewness and kurtosis with climate and their geographical patterns suggested that rare phenotypes at edges of trait space were selected in harsher environments. Our study suggested that environmental filtering (especially climate variability) was the dominant process of functional assembly for forest communities in the subtropical region along geographical gradients.

Unveiling ecological assembly rules from commonalities in trait distributions

Deciphering the effect of neutral and deterministic processes on community assembly is critical to understand and predict diversity patterns. The information held in community trait distributions is commonly assumed as a signature of these processes, but empirical and modelling attempts have most often failed to untangle their confounding, sometimes opposing, impacts. Here, we simulated the assembly of trait distributions through stochastic (dispersal limitation) and/or deterministic scenarios (environmental filtering and niche differentiation). We characterized the shape of trait distributions using the skewness-kurtosis relationship. We identified commonalities in the co-variation between the skewness and the kurtosis of trait distributions with a unique signature for each simulated assembly scenario. Our findings were robust to variation in the composition of regional species pools, dispersal limitation and environmental conditions. While ecological communities can exhibit a high degree of idiosyncrasy, identification of commonalities across multiple communities can help to unveil ecological assembly rules in real-world ecosystems.

Stomatal Arrangement Pattern: A New Direction to Explore Plant Adaptation and Evolution

The arrangement patterns of stomata on the leaf surface influence water loss and CO₂ uptake via transportation and diffusion between stomata, the sites of photosynthesis, and vasculature. However, the quantification of such patterns remains unclear. Based on the distance between stomata, we developed three independent indices to quantify stomatal arrangement pattern (SAP). "Stomatal evenness" was used to quantify the regularity of the distribution of stomata based on a minimum spanning tree, "stomatal divergence" described the divergence in the distribution of stomata based on their distances from their center of gravity, and "stomatal aggregation" was used to quantitatively distinguish the SAP as clustered, random, or regularly distributed based on the nearest-neighbor distances. These three indices address the shortcoming of stomatal density that only describes "abundance" and may, collectively, have a better capacity to explore crop development, plant adaptation and evolution, and potentially ultimately enable a more accurate reconstruction of the palaeoclimate.

Strong Environmental Filtering Based on Hydraulic Traits Occurring in the Lower Water Availability of Temperate Forest Communities

The trait-based approaches have made progress in understanding the community assembly process. Here, we explore the key traits that may shape community assembly patterns of the same community type but within different water availabilities. Natural Quercus wutaishanica forests were chosen as a suitable study system to test the difference between economic and hydraulic traits across water availability on the Loess Plateau (LP, drought region) and Qinling Mountains (QL, humid region) of China. A total of 75 plots were established separately in two sites, and 12 functional traits (seven hydraulic traits and five economic traits) of 167 species were studied. Community-weighted mean trait values and functional diversity indices were compared between the two sites. Canonical component analysis was performed to infer whether the changes of community traits and their relationships are driven by intraspecific variation or species turnover. Evidence for likely community assembly processes was tested using the null model to determine whether functional structure among seven hydraulic traits and five economic traits was dominated by different ecological processes between two sites. We found that forests in the Loess Plateau and Qinling Mountains showed different hydraulic and economic traits. Hydraulic and economic traits coupled at the community level were driven by species turnover. Hydraulic traits showed more significant convergent patterns on LP than that in QL. Our results suggest a strong environmental filtering process occurred in hydraulic-based community assembly in the temperate forest with low water availability. Reveal the relationship of hydraulic and economic traits at the community level. Emphasize the critical role of multi-dimensional traits selecting like hydraulic traits in community ecology.