Variability Of Leaf Functional Traits Under Environmental Change And Its Impacts On The Simulation Of Ecosystem Productivity

Leaf functional traits of terrestrial plants are closely related to their survival,growth and reproductivity,and can individually or jointly indicate the response of plants to environmental changes.In addition,the discovery of‘leaf economic spectrum'significantly improves our understanding of how plants optimize their functions through the trade-offs between functional traits.Along with the continuous development of new theories and new methods for leaf functional traits,numerous studies have begun to explore the response of leaf functional traits to global environmental changes.However,the previous studies mainly display how leaf functional traits vary along environmental gradients,which result from both interspecific differences and environmental impacts.In addition,recent advances have incorporated leaf trait relationships into the simulation of ecosystem productivity.However,the robustness of leaf trait relationships under environmental changes have long been limiting the predictive utility of such empirical correlations.To address the above problems,this study constructed a global database of leaf functional traits from manipulative experiments.Based on the database,we further quantified the response of plant functional traits and their relationships to environmental changes.In addition,we developed a traceability framework to evaluate the relative contributions of plant functional traits to the inter-model differences in simulated ecosystem productivity.Furthermore,we also incorporated the results from manipulative experiments into the terrestrial biosphere model to simulate the influence of changes in leaf functional traits on ecosystem productivity.The major conclusions were outlined below:?1?According to the investigation of extensive literatures,we constructed a global database of leaf functional traits from 515 species under warming,drought,elevated CO₂ and nitrogen addition treatment,and quantified the response of leaf functional traits to environmental changes and the influence factors.The meta-analysis showed that elevated CO₂ and nitrogen addition were the major environmental factors that affected leaf functional traits.The elevated CO₂ enhanced leaf photosynthetic rate,but significantly decreased specific leaf area and leaf nitrogen.In contrast,the nitrogen addition facilitated leaf photosynthetic rate and leaf nitrogen,but had no significant effect on specific leaf area.The response of leaf functional traits was also affected by treatment strengths and duration,and differed between plant functional types.The established database provides valuable support for the trait-based studies,and the response ratios of leaf functional traits are important evidences for simulations of how plants will respond to future environmental conditions.?2?Based on the database,we further tested the robustness of leaf trait relationships under environmental changes and the potential mechanisms.The two-dimensional vector graphics showed that the response directions of paired traits were greatly different between species,and were mostly contrary to the directions of the intrinsic leaf trait relationships.However,the slopes of the interspecific trait relationships held stable under global environmental changes,while only their elevations varied.The unaltered slopes resulted from the divergent directions of changes in paired traits with asymmetric responses.In addition,we showed that the varied elevations were affected by experimental types and treatment strength,and differed between plant functional types.The robust interspecific trait relationships demonstrate the feasibility of incorporating leaf functional trait into models for a more realistic presentation of plant responses.?3?Based on the decomposability of ecosystem productivity,we developed a traceability framework to evaluate the inter-model difference in simulated ecosystem productivity.With the outputs from 15 terrestrial biosphere models,we found that SLA explained 77%of the inter-model difference in leaf area index,which contributed 90%to the simulated GPP differences.The modeled spatial variabilities of plant functional traits were generally lower than the local observed datasets.Overall,these findings together suggest a high priority to reduce model difference from a better understanding of the biogeographical and ecological variations in leaf functional traits.?4?Implication of incorporating changes in leaf functional trait under climate change into the simulation of ecosystem productivity.Based on the results from elevated CO2 experiments and the terrestrial biosphere model CABLE,we estimated the influence of changes in leaf functional traits on ecosystem productivity.According to the simulations with different assumptive scenarios,we found that the acclimation of specific leaf area in response to elevated CO₂ significantly reduced plant growth,but didn't affect the net ecosystem productivity.Differently,the further consideration of the acclimation of leaf trait relationship amplified the plant growth by 23%during elevated CO₂.In addition,the acclimation of leaf trait relationship also led to large amount of additional CO₂ absorption in the northern mid-high latitudes and the southern low latitudes.Overall,this study quantified the response of plant functional traits to environmental changes and their influence on the simulation of ecosystem productivity.This model-experiment synthesis suggests that plant trait acclimation should be considered in the projections of plant responses and provide additional constraints for modeled ecosystem productivity.