Linking individual and species-level leaf traits with ontogenetic development stage to explain tree performance under competition and environmental contexts

To verify how species traits and individual traits link ontogenetic size, external biotic and abiotic factors to influence tree performance. In a temperate natural forest in northeastern China, we measured dynamic performance, size, as well as competition, topography, and soil variables as biotic and abiotic variables for all 1320 trees of 17 species in 62 monitoring plots from 2010-2020. For each individual tree, we also measured five typical functional traits representing leaf size and elemental content: leaf area, specific leaf area, leaf dry matter content, leaf nitrogen content, and leaf carbon : nitrogen ratios. These traits are not only strongly associated with performance, but trade-offs between traits have previously been shown to express plant acquisitive-conservative strategy characteristics. Reconceptualized based on previous understanding of trait-based approach (Fig. 1). We first tested the direct explanatory effects of species traits and individual traits on performance in multifactorial contexts. We first tested the direct explanatory effects of species traits and individual traits on performance in multifactorial contexts. Subsequently, we analyzed the moderating and mediating effects of these two levels of traits in explaining ontogenetic size, external competition, and environmental influences on performance. The following three questions were posed in response to the results:

QI: Do species and individual traits differ in directly explaining performance in a multifactor context that includes ontogenetic size, external biotic and abiotic factors?

QII: How species and individual traits explain the effect of ontogenetic size on performance by moderating and mediating effects.

QIII: Can traits at the species and individual level influence competition- and environment-performance relationships through trait-based approaches? Does ontogenetic size work jointly with traits at different levels in this process?

为探明物种性状与个体性状如何与个体发育大小、外界生物及非生物因子共同作用，进而影响树木生长表现。本研究于中国东北温带天然林中开展，于2010-2020年间对62个监测样地内17个物种的1320株树木进行了动态生长表现、个体大小，以及作为生物与非生物因子的竞争状况、地形特征与土壤属性的测定。针对每株个体树木，本研究还测定了5个典型功能性状，涵盖叶片大小与元素含量两类特征：叶面积（leaf area）、比叶面积（specific leaf area）、叶干物质含量（leaf dry matter content）、叶氮含量（leaf nitrogen content）以及叶碳氮比（leaf carbon : nitrogen ratios）。这些性状不仅与树木生长表现紧密相关，且性状间的权衡关系此前已被证实可体现植物的获取-保守策略特征。本研究基于现有基于性状的研究方法（trait-based approach）进行了概念重构（Fig. 1）。我们首先在多因子背景下检验了物种性状与个体性状对树木生长表现的直接解释效应。我们首先在多因子背景下检验了物种性状与个体性状对树木生长表现的直接解释效应。随后，我们分析了这两个层级的性状在解释个体发育大小、外界竞争与环境因子对树木生长表现的影响时所发挥的调节与中介效应。基于研究结果，本研究提出以下三个科学问题：
QI: 在包含个体发育大小、外界生物与非生物因子的多因子背景下，物种性状与个体性状对树木生长表现的直接解释效应是否存在差异？
QII: 物种性状与个体性状如何通过调节与中介效应，阐释个体发育大小对树木生长表现的影响？
QIII: 基于性状的研究方法，物种与个体层级的性状能否调控竞争-生长表现以及环境-生长表现之间的关系？在此过程中，个体发育大小是否与不同层级的性状共同发挥作用？