Data_Sheet_1_Differential Investment Strategies in Leaf Economic Traits Across Climate Regions Worldwide.docx

The leaf economics spectrum (LES) is the leading theory of plant ecological strategies based on functional traits, which explains the trade-off between dry matter investment in leaf structure and the potential rate of resource return, revealing general patterns of leaf economic traits investment for different plant growth types, functional types, or biomes. Prior work has revealed the moderating role of different environmental factors on the LES, but whether the leaf trait bivariate relationships are shifted across climate regions or across continental scales requires further verification. Here we use the Köppen–Geiger climate classification, a very widely used and robust criterion, as a basis for classifying climate regions to explore climatic differences in leaf trait relationships. We compiled five leaf economic traits from a global dataset, including leaf dry matter content (LDMC), specific leaf area (SLA), photosynthesis per unit of leaf dry mass (Amass), leaf nitrogen concentration (Nmass), and leaf phosphorus concentration (Pmass). Moreover, we primarily used the standardized major axis (SMA) analysis to establish leaf trait bivariate relationships and to explore differences in trait relationships across climate regions as well as intercontinental differences within the same climate type. Leaf trait relationships were significantly correlated across almost all subgroups (P < 0.001). However, there was no common slope among different climate zones or climate types and the slopes of the groups fluctuated sharply up and down from the global estimates. The range of variation in the SMA slope of each leaf relationship was as follows: LDMC–SLA relationships (from −0.84 to −0.41); Amass–SLA relationships (from 0.83 to 1.97); Amass–Nmass relationships (from 1.33 to 2.25); Nmass–Pmass relationships (from 0.57 to 1.02). In addition, there was significant slope heterogeneity among continents within the Steppe climate (BS) or the Temperate humid climate (Cf). The shifts of leaf trait relationships in different climate regions provide evidence for environmentally driven differential plant investment in leaf economic traits. Understanding these differences helps to better calibrate various plant-climate models and reminds us that smaller-scale studies may need to be carefully compared with global studies.

叶片经济谱（leaf economics spectrum, LES）是基于功能性状的主流植物生态策略理论，阐释了叶片结构干物质投入与资源潜在返还速率之间的权衡关系，揭示了不同植物生长型、功能型或生物群区的叶片经济性状投入的普遍规律。既往研究已阐明不同环境因子对LES的调控作用，但叶片性状双变量关系是否会随气候区域或大陆尺度发生变化，仍有待进一步验证。本研究采用应用广泛且稳健的柯本-盖格气候分类（Köppen–Geiger climate classification）作为气候区域划分依据，以探究叶片性状关系的气候差异。我们从全球数据集中共整理得到5项叶片经济性状，分别为叶片干物质含量（leaf dry matter content, LDMC）、比叶面积（specific leaf area, SLA）、单位叶干重光合速率（photosynthesis per unit of leaf dry mass, Amass）、叶片氮浓度（leaf nitrogen concentration, Nmass）以及叶片磷浓度（leaf phosphorus concentration, Pmass）。此外，本研究主要采用标准化主轴分析（standardized major axis, SMA）构建叶片性状双变量关系，以探究不同气候区域间的性状关系差异，以及同一气候类型下的洲际差异。几乎所有亚组的叶片性状关系均呈显著相关（P < 0.001）。但不同气候带或气候类型间并不存在统一的斜率，且各亚组的斜率相较于全球估计值呈现出显著的上下波动。各项叶片性状关系的SMA斜率变异范围如下：LDMC–SLA关系（-0.84至-0.41）；Amass–SLA关系（0.83至1.97）；Amass–Nmass关系（1.33至2.25）；Nmass–Pmass关系（0.57至1.02）。此外，在草原气候（Steppe climate, BS）或温带湿润气候（Temperate humid climate, Cf）下，不同大陆间的斜率存在显著异质性。不同气候区域下叶片性状关系的变化，为环境驱动的植物叶片经济性状差异化投入提供了证据。明晰这些差异有助于更好地校准各类植物-气候模型，同时也提醒我们，小型尺度研究需谨慎与全球尺度研究进行比对。