Data from: Trait syndromes among North American trees are evolutionarily conserved and show adaptive value over broad geographic scales

Adaptive syndromes and their evolutionary constraints represent a powerful construct for understanding plant distributions. However, it is unclear how the species requirements to face multiple stressors promotes syndrome formation and to which abiotic stressors these syndromes show adaptive value over broad geographic scales. We combined local occurrence data from the U.S. Forest Inventory and Analysis (FIA) of 219 angiosperm and 85 gymnosperm species living across the conterminous US with phylogenies and trait data to identify tree syndromes, their evolutionary conservatism, and their adaptive value over broad scales. Factor analyses and evolutionary model selection revealed that trees possess functional trait syndromes that are strongly conserved. Major syndromes at the species level differed between angiosperms and gymnosperms. While the two main syndromes in angiosperms were related to cold and drought-waterlogging tolerance, in gymnosperms a trade-off between shade and drought tolerance was the main syndrome followed by a growth-fire resistance syndrome. Additional RLQ and fourth-corner approaches revealed that trait syndromes at the community level were broadly similar to those observed at the species level for angiosperms, although this was less clear for gymnosperms. This suggests that syndrome evolution has played an important role on angiosperm distributions, whereas additional ecological factors explain gymnosperm distributions. Importantly, syndromes show adaptive value, as they were geographically associated with several environmental variables showing structure from continental to local scales, being temperature the main abiotic stressor. Our results indicate that across the conterminous US tree species possess clear syndromes that are subjected to strong evolutionary constraints driving tree species and forest community distribution.

适应综合征（adaptive syndrome）及其进化约束是解析植物分布格局的极具价值的研究框架。然而，目前仍不明确物种应对多重胁迫的需求如何促进适应综合征的形成，以及在大地理尺度下这些综合征对哪些非生物胁迫具有适应价值。本研究整合了分布于美国本土的219种被子植物（angiosperm）与85种裸子植物（gymnosperm）的美国森林资源清查与分析项目（U.S. Forest Inventory and Analysis, FIA）本地出现记录数据，结合系统发育（phylogeny）数据与功能性状（trait）数据，以识别树木适应综合征、其进化保守性以及大尺度下的适应价值。因子分析（factor analysis）与进化模型选择（evolutionary model selection）结果显示，树木拥有高度保守的功能性状综合征。物种水平的主要适应综合征在被子植物与裸子植物之间存在显著差异：被子植物的两种主要综合征分别与耐寒性、耐旱耐涝性相关；而裸子植物的主要综合征为耐荫性与耐旱性之间的权衡，其次为生长-抗火综合征。额外采用RLQ分析与第四角分析（fourth-corner analysis）后发现，被子植物群落水平的性状综合征与物种水平观测到的结果大体相似，但裸子植物的这一规律并不明显。这表明适应综合征的演化在被子植物的分布格局中发挥了重要作用，而裸子植物的分布则需通过其他生态因子加以解释。值得注意的是，适应综合征展现出适应价值：它们在地理分布上与多个环境变量显著相关，这些变量的结构从大陆尺度延伸至局地尺度，其中温度是最主要的非生物胁迫因子。本研究结果表明，在美国本土范围内，树木物种拥有明确的适应综合征，且受到强烈的进化约束，这些约束驱动了树木物种与森林群落的分布格局。