Simplification of plant trait networks among communities along a climatic aridity gradient

Plant ecological strategies are shaped by numerous functional traits and
their tradeoffs. Trait network analysis enables testing hypotheses for the
shifting of trait correlation architecture across communities differing in
climate and productivity. We built plant trait networks (PTNs)
for 118 species within six communities across an aridity gradient, from
forest to semi-desert across the California Floristic Province based on 34
leaf and wood functional traits, representing hydraulic and photosynthetic
function, structure, economics, and size. We developed hypotheses for the
association of PTN parameters with climate and ecosystem properties, based
on theory for the adaptation of species to low resource/stressful
environments, versus higher resource availability with greater potential
niche differentiation. Thus, we hypothesized that across community PTNs,
trait network connectivity (i.e., the degree traits are intercorrelated)
and network complexity (i.e., the number of trait modules, and the degree
of trait integration among modules) would be lower for communities adapted
to arid climates, and higher for communities adapted to greater water
availability, similarly to trends expected for phylogenetic diversity,
functional richness and productivity. Further, within given PTNs, we
hypothesized that traits would vary strongly in their network connectivity
and that the traits most centrally connected within PTNs would be those
with the least across-species variation. Across communities from more arid
to wetter climates, PTN architecture varied from less to more
interconnected and complex, in association with functional richness, but
PTN architecture was independent of phylogenetic diversity and ecosystem
productivity. Within community PTNs, traits with lower species variation
were more interconnected.   Synthesis.  The
responsiveness of PTN architecture to climate highlights how a wide range
of traits contribute to physiological and ecological strategies with an
architecture that varies among plant communities. Communities in more arid
environments show a lower degree of phenotypic integration, consistent
with lesser niche differentiation. Our study extends the usefulness of
PTNs as an approach to quantify tradeoffs among multiple traits, providing
connectivity and complexity parameters as tools that clarify plant
environmental adaptation and trait associations that would influence
species distributions, community assembly and ecosystem resilience in
response to climate change.

植物生态策略由众多功能性状及其权衡关系共同塑造。性状网络分析（Trait Network Analysis）可用于检验不同气候和生产力水平的群落间性状关联架构转变的相关假说。
我们基于加州植物区省（California Floristic Province）内沿干旱梯度、从森林到半荒漠分布的6个群落中的118个物种，结合34项涵盖水力、光合功能、结构、经济策略及体型的叶片和木材功能性状，构建了植物性状网络（Plant Trait Networks, PTNs）。
我们基于物种适应低资源/胁迫环境，以及高资源可获得性伴随更显著生态位分化的相关理论，提出了植物性状网络参数与气候及生态系统属性间关联的假说。据此，我们推测：在不同群落的植物性状网络中，性状网络连通性（即性状间相互关联的程度）与网络复杂度（即性状模块的数量，以及模块间性状整合的程度），将与系统发育多样性、功能丰富度及生产力的预期趋势一致——适应干旱气候的群落其连通性与复杂度更低，而适应更高水分可获得性的群落则更高。
此外，在单个植物性状网络内部，我们推测不同性状的网络连通性差异显著，且在网络中处于核心连接位置的性状，其种间变异程度最低。
沿从干旱到湿润的气候梯度，群落的植物性状网络架构从连通性与复杂度较低逐步转向较高，且该变化与功能丰富度相关，但与系统发育多样性及生态系统生产力无关。在单个群落的植物性状网络中，种间变异程度更低的性状具有更高的连通性。
综上，植物性状网络架构对气候的响应性表明，众多性状共同塑造了生理与生态策略，而这类架构在不同植物群落间存在差异。生长于更干旱环境的群落，其表型整合程度更低，这与较弱的生态位分化特征相符。本研究拓展了植物性状网络作为量化多性状间权衡关系的方法的应用价值，其提出的连通性与复杂度参数可作为量化工具，阐明植物的环境适应机制以及会影响物种分布、群落组装和生态系统应对气候变化韧性的性状关联模式。