The role of riparian functional and phylogenetic diversity on leaf litter processing in rivers

While taxonomic diversity mediates changes in ecosystem function is
well-studied, how deeper dimensions of biodiversity, specifically
phylogenetic and functional, independent of taxonomic diversity, drive
important processes is understudied. The overarching goal of this work
was to determine the role of these dimensions of biodiversity
independently and/or interactively explain carbon processing in
rivers. Here, we explicitly link community structure and subsequent
traits of riparian forests to adjacent ecosystem processing of carbon
(e.g., leaf litter). This was accomplished by examining how forests
are actually structured in addition to experimental manipulations of
phylogenetic and functional diversities of riparian forest community
inputs of leaf litter to streams. Experimental field manipulations
were carried out in three Piedmont headwater streams to answer the
following questions: (1) Does existing variation in taxonomic,
functional and phylogenetic diversity of riparian communities
differentially drive decomposition in rivers? And (2) Independent of
taxonomic diversity, how does functional and phylogenetic diversity of
leaf litter assemblages influence rates of decomposition in rivers? We
observed significant interspecific variation in breakdown among 30
riparian tree species, in addition to significant relationships
between breakdown rate and important foliar tissue chemistries.
Breakdown of mixtures that reflected the composition of the riparian
species composition did not vary with functional nor phylogenetic
diversity, but breakdown of litter mixtures was higher than that of
single species. In a separate study, when manipulated independently,
functional and phylogenetic diversity were positively related to
breakdown, and explained similar degrees of variation. These results
are important to understand in light of deepening knowledge of the
role different dimensions of biodiversity take in explaining ecosystem
function, as well as how these measures can be used as tools in
habitat restoration practice.

尽管分类多样性（taxonomic diversity）调控生态系统功能变化的研究已较为充分，但独立于分类多样性的生物多样性更深维度——尤其是系统发育多样性（phylogenetic diversity）与功能多样性（functional diversity）——如何驱动关键生态过程，相关研究仍较为匮乏。
本研究的核心目标，是明确上述生物多样性维度如何独立或交互地解释河流碳循环过程。
本研究中，我们明确将河岸森林的群落结构及其功能性状，与毗邻水体的碳循环过程（如叶片枯落物（leaf litter）分解）建立关联。
该目标的达成，一方面通过实地调查河岸森林的天然群落组成结构，另一方面通过对输入溪流的河岸森林枯落物群落的系统发育与功能多样性开展实验操控。
本研究在皮埃蒙特（Piedmont）地区的3条山前源头溪流中开展野外操控实验，以解答以下两个核心问题：
1. 河岸群落的分类、功能与系统发育多样性的天然差异，是否会对河流中的分解过程产生差异化影响？
2. 在独立于分类多样性的前提下，枯落物组合的功能与系统发育多样性，如何影响河流中的枯落物分解速率？
本研究观测到30种河岸乔木的枯落物分解速率存在显著的种间差异，同时发现分解速率与叶片关键组织化学特征之间存在显著相关关系。
模拟河岸天然物种组成的枯落物混合样，其分解速率并未随功能多样性或系统发育多样性发生显著变化，但混合枯落物的分解速率显著高于单一物种枯落物。
在另一项独立操控实验中，当功能多样性与系统发育多样性被单独调控时，二者均与分解速率呈正相关关系，且对分解速率变异的解释度相近。
鉴于当前学界对生物多样性不同维度调控生态系统功能的认知不断深化，且上述多样性指标可作为栖息地修复实践的辅助工具，本研究结果具有重要的理论与应用价值。