Riparian Plant Genotype by Environment Interactions:Eeffects on Leaf Litter Quality, in-Stream Decomposition, and Aquatic Biodiversity

河岸植被的凋落物为许多河流食物网提供了重要的能量来源。这些凋落物的质量强烈影响它们在溪流中的分解速度及其所支持的水生生物的多样性和生产力。单一物种或杂交复合体内的遗传变异对凋落物质量变化的影响程度尚不清楚，但可能至关重要，特别是在西南高海拔河岸生态系统中，两种棉杨及其杂交构成了80-95%的河岸植被。此外，众所周知，诸如虫食和干旱等环境胁迫的影响取决于杨木的基因型，但这种基因型如何通过环境相互作用影响凋落叶质量和溪流加工，对于杨木来说尚不清楚，据我们所知，对于任何其他河岸物种来说也不清楚。这项研究将确定水生生物多样性和生态系统过程是否与棉杨杂交带相似。拥有已知基因型的纯棉和杂交棉的普通花园将被用来确定棉杂交复合体内的遗传变异如何影响凋落物质量、流中分解（包括质量损失和养分释放）、微生物分解者（细菌和真菌）和无脊椎动物的定植和多样性。这项实验工作将通过对进入溪流的凋落物的自然调查来补充，以确定从科罗拉多到墨西哥的流域自然普遍存在的四种杨木杂交类型（弗里蒙特、窄叶、F1和回交）的凋落物的重要性和分布。最后，通过对照试验研究杨木杂交类型和环境胁迫（干旱和草食），确定遗传与环境相互作用如何改变溪流中凋落物质量、凋落物加工和生物多样性。这项研究将解决我们对水生群落和生态系统过程以及陆水相互作用的理解中的这些关键未知数。

Litterfall from riparian vegetation provides a critical energy source for many stream food webs. The quality of those litter inputs strongly influences their rate of decomposition in the stream and the diversity and productivity of aquatic organisms they support. The extent to which genetic variation within a single species or hybrid complex contributes to variation in litter quality is not well understood, but could be critical, particularly in high-elevation riparian ecosystems in the southwest, where two species of cottonwoods and their hybrids constitute 80-95% of the riparian vegetation. Furthermore, the effects of environmental stress such as insect herbivory and drought are known to depend on cottonwood genotypes, but how such genotype by environment interactions affect leaf litter quality and in- stream processing is not known for cottonwoods, nor, to our knowledge, for any other riparian species.This study will determine whether aquatic biodiversity and ecosystem processes are similarly linked to cottonwood hybrid zones. Common gardens with pure and hybrid cottonwoods of known genotypes will be used to determine how genetic variation within the cottonwood hybrid complex affects litter quality, in- stream decomposition (including mass loss and nutrient release), and colonization and diversity of microbial decomposers (bacteria and fungi) and invertebrates. This experimental work will be supplemented with natural surveys of litter entering streams to determine the importance and distribution of litter from each of four cottonwood cross-types (Fremont, narrowleaf, F1, and backcross) that are naturally ubiquitous in watersheds from Colorado to Mexico. Finally, controlled experiments crossing cottonwood cross-types and environmental stress (drought and herbivory) will be used to determine how genetic by environment interactions alter litter quality and litter processing and biodiversity in streams. This research will address these critical unknowns in our understanding of aquatic community and ecosystem processes and terrestrial-aquatic interactions.