Causes of Depth Zonation in Emergent and Floating Aquatic Plants

在世界各地的湖泊中，涌现的、漂浮的和淹没的水生植物显示出一种独特的但无法解释的深度分区。PI建议测试一个新的假设，从竞争的角度来解释这种模式，这种模式受叶片高度、相对非生产性支持组织的分配以及在不同深度维持正的全植物碳平衡的能力的影响。这一假设解释了环境条件和植物特征对地带性的影响（包括最近记录的一些趋势）。提出了现场操作来确定：紧急情况是否竞争性地将漂浮物种从浅水中排除（基于去除实验）；在其最大深度，突生物种和漂浮物种是否接近年净生长量（基于移植到各种深度的切割测量）；观察到的净生长随深度下降的模式是否归因于对支持组织的分配增加（基于叶片人口统计学、支持组织异速生长和组织构建成本作为深度函数的研究）；淹没植物的密床是否限制了中营养化和富营养化湖泊的最大水深（基于去除实验）；以及大叶睡莲（如睡莲）是否竞争性地排斥小叶漂浮物种（如Brasenia），通过激烈的竞争（机械磨损）或叶片覆盖（基于移除实验和叶片重叠分析以及两组共同发生的叶片人口统计学）从浅水中迁移。这些实验将在目前比较研究的10湖生育梯度的代表性子集（海伦湖，风布丁湖，野猫湖，美丽湖）中进行。

Emergent, floating, and submersed aquatic plants show a characteristic but unexplained zonation by depth in lakes throughout the world. The PI proposes to test a new hypothesis to account for this pattern in terms of competition, as influenced by differences between growth forms in leaf height, allocation to relatively unproductive support tissue, and ability to maintain a positive whole-plant carbon balance at different depths. This hypothesis accounts for several trends (including some recently documented) in zonation as a function of environmental conditions and plant characteristics. Field manipulations are proposed to determine: Whether emergents competitively exclude floating species from shallow water (based on removal experiments); Whether emergent and floating species are near net annual growth at their maximum depths (based on measurements on cutting transplanted to a variety of depths); Whether the observed pattern of decline in net growth with depth is attributed to increased allocation to support tissue (based on studies of leaf demography, the allometry of support tissue, and tissue construction costs as a function of depth); Whether dense beds of submersed plants limit the maximum depth of water in mesotrophic and eutrophic lakes (based on removal experiments); and Whether large-leaved waterlilies (e.g., Nymphaea) competitively exclude smaller-leaved floating species (e.g., Brasenia, Potamogeton) from shallow water via aggressive competition ( mechanical abrasion) or leaf overriding (based on removal experiments and analysis of leaf overlap and leaf demography where the two groups co-occur). These experiments would be conducted in a representative subset (Helen Lake, Wind Pudding Lake, Wildcat Lake, Beautiful Lake) of a 10-lake fertility gradient that is currently the subject of comparative studies.