Shifts in Aboveground Biomass Allocation Patterns of Dominant Shrub Species across a Strong Environmental Gradient

Most plant biomass allocation studies have focused on allocation to shoots versus roots, and little is known about drivers of allocation for aboveground plant organs. We explored the drivers of within-and between-species variation of aboveground biomass allocation across a strong environmental resource gradient, i.e., a long-term chronosequence of 30 forested islands in northern Sweden across which soil fertility and plant productivity declines while light availability increases. For each of the three coexisting dominant understory dwarf shrub species on each island, we estimated the fraction of the total aboveground biomass produced year of sampling that was allocated to sexual reproduction (i.e., fruits), leaves and stems for each of two growing seasons, to determine how biomass allocation responded to the chronosequence at both the within-species and whole community levels. Against expectations, within-species allocation to fruits was least on less fertile islands, and allocation to leaves at the whole community level was greatest on intermediate islands. Consistent with expectations, different coexisting species showed contrasting allocation patterns, with the species that was best adapted for more fertile conditions allocating the most to vegetative organs, and with its allocation pattern showing the strongest response to the gradient. Our study suggests that co-existing dominant plant species can display highly contrasting biomass allocations to different aboveground organs within and across species in response to limiting environmental resources within the same plant community. Such knowledge is important for understanding how community assembly, trait spectra, and ecological processes driven by the plant community vary across environmental gradients and among contrasting ecosystems.现有植物生物量分配（biomass allocation）的相关研究多聚焦于地上营养器官与根系的分配模式，而关于植物地上器官生物量分配驱动因素的认知仍较为匮乏。我们沿强烈的环境资源梯度，探究了种内和种间水平上地上生物量分配的驱动因素：具体而言，研究选取瑞典北部30个已形成森林的岛屿构成长期演替序列（chronosequence），该序列上土壤肥力与植物生产力逐渐降低，而光照可利用性逐步提升。针对每个岛屿上共存的3种优势林下矮灌木物种，我们估算了两个生长季内采样年份产生的总地上生物量分配给有性生殖器官（即果实）、叶片与茎秆的比例，以此明确在种内和群落整体水平上，生物量分配如何响应该演替序列。与预期相悖的是，种内分配给果实的生物量在肥力较低的岛屿上最少，而群落整体水平上分配给叶片的生物量在中等肥力岛屿上最高。与预期相符的是，不同共存物种展现出截然不同的分配模式：其中最适应高肥力环境的物种将最多生物量分配给营养器官，且其分配模式对环境梯度的响应最为显著。本研究表明，在同一植物群落中，共存的优势植物物种可依据受限的环境资源，在种内和种间水平上对不同地上器官展现出差异显著的生物量分配模式。该研究结果有助于理解群落构建、性状谱以及由植物群落驱动的生态过程如何随环境梯度变化，以及在不同生态系统间存在的差异。