根系分布不同的两种共存草原植物的水分利用策略：稳定同位素实验证据

Species coexistence is the prerequisite for the community assembly and biodiversity maintenance. Therefore, the mechanisms of species coexistence have been the central issue and the controversial focus in community ecology. The communities with coexistence of shallow-rooted Allium polyrrhizum and deep-rooted Stipa krylovii are widely distributed in the Inner Mongolia grasslands, which can be used as model species to study the mechanisms of species coexistence. Water availability is an important factor limiting community structure and functions in this grassland ecosystem, thus contrasting water use strategies among different species are strongly correlated with their coexistence within the community. We hypothesize that shallow-rooted species can effectively use the rainfall with low intensity but high frequency. Formation of the transient absorption characteristics of surface water during the evolution make the plants take up water fast but cannot conserve the water for the shallow-rooted species. However, on the other hand, the response is opposite for the deep-rooted species. Taken together, the two species can coexist due to the differentiation of water sources. To test our hypothesis, our research project will integrate manipulative precipitation experiment and field investigation, use stable isotope technology, analyze the growth responses of the two species to changes in precipitation patterns, and compare the differences in their root distribution, root architecture, and water uptake and storing capacity. Our project aims to uncover the water resource utilization strategies of species with different root vertical distribution, to clarify the station of water niche separation between shallow-rooted and deep-rooted species and their underlying root morphological and physiological mechanisms in a typical community.This study will improve our understanding of the mechanisms of species coexistence and community assembly rule.

物种共存是植物群落构建和生物多样性维持的前提，因此物种共存机制是当今群落生态学的核心问题和争论焦点。浅根系植物多根葱和深根系植物克氏针茅的共生群落广泛分布于内蒙古草原区，成为研究物种共存的模式种对。由于水分是草原群落首要的限制因子，物种共存机制很可能与其水分利用的差异有关。我们断定浅根系多根葱会更有效地利用小强度（但高频次）的降雨，因而作为长期进化而形成的吸收稍纵即逝的表层水分的适应特征，其根系可能吸水快、但保水弱，而克氏针茅则恰好相反，从而实现对降雨来源水分的分割利用而稳定共存。为验证该假设，本项目拟通过野外观测与模拟降雨的盆栽实验，运用稳定同位素示踪技术，对比二者对不同降雨格局的生长响应、根系分布、根系构型及根系吸水与保水能力的差异，揭示两个物种的水分利用策略，阐明其生态位分化状态及其根系形态学和生理学基础，对阐释物种共存机制和群落构建规则具有重要意义。

浅根系植物多根葱（Allium polyrhizum）和深根系植物克氏针茅（Stipa krylovii）的共生群落广泛分布于内蒙古草原区，是研究物种共存机制的理想模式种对。为了验证多根葱和克氏针茅对环境资源的利用方式存在差异，本项目通过野外观测与模拟降雨的盆栽实验，对比二者对不同降雨格局的生长响应、根系分布、根系构型及根系吸水与保水能力的差异，揭示两个物种的水分利用策略，阐明其生态位分化状态及其根系形态学和生理学基础，对阐释物种共存机制和群落构建规则具有重要意义。. 结果发现，在面对环境变化时，多根葱对放牧做出适应性策略是通过促进植株地下部分生长，从而增加了根冠比，而克氏针茅对放牧更为敏感，抑制了地上、地下的生长。在放牧干扰下，多根葱根通过增加大径级根系的比例来提高水分和养分等的吸收能力；克氏针茅通过增加小径级的比例适应生态环境变化。多根葱根系长度、根系表面积和根系体积的累积贡献率为92.46%；而克氏针茅根系长度、根系分叉数、根系表面积和根尖数累积贡献率为93.36%。. 多根葱地下部分对养分和水分的竞争中占据主导地位，而克氏针茅的地上部分在总竞争能力中占有主导地位。多根葱将积累物质更多分配地下倾向，采用生理忍耐对策，维持基本生长；而克氏针茅趋向采用竞争对策，积累物质用于地上生长，这一发现在盆栽控制实验中得以验证。盆栽控制实验结果表明，不同降雨格局以及不同的播种方式对多根葱和克氏针茅的生物量、蒸腾速率、气孔导度等光合指标具有影响。在单播条件下，小降雨多次事件中，克氏针茅净光合速率、气孔导度和蒸腾速率均高于多根葱，胞间二氧化碳浓度则与之相反；在中雨和大雨时则为多根葱高于克氏针茅，这也充分的证明了克氏针茅在生长过程中以先生长地上部分生活的策略。二者对于环境资源的分割利用，使其在群落演替中稳定共存。