西南亚高山针叶林主要树种根系对水-氮耦合效应的响应及其与地上生长的关联

Notable changes are happening in global climate, which character with extrem climate event, nitrogen deposition and so on. While we had little knowledge about the responses and feedback of belowground ecological processes to climate change. It is well known that there are significant soil water-nitrogen interaction effect on plants. The studies focused on the aboveground of plant, only limited effort has been made to blowground, which to some extent limits the understanding of belowground processes in forest ecosystems. However, the root sense and response firstly to soil environment, and regulate the growth and development of plant. So in this study, Picea asperata and Betula albo-sinensis, the dominating species of subalpine forest in the southwest of China, eastern Tibetan Plateau, would be used as materials, and the root of plant as breakthrough point. We would conduct a controlled experiment (soil water would be controlled and nitrogen deposition simulated as watering NH4NO3 solution with different concentration to soil) to study the responses of root to water-nitrogen interaction in growth, distribution and physiology, its mechanism and the regulation to aboveground of plant, through the non-invasive micro-test technique (NMT) and stable isotope 15N enrich method. The aim of this study would be to: (1) clarify the response of root to water-nitrogen interaction in different levels; explain the lifespan of fine root in physiology and function to break the limit of "the optimum allocation paradigm". (2) reveal the biological linkage of the aboveground and belowground from the root function of the nutrient absorption, along "nitrogen absorption - movement - distribution" in plant. This project will greatly advance and deepen the development of root ecology. Also, this information will be valuable for providing a more comprehensive view to understand the whole effect of water-nitrogen interaction to plant in the "soil-plant" system.

全球正经历着极端气候事件增加、氮沉降等为主要特征的显著变化，而地下生态过程对气候变化的响应和反馈知之甚少。土壤水分及氮有效性对植物的影响有显著的耦合效应，但相关研究主要集中在地上部分，而对直接接触、响应土壤环境并调控地上生长的根系未见研究。本项目以西南亚高山针叶林主要树种粗枝云杉和红桦为材料，根系为切入点，通过控制试验设置土壤水分、模拟氮沉降，结合稳定同位素示踪和非损伤微测技术，重点研究水-氮耦合效应下根系在生长、分布及生理活性等方面的响应机制及对地上的调控，试图：1）阐明根系对水-氮耦合效应在不同层面的应答，以突破传统的"优化配置"理论，从生理、功能方面解释细根寿命；2）从养分吸收功能入手，以"N素的吸收-运转-分配"为主线，揭示地上、地下的生物学关联。本项目的实施可加深和提升根系生态学的理论研究；同时，为理解在"土壤-植物"系统中水-氮耦合效应对植物的整体影响提供新的、全面的认识。

降水的时空分配及土壤N有效性不均导致全球水氮分布的异质性，而植物根系对土壤水氮有效性的响应和反馈知之甚少。本项目以西南亚高山针叶林主要树种粗枝云杉(Picea asperata)和红桦(Betula albosinensis)为材料，着重研究水（土壤含水量为40、50、60、80和100%FC）-氮（施氮浓度为N0、N20、N40 g m-2yr-1）耦合效应下根系的响应及对地上的调控。结果表明：根系可改变形态结构以适应土壤水氮状况，水分胁迫下降低根系平均直径、组织密度和根系总表面积，增大比根长和比表面积。充足的水分能提高根系活性及对NH4+、NO3-的吸收，而水分胁迫造成根系膜脂过氧化程度加剧。施氮对根系形态的影响因土壤水分状况而异：随土壤水分的增加，依次表现为抑制效应、无显著影响和促进作用。.随土壤水分的增加，云杉的碳同化速率呈现S型（N0和N20）/线性（N40）的响应，水分利用效率（WUE）呈指数（N0和N40）/线性（N20）响应，光合-氮利用效率（PNUE）呈S型（N0）/指数（N20）/线性（N40）响应；红桦的碳同化速率、WUE和PNUE均呈S型响应。植物生物量积累对水氮的响应存在阈值：随土壤水分增加，云杉的生物量积累呈线性（N0和N20）/S型（N40）增加，响应水氮的阈值较宽，基本在40%FC开始响应，到100%FC达到饱和。施氮能促进生物量的积累，施氮浓度越大效果越明显。无论施氮与否，随土壤含水量的增加，红桦生物量积累都呈现S型曲线响应，生物量在55%FC开始响应，在65%FC（N0和N20）/76% FC（N40）左右出现饱和值。本研究基于根系形态和生理活性的研究，从植物对N的吸收、WUE和PNUE的响应，并结合生物量的分配，通过地上、地下的生物学关联解释了水氮耦合下植物的生长表现，为 “土壤-植物”系统中水氮耦合效应对植物的整体影响提供了全面的认识。

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