黄土丘陵区乡土草种对水氮耦合的响应机制研究.

Increasing drought stress and nitrogen deposition, as controversial global environmental issues，would distinctly affect the function and processe of terrestrial ecosystems in China．In this research，two native dominant grasse species of Bothriochloa ischaemum and Lespedeza davurica in natural grassland in the loess hill-gully region will be used as main investigated materials. The grassland community and eco-physiological response of dominant species to climatic change (drought stress and nitrogen deposition ) will be investigated base on field investigation and potted experiment. The coupling relations among soil water, nitrogen addition and grassland characteristics will be investigated through the analytical research of the species composition, species diversity, ecological niche, aboveground biomass, root characteristics of natural grassland and the eco-physiological characteristics of dominant species. Interspecific interaction and the eco-physiological characteristics of two native species at each growth period under different soil water and nitrogen conditions will be also conducted on the basis of potted experiment, in order to clarify the competitive relationship and coexistence between two dominant species. Those research results will help us understand the adaption mechanism and response of dominant species to climate change, and provide the eco-physiological theory basis for grassland restoration and construction cultivated pastures using native grass in the loess hill-gully region.

干旱胁迫和大气氮沉降持续增加作为引起全球气候变化的重要因素，已严重影响我国草地生态系统的结构与功能。项目在前期研究的基础上提出以黄土丘陵区草地植物群落优势种白羊草和达乌里胡枝子为对象，基于野外群落观测与室内控制试验，系统研究草地群落特征及其优势种生理生态特性对干旱胁迫与氮沉降气候变化因素的响应。通过分析草地植物群落物种组成、生物多样性、生态位、地上生物量和根系特征以及优势草种生理生态特性，探明群落优势种对水分胁迫和土壤氮素添加的响应过程及其与群落特征间的耦合关系；通过研究两草种混播下生理生态特性与种间关系的生育期动态变化规律及物种差异，阐明不同土壤水氮耦合条件下二者竞争与共存关系的生理生态基础。研究成果揭示黄土丘陵区群落优势草种对气候变化的响应与适应机制，为该地区退化草地植被恢复与管理以及利用乡土草种优化配置人工草地提供生态学依据。

土壤水分和氮素含量作为影响草地生态系统的关键因子，对半干旱区草地植物群落物种组成、生物多样性、净生产力及其优势种的生理生态特征等起决定性作用。深入探讨半干旱区草地群落及其优势草种对土壤水分和氮素添加耦合响应的生理生态机制，对该区退化草地植被恢复与管理具有重要理论与实践意义。本项目以黄土丘陵半干旱区不同撂荒年限白羊草和达乌里胡枝子草地群落、不同混播比例的人工草地为研究对象，系统研究其对水分和氮素添加的响应过程与机制。结果表明：水氮添加显著影响了白羊草和达乌里胡枝子草地群落地上部分生物量、优势种生物量和多样性指数，以白羊草群落的响应较为敏感；氮素添加促进了白羊草与达乌里胡枝子草地群落的丰富度指数，且提高了白羊草的重要值而降低了达乌里胡枝子的重要值；白羊草和达乌里胡枝子叶绿素荧光参数对水氮添加无明显响应规律，但白羊草的实际光化学量子效率显著低于达乌里胡枝子；氮素添加明显增加了白羊草群落的优势种全N含量，但降低了全P含量；氮素添加明显增加土壤铵态氮和硝态氮含量，而水分添加影响不显著；氮素添加提高了白羊草和达乌里胡枝子混播群落的生物量，且随白羊草所占比例的增加而升高；不同混播群落中达乌里胡枝子的全N和全P含量显著高于白羊草，土壤全N含量随土壤深度增加而降低；不同混播比例下白羊草叶片光化学淬灭参数显著高于白羊草，但其非光化学淬灭参数呈相反趋势。该研究成果不仅有利于我们增加对半干旱区草地群落对土壤水氮添加响应机制的认识，也可为利用乡土草种在该区建植人工草地提供理论支撑。