黄土丘陵区天然草地群落及其优势种对脉冲降雨的响应

Rain pulse, which refers to infrequent and discrete precipitation events, is one of the typical characteristics of natural environment in semiarid Loess Plateau, and also main factor affecting and activating ecological processes and community evolution in local vegetation ecosystem. The research will take natural grassland communities and its two dominant species (Bothriochloa ischaemum, a C4 perennial herbaceous grass and Lespedeza davurica, a C3 perennial leguminous subshrub) as research objects, after carrying on vegetation survey, in-situ observation and rainfall manipulation experiments, to investigate the hydrological process of natural grassland community under different rain pulse events, clarifying rainfall redistribution features and seasonal dynamics of the communities and pulse rain fall threshold value that cause grassland community characteristics change, and to reveal the coupled relations between response processes and differences of the two species and the natural grassland communities; after comparing the main eco-physiological processes of the two dominant species under different rain pulse events, to reveal the response and difference of the two species under different rain pulse events, and their role and contribution to community characteristics change. The research will enhance our ecological understanding of the hydrological relations between rainfall and natural vegetation in semiarid Loess Plateau, and provide scientific evidences for proper evaluating the self recovery potential of the degraded natural grasslands, and for forecasting the succession trend of natural grassland community and dominant species under the background of precipitation pattern change in semiarid loess hilly-gully region.

降雨呈间歇式脉冲供应既是黄土高原半干旱区自然环境的典型特征，也是驱动该区天然草地群落特征及其主要生态过程发生改变的主要影响因素。本项目选取陕北黄土丘陵区天然草地群落及其优势种（白羊草与达乌里胡枝子）为研究对象，采用群落调查、定点观测和模拟降雨试验相结合的方法，通过研究不同脉冲降雨量条件下天然草地群落水文学过程，阐明天然草地群落降雨再分配特征及其季节动态，明确引起草地群落特征改变的脉冲降雨阈值与群落构成关系，探明黄土丘陵区脉冲降雨-草地群落-土壤水分间耦合关系；通过对比研究天然草地和模拟降雨草地群落优势种主要生理生态过程，揭示两优势种对不同等级脉冲降雨量的响应过程与差异及其对群落特征改变的作用和贡献。研究结果将丰富黄土高原半干旱区降雨与天然植被间水文关系的生态学解释，为黄土丘陵区天然退化草地恢复潜力与环境效应评价，以及预测在降雨格局改变背景下天然草地群落及主要优势种的演变趋势提供科学依据。

脉冲降雨是驱动半干旱黄土丘陵区草地群落主要生态过程发生改变的重要因素。研究天然草地群落及其优势种对脉冲降雨的响应过程与差异，揭示天然群落对脉冲降雨的再分配特征及其季节有效性，可为预测降雨格局改变背景下草地群落演变趋势提供科学依据。项目系统研究了天然草地群落主要种叶片润湿性和叶片持水力特征，比较了叶片近轴面和远轴面、坡向(阳坡和阴坡)间以及立地条件(川地和山地)间差异；得出了59种植物降雨截留特性及其影响因素，比较了典型群落脉冲降雨后的土壤水分变化特征，明确了不同年限退耕草地群落季节降雨截留量的变异性特征，揭示了天然草地群落降雨再分配水文学过程及群落响应；阐明了主要草地群落优势种对脉冲降雨/土壤水分变化响应差异的生理生态基础，得出了天然草地群落CO2通量特征对脉冲降雨的响应。总体表明：脉冲降雨条件下，草地群落优势种光合生理对脉冲降雨的响应速度和程度由群落类型、降雨量、物种和生长季节共同决定；降雨对群落土壤呼吸具有激发效应，其激发程度和持续时间与降雨量大小、生长季节、土壤前期含水量、群落类型以及主要构成种生活型有关。明确得出脉冲降雨对黄土丘陵区天然草地的效应主要受群落构成物种属性和群落特征影响；小降雨事件主要激发群落优势种的光合生理响应，只有大降雨事件才可引起草地群落及其构成种的生物量响应；草地群落土壤呼吸对脉冲降雨量存在响应阈值，其大小与群落特征有关；水量平衡法是测定冠层降雨截留量较准确的方法。项目执行期间，主要成员共参加6次国内外学术会议（包括2次国际学术会议和4次国内学术会议），其中大会报告1次，分组报告2次。围绕项目主体研究内容，共发表学术论文17篇（SCI收录期刊论文7篇，CSCD期刊论文10篇），培养毕业研究生9名（博士生2名，硕士生7名）。获批发明专利1项。

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