黄土丘陵区植物竞争对土壤水分变化的响应

As an important role in determining community establishment, the responses of plant competition to environmental factors can regulate the community structure and change the pathway of community succession. This is the fundamental applicable key of vegetation recovery. In Loess Hilly Region, soil water is one of the most limiting factors of plant growth, consequently, understanding the responses of plant competition to soil water fluctuation is very important for us to carry out local revegetation. In this program, the following subjects are planed to be carried out: 1)The responses of plant competition intensity among local co-existing species and seral species, and their relative competitive ability and hierarchy on soil water fluctuation, are planed to be conducted by field experiments using community density series method (CDS method) and by pot experiments using phytometer method; 2)the links between the growth differences of co-existing species in pulse period of soil water and their death rate in inter-pulse period, will be investigated in the CDS treatment;3) the association between the abundance of co-existing species and their relative competitive ability, and the association between the successional niche positions of seral species and their competitive hierarchy, will be analyzed. Additionaly, the competitive ability and hierarchy of co-existing species in natural community will be assessed numerically with the data of individual-based investigation, and parameterized using Voronoi area and exntended logistic model. All the above subjects are aimed to illistrate the driving process of vegetation succession caused by the responses of plant competition to soil water fluctuation, and to evaluate the importance of plant competition acting on the establishment of community in the local region. The results of this program are expected to guide revegetation of Loess Hilly Region.

植物竞争是群落构建的中心环节。环境因素通过植物竞争对群落结构与动态的调控作用更是植被恢复的理论基础。在黄土丘陵区，土壤水分是植物生长的主要限制性因素，因此，研究植物竞争对土壤水分变化的响应对该区植被恢复具有重要意义。本研究以黄土丘陵区撂荒群落中共存种和序列种为研究对象，利用CDS、Phytometer试验，研究演替过程中群落共存种和演替序列种间的竞争强度、相对竞争能力和等级对变化的土壤水分条件的响应；高水期有/无竞争条件下群落共存种生长差异和低水期群体死亡率关系；分析群落共存种、演替序列种相对竞争能力与其相对多度、演替地位的关系。在此基础上，利用Voronoi面积等数量分析方法，建立和验证自然条件下群落共存种竞争能力的评价方法。结合引起该区土壤水分可利用性降低的主要因素的定位观测，研究土壤水分通过植物竞争对植被演替的作用机制及其在群落组建中的相对重要性，为该区植被恢复提供理论依据。

植物竞争是塑造植物形态、生活史以及植物群落结构和动态特征的主要动力之一，对理解群落演替具有重要意义。水分是黄土丘陵区植物生长的主要限制性因素。植物竞争是资源的争夺，特别是限制性资源及其可利用性。因此在黄土丘陵区，土壤水分的变化对群落共存种间竞争过程和结果具有重要影响。因此从群落水平的基础上，研究土壤水分与群落共存种的相互作用及对种间竞争的影响，将为黄土丘陵区植被恢复和重建工作提供理论依据。. 利用种对组合法与CDS法，研究了不同水分条件下（45%，60%和75%田间含水量），撂荒群落共存草种和演替序列种相对竞争能力、竞争等级，结果表明群落共存种在水分较好条件下竞争强度较大，而在水分较差条件下竞争强度较小。从适宜水分条件到严重干旱胁迫，演替前期序列种相对竞争能力有所降低，而演替后期种增加。演替序列种相对竞争能力、竞争等级与其演替生态位置正相关，群落共存种的相对竞争能力与竞争等级可以解释演替方向的17%左右。演替进程的剩余原因，可能是由其它过程决定的，如群落共存种的生理生态特性（在水分作为限制性因素时，主要表现为耐旱性差异）和随机过程。其中群落共存种的水分生理生态特性表现为演替序列种的主要耐旱指标与其演替生态位置为正相关，较为耐旱，可以解释土壤旱化趋势的演替进程。. 自然条件下群落共存种相对竞争能力和竞争等级的评价方法。采用野外基于点格局和植物生长表现的调查，将植物生长表现表达为含Voronoi面积函数的限制性资源生长方程。经边界拟合后使用植物平均占有Voronoi面积，单位占有面积的植物生长表现来衡量植物的相对竞争能力与竞争等级。二者对演替后期植物的相对多度解释更高，对演替前期群落共存种的相对多度解释程度低。说明植物的相对竞争能力与竞争等级对演替后期的群落组建密切相关。植物平均占有Voronoi面积，单位占有面积的植物生长表现与植物演替生态位置也呈正相关。说明植物相对竞争能力与竞争等级是群落演替演替的驱动力之一。