水分限制对喀斯特坡地灌草群落正向演替的影响及其机理

Plant established in karst region of Southwest China endures two kinds of, seasonal and karst (because of the specific characteristics of karst habitats) drought stresses simultaneously, while communities in different stages distributed unevenly under natural restoration. However, there is still lack of knowledge of the effect of water restriction on the forward succession of community that always stayed in early successional stage, which limited the improvement of the ecohydrological functions of vegetation in this area. In this project, plots of shrub-grassland (the representative of community in early successional stage) and secondary forest (the representative of community in late successional stage) will be selected first from hillslopes that under the same period of natural restoration. In order to reveal the overall plant-water conditions in different communities as well as the related plant water use patterns, parameters like predawn leaf water potential and plant functional traits, which can reflect the response and adaptive features of plant to environmental conditions, will be tracking measured and clustering analyzed. Based on the removal experiment (remove the dominated annual species and leave the perennial species along) that will be conducted in the shrub-grassland, together with the monitoring of the effects of different treatments on water environment, possible methods that could improve plant-water condition will be concluded, and the possible path that can facilitate the settlement of species of late successional stages in early stage communities (like shrub-grassland) will be further discussed. The effects of water restriction on the forward succession of shrub-grassland community on degraded karst hillslope, as well as the related mechanisms, will be revealed based on all above results. The related achievements of this project will not only benefit the exploration of artificial inducement that could improve the ecohydrological functions of vegetation in karst region of Southwest China, but also help the enrichment of the theory and technique in restoration ecology of karst ecosystem.

植物承受双重水分胁迫的西南喀斯特地区，退化生态系统自然恢复条件下演替初期与后期群落交错分布，但目前关于水分限制对长期处于演替初期群落正向演替的影响及机理仍缺乏充分认识，严重制约了区域植被生态水文功能的提升。本项目针对这一关键科学问题，选取喀斯特坡地经历相同自然恢复年限处于演替初期灌草丛和演替后期次生林群落的典型样地，通过对植物水势与功能性状等能反应植物响应与适应特征指标的跟踪测定与聚类分析，阐明不同演替阶段群落植物水分环境及对应植物水分利用的整体差异特征；结合对灌草丛群落优势一年生植物的剔除试验，监测不同处理的水分效应，分析改善植物水分环境的可能方法；同时探索促进演替后期物种定居的可能途径；以期揭示水分限制对喀斯特坡地灌草群落正向演替的影响及机理。研究成果不仅有益于提升区域植被生态水文功能人工诱导措施的探索，而且有助于丰富喀斯特生态系统恢复生态学的理论与技术。

植物承受季节性干旱和岩溶干旱双重水分胁迫的西南喀斯特地区，退化生态系统自然恢复条件下演替初期与后期群落交错分布，但目前关于水分限制对长期处于演替初期群落正向演替的影响及机理仍缺乏充分认识，这进一步限制了探索人工诱导促进植被正向演替可能途径的尝试，不利于西南喀斯特地区植被恢复重建及区域植被生态水文功能的协同提升。为此，本项目首先选择经历相同自然恢复年限但分别呈现灌草丛和次生林群落特征的相邻坡地典型样地，在调查分析不同坡位两种群落基质特性、物种组成、结构和多样性差异特征的基础上，揭示了生境特征在群落演替中的主控作用，即无表土覆盖的出露基岩生境植被多演替至次生林阶段，而基岩出露率较低的土石混合生境植被多停留在灌草丛阶段；为了实现对不同群落及对应生境植物水分利用特征的对比分析，构建了适宜于多石环境的植物水分来源定性和定量分析方法，论证了全新的从水分补给与消耗特性角度划分潜在水分来源思路的可行性与优势，并基于这一思路首次实现了对不同演替阶段群落植物水分来源差异特征的分析；与植物水分来源即获取对应的是水分运输与消耗特征，基于对不同群落代表性植物枝、叶水力特性和叶片稳定碳同位素值的测定与分析，弄清了不同演替阶段代表性植物在水分传导效率性与安全性权衡以及水分消耗保守性高低方面差异特征；围绕不同演替阶段植物水分利用差异特征的研究结果，结合对不同坡位灌草丛群落下垫面岩土剖面持水环境特征的分析，认为先锋尤其是草本植物对浅层土壤水分的竞争限制了演替后期植物种的定居与繁衍即植被正向演替，结合群落结构优化实验，提出了以提升小雨量降雨有效性为目标的改善浅层土壤水分环境、促进植被正向演替的人工诱导方案。该项目的完成一方面深化了对亚热带湿润喀斯特地区植物-水分关系的系统认识，研究思路和方法亦能为多石土壤环境地区的相关研究提供有益借鉴，另一方面，在围绕机理性认识提出假设、结合控制性实验提出人工诱导方案方面，迈出了坚实一步。