石漠化喀斯特生态系统养分循环对植被恢复的限制性

The karst landscape in southwestern China is one of the most typical landscapes developed on carbonate bedrock in the world. Rock-desertification has been the most serious ecological and environmental problem in the fragile karst habitats. It is hypothesized that the shortage of mineral nutrients, resulting from the limited amount of total soil mass, could be a crucial factor in limiting the vegetation recovery in karst rock-desertification regions. This proposal is aimed to elucidate the key limiting nutrients of the karst vegetation. The multiple nutrient cycling of secondary successional karst ecosystems will been systematically studied by investigating the major nutrient pools and fluxes within the ecosystems, such as vegetation nutrient pool, soil nutrient pool, forest floor nutrient pool, nutrient accumulation, and nutrient return through litterfall. The dynamics and translocations of the main nutrient pools within karst ecosystems during the secondary successional processes will be analyzed, and the vegetation nutrient requirement, annual nutrient uptake, annual nutrient return, and the changes in nutrient stocks in the soil are also to be quantified. Furthermore, the ecological stoichiometry and nutrient resorption patterns of karst plants with different functional groups will be studied by measuring and analyzing multiple nutrient concentrations in green leaves and leaf litter at different vegetation successional stages. Finally, based on the studies of the nutrient cycling of karst ecosystems and the ecological stoichiometry of karst plants, this proposal could reveal the key nutrients limiting the vegetation recovery of the karst ecosystems at different successional stages. The different nutrient limitations and diversified nutrient use strategies among different plant functional groups, as well as the shifting degrees of limitation by different elements during the vegetation recovery, will also be elucidated, which could contribute to the success of re-vegetation programs in the karst rock-desertification regions, via providing fundamental data for the nutrient management and plant species selection.

我国西南喀斯特地区是全球喀斯特发育最强烈的典型区域。石漠化已成为该地区最严重的生态与环境问题。土壤总量少而导致的养分总量不足可能是限制石漠化地区植被恢复的重要因素。本项目拟选择典型喀斯特生态系统，通过调查不同恢复阶段植被、土壤和凋落物层的养分储量，在研究凋落物生产与分解过程中的养分循环的基础上，分析植被恢复过程中生态系统各个养分库的动态变化与转移，计算每个恢复阶段植物群落的养分需求量、年吸收量与归还量和土壤的养分供给能力，揭示石漠化喀斯特生态系统的养分限制因素；通过测定植物成熟叶与凋落叶的养分元素含量，研究喀斯特不同功能群植物的生态化学计量特征与养分重吸收特征及其在植被恢复过程中的动态变化，揭示不同功能群植物养分限制因素与养分利用策略的差异性，以及植被恢复过程中养分限制作用的相互转化趋势。通过以上研究，阐明石漠化治理过程中养分调控的机理和物种合理配置的原理，为治理喀斯特石漠化提供理论依据。

我国西南喀斯特区是全球喀斯特发育最强烈的典型区域。石漠化已成为该地区最严重的生态与环境问题。土壤总量少而导致的养分总量不足可能是限制石漠化地区植被恢复的重要因素。本项目选择后寨河典型喀斯特小流域为研究区域，在广泛植被考察与重点调查90个植被样方的基础上，总结了不同恢复阶段的主要植被类型及其群落学特征，绘制了后寨河喀斯特小流域的植被图（1:10000），并估算了整个小流域植被恢复的固碳潜力。选择稀灌草丛、藤刺灌丛、乔灌林与次生乔木林4个主要恢复阶段，调查不同恢复阶段植被、土壤和凋落物层的养分储量，分析植被恢复过程中生态系统各个养分库的动态变化与转移，计算了每个恢复阶段植物群落的养分需求量和土壤的养分供给能力，表明土壤有效态养分的不足是限制植被恢复的重要因素。通过研究喀斯特不同功能群植物的生态化学计量特征与养分重吸收特征，发现喀斯特植物叶片养分含量显著低于全国平均水平。根据多种养分元素的含量、比例关系与波动性，得出喀斯特区植物主要所到P的限制，提高养分重吸收率是喀斯特植物重要的养分利用策略。同时，研究了喀斯特优势树种凋落叶的分解过程，表明N是限制该区域凋落叶分解的主要养分因素，而凋落叶混合加速了分解过程。落叶树种通过加速常绿树种凋落叶的分解，促进了喀斯特生态系统养分循环与再利用。最后，通过对退化喀斯特稀灌草丛的施肥试验得出，喀斯特稀灌草丛受到N、P、K三种养分的共同限制，其中N和P是主要限制因子；植物功能群水平上，禾草主要受到N和P的限制，杂类草主要受P限制，灌木受3种养分的限制，其中P是最主要的因子。施用矿物养分有助于促进退化喀斯特草丛的恢复演替。通过以上研究，阐明了石漠化治理过程中养分调控的机理和物种合理配置的原理，为治理喀斯特石漠化提供了理论依据。