水文环境变化对江汉湖群大型水生植物腐烂分解的影响及其机制

The reverse process of plant production - the decomposition of plant litter - is one of the most important ecosystem processes in the biosphere, and thus plant decomposition stands out as a central topic of biodiversity because of its primary implications regarding the carbon and nutrient cycling and the resulting role in ecosystem structure and functioning. Many studies have shown that environmental factors can profoundly alter the decomposition dynamics, indicating that the environmental controls of plant decomposition, as well as the mechanistic basis behind environmental condition effects on decomposition, is central to understanding the ecosystem functioning. To date, a growing number of evidences in both terrestrial and aquatic systems have yielded much insight into the relevance of environmental controls for plant decomposition. Studies focused on the environmental controls of plant decomposition, however, are less numerous and even few in aquatic ecosystem compared with terrestrial ecosystem. The possible underlying mechanisms behind water regime on aquatic decomposition have not been sufficiently explored. Being one of the main parts of the freshwater lakes in the middle and lower of the Yangtze river, Jianghan lake groups is rich in aquatic macrophytes. Most aquatic plant biomass entering the dead organic matter pool will readily arrest decomposition and deliver carbon, nitrogen and phosphorus and other elements to the surroundings. However, scant information is available on breakdown and decomposition of aquatic macrophytes in these freshwater lakes, where hydrological alterations (i.e. water fluctuation, alternation of the duration and timing of flooding and drying and sedimentation) associated with anthropogenic disturbances like dams and reservoirs are high. Though aquatic decomposition is a pivotal component of ecosystem functioning in aquatic systems, the effects of hydrological alterations on aquatic decomposition are poorly known. By using decomposition experiments in laboratory and in the field, we aim at investigating the responsive effects of aquatic plant decomposition to hydrological alterations and the potential underlying mechanisms for the decomposition. More specifically, we tested whether (i) the decomposition rates are affected by plant species traits and litter diversity and aquatic decomposer systems under different water regime; (ii) plant decomposition tends to prefer resource rich in labile compounds and nutrients; (iii) there are any effects of hydrological alterations on aquatic decomposition and the underlying mechanisms for the decomposition dynamics; and (iv) general relationship exist between aquatic decomposition and biodiversity. The experimental evidences and comparative analysis we provide will foster the understanding of the mechanistic basis on aquatic decomposition, and group better the relationship between plant decomposition and biodiversity.

大型水生植物作为湖泊生物多样性的重要组成成分，其腐烂分解对湖泊生态系统将产生有力的影响。江汉湖群是全国湖泊密集度最大的淡水湖泊群，水生生物资源丰富，大型水生植物物种多样性高、分布广、生物量大、生活型齐全。由于人类活动的强烈干扰，近代江汉湖群水文情势发生了极大变化，这直接影响着湖泊有机物质的合成-分解过程，但围绕水文环境变化对湖泊大型水生植物分解的影响及其机制尚缺少研究。本项目以江汉湖群大型水生植物为研究对象，以关键水文环境变化及由其引起的生物群落改变对植物分解的影响机制为研究目标，围绕植物分解对环境（水位波动、干湿交替、泥沙淤积）和生物（微生物、无脊椎动物、植物）作用的响应机制研究，通过野外调查、野外原位实验和室内控制实验，揭示水文环境变化对湖泊大型水生植物分解的影响及其机制，探讨水文特征改变情景下植物分解与生物多样性的关系，以丰富和充实湖沼学的科学内涵，为科学管理湖泊提供理论依据。

环境变化对植物分解的影响及其机制研究是生态学领域关注的重点。已有研究多局限于陆生植物分解方面，对水生植物分解规律的认识有限。本研究围绕水生植物分解对水环境和生物作用改变的响应机制等内容开展了工作。主要结果如下：1. 9种水生植物叶分解的研究表明，叶质量特征是影响叶分解速率和N、P元素释放动态的重要因子。2. 苦草、微齿眼子菜及其混合分解对埋深的响应研究表明，泥沙埋深降低了三种材料的分解速率和N、P元素释放，物种混合的元素释放在分解后期产生了拮抗效应。3. 荇菜和菹草混合分解的研究表明，物种混合分解存在非加和效应，混合效应不但与材料初始质量特征有关，也具有分解时间依赖性。4. 荇菜、菹草及其混合分解对水生无脊椎动物作用的响应研究表明，分解者动物促进了三种材料的分解速率和N、P元素的释放，物种混合N元素的释放速率与分解者动物作用有关。5. 桤木、厚朴及其混合分解对干湿交替响应的研究表明，水淹时间影响分解速率，但干湿交替频率的变化的影响不显著，干湿交替引起的分解者动物和微生物活动改变影响了枯落物的分解。6. 菱和苦草在水柱不同位置的分解研究表明，水表层、水-底质界面和包埋中植物的分解速率和NP释放存在差异，这不仅与功能摄食类群的垂直生态位特点有关，也与细菌和真菌的活动有关。7. 桤木、厚朴及其混合在卵砾石、粗沙和泥三种底质中的分解研究表明，分解者动物丰富度与分解速率呈正相关，微生物总生物量与干重损失速率不相关。8. 桤木、柳杉及其混合在四个库区中的分解研究表明，随海拔升高，三种材料的分解速率降低，N、P元素的释放速率在桤木和混合分解中无明显差异，柳杉在分解后期N、P发生积累。在分解的不同阶段细菌和真菌对分解的贡献不同。9. 荇菜、菹草及其混合分解对四个NP浓度的响应研究表明，分解时间和营养水平及其交互作用对三种材料的干重剩余率、NP元素释放均有显著影响。本研究取得的进展将对水生植物分解研究的深入开展起到积极的推动作用。