鄱阳湖湿地3种优势植物枯落物分解过程及碳氮同位素分异特征

Variation characteristics of the decomposition process δ^(13)C and δ^(15)N of three dominant plant litter in Lake Poyang wetland

植物枯落物分解是维持湿地生态系统能量流动、物质循环和养分平衡的关键生态过程。于2017年11月—2018年4月在鄱阳湖湿地开展野外原位分解实验。利用分解袋法对3种优势植物芦苇(Phragmites australis)、南荻(Triarrhena lutarioriparia)和薹草(Carex cinerascens)枯落物纤维素和木质素分解过程和δ^(13)C、δ^(15)N分异特征开展了模拟实验研究。结果表明:芦苇、南荻和薹草枯落物的纤维素和木质素的分解速率、干物质残留率以及δ^(13)C、δ^(15)N差异性极显著,造成这种差异的主要原因是不同种类植物枯落初始化学特性的不同,尤其是C/N和木质素/N的不同。枯落物中纤维素和木质素的分解速率都表现芦苇最大,薹草次之,南荻最小。Olson负指数衰减模型能非常好地模拟和预测3种植物枯落物的分解过程。伴随分解过程,3种植物枯落物δ^(13)C上下波动,总体上呈显著降低的趋势,而δ^(15)N则都呈现波动性的略有升高趋势,这说明在枯落物分解过程的不同阶段内,受枯落物基质质量和微生物代谢活动的双重影响,^(13)C与^(15)N既有释放也有富集。δ^(13)C与枯落物纤维素和木质素分解速率都有极显著的正相关关系。δ^(15)N与分解速率相关性不显著,这说明除了氮元素的迁移转化外,还有其他因素影响δ^(15)N的变化。本研究有助于加深枯落物分解过程中基质质量调控机制的认识,深化对鄱阳湖湿地生物地球化学循环过程的科学理解。

Litter decomposition is an important ecological process for maintaining energy flow,material cycling and nutrient balance in wetland ecosystems.From November 2017 to April 2018,a field decomposition experiment was conducted in the Lake Poyang wetland.The decomposition process and δ^(13)C, δ^(15)N differentiation characteristics of cellulose and lignin in the litter of three dominant plants,Phragmites australis,Triarrhena lutarioriparia and Carex cinerascens,were investigated using the decomposition bag method.The results showed that there were significant differences in cellulose and lignin residues,decomposition rate and δ^(13)C, δ^(15)N among the three plant litter types during the 150 d experiment.The main cause of these differences was attributed to the initial chemical properties of the different plant litter types,especially differences in C/N and lignin/N.The decomposition rate of litter cellulose and lignin was fastest in P.australis,followed by C.cinerascens and T.lutarioriparia.The decomposition process of the three plant litters was simulated and predicted using the Olson negative exponential decay model.During the decomposition of the three plant litters, δ^(15)C fluctuated continuously but showed an overall significant decreasing trend,while δ^(15)N for all litter types showed a slightly increasing trend in volatility,indicating that it was influenced by both substrate quality and microbial metabolic activities at different stages of decomposition.There was a significant positive correlation between δ^(13)C and the decomposition rate of cellulose and lignin in the litter.However,the correlation between δ^(15)N and the decomposition rate was not significant,indicating that there are other factors besides the migration and transformation of nitrogen elements that affect the change in δ^(15)N.This study can contribute to a better scientific understanding of the substrate quality control mechanism in the process of litter decomposition,and provide a scientific basis for the protection and restoration of Lake Poyang wetland.