杉木凋落叶分解过程气态有机碳释放及其对氮沉降的响应

Gaseous organic carbon (GOC) is the carbon in the form of volatile organic compounds (VOCs), GOC emission is an important carbon loss pathway of decomposing litters, and plays an important role in forest surface carbon cycling. However, few studies have been conducted on the release of GOC from decomposing litters, and how nitrogen deposition will affect the emission species and amount of VOCs from decomposing litters, thus changing the contribution of GOC in forest surface carbon cycle is also unclear. In this project, long-term canopy nitrogen addition experiment of a mature Chinese fir forest will be used. An improved litter decomposition method and GC-MS trace gas analysis technique will be employed, with the first objective to study the species and rate of VOCs emission from decomposing Chinese fir leaf litter and its response to nitrogen deposition. Then, according to the results of GOC、CO2-C and CH4-C, to estimate the contribution of GOC to total gaseous C loss of litters in the decomposition process. Also, the effect of nitrogen deposition on this contribution will be estimated. Finally, by using of molecular biology, the microbial mechanism of major VOCs emissions from decomposing litters under the background of nitrogen addition will be discussed. Overall, the project results will provide reliable data for forest ecosystem C cycle models, and it also can provide new insights into forest surface C cycling processes and mechanisms.

气态有机碳(GOC)即挥发性有机化合物(VOCs)形态的碳，GOC释放作为凋落叶分解过程碳损失的重要途径，在森林地表碳循环中具有重要作用。然而，目前对凋落叶分解过程GOC释放的认识还十分有限，且氮沉降将如何影响凋落叶分解过程中GOC释放对总气态碳损失的贡献及微生物机制仍不清楚。本项目拟以杉木人工林冠层氮沉降试验平台为基础，以杉木凋落叶为研究对象，采用凋落叶围隔分解实验方法，首先运用热解析/预浓缩-GC-MS技术，研究杉木凋落叶分解过程VOCs的释放种类和释放量及其对氮沉降的响应；进一步结合GOC、CO2-C和CH4-C通量结果，估算杉木凋落叶分解过程中GOC释放对总气态碳损失的贡献，以及氮沉降对这种贡献的影响；最后借助高通量测序等分子生物学手段，初步揭示氮沉降对杉木凋落叶分解过程GOC释放影响的微生物机制。研究结果将为森林生态系统碳循环模型提供可靠数据，并可为森林地表碳循环过程提供新认知。

凋落叶分解过程以挥发性有机化合物形态释放的碳（GOC）可能是凋落叶分解过程重要的碳损失途径。然而，目前对凋落叶分解过程GOC释放的认识还十分有限。近年来，氮沉降加剧已成为全球性问题， 但是氮沉降将如何影响凋落叶GOC 释放及其相关机制尚不清楚。本项目重点以杉木和木荷凋落叶为研究对象，研究了氮添加条件下杉木和木荷凋落叶分解过程VOCs的释放种类和速率，并结合两种凋落叶分解过程理化性质及微生物群落特征分析了影响凋落叶VOCs释放的主要因素。本项目主要研究结果为：（1）不同凋落叶种类在分解过程中释放的GOC量具有显著差异，凋落叶GOC释放量主要集中在凋落叶分解早期。（2）杉木和木荷凋落叶分解过程检测到的总GOC释放量约占CO2释放量的0.27%和0.34%。（3）氮添加会显著增加两种凋落叶分解早期CO2释放量，但显著降低两种凋落叶分解早期GOC的释放。（4）整体上看，氮添加对两种凋落叶分解早期微生物群落组成无显著影响；但氮添加显著改变了两种凋落叶分解早期15N 、13C和C/N。冗余分析结果表明，凋落物理化性质可能是影响两种凋落叶分解早期VOCs释放的重要原因。同时，氮添加对土壤VOCs总通量无显著影响，但会影响某些主要VOCs的释放速率；土壤水分改变对一些土壤主要VOCs通量的影响大于氮添加。氮添加对杉木叶片的异戊二烯释放速率无显著影响；但干旱条件下氮添加显著增加杉木异戊二烯释放速率，降低单萜烯释放通量。上述研究结果可为森林生态系统碳通量模型提供基础数据，并可为深入理解森林碳循环过程提供新视角。本项目已发表论文6篇，其中SCI论文3篇。发表的论文有4 篇标记“国家自然科学基金”为第一资助，2篇标记“国家自然科学基金”为第二资助。目前，本项目已经超额完成了本项目规定的发表论文的任务要求。