增温对我国东北地区典型树种细根分解的影响

Global warming has been considered as one major component of global change and is predicted to increase in the future, which will greatly influence the process of terrestrial ecosystem. Fine root decomposition represents a large pool of carbon and nutrient cycling in forest ecosystems, which may be potentially affected by the global warming. Yet the effects of global warming on fine root decomposition have rarely been examined. The objective of this study is to experimentally examine the effects of enhanced soil temperature (beginning in 2016, in six applications per treatment) on fine root decomposition among four common temperate tree species (Quercus mongolica Fisch., Fraxinus mandshurica Rupr.,; Larix gmelinii Rupr. and Juglans mandshurica) in a temperate forest in northeastern China (Qingyuan Forest Ecology Station). Three simultaneous litter bag experiments will be used to determine whether the effects of enhanced soil temperature on fine root decomposition (if it occurs) results primarily from direct limitation by increased soil nutrient availability or indirectly, from increased substrate of fine root litter, or both. Furthermore, the response of the following extracellular enzyme activity to enhanced soil temperature will be observed: two enzymes involved in cellulose decomposition; two enzymes involved in decomposition of lignin; an enzyme involved in chitin decomposition; and an enzyme involved in mineralizing ester-bonded phosphate. In addition to measuring enzyme activity of decomposing substrates, we also will measure the response of microbial community composition (phospholipid fatty acids of bacteria, actinomycete and fungi of microbial community and the relative abundances of Gram-negative and Gram-positive bacteria) to enhanced soil temperature in order to determine whether treatments were affecting decomposition by altering its microbial community. This study will inform modeling efforts that aim to determine the effects of elevated global warming on regional and global carbon and N cycling, providing much-needed context and perspective for empirical studies of the effects of global warming on decomposition.

气候变暖作为全球变化的主要现象之一，深刻影响陆地生态系统过程。全球变暖通过环境因素、凋落物质量以及分解者影响凋落物分解过程，并进一步影响土壤养分周转和碳库动态。根系分解是森林生态系统地下养分和有机质输入的主要途径，目前增温对凋落物分解影响的研究多集中于地上叶片，而忽略了根系分解。本研究拟以东北地区典型针阔混交林常见树种落叶松、水曲柳、核桃楸和蒙古栎为研究对象（清原站），对土壤连续增温2℃，通过3个相互补充的独立实验来研究增温对不同根序细根分解的影响：1）土壤环境变化；2）凋落物基质变化；3）两者共同变化对细根分解的影响。同时结合细根分解过程中微生物群落组成（细菌、真菌、放线菌、革兰氏阳性及阴性菌的磷脂脂肪酸含量）和分解酶活性测定（纤维素降解酶、木质素降解酶、几丁质降解酶及磷酸酶），综合探讨增温对细根分解的影响机理，并构建不同根序细根分解对增温响应差异与凋落物基质（尤其是木质素）含量的关系。

严格按照项目任务书中的执行计划，以位于辽宁省清原县森林生态系统定位研究站典型的针阔混交林为研究对象，通过红外辐射加热器对0-10 cm矿质土壤增温2℃的方法，如期开展了项目任务书的3个相互独立的补充实验：1）土壤环境变化；2）凋落物基质变化；3）两者共同变化对细根分解的影响。同时结合细根分解过程中微生物群落组成和分解酶活性的测定，探讨了增温对细根分解的影响机理，并构建细根分解对增温响应的强度与根系木质素含量的关系。研究结果表明，增温均不同程度促进了东北地区常见的四个温带树种（落叶松、水曲柳、核桃楸和蒙古栎）细根的分解速率，促进程度为15%-31%。然而，对于不同根序以及不同树种之间的促进程度存在较大差异。增温对高级根的促进程度要高于低级根，对木质素含量较低的根系促进程度高于木质素含量较高的树种。