Effects of experimental soil warming and precipitation reduction on the quantity and structure of soil dissolved organic matter of Cunninghamia lanceolata plantations in subtropical China
Temperature and moisture are important to the structure and function of forest ecosystems. In future decades, global warming and variations in precipitation patterns will be the major climatic characteristics. Global warming is suggested to accelerate the decomposition of soil organic matter (SOM),and thereby to increase the carbon flux. Altered rainfall amounts might affect plant growth and soil structure. As a crucial component of forests,dissolved organic matter (DOM) plays an important role in such ecological processes. It is central to the questions of carbon decomposition /sequestration in soils and nutrient availability to microorganisms and plants. Natural evergreen broad-leaved forests make up the typical vegetation in the subtropical zone of China,but large areas of natural forests have been transformed to Cunninghamia lanceolata plantations. Therefore,it is critical that we should explore the effects of warming and precipitation variations on the dynamic changes of DOM in these plantations. In this article,we investigated the effects of simulated soil warming, 50% precipitation reduction,and the combination of the two factors on the quantity and composition of soil DOM. There were four treatments (three replicates per treatment) effects studied: (1) no warming and natural precipitation; (2) warming and natural precipitation; (3) no warming and precipitation reduction; and (4) warming and precipitation reduction. The soil samples were collected in October 2014,January 2015,and April 2015,respectively. To learn more about the relationships of DOM with temperature and moisture,we also measured the soil microbial biomass carbon and microbial biomass nitrogen. The results showed that the quantity of DOM increased after soil warming in both 010cm and 1020cm soil layers. In addition,the aromaticity and humification degree of DOM decreased after warming. In our study, soil warming could accelerate the loss of DOM and restrain the stability of carbon. The impacts of the precipitation reduction treatment on DOM production showed a seasonal pattern. In particular,the quantity of DOM was reduced but its aromaticity and humification degree were enhanced in the drought season (October 2014 and January 2015),whereas in the rainy season (April 2015),the quantity of DOM had increased since the growth of microorganisms and the content of aromatic compounds were reduced simultaneously. Under the combination of warming and precipitation reduction,the quantity of DOM increased because of accelerated decomposition of SOM. Moreover,the DOM structure became simpler through the interaction of the two factors. The effects of temperature and moisture on the quantity and structure of soil DOM are sophisticated. We will continue to estimate the impacts of warming and precipitation reduction on soil microbes,organic matter,and other elements with long-term observational data to attain a more profound comprehension about carbon and nitrogen cycling under global climate change.