【氮转化】Dolaporn S. Novem Auyeung Vidya Suseela Jeffrey S. Dukes. Warming and drought reduce temperature sensitivity of nitrogen transformations. Global Change Biology 201319(2): 662–676

Abstract

Shifts in nitrogen (N) mineralization and nitrification rates due to global changes can influence nutrient availability which can affect terrestrial productivity and climate change feedbacks. While many single-factor studies have examined the effects of environmental changes on N mineralization and nitrification few have examined these effects in a multifactor context or recorded how these effects vary seasonally. In an old-field ecosystem in Massachusetts USA we investigated the combined effects of four levels of warming (up to 4 °C) and three levels of precipitation (drought ambient and wet) on net N mineralization net nitrification and potential nitrification. We also examined the treatment effects on the temperature sensitivity of net N mineralization and net nitrification and on the ratio of C mineralization to net N mineralization. During winter freeze–thaw events snow depth and soil freezing depth explained little of the variation in net nitrification and N mineralization rates among treatments. During two years of treatments warming and altered precipitation rarely influenced the rates of N cycling and there was no evidence of a seasonal pattern in the responses. In contrast warming and drought dramatically decreased the apparent Q₁₀ of net N mineralization and net nitrification and the warming-induced decrease in apparent Q₁₀ was more pronounced in ambient and wet treatments than the drought treatment. The ratio of C mineralization to net N mineralization varied over time and was sensitive to the interactive effects of warming and altered precipitation. Although many studies have found that warming tends to accelerate N cycling our results suggest that warming can have little to no effect on N cycling in some ecosystems. Thus ecosystem models that assume that warming will consistently increase N mineralization rates and inputs of plant-available N may overestimate the increase in terrestrial productivity and the magnitude of an important negative feedback to climate change.

【土壤微生物群落功能结构】Yunfeng Yang Linwei Wu Qiaoyan Lin Mengting Yuan Depeng Xu Hao Yu Yigang Hu Jichuang Duan Xiangzhen Li Zhili He Kai Xue Joy van Nostrand Shiping Wang Jizhong Zhou. Responses of the functional structure of soil microbial community to livestock grazing in the Tibetan alpine grassland. Global Change Biology 201319(2): 637–648

Abstract

Microbes play key roles in various biogeochemical processes including carbon (C) and nitrogen (N) cycling. However changes of microbial community at the functional gene level by livestock grazing which is a global land-use activity remain unclear. Here we use a functional gene array GeoChip 4.0 to examine the effects of free livestock grazing on the microbial community at an experimental site of Tibet a region known to be very sensitive to anthropogenic perturbation and global warming. Our results showed that grazing changed microbial community functional structure in addition to aboveground vegetation and soil geochemical properties. Further statistical tests showed that microbial community functional structures were closely correlated with environmental variables an