Direct and indirect effects of nitrogen enrichment on soil organisms and carbon and nitrogen mineralization in a semi‐arid grassland
Direct and indirect effects of nitrogen enrichment on soil organisms and carbon and nitrogen mineralization in a semi‐arid grassland
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氮富集对半干旱草原土壤生物及碳氮矿化的直接和间接影响
DOI：
10.1111/1365-2435.132
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发表时间：
2019
影响因子：
5.2
通讯作者：
Bai, Yongfei
中科院分区：
文献类型：
--
作者：
Chen, Dima;Xing, Wen;Lan, Zhichun;Saleem, Muhammad;Wu, Yunqiqige;Hu, Shuijin;Bai, Yongfei
预计本世纪蒙古高原半干旱草原将经历人为活性氮的高输入。然而，目前尚不清楚氮肥是如何直接影响土壤生物和养分循环的(即，在没有植物输入土壤的情况下)，还是通过氮肥对土壤中与植物相关的输入的变化间接影响土壤生物和养分循环。为了测试氮肥对土壤生物(细菌、真菌和线虫)及其相关的C和N矿化的直接和间接影响，我们在1999年在半干旱草原上建立的六级氮肥试验的每一块地块中指定了两个子区(有植物和没有植物)。2014年，在建立了有植物和没有植物的小区后，无论植物是否被移走，由于生物量或丰度的下降，氮的增加大大改变了土壤细菌、真菌和线虫的群落结构。增施氮肥还降低了土壤碳素矿化速率和土壤氮素矿化多样性(真菌除外)，并导致土壤氮素矿化的驼峰型响应。由于土壤基质或食物资源的减少，植物移栽降低了土壤生物的生物量或丰度以及C和N矿化速率。植物移栽引起的变化(无植物小区与有植物小区的比率)分析表明，微生物和C、N矿化速率并没有随着N肥的增加而增加，但线虫随着N肥的增加而增加，这表明植物移植物对土壤生物和矿化的影响取决于营养水平和营养状况。令人惊讶的是，在大多数变量中，N的增加和植物移植物之间没有统计上的相互作用。这表明与植物有关的输入并没有从本质上改变N肥对土壤有机体或矿化的影响。结构方程模型证实，土壤群落和矿化速率的变化更多地受到氮素增加的直接影响(通过土壤酸化和增加氮素有效性)，而不是受与植物有关的间接影响。我们的结果为深入了解未来N沉积和植被的变化可能如何改变草原生态系统的地下群落和过程提供了洞察。
Semi‐arid grasslands on the Mongolian Plateau are expected to experience high inputs of anthropogenic reactive nitrogen in this century. It remains unclear, however, how soil organisms and nutrient cycling are directly affected by N enrichment (i.e., without mediation by plant input to soil) vs. indirectly affected via changes in plant‐related inputs to soils resulting from N enrichment.To test the direct and indirect effects of N enrichment on soil organisms (bacteria, fungi and nematodes) and their associated C and N mineralization, in 2010, we designated two subplots (with plants and without plants) in every plot of a six‐level N‐enrichment experiment established in 1999 in a semi‐arid grassland.In 2014, 4 years after subplots with and without plant were established, N enrichment had substantially altered the soil bacterial, fungal and nematode community structures due to declines in biomass or abundance whether plants had been removed or not. N enrichment also reduced the diversity of these groups (except for fungi) and the soil C mineralization rate and induced a hump‐shaped response of soil N mineralization. As expected, plant removal decreased the biomass or abundance of soil organisms and C and N mineralization rates due to declines in soil substrates or food resources.Analyses of plant‐removal‐induced changes (ratios of without‐ to with‐plant subplots) showed that micro‐organisms and C and N mineralization rates were not enhanced as N enrichment increased but that nematodes were enhanced as N enrichment increased, indicating that the effects of plant removal on soil organisms and mineralization depended on trophic level and nutrient status.Surprisingly, there was no statistical interaction between N enrichment and plant removal for most variables, indicating that plant‐related inputs did not qualitatively change the effects of N enrichment on soil organisms or mineralization. Structural equation modelling confirmed that changes in soil communities and mineralization rates were more affected by the direct effects of N enrichment (via soil acidification and increased N availability) than by plant‐related indirect effects. Our results provide insight into how future changes in N deposition and vegetation may modify below‐ground communities and processes in grassland ecosystems.A plain language summary is available for this article.