Key Laboratory of Agro-Ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410125, China; Guangxi Key Laboratory of Karst Ecological Processes and Services, Huanjiang Observation and Research Station for Karst Ecosystems, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Huanjiang 547100, China.
Section of Microbial Ecology, Department of Biology, Lund University, Lund 223 62, Sweden.
Sci Total Environ. 2023 Jul 1;880:163236. doi: 10.1016/j.scitotenv.2023.163236. Epub 2023 Apr 6.
Microbial carbon use efficiency (CUE) and nitrogen use efficiency (NUE) are key parameters determining the fate of C and N in soils. Atmospheric N deposition has been found to heavily impact multiple soil C and N transformations, but we lack understanding of the responses of CUE and NUE to N deposition, and it remains uncertain whether responses may be mediated by topography. Here, a N addition experiment with three treatment levels (0, 50 and 100 kg N ha yr) was conducted in the valley and on the slope of a subtropical karst forest. Nitrogen addition increased microbial CUE and NUE at both topographic positions, but the underlying mechanisms differed. In the valley, the increase in CUE was associated with an increase in soil fungal richness:biomass and lower litter C:N, whereas on the slope, the response was linked with a reduced ratio of dissolved soil organic C (DOC) to available phosphorus (AVP) which reduced respiration, and increased root N:P stoichiometry. In the valley, the increase in NUE was explained by stimulated microbial N growth relative to gross N mineralization, which was associated with increased ratios of soil total dissolved N:AVP and fungal richness:biomass. In contrast, on the slope, the increase in NUE was attributed to reduced gross N mineralization, linked to increased DOC:AVP. Overall, our results highlight how topography-driven soil substrate availability and microbial properties can regulate microbial CUE and NUE.
微生物碳利用效率（CUE）和氮利用效率（NUE）是决定土壤中碳和氮命运的关键参数。大气氮沉降已被发现对多种土壤碳和氮转化产生重大影响，但我们对氮沉降对 CUE 和 NUE 的响应知之甚少，并且不确定这些响应是否可能受到地形的调节。在这里，在亚热带喀斯特森林的山谷和山坡上进行了一项氮添加实验，有三个处理水平（0、50 和 100 kg N ha yr）。氮添加增加了两种地形位置的微生物 CUE 和 NUE，但潜在机制不同。在山谷中，CUE 的增加与土壤真菌丰富度的增加有关：生物量和较低的凋落物 C:N，而在山坡上，响应与溶解土壤有机碳（DOC）与有效磷（AVP）的比例降低有关，这降低了呼吸作用，并增加了根 N:P 化学计量比。在山谷中，NUE 的增加是由于微生物氮生长相对于总氮矿化的刺激，这与土壤总溶解氮：AVP 和真菌丰富度：生物量的比值增加有关。相比之下，在山坡上，NUE 的增加归因于总氮矿化的减少，这与 DOC:AVP 的增加有关。总体而言，我们的研究结果强调了地形驱动的土壤基质可用性和微生物特性如何调节微生物 CUE 和 NUE。
