Climate change is exposing high-latitude systems to warming and a shift towards more shrub-dominated plant communities, resulting in increased leaf-litter inputs at the soil surface, and more labile root-derived organic matter (OM) input in the soil profile. Labile OM can stimulate the mineralization of soil organic matter (SOM); a phenomenon termed "priming". In N-poor subarctic soils, it is hypothesized that microorganisms may "prime" SOM in order to acquire N ("microbial N-mining"). Increased leaf-litter inputs with a high C/N ratio might further exacerbate microbial N demand, and increase the susceptibility of N-poor soils to N-mining. We investigated the N-control of SOM mineralization by amending soils from climate change simulation treatments in the subarctic (+1.1°C warming, birch litter addition, willow litter addition, and fungal sporocarp addition) with labile OM either in the form of glucose (labile C; equivalent to 400 µg C g-1 fwt soil) or alanine (labile C + N; equivalent to 400 µg C and 157 µg N g-1 fwt soil), to simulate rhizosphere inputs. Surprisingly, we found that despite five-years of simulated climate change treatments, there were no significant effects of the field-treatments on microbial process rates, community structure or responses to labile OM. Glucose primed the mineralization of both C and N from SOM, but gross mineralization of N was stimulated more than that of C, suggesting that microbial SOM-use increased in magnitude and shifted to components richer in N (i.e. selective microbial N-mining). The addition of alanine also resulted in priming of both C and N mineralization, but the N mineralization stimulated by alanine was greater than that stimulated by glucose, indicating strong N-mining even when a source of labile OM including N was supplied. Microbial carbon use efficiency was reduced in response to both labile OM inputs. Overall, these findings suggest that shrub-expansion could fundamentally alter biogeochemical cycling in the subarctic, yielding more N available for plant uptake in these N-limited soils, thus driving positive plant-soil feedbacks.

中文翻译：

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模拟的根际沉积物诱导微生物 N 开采，这可能会加速亚北极地区的灌木化

气候变化使高纬度系统面临变暖和向更多以灌木为主的植物群落的转变，导致土壤表面的凋落物输入增加，以及土壤剖面中更不稳定的根源性有机物质 (OM) 输入。不稳定的有机质可以刺激土壤有机质（SOM）的矿化；一种称为“启动”的现象。在贫氮的亚北极土壤中，假设微生物可以“启动”SOM 以获取 N（“微生物 N-挖掘”）。增加具有高 C/N 比的凋落物输入可能会进一步加剧微生物对 N 的需求，并增加贫氮土壤对 N 开采的敏感性。我们通过修改亚北极气候变化模拟处理中的土壤（+1.1°C 变暖，添加桦木凋落物，柳凋落物添加和真菌孢子果添加）具有葡萄糖（不稳定 C；相当于 400 µg C g-1 fwt 土壤）或丙氨酸（不稳定 C + N；相当于 400 µg C 和 157 µg N）形式的不稳定有机质g-1 fwt 土壤），模拟根际输入。令人惊讶的是，我们发现尽管进行了五年的模拟气候变化处理，现场处理对微生物过程速率、群落结构或对不稳定 OM 的反应没有显着影响。葡萄糖引发了 SOM 中 C 和 N 的矿化，但 N 的总矿化比 C 更受刺激，这表明微生物 SOM 的使用量增加并转向富含 N 的成分（即选择性微生物 N 开采）。丙氨酸的加入也引发了 C 和 N 矿化，但丙氨酸刺激的 N 矿化大于葡萄糖刺激的 N 矿化，表明即使提供了包括 N 在内的不稳定 OM 来源，也有很强的 N 开采。微生物碳利用效率因两种不稳定的有机质输入而降低。总体而言，这些发现表明，灌木扩张可以从根本上改变亚北极地区的生物地球化学循环，在这些受氮限制的土壤中产生更多可供植物吸收的氮，从而推动植物 - 土壤的正反馈。