Thomsen Theis, Schostag Morten Dencker, Priemé Anders, Donhauser Jonathan
Department of Biology, University of Copenhagen, Copenhagen, Denmark.
Department of Biotechnology and Biomedicine, Technical University of Denmark, Lyngby, Denmark.
Glob Chang Biol. 2025 Sep;31(9):e70502. doi: 10.1111/gcb.70502.
Climate change increases the frequency and intensity of drought events, yet the mechanisms of microbe-mediated soil carbon (C) and nitrogen (N) cycling under drought are poorly understood. We conducted a microcosm experiment with a Greenlandic soil subjected to five levels of drought, reducing water content from 180% to 15% over the course of 3 weeks followed by rewetting, mimicking a natural drought event. We linked changes in microbial gene expression related to stress response as well as C and N cycling with greenhouse gas (GHG) emissions, extracellular enzyme activities, and soil C and N status. Maximum changes in gene expression occurred at intermediate levels of drought (80% water content), characterized by acclimation of microbial physiology to drought conditions, including production of osmolytes as well as cell wall and membrane modifications. This peak in gene expression changes marked a tipping point associated with a pronounced decline in microbial respiration as well as extracellular enzyme activities under more intense drought conditions. Interestingly, C-cycling gene expression correlated with soil dissolved organic nitrogen (DON), NH , NO and PO contents. Moreover, N-cycling gene expression correlated with PO contents and with the activity of laccases. These findings highlight linkages between microbial C, N, and P cycling because of stoichiometric constraints under drought. 24 h after rewetting, we found a shift in microbial expression of C usage genes towards more labile compounds, and an increase in genes related to anabolic activity and signaling, but no signatures of stress responses, suggesting that the microbial community had overcome rewetting-induced changes in osmotic pressure and allocated metabolic activity to growth. Overall, we show that microbial physiological drought responses and microbial resource usage related to C:N:P stoichiometry are key mechanisms of C and N cycling in the Arctic soil under drying and rewetting.
气候变化增加了干旱事件的频率和强度，但干旱条件下微生物介导的土壤碳（C）和氮（N）循环机制仍知之甚少。我们用格陵兰土壤进行了一项微观实验，使其遭受五个干旱水平，在3周内将含水量从180%降至15%，随后再湿润，模拟自然干旱事件。我们将与应激反应以及碳和氮循环相关的微生物基因表达变化与温室气体（GHG）排放、胞外酶活性以及土壤碳和氮状况联系起来。基因表达的最大变化发生在中等干旱水平（含水量80%），其特征是微生物生理适应干旱条件，包括渗透调节物质的产生以及细胞壁和细胞膜的修饰。这种基因表达变化的峰值标志着一个临界点，与更强烈干旱条件下微生物呼吸以及胞外酶活性的显著下降相关。有趣的是，碳循环基因表达与土壤溶解有机氮（DON）、NH 、NO 和PO 含量相关。此外，氮循环基因表达与PO 含量以及漆酶活性相关。这些发现突出了干旱条件下由于化学计量限制导致的微生物碳、氮和磷循环之间的联系。再湿润24小时后，我们发现微生物碳利用基因的表达转向更不稳定的化合物，与合成代谢活性和信号传导相关的基因增加，但没有应激反应的迹象，这表明微生物群落克服了再湿润引起的渗透压变化，并将代谢活动分配到生长中。总体而言，我们表明微生物生理干旱反应以及与碳氮磷化学计量相关的微生物资源利用是北极土壤在干燥和再湿润过程中碳和氮循环的关键机制。
