Predicted climate change extremes, such as severe or prolonged drought, may considerably impact carbon (C) and nitrogen (N) cycling in water-limited ecosystems. However, we lack a clear and mechanistic understanding of how extreme climate change events impact ecosystem processes belowground. This study investigates the effects of five years of reoccurring extreme growing season drought (66% reduction, extreme drought treatment) and two-month delay in monsoon precipitation (delayed monsoon treatment) on belowground productivity and biogeochemistry in two geographically adjacent semi-arid grasslands: Chihuahuan Desert grassland dominated by Bouteloua eriopoda and Great Plains grassland dominated by B. gracilis. After five years, extreme drought reduced belowground net primary productivity (BNPP) in the Chihuahuan Desert grassland but not in the Great Plains grassland. Across both grasslands, extreme drought increased soil pH and available soil nutrients nitrate and phosphate. The delayed monsoon treatment reduced BNPP in both grasslands. However, while available soil nitrate decreased in the Chihuahuan Desert grassland, the delayed monsoon treatment overall had little effect on soil ecosystem properties. Extreme drought and delayed monsoon treatments did not significantly impact soil microbial biomass, exoenzyme potentials, or soil C stocks relative to ambient conditions. Our study demonstrates that soil microbial biomass and exoenzyme activity in semi-arid grasslands are resistant to five years of extreme and prolonged growing season drought despite changes to soil moisture, belowground productivity, soil pH, and nutrient availability.

预测的极端气候变化，例如严重或长期干旱，可能会显着影响水资源有限的生态系统中的碳 (C) 和氮 (N) 循环。然而，我们对极端气候变化事件如何影响地下生态系统过程缺乏清晰和机械的理解。本研究调查了五年重复发生的极端生长季节干旱（减少 66%，极端干旱处理）和两个月的季风降水延迟（延迟季风处理）对两个地理上相邻的半干旱草原地下生产力和生物地球化学的影响：奇瓦瓦荒漠草原以布特卢亚足足纲为主，大平原草原以薄壁草为主。五年后，极端干旱降低了奇瓦瓦沙漠草原的地下净初级生产力（BNPP），但大平原草原没有。在这两个草原上，极端干旱增加了土壤的 pH 值和可用的土壤养分硝酸盐和磷酸盐。延迟的季风处理降低了两个草原的 BNPP。然而，虽然吉娃娃沙漠草地的有效土壤硝酸盐减少，但季风延迟处理总体上对土壤生态系统特性影响不大。相对于环境条件，极端干旱和延迟季风处理不会显着影响土壤微生物生物量、外酶潜力或土壤碳储量。