Plant roots are the primary source of soil organic carbon (C) and critically support the growth and activities of microbes in the rhizosphere. Climate change factors may, however, modify root-microbial interactions and impact C dynamics in the rhizosphere. Yet, the direction and magnitude of interactive climate change effects, as well as the underlying mechanisms, remain unclear. Here we show evidence from a field experiment demonstrating that warming and precipitation changes strengthen root controls over litter decomposition in a semi-arid grassland. While warming and precipitation reduction suppressed microbial decomposition of root litter regardless of the root presence, precipitation increase stimulated litter decomposition only in the absence of roots, suggesting that plant competition for water constraints the activities of saprophytic microbes. Root presence increased microbial biomass but reduced microbial activities such as respiration, C cycling enzymes and litter decomposition, indicating that roots exert differential effects on microbes through altering C or water availability. In addition, nitrogen (N) input significantly reduced microbial biomass and microbial activities (respiration). Together, these results showed that alterations in soil moisture induced by climate change drivers critically modulate root controls over microbial decomposition in soil. Our findings suggest that warming-enhanced plant water utilization, combined with N-induced suppression of microbes, may provide a unique mechanism through which moderate increases in precipitation, warming and N input interactively suppress microbial decomposition, thereby facilitating short-term soil C sequestration in the arid and semi-arid grasslands.

植物根是土壤有机碳（C）的主要来源，并在根际中关键地支持微生物的生长和活性。但是，气候变化因素可能会改变根微生物相互作用并影响根际中的碳动态。然而，相互作用的气候变化影响的方向和程度以及潜在的机制仍不清楚。在这里，我们从野外实验中获得的证据表明，变暖和降水变化增强了半干旱草原凋落物分解的根部控制。尽管变暖和减少降水抑制了根凋落物的微生物分解，而无论根系是否存在，但降水增加仅在没有根的情况下刺激了凋落物分解，这表明植物对水的竞争限制了腐生微生物的活动。根系的存在增加了微生物的生物量，但减少了微生物的活动，如呼吸，碳循环酶和凋落物分解，表明根系通过改变碳或水的利用率而对微生物产生不同的影响。此外，氮输入显着降低了微生物的生物量和微生物活性（呼吸作用）。总之，这些结果表明，气候变化驱动因素引起的土壤水分变化严重调节了土壤微生物分解的根部控制。我们的发现表明，变暖的植物水分利用与N诱导的微生物抑制相结合，可能提供一种独特的机制，通过该机制可以适度增加降水，