Biogeochemical processes catalyzed by soil microorganisms depend on the soil water content (SWC). Yet, little is known about the sensitivity of non-symbiotic N₂ fixation to changes in SWC in comparison to carbon (C) and net nitrogen (N) mineralization. Therefore, we determined the rates of N₂ fixation, C mineralization, and net N mineralization in soils at five SWCs that were created by water addition to the field-moist soil (rewetting), resulting in SWCs of 20, 40, 60 and 80% of the soil water holding capacity (WHC) which correspond to 14, 28, 42, and 57% water-filled pore space (WFPS). The soils originated from an arid, semiarid, Mediterranean, and humid site located in the Coastal Cordillera of Chile. The N₂ fixation rate was measured immediately after the adjustment of the SWC and additionally after a five-day pre-incubation period. We found that the rates of all three processes where higher in the rewetted soils compared to the field-moist soils, but the sensitivity to changes in SWC differed between the processes. N₂ fixation tended not to increase with increasing SWC beyond 20% WHC. Furthermore, the N₂ fixation rate increased faster after rewetting in the soils of the semiarid and Mediterranean zone than in the soil of the humid zone. In contrast, C mineralization reached the highest rate at 80% WHC in the soil of the humid zone and at 60% and 80% WHC in the soils of the other three climate zones. The net N mineralization rate was highest at 40% and 60% WHC in the soils of the semiarid and Mediterranean zone, and was significantly decreased at 80% WHC compared to 60% WHC. Our study shows, first, that N₂ fixation is less sensitive to changes in SWC than C and net N mineralization and tends to be already at its maximum in a given soil at low SWC, i.e., 20% WHC. This is likely because the diffusion of N₂ in soil does not increase with the SWC, in contrast to the diffusion of organic solutes which are the substrate of C and N mineralization. Second, our results indicate that the N₂ fixation rate increases more quickly in response to rewetting of soils of the more arid climate zones than of the humid zone, which might indicate a microbial adaptation to the climate conditions. The results have important implications since they suggest that the N₂ fixation rate is likely less affected than the C and net N mineralization rates by decreases in the SWC that might occur more frequently in the future due to climate change.

土壤微生物催化的生物地球化学过程取决于土壤含水量（SWC）。_{然而，与碳 (C) 和净氮 (N) 矿化相比，非共生 N 2}固定对 SWC 变化的敏感性知之甚少。因此，我们确定了土壤中的 N ₂固定率、C 矿化率和净 N 矿化率，这些 SWC 是通过向田间潮湿土壤中加水（再润湿）产生的，导致 SWC 为 20、40、60 和 80土壤持水量 (WHC) 的百分比，对应于 14、28、42 和 57% 的充水孔隙空间 (WFPS)。土壤来自位于智利沿海科迪勒拉的一个干旱、半干旱、地中海和潮湿的地方。N ₂在调整 SWC 后立即测量固定率，另外在 5 天的预孵育期后测量。我们发现，与田间湿润土壤相比，再润湿土壤中所有三个过程的速率都较高，但不同过程对 SWC 变化的敏感性不同。N ₂固定不随 SWC 超过 20% WHC 增加而增加。此外，N ₂在半干旱和地中海地区的土壤中，再润湿后的固定率比在潮湿地区的土壤中增加得更快。相比之下，C 矿化率最高，在湿润区土壤中达到 80% WHC，在其他三个气候区土壤中达到 60% 和 80% WHC。在半干旱和地中海地区的土壤中，净氮矿化率最高，分别为 40% 和 60% WHC，与 60% WHC 相比，在 80% WHC 时显着下降。我们的研究表明，首先，N ₂固定对SWC 变化的敏感性低于C 和净N 矿化，并且在给定的低SWC 土壤（即20% WHC）中往往已经达到最大值。这可能是因为 N _2的扩散与作为 C 和 N 矿化底物的有机溶质的扩散相反，土壤中的 SWC 不随 SWC 增加。其次，我们的研究结果表明，与潮湿地区相比，更干旱气候区的土壤再润湿后，N ₂固定率增加得更快，这可能表明微生物对气候条件的适应。该结果具有重要意义，因为它们表明由于未来气候变化可能更频繁地发生SWC，N ₂固定率可能比C 和净N 矿化率的影响更小。