Department of Civil and Environmental Engineering, Box 90287, Duke University, Durham, North Carolina 27708, USA.
Ecology. 2012 Apr;93(4):930-8. doi: 10.1890/11-0026.1.
Soil heterotrophic respiration and nutrient mineralization are strongly affected by environmental conditions, in particular by moisture fluctuations triggered by rainfall events. When soil moisture decreases, so does decomposers' activity, with microfauna generally undergoing stress sooner than bacteria and fungi. Despite differences in the responses of individual decomposer groups to moisture availability (e.g., bacteria are typically more sensitive than fungi to water stress), we show that responses of decomposers at the community level are different in soils and surface litter, but similar across biomes and climates. This results in a nearly constant soil-moisture threshold corresponding to the point when biological activity ceases, at a water potential of about -14 MPa in mineral soils and -36 MPa in surface litter. This threshold is shown to be comparable to the soil moisture value where solute diffusion becomes strongly inhibited in soil, while in litter it is dehydration rather than diffusion that likely limits biological activity around the stress point. Because of these intrinsic constraints and lack of adaptation to different hydro-climatic regimes, changes in rainfall patterns (primary drivers of the soil moisture balance) may have dramatic impacts on soil carbon and nutrient cycling.
土壤异养呼吸和养分矿化强烈受到环境条件的影响，特别是降雨事件引发的水分波动。当土壤水分减少时，分解者的活性也会降低，通常微小动物比细菌和真菌更早地承受压力。尽管个别分解者群体对水分可用性的反应存在差异（例如，细菌通常比真菌对水分胁迫更敏感），但我们表明，在土壤和地表凋落物中，分解者在群落水平上的反应不同，但在生物群落和气候条件下相似。这导致了一个几乎恒定的土壤水分阈值，对应于生物活性停止的点，在矿物质土壤中约为-14 MPa 的水势，在地表凋落物中为-36 MPa。事实证明，该阈值与土壤中溶质扩散强烈受到抑制的土壤水分值相当，而在凋落物中，可能是脱水而不是扩散限制了压力点周围的生物活性。由于这些内在的限制和缺乏对不同水热气候条件的适应，降雨模式的变化（土壤水分平衡的主要驱动因素）可能会对土壤碳和养分循环产生巨大影响。
