Mapping soil microbial residence time at the global scale

Soil microbes ultimately drive the mineralization of soil organic carbon and thus ecosystem functions. We compiled a dataset of the seasonality of microbial biomass carbon (MBC) and developed a semi-mechanistic model to map monthly MBC across the globe. MBC exhibits an equatorially symmetric seasonality between the Northern and Southern Hemispheres. In the Northern Hemisphere, MBC peaks in autumn and is minimal in spring at low latitudes (<25° N), peaks in the spring and is minimal in autumn at mid-latitudes (25°-50° N), while peaks in autumn and is minimal in spring at high latitudes (>50° N). This latitudinal shift of MBC seasonality is attributed to an interaction of soil temperature, soil moisture, and substrate availability. The MBC seasonality is inconsistent with patterns of heterotrophic respiration, indicating that MBC as a proxy for microbial activity is inappropriate at this resolution. This study highlights the need to explicitly represent microbial physiology in microbial models. The interactive controls of environments and substrate on microbial seasonality provide insights for better representing microbial mechanisms in simulating ecosystem functions at the seasonal scale.

土壤微生物是土壤有机碳矿化过程乃至生态系统功能实现的核心驱动力。我们整合了一套微生物生物量碳（Microbial Biomass Carbon, MBC）的季节动态数据集，并构建了半机制模型以绘制全球逐月MBC的空间分布格局。MBC的季节动态在南北半球呈现赤道对称特征。在北半球，低纬度地区（北纬<25°）的MBC峰值出现在秋季，春季达到最低值；中纬度地区（北纬25°-50°）的MBC峰值则在春季，秋季为最低值；而高纬度地区（北纬>50°）的MBC峰值再次出现在秋季，春季为最低值。MBC季节动态的这种纬度转变，源于土壤温度、土壤水分与底物有效性的共同交互调控。MBC的季节动态模式与异养呼吸的季节模式并不一致，这表明在此分辨率下，将MBC作为微生物活性的替代指标并不恰当。本研究强调，在微生物模型中需明确纳入微生物生理过程。环境与底物对微生物季节动态的交互调控机制，为在季节尺度上模拟生态系统功能时更精准地表征微生物过程提供了新思路。