Mycorrhizal Types Modulate Responses of Global Soil Microbial Biomass to Environments Across Varied Land Use Types

Soil microbial biomass (SMB) is a fundamental contributor to soil ecosystem services. Mycorrhizal fungi, a significant group of soil microbes, play essential roles in regulating carbon allocation and nutrient cycles. Acknowledging the profound importance of SMB and mycorrhizal symbiosis, our objective was to explore how mycorrhizal types modulate the global patterns of SMB across varied land use types (LUTs). Using data from 329 independent studies, we categorized vegetation species with defined mycorrhizal types into arbuscular mycorrhizal (AM) type (with 958 observations) or mixed AM and ectomycorrhizal (AM + ECM) type (with 481 observations). This categorization served as the foundation for our investigation into the impacts of various LUTs and environmental conditions (mean annual temperature, and mean annual precipitation, MAP) on global SMB patterns associated with specific mycorrhizal associations. The overall mean value of SMB was remarkably higher under AM + ECM type (92.23 +/- 4.73 nmol/g) compared with that under AM type (49.45 +/- 1.87 nmol/g) at a global scale. The primary factor contributing to this difference was the natural system. Additionally, the AM + ECM type (0.19 +/- 0.01) exhibited a higher F:B ratio (Fungi-to-bacteria ratio) than the AM type (0.16 +/- 0.001), attributed to the cumulative effects of different LUTs. Furthermore, SMB was markedly positively affected by aridity index under AM type and negatively influenced by temperature under AM + ECM type. Besides, MAP had a pronounced positive impact on SMB under AM type, while exhibiting a negative impact under AM + ECM type. Our study presented evidence affirming the essential role of mycorrhizal associations in shaping global patterns of SMB in response to environmental factors across varied LUTs. Soil microbial biomass (SMB) was significantly higher under arbuscular mycorrhizal + ectomycorrhizal (AM + ECM) type compared to that under AM type, with this difference being most pronounced in the natural system AM + ECM type had a higher F:B ratio than the AM type, attributed to the cumulative effects of different LUTs SMB exhibited a notable increase with aridity index under AM type, and a slight yet significant decrease with temperature under AM + ECM type