Biochar application induces different responses of bacterial and fungal communities to metabolic limitation

Biochar, an environmentally friendly soil amendment, has the potential to alleviate soil degradation. However, the mechanisms and effects of biochar addition on soil microbes and metabolic limitation in degraded soils are still ambiguous because of the complex ecosystem and the varying conditions of planting. Therefore, a field experiment with six biochar application rates (0, 24, 60, 96, 132, and 168 Mg ha(-1), applied in the 0-20 cm soil layer) was conducted in a loessial soil without planting to determine the response of metabolic limitation and the microbial community to the biochar application rate. Soil samples were collected in mid-May and mid-August (before and during the rainy season). The results showed that the soil microbial metabolic activity without biochar application was phosphorus (P) limited in mid-May (vector angle = 81.37 +/- 0.31 degrees) and nitrogen (N) limited in mid-August (vector angle = 27.36 +/- 1.54 degrees), and nutrient limitations generally decreased in the biochar treatments. Structural equation modeling indicated that microbial metabolic restriction was mainly influenced by biochar-induced changes in element stoichiometric ratios and available phosphorus (p < 0.05). Under the influence of biochar content, only the carbon (C) limitation influenced bacterial composition by directly or indirectly affecting dissolved organic carbon and NO3--N. However, the fungal composition was strongly shaped by both C limitation and P/N limitation. Our results indicated that the soil P status and its stoichiometric ratios play an important role in the biochar effects on metabolic limitation and that bacteria and fungi have different compositional responses to metabolic limitation in loessial soil.