Soil bacteria respond intensely to resource limitations regulated by edaphic properties during secondary succession on a semiarid abandoned farmland

Disproportionate inputs of carbon (C), nitrogen (N), and phosphorus (P) following plant succession typically induce microbial resource limitations. Such limitations are directly relevant to the fate of soil element cycles. However, it is not well understood how generalizable patterns of resource constraints act on soil microbial communities during the natural succession of abandoned farmlands, nor their driving forces. To this end, the potential activities of C-, N-, and P-acquiring enzymes, soil properties, plant characteristics, and soil microbial community composition and diversity were investigated along a 30-year successional chronosequence following agricultural abandonment on the Chinese Loess Plateau. Ecoenzymatic stoichiometry revealed a decrease in C limitation following succession, and soil microorganisms were primarily limited by N in the 10th year of succession but limited by P in the 20th and 30th years. Soil physicochemical properties cumulatively contributed 62.59% and 59.33% to the variations in microbial C and nutrient limitations, respectively. In particular, soil organic C content, C:N and C:P ratios, microbial biomass, and pH strongly affected microbial element limitations. Plant characteristics had minor effects on microbial resource constraints, accounting for 37.41% and 40.67% of the variance in microbial C and nutrient limitations, respectively. In comparison, plant diversity affected soil microbial element limitations more than plant family composition. Notably, the bacterial alpha and beta diversities, as well as the relative abundances of dominant phyla, such as Actinobacteria, Bacteroidetes, Proteobacteria, Acidobacteria, Gemmatimonadetes, and Planctomycetes, were significantly more associated with resource limitations than soil fungal community. Collectively, these findings suggest that the variable patterns of microbial element limitations were predominantly the result of changing soil properties across distinct successional stages, with soil bacteria responding more strongly than fungi to changes in microbial element limitations.