Effects of chicken farming on soil extracellular enzyme activity and microbial nutrient limitation in Lei bamboo forest (Phyllostachys praecox) in subtropical China

Abstract Bamboo-chicken farming (BCF) is an emerging land-use type in southeast Asia; however, the impacts of BCF on the metabolic requirements of soil microbial communities and on carbon sequestration are unclear. In this study, the distances (5, 15, 25, and 35 m) from the hen house were used to characterise the different grazing densities. Surface soil (0–20 cm) from four grazing densities in a BCF system and a control forest comprising pure Lei bamboo (Phyllostachys praecox) was investigated. Soil physicochemical properties, microbial biomass (C, N, and P), and extracellular enzymatic activities (EEAs) were determined, and soil ecoenzymatic stoichiometries (EESs) and microbial carbon use efficiencies (CUEs) were quantified. We found that the EEAs (β-1,4-glucosidase, BG; β-1,4-N-acetylglucosaminidase, NAG; L-leucine aminopeptidase, LAP; and alkaline phosphatase, ALP) were significantly enhanced with increasing grazing density, and significant differences in microbial investments in C-, N-, and P-acquiring enzymes were observed across the different grazing densities. The high degree of microbial elemental homeostasis (H′C:N = 16.95 and H′C:P = 11.49) indicates that soil microorganisms could maintain stoichiometric homeostasis under different grazing density conditions. Although the microbial community was limited by carbon and nitrogen in the control bamboo forest, these limitations were gradually alleviated as the grazing density increased. In addition, the microbial CUE (both CUEC:N and CUEC:P) increased with higher grazing densities. However, no significant difference was observed in soil organic carbon at different grazing densities, which may be due to the reductions in organic matter input from litter and roots in the BCF system. This study revealed the different patterns of soil C:N:P stoichiometry and ecoenzymatic stoichiometry with increasing grazing density. The high soil microbial CUE observed in the BCF system does not indicate high soil C sequestration. In contrast, reduced soil microbial biomass and increased available P at high grazing density conditions could pose high risk for sustainable land use.