Biological indicators affected by land use change, soil resource availability and seasonality in dry tropics

Abstract

Abstract Land use change (LUC) in tropics, explicitly from forest to conventional agriculture, is negatively affecting soil health and productivity. However, effect of such LUC on soil biological properties are poorly known in dry tropical environment. This study aimed to determine the impact of such LUC and climate seasonality on soil biological properties (microbial and enzyme activities), and to also explore the role of soil resources (C, N and P) in driving soil biological properties during this environmental change. Soil biological indicators of topsoil (0–15 cm) were measured on a seasonal basis in the natural forest, fallow and agricultural land. Soil microbial biomass C (Cmic), CO2 efflux (Cefflux) and hydrolytic enzyme activities (acid phosphatase, alkaline phosphatase, β-glucosidase, dehydrogenase, fluorescein diacetate) were generally higher in the forest followed agriculture and fallow. The lower level of these biological variables in agriculture soils were possibly due to lower total soil organic carbon (SOC), labile SOC (particulate OC; POC), total N and P, and cropping disturbance (i.e., fertilization) induced higher inorganic N and P. Whereas, lower biological activities in fallow soils were mainly attributed lower plant activity (i.e. litter production and root activity). In contrast, oxidative enzyme (particularly peroxidase) activities were higher in agriculture followed by the forest and fallow, which might be attributed to higher soil oxygenation from tillage in agriculture and higher persistent SOC (non-particulate OC; NPOC). Seasonal variation in soil biological properties was identical among land uses, though its extent was greater in the forest than fallow and agriculture, indicating LUC can alter the degree of seasonality in biological properties. In addition, the higher specific enzyme activities (i.e., enzyme activities per unit of Cmic) and microbial metabolic quotient (qCO2) in the fallow followed by agriculture and forest, indicating the higher degree of stress on soil microbes after the deforestation than cropping. Whereas, the higher specific enzyme activities and qCO2 in agriculture possibly attributed to higher microbial nutrients demand and lower SOC accumulation. Collectively, our results reveal the significant effects of deforestation and agriculture on soil biological activities and improve our understanding of the potential mechanism driving these effects.