Ecological effects of soil physicochemical properties and copper speciation on the microbial properties associated with land use management in cacao production

Abstract

Soil microbial functioning heavily influenced by heavy metals, is critical to soil health. We investigated the response of soil microbial properties to Cu speciation and soil physicochemical properties at two depths (0–15 and 15–30 cm) in the natural field (NAF), conventional- (CCM), and organic cacao management (OCM) in Ghana. A sequential extraction technique was used to quantify Cu into labile, potentially stable, and stable speciation. Soil physicochemical properties, microbial biomass, basal respiration, enzyme activity, and microbial counts were measured. Microbial- and metabolic quotients (qCO2) were calculated. Cu speciation and microbial properties were largely influenced by land management vis-à-vis soil depth. Except for basal respiration and qCO2 which were dominant at CCM, the other microbial properties increased in NAF > OCM > CCM. CCM had the maximum labile Cu while NAF had the least. Potentially stable and stable Cu were dominant at OCM. Labile Cu negatively affected soil microbial properties except for basal respiration and qCO2, which had a positive effect. However, when labile Cu co-varied with potentially stable and stable Cu or soil organic carbon (SOC), it positively affected microbial properties. The relationship between soil microbial and physicochemical properties was stronger than Cu speciation. The negative effect of labile Cu on microbial biomass, microbial count, and enzyme activity was masked by pH, clay, and SOC. Overall, Cu speciation and soil physicochemical parameters jointly altered microbial properties which varied with the land management systems. This study provides novel insight into the microbial properties in cacao soils associated with land management systems.