Simultaneous determination of multiple soil enzyme activities for soil health-biogeochemical indices

Enzyme activities (EAs) are soil health indicators of changes in soil biogeochemical cycling potential. β-glucosidase, β-glucosaminidase, acid phosphomonoesterase, and arylsulfatase are commonly assayed as indices of C, C and N, P and S cycling, respectively. These EAs can be measured in air-dried soil with appropriate substrates following similar assay conditions. Although the assays are similar, the current protocol is to measure each single EA independently. Subsequently, different approaches have been used to obtain a single index for all EAs (e.g., geometric mean of the sum of all EAs divided by the number of enzymes) to represent biogeochemical cycling and soil organic matter (SOM) dynamics. However, the burgeoning interest in soil health has created a need for high-throughput (and simpler) assays that are more cost effective compared to measuring multiple enzymes independently. Therefore, we evaluated simultaneous determination of two to three EAs in the same soil sample in the following combined assays: 1) β-glucosidase and acid phosphomonoesterase (C and P cycling), 2) β-glucosaminidase and arylsulfatase (C, N and S cycling), 3) β-glucosidase and β-glucosaminidase (C and N cycling), and 4) β-glucosidase, acid phosphomonoesterase and β-glucosaminidase (biogeochemical potential index). The results from combined EAs showed significant correlations with the sum of EAs calculated from individual assays (r > 0.931, p < 0.001). The combined EAs also showed positive significant correlations with soil organic C (r = 0.765-0.96, p < 0.001). We provide four options to assay multiple enzymes simultaneously, which reduces the time, resources, and chemical wastes generated from assaying the four enzyme activities individually.