Simultaneous determination of β-glucosidase, β-glucosaminidase, acid phosphomonoesterase, and arylsulfatase activities in a soil sample for a biogeochemical cycling index

Four enzymes activities (EAs) have been targeted as soil health indicators for their important role in reactions releasing bioavailable nutrients within C (beta-glucosidase), N and C (beta-glucosaminidase), P (acid phosphomonoesterase) and S (arylsulfatase) cycling. Traditionally these EAs are assayed independently on air-dried soil by measuring the release of p-nitrophenol from a substrate analog. Previously, we suggested a novel approach to assess multiple EAs simultaneously in the same soil sample by adding two or three substrates to obtain a comparable index. Our current study provides a combined assay for simultaneous determination of these four EAs in the same soil sample. For the incubation step of our combined assay, we tested modified universal buffer (MUB) because it is used for assaying beta-glucosidase and acid phosphomonoesterase activities and tested acetate buffer as it is used for assaying beta-glucosaminidase and arylsulfatase activities. Using the acetate buffer (pH 5.8) for the combined assay showed the lowest percent of difference (average of - 14%) compared with the sum of individual EAs, and showed positive significant correlations (p < 0.001) with the sum of the individual EAs (r = 0.97) and with soil organic C (r = 0.94) and total nitrogen (TN) (r = 0.93). This combined acetate buffer assay (CNPS activity) differentiated among agroecosystems similarly to the sum of the individual EAs in Texas soils (cotton < grass < Conservation Reserve Program) and both approaches showed a tendency for higher activities in a diversified rotation compared to corn-soybean and a grass system for Minnesota soils. Use of the novel CNPS activity will provide a uniform biogeochemical cycling index while reducing time and resources compared to assaying the EAs individually.