Effects of land-use change from grassland to forest on soil sulfur and arylsulfatase activity in New Zealand

Abstract

The effects of land-use change from grassland to forest on soil sulfur (S) and arylsulfatase enzyme activity were investigated by comparing soils under unimproved grassland and an adjacent 19-year-old exotic forest stand (mixture of Pinus ponderosa and P. nigra). Results showed that concentrations of organic S in topsoil under forest were significantly lower [418 µg/g (0–5 cm), 398 µg/g (5–10 cm)] than corresponding soil depths under grassland [541 µg/g (0–5 cm), 468 µg/g (5–10 cm)]. On the other hand, inorganic S concentrations were significantly higher in soil under forest at all depths compared with grassland. The inorganic S concentration in soil under grassland increased with depth, but there was no significant difference observed at different depths under forest. The decrease in organic S [and organic carbon (C)] in soil under forest was due to the enhanced mineralisation of organic components. The accumulation of inorganic S in the soil profile under forest was mainly attributed to enhanced mineralisation, although decreased leaching, increased sulfate-S adsorption, and increased atmospheric inputs by canopy interception of aerosols could have contributed. Microbial biomass C and S and arylsulfatase activity were higher in topsoil under grassland than forest. Lower arylsulfatase activities under forest compared with grassland at the time of sampling suggest that mineralisation of organic S under forest was not currently mediated primarily by enzyme activity, although enzyme activity may have been important at earlier stages of forest development. Arylsulfatase activity was significantly correlated with soil organic C, water-soluble C, microbial biomass C, total S, organic S, and microbial biomass S in soil under grassland and forest. Significant concentrations of organic S and microbial biomass S were present in the forest floor (litter and fermentation layers). These pools would be important for S cycling and availability in forest ecosystems. S mineralisation, S fractions, microbial biomass S, microbial biomass C.