Comparison of soil microbial properties and fauna under tussock-grassland and pine plantation

To investigate responses of selected soil characteristics to vegetation changes in high-country soils, samples were collected from under unburned Chionochloa rigida grassland, burned C. rigida, 12-year-old Pinus radiata trees and from glades within pine forest where trees had failed to grow. Under P. radiata there were lower soil pH and exchangeable Ca, Mg, K and Fe, while lower microbial C, N and P in the plantation confirmed other findings that P. radiata reduces C, N and P pools in mineral soil. Relatively small differences in microbial biomass C and P between tussock >25 and <14 years since burning suggest that burning has a lesser effect than P. radiata on these properties. Burning, however, affected biomass N. Numerical abundance of megascolecid earthworms was greatest in tussock-grassland and in glades; they were least abundant under P. radiata. However, the heaviest individual earthworms occurred under P. radiata and in glades. Indices suggest a less stable or more rapidly reproducing nematode fauna under P. radiata; nematode generic diversity was lowest under P. radiata. Although the four vegetation types affected soil properties in various ways, most properties under the P, radiata plantation were most different. The decline in microbial biomass C, N and P and the microbial C: organic C ratio under P. radiata suggest lower organic matter inputs into the soil, and as such could be regarded as a decline in ecological sustainability. The associated shift in the structure of the biotic community observed in this study emphasizes the role of biotic factors as independent variables for monitoring soil organic matter dynamics under different land-uses.