SOIL DECOMPOSITION POTENTIAL IN RELATION TO ENVIRONMENTAL-FACTORS ON MARION-ISLAND (SUB-ANTARCTIC)

Decomposition potentials in Marion Island (47-degrees-S, 38-degrees-E) soils, as measured by the loss of tensile strength of buried cotton s trips, lie at or near the upper extremes of the range found in tundras and related ecosystems. These high decomposition rates are related pa rtly to the relative warmth of Marion Island and absence of very cold winters, but also, especially in the more active sites, to high soil n utrient contents and near-optimal moisture. Variation in TSL between s ites was attributed to particular soil variables. Multiple regression analysis showed soil moisture and fertility to be the most significant of these, with temperature apparently not important in distinguishing between sites. However, the absence of a warm summer probably retards decomposition at some sites. The two strongest vectors yielded by pri ncipal components analysis of a range of soil physical, chemical and m icrobiological variables both accounted for a significant proportion o f TSL variation across sites. These vectors represented gradients from organic, eutrophic to mineral, oligotrophic soils, and from warm, wet to cold, dry soils; trends similar to those found in previous analyse s of a wider range of edaphic and botanical variables for the island, the sub-Antarctic as a whole, and also in bipolar comparisons. The fac t that these trends have been shown to be associated with a variety of ecological processes, suggests that the cotton-strip assay measures a n intrinsic property of ecosystem functioning.