MICROBIAL BIOMASS, AND C AND N MINERALIZATION, IN LITTER AND MINERAL SOIL OF ADJACENT MONTANE ECOSYSTEMS IN A SOUTHERN BEECH (NOTHOFAGUS) FOREST AND A TUSSOCK GRASSLAND

Comparisons were made of total and microbial C and N pools and C and N metabolism in litter and mineral soil of a mountain beech (Nothofagus solandri var. cliffortioides) forest, ca. 100 m below timberline, and an adjacent tussock grassland (dominated by Chionochloa pallens), ca. 100 m above timberline, in Canterbury, New Zealand. Mean annual preci pitation at the sites is ca. 1600 mm and mean annual air temperature c a. 6 degrees C. The silt loam soils are Andic Dystrochrepts. Total C a nd N and microbial C and N contents in litter and mineral soil (0-50 c m depth) differed appreciably in the two ecosystems and were 1.41, 2.0 0, 1.71 and 1.98 times, respectively, greater on an area basis at the grassland than at the forest site. Ratios of microbial C-to-total C, m icrobial N-to-total N and microbial C-to-N generally declined with pro file depth. CO2-C production, per unit of total C, and metabolic quoti ents (qCO(2) values) tended to be greater in mineral soil from the for est than from the grassland. CO2-C production, calculated on an area b asis to 50 cm depth of mineral soil, was similar in both ecosystems. N et N mineralization (during 0-56 days at 25 degrees C) was appreciable in the forest litter, but absent in tussock litter; it was similar in both systems at 0-10 cm and 20-50 cm depths of mineral soil, but was lower in the forest than in the grassland at 10-20 cm depth. Nitrifica tion was not detected in the litter samples and was either absent or v ery low in the samples of mineral soil. Results, overall, show that ma rked differences in soil and microbial properties can occur in adjacen t, indigenous ecosystems in almost the same climatic environment. Alth ough sail microbial biomass levels were lower in the forest than in th e grassland, the potential metabolic activity of the component microor ganisms tended to be greater in the forest. The relevance of these res ults to the turnover of organic matter in these ecosystems is briefly discussed. (C) 1997 Elsevier Science Ltd.