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Nitrification and denitrification in an alpine meadow soil of the eastern Tibetan Plateau

Nitrification and denitrification represent two of the main biological processes involved in the N cycle, which contribute to the regulation of NO3 availability to plants reduction to N2 (Vitousek et al., 1982; Conen et al., 2000). Moreover, they represent the main source of the greenhouse gas N2O in terrestrial ecosystems (Williams et al., 1992). Both processes are directly limited by substrate availability (NH4 , NO3 , organic C) and low temperatures, and indirectly by water content and soil capacity to retain water (Granli & Bøkman, 1994). In an alpine meadow ecosystem on the Tibetan Plateau, being characterized by an extreme climate with low temperatures and a short vegetation season, inorganic (available) N is usually present in low concentrations, although alpine meadow soils are noted for their large quantities of total N; most of this resides in organic (unavailable) form (Cao & Zhang, 2001). Therefore, knowledge of N transformation in highly N limited and fragile alpine ecosystems is necessary for managing both the N supply to the pasture grass crop and the potential N losses to the environment. However, there are no available data on soil nitrification and denitrification activities in the region. In this study we measured the seasonal dynamics of nitrification and denitrification in an alpine meadow soil on the eastern Tibetan Plateau.