Plant effects on soil carbon storage and turnover in a montane beech (Nothofagus) forest and adjacent tussock grassland in New Zealand

Land cover is a critical factor that influences, and is influenced by, atmo spheric chemistry and potential climate changes. As considerable uncertaint y exists about the effects of differences in land cover on below-ground car bon (C) storage, we have compared soil C contents and turnover at adjacent, unmanaged, indigenous forest (Nothofagus solandri var. cliffortiodes) and grassland (Chionochloa pallens) sites near the timberline in the same climo -edaphic environment in Craigieburn Forest Park, Canterbury, New Zealand. Total soil profile C was 13% higher in the grassland than in the forest (19 .9 v. 16.7 kg/m(2)), and based on bomb C-14 measurements, the differences m ainly resulted from more recalcitrant soil C in the grassland (5.3 v. 3.0 k g/m(2)). Estimated annual net primary production was about 0.4 kg C/m(2) fo r the forest and 0.5 kg C/m(2) for the grassland; estimated annual root pro duction was about 0.2 and 0.4 kg C/m(2), respectively. In situ soil surface CO2-C production was similar in the grassland and the forest. The accumula tion of recalcitrant soil C was unrelated to differences in mineral weather ing or soil texture, but was apparently enhanced by greater soil water rete ntion in the grassland ecosystem. Thus, contrary to model (ROTHC) predictio ns, this soil C fraction could be expected to respond to the effects of cli mate change on precipitation patterns. Overall, our results suggest that the different patterns of soil C accumula tion in these ecosystems have resulted from differences in plant C inputs, soil aluminium, and soil physical characteristics, rather than from differe nces in soil mineral weathering or texture.