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

Abstract

Land cover is a critical factor that influences, and is influenced by, atmospheric chemistry and potential climate changes. As considerable uncertainty exists about the effects of differences in land cover on below-ground carbon (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/m² ), and based on bomb ¹⁴C measurements, the differences mainly resulted from more recalcitrant soil C in the grassland (5.3 v. 3.0 kg/m² ). Estimated annual net primary production was about 0.4 kg C/m² for the forest and 0.5 kg C/m² for the grassland; estimated annual root production was about 0.2 and 0.4 kg C/m² , respectively. In situ soil surface CO₂ -C production was similar in the grassland and the forest. The accumulation of recalcitrant soil C was unrelated to differences in mineral weathering or soil texture, but was apparently enhanced by greater soil water retention in the grassland ecosystem. Thus, contrary to model (ROTHC) predictions, this soil C fraction could be expected to respond to the effects of climate change on precipitation patterns.

Overall, our results suggest that the different patterns of soil C accumulation in these ecosystems have resulted from differences in plant C inputs, soil aluminium, and soil physical characteristics, rather than from differences in soil mineral weathering or texture.