TitleNitrogen, organic carbon and sulphur cycling in terrestrial ecosystems: linking nitrogen saturation to carbon limitation of soil microbial processes
Publication TypeMiscellaneous
Year of Publication2013
AuthorsKopacek, J, Cosby, BJ, Evans, CD, Hruska, J, Moldan, F, Oulehle, F, Tahovska, K, Wright, RF
Keywordsacidification, Carbon, forest soil, Modelling, Nitrogen, sulphur

Elevated and chronic nitrogen (N) deposition to N-limited terrestrial ecosystems can lead to `N saturation', with resultant ecosystem damage and leaching of nitrate (NO3 (-)) to surface waters. Present-day N deposition, however, is often a poor predictor of NO3 (-) leaching, and the pathway of the ecosystem transition from N-limited to N-saturated remains incompletely understood. The dynamics of N cycling are intimately linked to the associated carbon (C) and sulphur (S) cycles. We hypothesize that N saturation is associated with shifts in the microbial community, manifest by a decrease in the fungi-to-bacteria ratio and a transition from N to C limitation. Three mechanisms could lead to lower amount of bioavailable dissolved organic C (DOC) for the microbial community and to C limitation of N-rich systems: (1) Increased abundance of N for plant uptake, causing lower C allocation to plant roots; (2) chemical suppression of DOC solubility by soil acidification; and (3) enhanced mineralisation of DOC due to increased abundance of electron acceptors in the form of and NO3 (-) in anoxic soil micro-sites. Here we consider each of these mechanisms, the extent to which their hypothesised impacts are consistent with observations from intensively-monitored sites, and the potential to improve biogeochemical models by incorporating mechanistic links to the C and S cycles.