Contrasting nitrogen cycling between herbaceous wetland and terrestrial ecosystems inferred from plant and soil nitrogen isotopes across China

Understanding nitrogen (N) cycling in different ecosystems is crucial to predicting and mitigating the global effects of altered N inputs. Although wetlands have always been assumed to differ largely from terrestrial ecosystems in N cycling, evidence from direct comparison from the field along wide environmental gradients is lacking. Here, we hypothesized strong coupling of plant and soil δ15N in terrestrial ecosystems due to lower N inputs and losses but weak coupling of plant and soil δ15N in wetlands because of higher N inputs and losses.
We performed a large-scale field investigation on 26 pairs of herbaceous wetland and terrestrial sites across China covering 21 degrees of latitude and determined natural abundance of nitrogen isotopes (δ15N) in soils and leaves of 346 dominant and subordinate plant species. We analysed the relationships between leaf and soil δ15N and their drivers including plant functional types in these two types of ecosystems.
Plant functional types including my...