Contrasting patterns and controls of soil carbon and nitrogen isotope compositions in coastal wetlands of China

AimsNatural stable isotope compositions of carbon (delta C-13) and nitrogen (delta N-15) can reveal biogeochemical mechanisms that control ecosystem carbon (C) and nitrogen (N) processes. However, little is known about the latitudinal patterns and controlling mechanisms for soil delta C-13 and delta N-15 in coastal wetlands based on a large spatial scale.MethodsA total of 76 sites of coastal wetlands were sampled along a 5000 km transect across temperate-subtropical-tropical zones to explore biological and environmental controls on soil stable C and N isotopic compositions.ResultsThe results showed that soil delta C-13 (ranging from -27.5 parts per thousand to -18.3 parts per thousand) and delta N-15 (from 2.66 parts per thousand to 9.97 parts per thousand) varied over a broad geographic scale. The C4-plant (Spartina alterniflora) dominated sites have 2-6 parts per thousand higher delta C-13 values than those of other vegetation types, while mangrove soils have lower delta C-13 values compared to those of marshes; and soils with vegetated C4-plants and mangroves have 1-3 parts per thousand higher delta N-15 values relative to native grass marshes. There were no significant relationships between mean annual temperature (MAT) or precipitation (MAP) and delta C-13, but positive correlations between MAT and delta N-15, as well as MAP and delta N-15.ConclusionsVegetation composition and plant C inputs directly control the spatial variability of delta C-13 patterns. Simultaneously, climate and edaphic variables (e.g., soil water content, pH, and C availability) are the predominant factors influencing delta N-15 patterns. These findings provide new insights into soil organic matter turnover and response to climate and environmental changes and improve the prediction of C stability and burial in coastal wetlands.

Automated summary

This study investigated the natural stable isotope compositions of carbon and nitrogen in coastal wetlands at a large spatial scale. The results showed that the spatial variability of delta C-13 patterns is mainly controlled by vegetation composition and plant C inputs, while climate and edaphic variables influence delta N-15 patterns.