Factors affecting 13C enrichment of vegetation and soil in temperate grasslands in Inner Mongolia, China

Abstract

Soil organic carbon (SOC) dynamics are central to understanding the effects of environmental change on the carbon cycle of ecosystems. Vegetation and soil stable carbon isotope composition (δ13C), especially the difference of δ13C between surface soils and source vegetation (Δδ13C), can provide useful information about the SOC dynamics. The variations and patterns of vegetation and soil δ13C and Δδ13C along climatic and edaphic gradients were analyzed to improve the understanding of SOC dynamics in temperate grassland ecosystems. Soil and plant samples were collected along climatic and edaphic gradients. Meteorological data were extracted from a regional climate database, which was spatially interpolated based on the records at 107 climatic stations located in Inner Mongolia. δ13C, carbon and nitrogen contents of soil and plant, soil pH, soil clay, silt, and sand contents were determined. Δδ13C and soil C:N were calculated. The integrative effects of these factors were further estimated using stepwise regression, redundancy analysis (RDA) and T value biplots. As expected, soil δ13C was positively related to vegetation δ13C, and higher than the vegetation δ13C. Vegetation and soil δ13C and Δδ13C were all related to growing season precipitation (GSP) and growing season temperature (GST). However, when climatic and edaphic factors were considered together, vegetation δ13C was positively related to GST and soil C:N, soil δ13C was positively related only to GST, and Δδ13C was negatively related only to soil C:N. Unlike previous research conducted at the species level which only included C3 species, GST, instead of precipitation, was the dominant controlling factor of vegetation δ13C. GST influences vegetation δ13C mainly through its effect on relative abundance of C4 plants. Soil C:N rather than climatic factors is the dominant controlling factor of SOC decomposition, and the effects of climatic factors on SOC decomposition are indirect and induced by their effects on soil C:N through influencing species composition and plant C:N. Measuring vegetation δ13C, soil δ13C, and △δ13C simultaneously is necessary to comprehensively understand how environmental changes influence ecosystem carbon cycles.