Relationships between foliar carbon isotope composition and elements of C3 species in grasslands of Inner Mongolia, China

Abstract

Foliar elements and their ratios can be related to foliar carbon isotope composition (δ13C) through their involvement in plant transpiration, photosynthesis, and osmotic adjustment. In order to investigate these relationships in grasslands of Inner Mongolia, China, δ13C and element contents of dominant C3 species at 47 grassland sites were determined. For C3 species, δ13C showed no correlation with carbon (C), positive correlations with nitrogen (N), nitrogen:phosphorus ratio (N/P) and carbon:phosphorus ratio (C/P), and negative correlations with phosphorus (P), potassium (K), and carbon:nitrogen ratio (C/N), while correlation with P was subsidiary to positive correlation between P and K. These correlations indicate that plants in Inner Mongolia that survive in dry conditions may profit from their higher water use efficiency via stomatal regulation and N-related photosynthetic capacity rather than K-related osmotic adjustment and P-related photosynthetic capacity. Further, plants adapt to severe environments by having higher water and phosphorus use efficiency at the expense of nitrogen use efficiency. However, these correlations differed among plant functional groups (PFGs), e.g., δ13C was negatively correlated with N in shrubs in contrast to other life forms. A possible explanation is that shrubs adapt to low N availability by having lower photosynthetic nitrogen use efficiency (PNUE), so that N is not positively related to photosynthetic rate in shrubs. Obviously, data on stomatal conductance, PNUE, and cell osmotic pressure are needed to fully understand these correlations and the strategies of plants adapted to arid environments.