Spatial patterns of leaf carbon, nitrogen stoichiometry and stable carbon isotope composition of Ranunculus natans C.A. Mey. (Ranunculaceae) in the arid zone of northwest China

Leaf carbon concentrations (C%), nitrogen concentrations (N%), carbon–nitrogen ratio (C:N) and stable carbon isotope composition (δ13C) are key foliar traits with great ecological importance, but few studies have attempted to document the pattern of leaf C%, N%, C:N and δ13C value for aquatic macrophytes. In this study, we examined the pattern of leaf C%, N%, C:N and δ13C value of Ranunculus natans collected from 26 sites across northwest China, and tried to explore how different environmental conditions affect leaf C%, N%, C:N stoichiometry, and δ13C value. Results showed that leaf N%, C:N ratios and δ13C varied significantly among the 26 R. natnas collection sites, but leaf C% did not differ significantly. Our study found weak relationships between foliar N% and C:N of R. natans and altitude, latitude and longitude, which indicated that variability in foliar N%, C:N stoichiometry across diverse habitats may result from plant growth, development, metabolism, phenological and life history traits, rather than from variation in geographic environment. We also demonstrated that leaf δ13C values displayed a linear increase in altitudinal direction. The differences in δ13C values were likely caused by stomatal limitation rather than by nutrient-related changes in photosynthetic efficiency because δ13C values in R. natans were not correlated with foliar N concentrations. Our data support the previously proposed temperature-plant physiology hypothesis because there is a negative relationship between leaf N% of R. natans and temperature of water body where R. natans inhabits.