Foliar carbon, nitrogen, and phosphorus stoichiometry in a grassland ecosystem along the Chinese Grassland Transect

Carbon (C), nitrogen (N), and phosphorus (P) are the basic nutrient elements required for plant growth and function. Ecological stoichiometry provides an important method for the determination of plant nutrient utilization and the environmental adaptation strategies of plants. Studying the stoichiometry of C, N and P is crucial to the understanding of nutrient cycling and ecosystem stabilization mechanisms. Most studies so far have focused only on N and P stoichiometry for plant leaves and ignored the stoichiometry characteristics among C, N, and P. As a major element of plant dry matter, C, along with critical nutrient elements (N and P) could regulate and influence the consumption and fixation of organic matter in ecosystems. Therefore, it is necessary to study the ecological stoichiometry of C, N, and P in plants. Here, C, N and P concentrations and their ratios were measured for 329 foliar samples collected at 132 sites along the 4500 km-long Chinese Grassland Transect (CGT) that traverses the Inner Mongolian and Qinghai-Tibet Plateaus. The content of C, N, and P of plant leaves in grassland ranged from 257.40 to 590.77 mg/g, 4.49 to 45.85 mg/g, and 0.20 to 3.40 mg/g, with an average of 463.76 mg/g, 19.94 mg/g, 1.31 mg/g, respectively. The coefficient of variation (CV) of P was highest (0.47) while the CV values of C and N were 0.09 and 0.34, respectively. N and P were positively correlated (R2 = 0.491, P < 0.0001), in agreement with previous studies, while no significant correlation was found between C and P or between C and N. The ranges for C/N, N/P, and C/P were 10.93-93.67 (with an average of 26.86 and a CV value of 0.46) for C/N, 1.68-53.00 (with an average of 16.59 and a CV value of 0.39) for N/P, and 61.49-1995.24 (with an average of 436.77 and a CV value of 0.59) for C/P, respectively. The mass ratio of C:N:P in grassland plant was 440:17:1, and the atom ratio was 1136:43:1. C/N and C/P, C/N and N/P were positively correlated (R2 = 0.509, P < 0.0001; R2 = 0.410, P < 0.0001, respectively), while C/N and N/P were not significantly correlated. C concentrations of grassland plant in the Chinese Grassland Transect were close to those at the global scale, but lower than that in forests in China. N and P concentrations in grassland plant were lower than those in global terrestrial plants, while N concentrations were much higher but P concentrations were much lower than those in forest plants. C/N and C/P were relatively higher, reflecting the higher vegetative utilization efficiency of grassland vegetation. The CV of P was much higher and the N/P in this study was higher than 16, which indicated that grassland plants in China are more restricted by P elements. Our results could help to understand the relationship between C, N, and P stoichiometry in grassland plants and provide basic data for related ecological models.