Ecological stoichiometry of C, N, and P of invasive Phragmites australis and native Cyperus malaccensis species in the Minjiang River tidal estuarine wetlands of China

Abstract

Tidal estuarine wetlands of China are rich in plant diversity, but several global change drivers, such as species invasion, are currently affecting the biogeochemical cycles of these ecosystems. We seasonally analyzed the carbon (C), nitrogen (N), and phosphorus (P) concentrations in litters and soils and in leaves, stems, and roots of the C3 invasive species Phragmites australis (Cav.) Trin. ex Steud. and of the C4 native species Cyperus malaccensis var. brevifolius Boeckeler to investigate the effect of C3 plant invasion on C, N, and P stoichiometry in the C4 plant-dominated tidal wetlands of the Minjiang River. When averaged across seasons, the invasive species P. australis had higher N concentrations and lower P concentrations in leaves than the native species C. malaccensis. N and P concentrations were lower in litter (stem and leaf), whereas C concentrations in leaf litter were higher in P. australis than in C. malaccensis. The C, N, and P concentrations of the soil also did not differ, but plants had a lower C:N and much higher N:P ratios than soils. Root C:P and N:P ratios were lower in the growing season both in the invasive and the native species. The leaf C:N, C:P and N:P ratios peaked in summer. The invasive species had lower C:N ratio in leaves and roots, and higher N:P ratios in all biomass organs and litter than the native species, an effect related with the higher N-resorption capacity of the invasive species. Interspecific differences in C:N, C:P, and N:P ratios may likely reflect the differences in plant morphology, nutrient-use efficiency, and photosynthetic capacity between the C3 (P. australis) and C4 (C. malaccensis) plants. Our results generally suggested that the success of P. australis in these wetlands was related to its slow growth and higher resorption capacity of N and P. This implies a more conservative use of limited nutrients, particularly N, by P. australis, and to higher N concentration in its biomass thus potentially contributing to its invasiveness in these estuarine wetlands.