C, N and P stoichiometry of typical plants and soils in the Yellow River Delta Natural Reserve

The in-depth understanding of stoichiometry of plant and soil is beneficial for discovering convergence and divergence of ecosystem compositions, and forecasting response of ecosystem to environment change. The Yellow River Delta is an active and younger ecosystem, its' stoichiometry of plant and soil may impact ecosystem structure, function and stability. The aim of this study was to clarify the characteristics of carbon (C), nitrogen (N) and phosphorus (P) contents and stoichiometry of plants and soils in the Natural Reserve of Yellow River Delta. In the study, five vegetation communities from sea to inland were selected, which were Suaeda salsa, S. heteropter, Phragmites communis, Tamarix chinensis and Imperata cylindrical communities, to analyze contents of C, N and P of different organs of plants and soils. The results showed that C and P contents of plant leaf were higher than those of root, and those of stem were lowest for all the vegetation communities, except T. chinensis and I. cylindrica communitis. In I. cylindrica community, C and P contents were higher in plant stem than in root. N content of leaf was higher than of stem and that of root was lowest for all the vegetation communities. N:P ratio of leaf was lower than 12 and was not significantly different from that of root in all ecosystems. The average contents of soil organic C, total N and P were respectively 4.78 g·kg^-1, 0.32 g·kg^-1 and 0.53 g·kg^-1, with all lower than the national average. The differences in contents of soil C, N and P in different soil layers were insignificant. Soil stoichiometry ratio was significantly affected by vegetation type, but the spatial variability was insignificant. There was a significant correlation between contents of leaf organic C, N and P and stoichiometry ratios of C:N and C:P and then the contents of soil C and N in the 0-10 cm, 10-20 cm and 20-40 cm soil layers (P < 0.05). In conclusion, the results showed that the contents of C, N and P were stable in soil profile and lower than the national level. The low content of N affected the variations of C:N and C:P ratios. Consistent with C:P ratio of plant leaf and root, the cycles of the elements were stable in the ecosystem. Then N:P ratio of plant leaf was lower than 12. The findings in this study demonstrated that N was the limiting nutrient element in ecosystems of the Yellow River Delta Natural Reserve.