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Agricultural land use decouples soil nutrient cycles in a subtropical riparian wetland in China

Wang, Weiqi, Wang, Chun, Sardans, Jordi, Min, Qingwen, Zeng, Congsheng, Tong, Chuan, Peñuelas, Josep
Catena 2015 v.133 pp. 171-178
Phragmites australis, anthropogenic activities, carbon, carbon sequestration, cropland, emissions, estuaries, flowers, land use change, littoral zone, natural regeneration, nitrogen, nitrogen content, nitrogen fertilizers, phosphorus, potassium, rice, rivers, soil, soil nutrients, stoichiometry, vegetable growing, vegetation, wetlands, China
We examined the impact of human changes in land use on the concentrations and stoichiometric relationships among soil carbon (C), nitrogen (N), phosphorus (P) and potassium (K) in a Phragmites australis riparian wetland (Minjiang River estuary, China). We compared a natural (unaltered) wetland with five altered land uses: intertidal mudflat culture and vegetable, flower, fruit and rice cultivations. All these land uses decreased C, N and K soil concentrations relative to those in the P. australis wetland. The close relationship between total soil C and N concentrations, under all land uses, suggested that N was the most limiting nutrient in these wetlands. The lower N concentrations, despite the use of N fertilizers, indicated the difficulty of avoiding N limitation in the agricultural land. Croplands, except rice cultivation, had lower soil N:P ratios than the original P. australis wetland, consistent with the tendency of favoring species adapted to high rates of growth (low N:P ratio). The release of soil C was less and the soil C:N and C:P ratios higher in the natural P. australis riparian wetland than in the croplands, whereas C storage was more similar. The levels of soil C storage were generally opposite to those of C release, indicating that C release by respiration was the most important factor controlling C storage. Cropland soil management promotes faster nutrient and C cycles and changes in soil nutrient stoichiometry. These impacts can further hinder the regeneration of natural vegetation by nutrient imbalances and increase C-cycling and C emissions.