Ecological stoichiometry is the study of the balance of energy and multiple chemical elements. Generally, this perspective examines the causes and consequences of elemental imbalances between resources, producers, and consumers in the environment. C, N and P are key elements controlling organism growth. However, the relative needs of the elements are poorly quantified, and dependencies between elements are not well investigated. These three elements are strongly coupled in their biochemical functioning. Furthermore, the ecological stoichiometry of C, N and P is the indication for organic carbon decomposition and nutrition limit.
The element ratios in wetlands, especially for the estuarine wetlands, appear to be more variable than other ecosystems worldwide. Moreover, the studies on soil C, N and P stoichiometry have not been thoroughly studied. In fact, soil as the carrier of organisms and elements plays very important roles. Therefore, studies on C, N and P ecological stoichiometry of wetland soils will be favorable to clarify the available of nutrition and the cycle and balance of C, N and P.
An amount of approximately 18,000 km of coastline in China is covered by an estimated 12,000 km² of tidal estuary wetlands. These tidal wetlands are generally rich in animal and plant biodiversity and appear to have important biogeochemical roles within the entire estuary ecosystem. One of these important tidal wetland ecosystems is found within the Minjiang River estuary in southeast China, which is located at the transition of mid- and southern subtropical climate zones in China.
Phragmites australis is the dominant species in Minjiang River estuarine wetland and distributes everywhere from upper reach to lower river. Here we chose the Youxizhou wetland, Bianfuzhou wetland and Shanyutan wetland as the study areas and examined the ecological stoichiometric characteristics of wetland soils in different river reaches and their indication. In upper reach, the values of soil C/N, C/P, N/P (0-60 cm) of P. australis wetland were 36.5-51.3, 43.0-93.6 and 0.8-2.3, with averages of 44.1, 66.9 and 1.6, respectively. In middle reach, the values of soil C/N, C/P, N/P (0-60 cm) were 15.8-21.7, 28.0-72.2 and 1.6-4.2, with averages of 17.6, 45.7 and 2.6, respectively. In lower reach, the values of soil C/N, C/P, N/P (0-60 cm) were 13.5-19.8, 63.6-125.4 and 4.2-6.3, with averages of 16.4, 90.5 and 5.5, respectively. C/N, C/P and N/P ratios appeared various tendencies among wetlands in different reaches. Soil C/N ratios were in the order of upper reach>middle reach>lower reach, C/P ratios were in the order of lower river >upper river>middle river, while N/P ratios were in the order of lower reach>middle reach>upper reach. The variation of C/N, C/P, N/P ratios in soil profile of single reach was smaller than that among different reaches. Soil water and silt contents were the key factors controlling the change of C/N, C/P, N/P ratios of wetland soils in different reaches. Soil C/N and N/P ratios were preferable indication for anaerobic carbon decomposition.