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. Litter decomposition is a major source of nutrients to soil and the key process of biogeochemistry. Litter quality, the related microbe and the environmental factors all influence the litter decomposition rate. Nowadays, some researchers have examined the relationship of litter decomposition and the nutrient ecological stoichiometry, and proposed the ecological stoichiometry of C, N and P as the indication for litter decomposition and nutrition and energy release. The element ratios in wetlands, especially for the estuarine wetlands, appear to be more variable than other ecosystems. Moreover, the C, N and P stoichiometry during litter decomposition remains poorly understood.
An amount of 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 diversity 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. This study was conducted in the Shanyutan wetland (119°34'12″-119°40'40″E, 26°00'36″ -26°03'426″N), which is the largest tidal wetland (nearly 3120 ha) in the Minjiang River estuary. The climate is warm and wet, with a mean annual temperature of 19.6 ℃ and a mean annual precipitation of 1346 mm. The Shanyutan wetland is belt-shaped. The sediment surface at the study site is submerged for 3-3.5 hours during each tidal inundation. The vegetation mainly occupies two zones: a 150-200 m wide Scirpus lacustris zone close to the sea, and a 150 m wide Phragmites australis and Cyperus malaccensis var. brevifolius zone which extends from the intertidal zone to near the bank, Nowadays, Spartina alterniflora quickly invades the Shanyutan wetland and has become the single predominant species.
In order to clarify the characteristics of element ecological stoichiometry during litter decomposition, the decomposition of Spartina alterniflora and Cyperus malaccensis var. brevifolius litters was analyzed using mesh bags measurement from January to October in 2007. The results showed that the decomposition rate, nitrogen and phosphorus content of Spartina alterniflora litter were lower than those of Cyperus malaccensis var. brevifolius litter, but the caloric values of Spartina alterniflora litter were higher than those of Cyperus malaccensis var. brevifolius litter. The averaged values of C/N, C/P and N/P were 70.5 and 34.7, 2285.8 and 1210.4, 32.8 and 35.4 during the decomposition of Spartina alterniflora litter and Cyperus malaccensis var. brevifolius litter in near ditch habitat. The averaged values of C/N, C/P and N/P were 72.7 and 33.2, 2519.2 and 1167.0, 34.0 and 35.9 during the decomposition of Spartina alterniflora litter and Cyperus malaccensis var.
brevifolius litter in far ditch habitat. Compared with Cyperus malaccensis var. brevifolius litter, Spartina alterniflora litter had higher C/N, C/P and lower N/P in near and far ditch habitats. Spartina alterniflora litter had higher C/N and C/P, which indicated slower litter decomposition rates.