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 C 3 invasive species Phragmites australis (Cav.) Trin. ex Steud.and of the C 4 native species Cyperus malaccensis var. brevifolius Boeckeler to investigate the effect of C 3 plant invasion on C, N, and P stoichiometry in the C 4 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 C 3 (P. australis) and C 4 (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.Communicated by William E Rogers.Electronic supplementary material The online version of this article

Application of electron acceptors to mitigate CH4 emissions form paddy fields deserves special attention, especially for ferric iron oxides as its dominant role over all other redox species. Silicate iron slag is a by-product of the steel industry.We added it in the experiemental sites of paddy fields in the Fuzhou Plain, a subtropical coastal plain region.. After the addition of the silicate iron slag, the soil showed a lower soil Eh and higher pH, especially at the early period of cultivation(about one week). CH4 emission during the cultivation period significantly decreased, about 26.4%, 43.3% and 48.9% for 2 Mg ha-1, 4 Mg ha-1and 8 Mg ha-1 silicate iron slag treaments, respectively. In conclusion, silicate iron slag could be considered as an effective method to mitigate CH4 emissions from subtropical paddy fields.

Wetlands are important sources of methane emission. Methane anaerobic oxidation, aerobic oxidation and production, and dissolved methane are important process of methane metabolism. We studied methane metabolism and the soil influencing factors. Potential soil methane production, anaerobic oxidation and aerobic oxidation rates, and dissolved methane in soil porewater changed seasonally and the annual average was 21.15.1 μg g-1 d-1 , 11.03.9 μg g-1 d-1 , 20.95.8 μg g-1 d-1 , and 62.920.6 μmol l-1 , respectively. Potential soil methane production and anaerobic and aerobic oxidation were positively correlated among them and with soil pH and negatively correlated with soil redox potential (Eh). Potential soil methane production and aerobic and anaerobic oxidation rates were negatively related to pore soil methane concentration. Thus, the more water saturated the soil (the lower Eh), the higher its capacity to methane production was, but even higher was soil potential capacity to methane oxidation both in the same anaerobic circumstances and when the soil was suddenly submitted to aerobic conditions. All these results suggested a buffer effect in the methane balance in wetland areas, the environmental circumstances favoring methane production are also favorable to methane anaerobic oxidation.