Abstract: Human activities have significantly altered the environmental N and P status through changing both supply level and ratio, with consequences on ecosystem structure and function. To explore the effects of N and P supply on plant community structure of coastal wetland in the Yellow River Delta, a field manipulation experiment combined three supply levels and three N:P supply ratios (5:1, 15:1, 45:1) was conducted in 2015 and 2016. The results showed that the amount of N and P supply had significant effects on species diversity, while N:P supply ratio had neither significant main effects nor interactive effects. Species richness and Shannon index was highest at medium nutrient level, while Pielou index was maximal at low nutrient supply. Dominant species responded differently to the variation of relative supply of N and P. Neither supply level nor N:P supply ratio significantly affected the importance values of Tripolium vulgare,Cynanchum chinenseandPhragmites australis. In contrast, supply level had significant effects on the importance values ofSuaeda glaucaandSuaeda salsa.With the increases of supply level, the importance value ofS. glaucaincreased while that of S. salsadeclined. Under different N and P supply treatments,S. glaucashowed strongest impacts on species diversity, followedbyS. salsa, while P. australias had little influence on species diversity. Meanwhile, the responses of theimportance values of dominant species and species diversity to changes of N and P supply were different between 2015 and 2016, suggesting that the effects of N and P supply condition on plant community structure of coastal wetland would be mediated by air temperature, precipitation and other natural conditions.

Key words: statolith, Xisha islands waters, Sthenoteuthis oualaniensis, trace element, South China Sea