Soil nutrient contents in Yellow River delta wetlands with different plant communities.

Soil nutrient contents were measured in 31 study plots of the supratidal zone wetland of Yellow River Delta(YRD)in order to reveal their changes in marsh soils with different plant communities.By the methods of spatial distribution as a substitute for time succession,different plant communities were chosen to substitute different periods of plant community succession.Results showed that there were obvious relationships among four plant communities and soil salt contents(SC)but there were no significant differences among water contents(WC),which also showed different succession periods of plant community to some certain.Along the positive succession direction of pant community,both the contents of soil organic matte(rSOM)and their variation coefficients showed the trend of"decreasing before increasing"along the water-salt gradients.The ratios of C/N were relatively higher in the middle of the successions than at the beginning or later stage.Total nitrogen(TN)contents showed an increase while NH4+ -N and NO3--N showed the trends of"decreasing after increasing".Total phosphorus(TP) contents had no significant variations with the succession.No significant differences were observed in total phosphorus(TP)and available phosphorus(AP)contents of wetland soils under four plant communities.The middle of the succession had the higher variation coefficients.In wetland soils under four plant communities,the ratios of C/N were all lower than 25.Correlation analysis showed that there were significantly positive correlations between TN、SOM and AP(P0.01).TP was significantly positively correlated with WC(P0.05).No significant correlations were found between NH4+ -N、NO3--N and TP with other soil properties.WC were significantly positively correlated with pH(P0.05) and both of them were negatively correlated with SC(P0.01).