Effects of Soil Physical and Chemical Properties on Soil Nitrogen and Phosphorus Fractions in Mangrove Wetland of the Pearl River Estuary

The typical artificial secondary mangrove wetland in the estuary of Pearl River has been chosen as the research object. A total of 48 soil samples have been collected at the soil profiles of 30 cm (10 cm for every layer) of the 16 places in Guangzhou Nansha Mangrove Wetland Park and Zhuhai Qiao Island Mangrove Nature Reserve. The indexes, such as TN, AN, TP, AP, pH, Granularity, OM, OC and Water content, have been tested. The results shows that the mass fraction of TN in the area ranges from 0.39 to 0.94 gkg-1 and the average value is 0.67 gkg-1. Moreover, AN ranges from 60.36 to 98.12 mgkg-1 and the average value is 75.63 mgkg-1. TP ranges from 0.39 to 0.94 gkg-1 and the average value is 0.67 gkg-1. AP ranges from 4.02 to 62.14 mgkg-1 and the average value is 20.04 mgkg-1. N/P ranges from 1.59 to 3.27 and the average value is 2.13. AN/AP ranges from 1.24 to 18.07 and the average value is 6.26. Those indexes stand at the medium level. Total nitrogen was positively correlated with organic carbon and total phosphorus (R2=0.826); organic nitrogen was positively correlated with sand ratio (R2=0.225); total phosphorus was positively correlated with total nitrogen, water content and available phosphorus, and negatively correlated with sand ratio (R2=0.838); available phosphorus is positively correlated with total phosphorus, sand, and total nitrogen, negatively correlated with organic matter (R2=0.754); N/P is positively correlated with organic carbon; negatively correlated with water content (R2=0.414); effective N /P is negatively correlated with cosmid and organic carbon (R2=0.285). The soil in this area is nitrogen-restricted, which is unfavorable for the recovery of mangrove growth at this stage. The overall quality of the soil can be improved by proper nitrogen addition.