Biogeochemical circulation and management countermeasures of N and P in coastal wetlands of southern Laizhou Bay Effects of Different Nitrogen Sources on Transformation and Availability of Inorganic Phosphorus in the Root-Soil Interface of Pinus thunbergii Seedlings Intraspecific Variations of Phosphorus Absorption and Remobilization, P Forms, and Their Internal Buffering in Brassica Cultivars Exposed to a P-Stressed Environment Study on the Relationship between 32P Absorption Vigour of Root Population and Canopy Apparent Photosynthetic Rate in Winter Wheat