Phosphorus Fractionation And Availability At Typical Stages Of Forest Succession Under Hilly Red Soil In Mid-subtropical Region

Phosphorus (P) is an essential nutrient for plant growth. P takes part in plant lifecycle in various forms. Because of non-renewable and inferior availability, P is the most crucial limiting nutrient factor for plant growth in terrestrial ecosystem especially in red soil region. Available P in soil can be easily adsorbed and rooted by soil particles, organic matters and other minerals, while more than 95% of total P in soil exist as slow acting forms, little portion of total P takes part in biological cycle. So it is quite important to study P availability for vegetation restoration and forest management.Four typical stages of forest succession including bare hillside, coniferous forest, mixed forest of conifer and hardwood tree, and evergreen broad-leaved forest were selected under hilly red soil in middle subtropical region in Nanchang university. Imporved Hedley method was selected to study soil P fractionation and availability, and N and P supply processes and their interactions. The main results are:(1) Most P forms in soil showed an obvious season fluctuation, and total available P showed the tendency of fall > summer > spring > winter.(2) Most P forms except sonic-P showed the tendency with the direct forest succession as broad-leaved forest > mixed forest > coniferous forest > bare hillside.(3) Soil NaOH-P showed the increasing tendency with direct forest succession, range from 5.7μg /g to 30μg /g. Meanwhile, NaOH-P is the highest value of P forms and also the main available P pool in four typical stages of forest succession.(4) Total P, available P and labile P in 0-15cm soil surface increased consistently with the direct forest succession, range from 160μg/g to 530μg/g, 13.8μg /g to 105μg /g, 1.4μg /g to 10.7μg /g, respectively. Therefore, soil P supply and availability were improved during the process of forest succesion.(5) Soil N/P ratio increased from bare hillside to mixed forest and decreased from mixed forest to broad-leaved forest, while the ratio of annual mineralization rate to available P and annual mineralization rate to labile P increased constantly. It suggested that N and P supply were optimized with forest succession, but the limitation of P was more serious than N in the primary stages of forest succession.We suggest that vegetation restoration is in favor of soil N and P supply improvement. It is feasible and effective that broad-leaved forest is considered as the final purpose of vegetation restoration at hilly red soil in mid-subtropical region.