Characteristics of Soil Phosphorus Fractions at Different Depths Across 4 Successional Stages in a Broadleaved Pinus koraiensis Forest

In order to explore the differences of soil phosphorus fractions in different forest community succession stages and different soil depths in broad-leaved Pinus koraiensis forest, the soil of broad-leaved P. koraiensis forest(natural Betula costata secondary forest, secondary broad-leaved forest, secondary coniferous and broad-leaved mixed forest and original broad-leaved P. koraiensis forest) in 4 different succession stages in Lesser Khingan Range was taken as the object to analyze the effects of different succession stages and different soil depths(0–10, 10–20, 20–40 cm) on soil phosphorus fractions(total phosphorus, available phosphorus, organic phosphorus and inorganic phosphorus). The findings demonstrate that with the progress of forest community succession, soil total phosphorus, available phosphorus, organic phosphorus, inorganic phosphorus, active organic phosphorus, moderately active organic phosphorus, Al-P and Fe-P showed a trend of first decreasing and then increasing, while moderately stable organic phosphorus, highly stable organic phosphorus, O-P and Ca-P showed a trend of first increasing and then decreasing. The contents of available phosphorus, moderately active organic phosphorus and Fe-P did not decrease significantly with the change of soil layer, and the content of Ca-P increased with the deepening of soil layer. The contents of total phosphorus, organic phosphorus, inorganic phosphorus, active organic phosphorus, moderately stable organic phosphorus, highly stable organic phosphorus, Al-P and O-P decreased with the deepening of soil layer.