Temporal variations in phosphorus fractions and phosphatase activities in rhizosphere and bulk soil during the development of Larix olgensis plantations

Abstract

Many studies have well reported nutrient deficiency and soil degradation focusing on soil N in pure plantations. However, few papers focused on soil P deficiency during pure plantation afforestation. We examined the variations in P fractions and phosphatase (P-ase) activities in the rhizosphere and bulk soils in Larix olgensis plantations of 16, 23, 34, and 49 y. Correlation analysis was applied to identify the relationships between available P and other P fractions and P-ase activities in the rhizosphere soil at different developmental stages. The stepwise regression models were established to explore their relationships with tree growth. The results showed that the deficiency of available P occurred in the rhizosphere micro-region relative to the bulk soil in the 34- and 49-y-old stands, which was related to the lower acid phosphatase activity, the deficient Fe-bound P, and occluded phosphate, as well as to soil pH in the rhizosphere soil during these periods. In addition, tree growth in the young and near-mature stands was significantly correlated with soil P fractions, and the main P fractions closely related to tree growth were total P, organic P, available P and inorganic P, followed by Ca-bound P and Fe-bound P. The decreases in average DBH and average height growth in the near-mature stand were related to the deficiency of available P in this period. Our results indicate that the development of Larix olgensis plantations affects the bioavailability of P through dynamic changes of P fractions and P-ase activities, which provides a theoretical base in future afforestation with Larix olgensis plantations.