Solubilization of aluminum-bound phosphorus by root cell walls: evidence from Chinese fir, Cunninghamia lanceolata

Abstract

This paper considered whether it was possible to activate nonavailable phosphorus (P) with tree root organs in lateritic soils. We investigated the cell wall content and P-solubilizing activity of xylem and phloem from six different sizes of roots from 10, 22, and 34 year old plantations of the Chinese fir Cunninghamia lanceolata (Lamb.) Hook. We found that, on average, cell wall content accounted for 81.07% of the root biomass (dry mass), and the mean solubilization of aluminum-bound phosphate by cell wall preparations was 1.89 g·kg−1. Tissue type (i.e., phloem or xylem) had a significant effect on cell wall content, with more cell wall material in the xylem, whereas P-solubilizing activity was greater in the phloem. In addition, the cell wall content of xylem increased with increasing root diameter, but P-solubilizing activity did not. A significant difference was also observed among the P-solubilizing activity of the three age classes, with lower P-solubilizing activity in the roots of 10 year old trees than in those of 22 and 34 year old trees. Since the establishment of Chinese fir plantations is increasing in southern China, where lateritic soils are widely distributed, the findings of the present study undoubtedly provide pertinent information for improving the utilization of nonavailable P by the cell walls of tree roots.