Intraspecific variations in activities of four classes of fine root phosphatases in Quercus serrata, a dominant deciduous oak, occurring across a wide soil phosphorus gradient in Japan

Abstract

Abstract Background and aims Phosphatase secretion by fine roots is an important phosphorus (P) acquisition strategy for plants growing under soil P deficiency. Four different classes of phosphatases degrade specific fractions of soil organic P respectively (phosphomonoesterase, PME degrading labile monoester P; pyrophosphatase, PyP for pyrophosphate; phytase, PhT for phytate; and phosphodiesterase, PDE for diester P). We investigated how plants depend on these phosphatases and how their activities are regulated. Methods Activities of four classes of phosphatases were measured in fine roots of Quercus serrata, which is a dominant deciduous oak in Japan. Root samples were collected from 14 sites that formed a wide soil P gradient. Activities of four classes of phosphatases were analyzed as releasing rate of product by colorimetric methods under a common laboratory condition. Results Activities of the three phosphatases that produced phosphate as their end product (i.e. PME, PyP and PhT) showed significant inter-site variations, while PDE activity was invariant. PME activity was higher by one to two-order(s) of magnitude than the others in all sites. In structural equation modeling, PME activity was negatively related to the concentration of labile inorganic P in soils, implying that PME was regulated by its product but not by substrate. Conclusion Quercus serrata appears to be mainly dependent on PME and the other phosphatases are complementary to PME. The variations patterns of activities among sites probably reflect cost-benefit balance of acquiring phosphate in Q. serrata. This regulatory mechanism may allow Q. serrata to grow across a wide soil P gradient.