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

Phosphatase secretion by 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 (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.

Activities of four phosphatases were measured in 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 phosphatases were analyzed as releasing rate of product under a common laboratory condition.

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.

PME appears to be the main phosphatase for Quercus serrata to acquire phosphate from organic P. PyP and PhT are assumed to play supplementary roles 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.