COS 204-6 - Intraspecific variations and control factors of fine-root phosphatase activities in Quercus serrata across a wide range of soil phosphorus gradient.

Abstract: Quercus serrata is a representative species of temperate forests in Japan and occurs across a wide range of soil phosphorus (P) gradient. In previous research, Quercus serrata forests in Japan showed an 8-fold difference in soil total P concentration. This suggests that there are adaptive mechanisms in this species to grow under contrasting soil P conditions. Trees secrete phosphatase from fine roots to hydrolyze soil organic P. There are four types of phosphatases, each specific to one soil organic P fraction (enzyme PME for monoester-P fraction, PDE for diester-P, PyP for pyrophosphate, and PhT for phytate). It is possible that P acquisition traits of Quercus serrata have intraspecific variation according to soil P status gradient. Our goal is to investigate intraspecific variations in the activities of four fine-root phosphatases and their control factors in Quercus serrata.

We sampled fine roots in 14 forests and measured the activities of four fine-root phosphatases. We considered the following factors which may control the phosphatase activities: soil organic P fraction (enzyme substrate), labile inorganic P (enzyme product), soil inorganic nitrogen (N) (enzyme resource), and leaf N:P ratio (tree demand for N vs P). We investigated the differences in the activities of each of the four fine-root phosphatases among 14 forests. A structural equation model (SEM) was derived to investigate the relations between the activities of four fine-root phosphatases and the control factors.

PME activity varied across forests and was the highest of the four in all forests. PDE activity did not vary across forests. PyP and PhT activities varied among forests, but the activities were consistently low. In the SEM, PME activity was negatively related to labile inorganic P (product of PME). PDE activity had a negative relation with monoester P (product of PDE).

Our results showed that there were intraspecific variations in fine-root phosphatase activities (PME, PyP, and PhT) in Quercus serrata. The main P acquisition pathway from organic P is via PME, and its activity is probably co-regulated by PDE. Both PME and PDE may be regulated by the concentration of enzyme products. Enzyme products seem to be important control factors for fine-root phosphatase activities. We suggest that Quercus serrata regulates the activities of fine-root phosphatase in response to control factors (enzyme products) either as adaptation or acclimation. This regulation mechanism may enable Quercus serrata to acquire P stably and to widely distribute across a wide soil P gradient.