Low phosphorus effects on the metabolism of rice seedlings

Abstract

Phosphorus‐stress‐induced (Psi) changes in shoot and root phosphorus (P) content (SPC and RPC) and use efficiency (SPUE and RPUE) defined as dry biomass production per unit of absorbed P, root acid phosphatase activity (RAPA), and excreted acid phosphatase activity (EAPA), were investigated for 5 rice genotypes under P‐sufficient (10 ppm Pi) and P‐stressed (0.5 ppm Pi) solution culture conditions. Genotypic tolerance to P‐stress was assessed based on less decrease in shoots and roots P content and larger increase in shoots and roots P use efficiency with decreasing P concentration from 10 ppm to 0.5 ppm in the culture solution. Plants were harvested 2 and 4 weeks after growing, respectively, for the parameter measurements. Significant (#0.01) genotypic differences in SPC and RPC were observed under P‐sufficient and P‐stressed conditions with the differences decreasing with length of growing period. On the contrary, significant (#0.01) genotypic differences in SPUE and RPUE were only found under P‐stress condition, but not under P‐sufficient condition, suggesting that genotypic variation in tolerance to P‐stress in terms of PUE could be screened under P‐stress conditions. More than 2‐fold genotypic differences in Psi‐RAPA and Psi‐EAPA were obtained after 2 weeks, followed by a decrease in Psi‐EAPA, but not in Psi‐RAPA. After 2 weeks, Psi‐EAPA was highly correlated to decrease in SPC and decrease in RPC measured after 2 and 4 weeks, respectively. Significant negative correlations were also found between decrease in SPC and increase in RPUE, and between decrease in SPC and decrease in RPC. The implications of these results in evaluating rice genotypic tolerance to P‐stress is discussed.