Organic phosphorus utilization by wheat plants under sterile conditions

Abstract

An experiment was set up to make a critical assessment of the role of organic P (Po) in soil solution in the nutrition of wheat plants under sterile conditions. Three concentration gradients of Po (17.08, 27.31 and 37.61 μM l-1) were created in a sterilized Oxisol by fertilization with a soil solution prepared by a dry freezing technique and containing antibiotics to minimize microbial growth. Due to the high P fixing capacity of the Oxisol and high buffering capacity of inorganic P (Pi), as compared to Po, a negligible change in Pi concentration occurred, due to fertilization after equilibrium in soil solution. Phosphorus supply had a positive effect on dry matter and P concentration of the plants. Acid phosphatase secretion by plant roots was 5–11 times higher in Po treatments than in the respective Pi treatments. No alkaline phosphatase activity was detected, confirming the absence of microbial activity in our system. Net P inflow into plants was significantly higher in the Pi + Po treatments at all three Po concentrations than in the respective Pi (control) treatment, providing evidence for the role of Po in the P nutrition of plants. It was hypothesized that plants secrete phosphatases in response to the presence of Po in soil solution and Po might be responsible for the increase in P influx to wheat plants.