Mechanisms of phosphorus acquisition for ponderosa pine seedlings under high CO2 and temperature

To test the hypothesis that elevated atmospheric CO2 and elevated temperature, simulating current and predicted future growing season conditions, act antagonistically on phosphorus acquisition of ponderosa pine, seedlings were grown in controlled-environment chambers in a two temperature (25/10 degrees C and 30/15 degrees C)xtwo CO2 (350 and 700 mu l(-1)) experimental design. Mycorrhizal seedlings were watered daily with a nutrient solution with P added in organic form as inositol hexaphosphate (64ppm P). Thus seedlings were challenged to use active forms of P acquisition. Elevated CO2 increased the relative growth rate by approx. 5% which resulted in an approx. 33% increase in biomass after 4 months. There was no main effect of temperature on growth. Increased growth under elevated CO2 and temperature was supported by increases in specific absorption rate and the specific utilization rate of P. The contribution of mycorrhizae to P uptake may have been greater under simulated future conditions, as elevated CO2 increased the number of mycorrhizal roots. There was no main effect of temperature on root phosphatase activity, but elevated CO2 caused a decrease in activity. The inverse pattern of root phosphatase activity and mycorrhizal infection across treatments suggests a physiological coordination between these avenues of P acquisition. The concentration of oxalate in the soil increased under elevated CO2 and decreased under elevated temperature. This small molecular weight acid solubilizes inorganic P making it available for uptake. Increased mycorrhizal infection and exudation of oxalate increased P uptake in ponderosa pine seedlings under elevated CO2, and there was no net negative effect of increased temperature. The increased carbon status of pine under elevated CO2 may facilitate uptake of limiting P in native ecosystems. (C) 1997 Annals of Botany Company.