Elevated atmospheric CO2 concentration alters the effect of phosphate supply on growth of Japanese red pine (Pinus densiflora) seedlings

Abstract

We demonstrated that the inorganic phosphate (Pi) requirement for growth of Japanese red pine (Pinus densiflora Sieb. & Zucc.) seedlings is increased by elevated CO2 concentration ([CO2]) and that responses of the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker & Couch to Pi supply are also altered. To investigate the growth response of non-mycorrhizal seedlings to Pi supply in elevated [CO2], non-mycorrhizal seedlings were grown for 73 days in ambient or elevated [CO2] (350 or 700 μmol mol-1) with nutrient solutions containing one of seven phosphate concentrations (0, 0.02, 0.04, 0.06, 0.08, 0.10 and 0.20 mM). In ambient [CO2], the growth response to Pi was saturated at about 0.1 mM Pi, whereas in elevated [CO2], the growth response to Pi supply did not saturate, even at the highest Pi supply (0.2 mM), indicating that the P i requirement is higher in elevated [CO2] than in ambient [CO2]. The increased requirement was due mainly to an altered shoot growth response to Pi supply. The enhanced Pi requirement in elevated [CO2] was not associated with a change in photosynthetic response to Pi or a change in leaf phosphorus (P) status. We investigated the effect of Pi supply (0.04, 0.08 and 0.20 mM) on the ectomycorrhizal fungus P. tinctorius in mycorrhizal seedlings grown in ambient or elevated [CO2]. Root ergosterol concentration (an indicator of fungal biomass) decreased with increasing Pi supply in ambient [CO2], but the decrease was far less in elevated [CO2]. In ambient [CO2] the ratio of extramatrical mycelium to root biomass decreased with increasing Pi supply but did not change in elevated [CO2]. We conclude that, because elevated [CO2] increased the Pi requirement for shoot growth, the significance of the ectomycorrhizal association was also increased in elevated [CO2]. © 2006 Heron Publishing.