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

Satoshi Kogawara (1, 2), Mariko Norisada (3), Takeshi Tange (1), Hisayoshi Yagi (4) and Katsumi Kojima (3)

1. Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan / 2. Corresponding author (kogawara@fr.a.u-tokyo.ac.jp) / 3. Asian Natural Environmental Science Center, The University of Tokyo, Tokyo 113-8657, Japan / 4. Faculty of Bioresources, Mie University, Mie 514-8507, Japan / Received August 19, 2004; accepted April 1, 2005; published online October 3, 2005

Summary

We demonstrated that the inorganic phosphate (P_i) 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 P_i supply are also altered. To investigate the growth response of non-mycorrhizal seedlings to P_i 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 P_i was saturated at about 0.1 mM P_i, whereas in elevated [CO₂], the growth response to P_i supply did not saturate, even at the highest P_i 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 P_i supply. The enhanced P_i requirement in elevated [CO₂] was not associated with a change in photosynthetic response to P_i or a change in leaf phosphorus (P) status. We investigated the effect of P_i 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 P_i 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 P_i supply but did not change in elevated [CO₂]. We conclude that, because elevated [CO₂] increased the P_i requirement for shoot growth, the significance of the ectomycorrhizal association was also increased in elevated [CO₂].

Keywords: ectomycorrhiza, ergosterol, photosynthesis, P_i requirement, root exudates.

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ISSN 0829-318X Copyright © 2002–2008 Heron Publishing

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