Effects of phosphorus and ectomycorrhiza on maritime pine seedlings (Pinus pinaster)

Abstract

The purpose of this study was to determine how ectomycorrhizal infection and phosphorus nutrition affect biomass, photosynthesis and root respiration in the host plant. Maritime pine (Pinus pinaster Soland. in Ait.) seedlings grown in containers filled with perlite–vermiculite were inoculated with the ectomycorrhizal fungus Hebeloma cylindrosporum (strain D3.25.9) and given 0 or 0.5 mM phosphate in the nutrient solution. Hebeloma cylindrosporum infection increased net photosynthesis and root respiration rates compared with those of non-mycorrhizal plants, but there was an accompanying 35 % depression in growth. The addition of phosphorus to non-mycorrhizal plants induced a rise in tissue phosphorus content which made them similar m that respect to mycorrhizal plants but did not result in increased photosynthesis. The nitrogen content of mycorrhizal plants was, moreover, lower than that of the control group. The data recorded were consistent with the photosynthate source-sink hypothesis. The increase in fixed carbon in mycorrhizal plants was unable to compensate for the increased carbon cost of the mycorrhizal root system.