EFFECTS OF VA MYCORRHIZAL COLONIZATION ON PHOTOSYNTHESIS AND BIOMASS PRODUCTION OF TRIFOLIUM-REPENS L

The influence of vesicular-arbuscular mycorrhizal (M) colonization on biomass production and photosynthesis of Trifolium repens L. was inves tigated in two experiments in which the foliar nitrogen and phosphorus contents of nonmycorrhizal (NM) plants were manipulated to be no lowe r than that of M plants. Throughout both experiments there was a stimu lation in the rate of CO2 assimilation of the youngest, fully expanded leaf of M compared with NR?I plants, In addition, M plants exhibited a higher specific leaf area compared with NM plants, a response that m aximized the area available for CO2 assimilation per unit of carbon (C ) invested, Despite the increased rate of photosynthesis in hi plants there,vas no evidence that the additional C gained was converted to bi omass production of M plants. It is suggested that this additional C g ained by colonized plants was allocated to the mycorrhizal fungus and that it is the fungus, by acting as a sink for assimilates, that facil itated the stimulation in the rate of photosynthesis of the plant part ner.