SYMBIOTIC VESICULAR-ARBUSCULAR MYCORRHIZAE INFLUENCE MAXIMUM RATES OFPHOTOSYNTHESIS IN TROPICAL TREE SEEDLINGS GROWN UNDER ELEVATED CO2

To investigate the importance of phosphorus and carbohydrate concentra tions in influencing photosynthetic capacity of tropical forest tree s eedlings under elevated CO2, we grew seedlings of Beilschmiedia pendul a (Sw.) Hemsl. (Lauraceae) under elevated CO2 concentrations either wi th or without vesicular-arbuscular (VA) mycorrhizae. VA-mycorrhizae in creased phosphorus concentrations in all plant organs (leaves, stems a nd roots). Maximum rates of photosynthesis (A(max)) measured under sat urating levels of CO2 and light were correlated with leaf phosphorus c oncentrations. VA-mycorrhizae also increased leaf carbohydrate concent rations, particularly under elevated CO2, but levels were low and with in the range observed in naturally occurring forest species. Root carb ohydrate concentrations were reduced in VA-mycorrhizal plants relative to non-mycorrhizal plants. These results indicate an important role f or VA-mycorrhizae in controlling photosynthetic rates and sink strengt h in tropical trees, and thus in determining their response to future increases in atmospheric CO2 concentrations.