INCREASED CO2 AND NUTRIENT STATUS CHANGES AFFECT PHYTOMASS AND THE PRODUCTION OF PLANT DEFENSIVE SECONDARY CHEMICALS IN SALIX-MYRSINIFOLIA (SALISB)

The effect of CO2 enrichment (700 and 1050 ppm) on phytomass, soluble sugars, leaf nitrogen and secondary chemicals of three Salix myrsinifo lia clones was studied in plants cultivated at very poor (sand seedlin gs) and moderate (peat seedlings) nutrient availability and under low illumination. The total shoot phytomass production of sand seedlings w as less than 10% of that of the peat seedlings. Carbon dioxide increas ed the total shoot phytomass of peat seedlings. When the ambient carbo n supply was doubled (to 700 ppm) the growth of sand seedlings was sli ghtly enhanced but 1050 ppm CO2 gave growth figures similar to those a t the control CO2 level. Leaf nitrogen content and total soluble sugar contents were significantly higher in peat seedlings than in sand see dlings. Leaf nitrogen showed a decreasing trend in relation to CO2 inc rease. On the other hand, CO2 did not have any clear-cut effect on tot al sugars. At the control CO2 level the content of salicortin, which i s a dynamic phenolic, was higher in the peat seedlings than in the san d seedlings, but salicin showed the opposite trend. CO2 enrichment con siderably decreased these phenolics in the peat seedlings. At the cont rol CO2 level, the content of more static phenolics, such as proanthoc yanidins, was higher in sand seedlings. An increased carbon supply con siderably increased static phenolics in the peat seedlings. Willow def ence against generalist herbivores is moderately decreased by enhancem ent of atmospheric carbon dioxide.