PHYSIOLOGICAL-CHANGES IN SOYBEAN TREATED WITH OZONE AND MOLYBDENUM

An open-top field chamber experiment was conducted to evaluate the impact of Molybdenum (Mo) addition to soil on the physiological changes in soybean (Glycine max L. Merrill) exposed to ozone (O-3). Plants grown with Mo (0, 1.0, or 2.0 mg kg(-1) soil dry weight) were exposed to O-3 (0, 0.06, or 0.12 mu mol mol(-1)) in open-top field chambers for 12 h d(-1) for 21 d with a N-free fertilizer, during the sensitive growth stage (R2). The rate of photosynthesis (PN), specific root nodule nitrogenase activity (SNA), leaf nitrogen (N), chlorophyll (chl-a, chl-b) and biomass of soybean were measured. The increase in O-3 levels significantly reduced PN, SNA, leaf-N, chl-a, chl-b, and biomass. Addition of Mo increased leaf-N, shoot, root, and nodule dry weights but did not change PN, SNA, or chlorophyll. The addition of Mo (2 mg kg(-1)) helped in significantly increasing PN and chlorophyll in the presence of 0.06 mu mol mol(-1) O-3 but no change was observed in the presence of 0.12 mu mol mol(-1) O-3.