Effects of genotype on the response of Populus tremuloides michx. To ozone and nitrogen deposition

Elevated O 3 concentrations and N deposition levels co -occur in much of eastern United States. However, very little is known about their combined effects on tree growth. The effects of three O 3 treatments: charcoal-filtered air, non-filtered air and O 3 , added at the rate of 80 ppb for 6 hr d −1 3 d per week), four N deposition levels (0, 10, 20 and 40 kg ha −1 yr −1 ), and their interactions on growth of two Populus tremuloides clones in open-top chambers at two sites 600 km apart in Michigan were examined. Our results revealed a highly significant fertilization effect of the N treatments, even at the 10 kg ha −1 yr −1 rate. Ozone alone induced foliar injury, but not significant growth reductions. There was an indication that O 3 decreased growth at the O N level, but this decrease was reversed in all N treatments by the N fertilization effect. Further study is needed to more fully understand the combined effects of N deposition and O 3 .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43906/1/11270_2004_Article_BF00480254.pd

Plântulas de soja 'Tracajá' expostas ao ozônio sob condições controladas

The objective of this work was to assess initial growth, biomass production, gas exchange and antioxidative defenses of soybean 'Tracajá' seedlings, cultivated in the Amazonian region, exposed to ozone under controlled conditions. Seeds germinated in pots were placed in two chambers, one with filtered air (AF) and other with filtered air plus 30 ppb of ozone (AF + O 3). At 10 and 20 days after sowing, gas exchange, growth and biomass were measured; at 20 days after sowing, antioxidative defenses (ascorbic acid and superoxide dismutase) were analyzed. Net photosynthesis, stomatal conductance, transpiration rate, height, leaf area and biomass were 16, 27, 11, 22, 29 and 18% smaller, respectively, in AF + O3 at 10 days after sowing. At 20 days after sowing, besides this parameters, root length, stem diameter and root:shoot ratio were 10, 15 and 12% smaller, respectively, although ascorbic acid concentrations and superoxide dismutase activity increased. Soybean 'Tracajá' seedlings have low tolerance to concentration of 30 ppb of ozone