Application of the electrostatic precipitator (ESP) dust to soil and leaves of Cajanus cajan, Vigna mungo, Vigna radiata, Vigna catjung and Glycina max increased biomass, chloroplast pigments, Chemical constituents and enzyme activities of leaves, besides crop productivity evidently indicating that the dust acted as a fertilizer. The net photosynthetic rate, photosystem 2 activity and rate of transpiration were not altered in špite of the dust forming a thin uniform coating ověř the leaf surface. The contents of intermediary N-compounds like allantoin, allantoic acid and total ureides of the leaves, which might serve as an indirect evidence of symbiotic N2-fixation, were higher in the treated plants. There were increments in free proline, soluble proteins, total nitrogen, nitrates, nitrites, soluble sugars and phenols in the treated plants. The concentrations of ffee amino acids, soluble starch, total sucrose and water soluble SH compounds of the leaves of the control and treated plants did not show any significant difference. The activity of superoxide dismutase was significantly higher which possibly indicated its role in alleviation of H2O2 and Oj toxicity. Enzymes like nitráte reductase, nitrite reductase, glutamine S3mthetase, acid and alkaline phosphatases, carbonic anhydrase, catalase, glutathione reductase and ascorbate peroxidase also functioned normally. In the treated plants, the concentration of ascorbic acid was significantly higher in the roots and nodules indicating the possible role of ascorbic acid in stress alleviation.
The effect of CO2 increase on gas exchange and water-use effíciency (WUE) in three temperate deciduous species (Fagus crenata, Ginkgo biloba and Alnus firma) under gradually-developing drought-stress was assessed. Seedlings were grown within transparent open-top cabinets and maintained for 4 monťhs at mean CO2 concentrations of either 350 (ambient; C350) or 700 pmol moT’ (elevated; C700) and combined with five water regimes [leaf water potential, higher than -0.3 (well- watered), -0.5 and -0.8 (moderate drought), -1.0 and lower than -1.2 MPa (serious drought-stress)]. Increase in CO2 concentration induced a 60 % average increase in net photosynthetic rate (P^) under well-watered conditions. The effect of C700 became more pronounced with drought stress established, with an 80 % average increase in at as low as -0.8 MPa; leaf conductance to water vapour transfer (gs) and transpiration rate (£), however, were significantly decreased. Consequently, WUE increased under drought, through drought stress affected potential E sooner than potential P^. The interaction of CO2 x drought stress on WUE was significant in that Pn was stimulated while E in C700 enriched plants resembled that of C350 plants under drought. Hence if a doubling of atmospheric CO2 concentration occurs by the mid 2U* century, then greater P^ in F. crenata, G. biloba and^. firma may be expected and the drought susceptibility of these species will be substantially enhanced.
Within each mango (Mangifera indica L.) tree there is a diversity in flowering ability among its terminál branches. Significant variations in net photosynthetic rate (Pn), transpiration rate, stomatal conductance (gj) and mesophyll efficiency (mesophyll capacity to fix CO2) were observed generally among the productive branches. However, the extent of variation was more pronounced in trees with irregular bearing habits (cv. Langra) as compared to regular bearers (cv. Romani). In generál, correlation coefficients indicated that variations in among n5 branches were mainly due to the mesophyll efficiency and g^, In regular bearing trees, the narrow range of variation in was related to a better mesophyll capacity. This in tum might result in higher carbon build-up of 05 branches which would háve helped them to flower regularly with minimum branch to branch variations.
Soybean [Glycine max (L.) cv. Jack] grown in open top chambers under controlled laboratory and field conditions was ušed to study the acclimation of leaf gas exchange processes to CO2 enrichment. Air inside the open top chambers was maintained at either 700-800 or 350-400 pmol(C02) mol'^(air). Leaf gas exchange rates were measured for some plants switched between treatments. When measmed in the C02-emiched atmosphere, stomatal conductances (gg) were higher in leaves grown in C02-enriched atmospheres than in those grown under ambient conditions, and the lower gg values for plants in the C02-enriched atmospheres were limiting to leaf net photosynthetic CO2 exchange rates (Pn). of enriched leaves was higher than those of the ambient Controls when measured at elevated CO2 levels in both controlled environment and field studies, while it was depressed in enriched leaves when measured imder ambient CO2 conditions, and this drop in Pn did not recover until 6-15 d after plants were placed back in ambient conditions.