Isolated and interactive effects of angular leaf spot (caused by Phaeoisariopsis griseola) and rust (caused by Uromyces appendiculatus) on leaf gas exchange and yield was studied in common bean (Phaseolus vulgaris L. cv. Carioca) plants. Gas exchange was measured on 37, 44, 51, and 58 d after planting using a portable photosynthesis system. The inoculation of plants with P. griseola (P), U. appendiculatus (U), and the combination of both pathogens (P+U) caused a significant reduction of net photosynthetic rate (PN) and yield. The reduction of stomatal conductance (gs), PN, and yield was higher under P and combination of P+U than under U treatment. By effect of U, the reduction on yield was higher than the reductions on gas exchange parameters. On the treatment P+U, a reduction of 23 % in PN and a correspondent reduction of 32 % in yield was observed. The interactive effects of the pathogens on yield could be explained in part by the decreases in gs and in PN of diseased bean leaves. The combined effect of both diseases on yield and gas exchange parameters suggests an antagonistic interaction. and W. C. Jesus Junior ... [et al.].
Leaf gas exchange characteristics were measured in twenty woody species that differ in succession status ranging from pioneer species (PS) to late succession species (LS) in a Brazilian rain-reforestation ecosystem. Photon-saturated photosynthetic rate, calculated per either a leaf area (PNA) or a dry mass (PNM) basis, differed among species. PNA and PNM were highest in PS and lowest in LS. Variation among species was 3-fold (from 7 to 23 μmol m-2 s-1) for PNA, and 5-fold (from 50 to 275 μmol kg-2 s-1) for PNM. The highest PNA (23 μmol m-2 s-1) and PNM (275 μmol kg-2 s-1) values were recorded in PS Croton urucurana, while the lowest PNA (7 μmol m-2 s-1) and PNM (50 μmol kg-2 s-1) values were recorded in LS Aspidosperma cylindrocarpon. A considerable overlap was recorded between PS and LS in values of stomatal conductance (gs), transpiration rate (E), and leaf mass to area ratio (ALM). However, C. urucurana also showed highest gs and E. PNM was highly correlated with ALM in both PS and LS (r=-0.75 and -0.90, respectively). The high values of instantaneous transpiration efficiency (ITE) and intrinsic water use efficiency (WUEi) were also observed in the PS when compared with the LS. and A. Nogueira ... [et al.].
Plants of Solanum curtilobum (from high altitude) and Solanum tuberosum (from low altitude) were grown in open-top chambers in a greenhouse at either ambient (AC, 360 µmol mol-1) or ca. twice ambient (EC, 720 µmol mol-1) CO2 concentrations for 30 d. CO2 treatments started at the reproductive stage of the plants. There were similar patterns in the physiological response to CO2 enrichment in the two species. Stomatal conductance was reduced by 59 % in S. tuberosum and by 55 % in S. curtilobum, but such a reduction did not limit the net photosynthetic rate (PN), which was increased by approximately 56 % in S. curtilobum and 53 % in S. tuberosum. The transpiration rate was reduced by 16 % in both potato species while instantaneous transpiration efficiency increased by 80 % in S. tuberosum and 90 % in S. curtilobum. Plants grown under EC showed 36 and 66 % increment in total dry biomass, whereas yields (dry mass of tubers) were increased by 40 and 85 % in S. tuberosum and S. curtilobum, respectively. EC promoted productivity by increasing PN. Thus S. tuberosum, cultivated around the world at low altitudes, and S. curtilobum, endemic of the highland Andes, respond positively to EC during the tuberisation stage. and N. Olivo, C. A. Martinez, M. A. Oliva.