Photosynthetic capacity and effect of drought on leaf gas exchange in two rubber (Hevea brasiliensis) clones
Krissada Sangsing(Department of Agriculture, Bangkok (Thailand). Office of Agricultural Research and Development Region 7. Surat Thani Rubber Research Center) | Roux, Xavier Le(UMR Ecologie Microbienne des Sols (CNRS-University Lyon 1), Villeurbanne (France)) | Poonpipope Kasemsap(Kasetsart University. Bangkhen Campus, Bangkok (Thailand). Faculty of Agriculture. Department of Agronomy) | Sornprach Thanisawanyangkura(Kasetsart University. Bangkhen Campus, Bangkok (Thailand). Faculty of Science. Department of Botany) | Kumut Sangkhasila(Kasetsart University. Bangkhen Campus, Bangkok (Thailand). Faculty of Agriculture. Department of Soil Science) | Gohet, Eric(Kasetsart University. Bangkhen Campus, Bangkok (Thailand). Doras Center, Cirad-cp Rubber Program) | Thaler, Phillipe(Kasetsart University. Bangkhen Campus, Bangkok (Thailand). Doras Center, Cirad-cp Rubber Program)
Photosynthetic capacity, water-use efficiency and nitrogen-use efficiency were compared between two different rubber clones, PB 260 and PB 217. Plants were grown in 50 cubic dm pots in a greenhouse at Clermont-Ferrand, France under controlled condition. Net CO2 assimilation rate at 1800 ppm CO2 (A sub(1800)) and at 360 ppm CO2 (A sub(360)), maximum carboxylation rate (V sub(cmax)), electron transport capacity (J sub(max)) and nitrogen-use efficiency (A sub(1800)/N sub(a), A sub(360)/N sub(a), V sub(cmax)/N sub(a) and J sub(max)/N sub(a)) of clone PB 260 were significantly higher than those of clone PB 217. However, the dark respiration rate (R sub(d)), the ratio of lightsaturated rate of electron transport and maximum rate of carboxylation (J sub(max)/V sub(cmax)), leaf mass per area (M sub(a), leaf nitrogen content (N sub(m)), leaf nitrogen per area (N sub(a)), water use efficiency (WUE), SPAD value (SPAD) and chlorophyll fluorescence ratio (F sub(v)/F sub (m)) were non- significantly different between these clones. Effects of drought on leaf gas exchange rates was also studied. Net CO2 assimilation rate (A), stomatal conductance (g sub(s)) and transpiration rate (E) showed a declining curve as a function of increased water stress. WUE was high under severe stress, due to a more rapid decrease of E than A. At 14 days after stress, gs and E decreased by 80-85 percent, while A decreased by 60-70 percent. Drought also reduced leaf water potential, which was possitively related to stomatal conductance. These results confirmed the potential genotypic variability of some photosynthetic traits under non-water-limited condition and stomatal behavior related with hydraulic properties during water stress in rubber trees.
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