PJB-2005-114
MITIGATION OF SALINITY EFFECTS ON SESBANIA ACULEATA L., THROUGH ENHANCED AVAILABILITY OF CARBON DIOXIDE
F. AZAM, F. AZIZ*, M.H. SIAL*, M. ASHRAF* AND S. FAROOQ
Abstract
Experiments were conducted to assess the effect of CO2 on growth and nitrogen fixation in Sesbania aculeata L., under different salinity and water regimes. Salinization of soil led to decrease in different growth attributes of the plants. The negative effect of salinity was mitigated to a significant extent at elevated CO2. Growth and N content of the plants was better when grown at 25 than 15% soil moisture level. Roots of Sesbania were densely nodulated, the weight of nodules being reduced with the increase in salinity but more at higher moisture level. The analysis of shoot material for total N and 15N showed significant amounts of N2 being fixed by the plants. The shoot contained 23-67% of the N from fixation under different growth conditions and 33-77% from the soil. Contribution of biological fixed N to the total N content of shoots decreased with salinity but was more at higher moisture in all the cases. Enclosure of plants in the polyethylene chamber led to an increase in the contribution of biologically fixed N to the total N of shoots irrespective of the soil conditions. Soil salinity had in general a depressing effect on contribution of biologically fixed N suggesting a decrease in the rhizobial activity vis-à-vis decreased photosynthate supply to the root-zone. Significantly higher amounts of N seemed to have been fixed at 25% than 15% soil moisture. Elevated CO2 favoured N2 fixation leading to a greater contribution of fixed N to the total plant N.
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