Photosynthetic response of sweet potato (Ipomoea batatas) to photon flux density and elevated carbon dioxide

摘要

The continuous rise in the atmospheric CO_2 due to anthropogenic activities is likely to benefit crop species with C3 photosynthetic pathway by enhancing photosynthetic efficiency and crop productivity. This is particularly important in the context of climate change and food security of ever increasing population amidst scarcity of natural resources. In the search of photosynthetically efficient climate smart genotypes. In the present study, the net photosynthetic rate (Pn), stomatal conductance (gs) and intercellular CO_2 (Ci) was studied in twelve contrasting sweet potato genotypes, viz. Sree Arun, Sree Badhra, Sree Kanaka, Kanhangad, Pusa Safed, Pusa Red, Kisan, Gouri, Sankar and ST-13, S-1464 and S-1466 under ambient (400 ppm) and e CO_2 (e CO_2) (600, 800 and 1000 ppm) and the Pn at photosynthetic photon flux densities (PPFDs), viz. 200, 400, 600, 800, 1000, 1200 and 1500 (j.mol/m ~2/h at 30掳C and 400 ppm CO_2 using portable photosynthesis system. The maximum Pn of ten sweet potato genotypes was recorded at PPFD of 1500 jimol/m~2/s and the increase in Pn at PPFDs above 1000 jimol/m~2/s were insignificant. The Pn steadily increased due to short-term (ten minutes) exposure at eCO_2 concentrations between 400 ppm and 1000 ppm in twelve sweet potato genotypes. The sweet potato genotypes had the average Pn of 26.30, 33.41,38.02 and 40.32碌m ol/m~2/sat 400, 600, 800 and 1000 ppm CO_2 respectively. However, the per cent of increment in Pn at eCO_2 significantly declined (average 5.98%) at CO_2 concentrations above 800 ppm. The genotypes Gouri, Sankar, Sree Arun, and S1466 had 61.00 - 74.3% hike in Pn at e CO_2 (1000 ppm) as compared to ambient CO_2 (400 ppm). The per cent increment in Pn significantly decreased at CO_2 concentrations above 600 ppm. The differences in Pn were statistically significant across sweet potato genotypes and CO_2 concentrations (P>0.001), whereas the Pn had a quadratic relation with the increase in CO_2 concentration (R~2=0.603). The gs steadily decreased at e CO_2 concentrations. The sweet potato genotypes had the average gs of 0.606, 0.508, 0.431, 0.376 mol H_2O/m~2/s at 400, 600, 800 and 1000 ppm CO_2 respectively. The per cent of decrease in gs at e CO_2 significantly increased (average 38.33%) at 1000 ppm CO_2. The differences in gs were statistically significant across sweet potato genotypes and CO_2 concentrations (P锛?.001). The sweet potato genotypes had the average Ci of 271.50, 405.20, 543.00, and 684.00碌mmol CO_2/mol air at 400, 600, 800 and 1000 ppm CO_2 respectively. However, the per cent of increment in Ci at e CO_2 significantly declined (average 25.70%) at CO_2 concentrations above 600 ppm. The differences in Ci were statistically significant across sweet potato genotypes and CO_2 concentrations (P>0.001), whereas the Pn had a quadratic relation with the increase in Ci (R ~2=0.504). The interaction effect of genotypes and CO_2 concentration on Ci, Pn and gs was insignificant. The differences in the total chlorophyll and protein content in the leaves of sweet potato genotypes were statistically significant. Nevertheless, the gas exchange parameters were not influenced by the total chlorophyll and protein content.