ABSTRACT
The frequency of drought will increase under further warming. The increase in atmospheric CO2 concentration, along with more frequent drought, will affect crop growth. We examined the changes of cell structure, photosynthetic physiology, antioxidant enzymes, osmotic regulatory substances, and yield of foxtail millet (Setaria ita-lica) leaves under different CO2 concentrations (ambient air CO2 concentration and ambient atmospheric CO2 concentration + 200 µmol·mol-1) and water treatment (soil moisture content maintained at 45%-55%, and 70%-80% of field capacity, representing mild drought and normal water condition, respectively). The results showed that elevated CO2 concentration increased the number of starch grains, the area of single starch grains, and the total area of starch grains in the chloroplast of millet mesophyll cells. Under mild drought condition, elevated CO2 concentration increased net photosynthetic rate of millet leaves at the booting stage by 37.9%, but did not affect water use efficiency at this stage. Elevated CO2 concentration increased net photosynthetic rate and water use efficiency of millet leaves under mild drought condition at the filling stage by 15.0% and 44.2%, respectively. Under mild drought condition, elevated CO2 concentration increased the content of peroxidase (POD) and soluble sugar in millet leaves at the booting stage by 39.3% and 8.0%, respectively, but decreased proline content by 31.5%. It increased the content of POD in millet leaves at the filling stage by 26.5% but decreased the content of MDA and proline by 37.2% and 39.3%, respectively. Under mild drought condition, elevated CO2 concentration significantly increased the number of grain spikes by 44.7% and yield by 52.3% in both years compared with normal water condition. The effect of elevated CO2 concentration on grain yield under mild drought conditions was higher than that under normal water condition. Under mild drought conditions, elevated CO2 concentration increased leaf thickness, vascular bundle sheath cross-sectional area, net photosynthetic rate, and water use efficiency of millet, improved the antioxidant oxidase activity, and changed the concentration of osmotic regulatory substances, alleviated the nega-tive effect of drought on foxtail millet, and finally increased the number of grains per ear and yield of foxtail millet. This study would provide a theoretical basis for millet production and sustainable agricultural development in arid areas under future climate change.
Subject(s)
Setaria Plant , Setaria Plant/physiology , Carbon Dioxide , Antioxidants , Droughts , Proline , Starch/pharmacologyABSTRACT
Mechanisms underlying leaf photosynthetic acclimation in winter wheat under elevation of CO2 concentration ([CO2]) remain unclear. The aim of the study was to investigate the effects of source-sink variation on photosynthetic acclimation induced by drought under elevated [CO2]. A winter wheat (Triticum aestivum L. 'Zhengmai 9023') pot experiment was conducted in open top climate chambers with [CO2] of 400µmol·mol-1 or 600 µmol·mol-1 and soil water content at 80%±5% or 55%±5% of field capacity. The parameters of chlorophyll fluorescence, electron transport rate, photosynthetic curve, leaf nitrogen content, and grain yield were measured at the elongation and heading stages. Under drought condition, leaf PSâ ¡ photochemical efficiency was not affected by elevated [CO2], but the maximum electron transport rate and the ratio of electron partitioned to carboxylation reaction in Calvin cycle was increased at the elongation stage, and thus the Rubisco carboxylation rate and maximum photosynthetic rate were increased. Although the maximum electron transportation rate and partitioning ratio of electron to carboxylation reaction in Calvin cycle remained high at the heading stage, the PSâ ¡ photochemical efficiency, Rubisco carboxylation rate, and triose phosphate utilization rate were decreased by elevated [CO2], which consequently reduced the maximum photosynthetic rate for plant under drought stress. Under drought condition, elevated [CO2] increased wheat tiller biomass, kernel number, and kernel weight per ear, but decreased infertile kernel number, resulting in an overall increase in grain weight. In conclusion, the elevated [CO2]-induced increase in wheat grain yield per tiller under drought condition was mainly caused by enhanced photosynthetic performance at the elongation stage. The photosynthetic acclimation in source leaves during the heading stage under elevated [CO2] was mainly attributed to the reduction in PSâ ¡ photochemical efficiency and triose phosphate utilization rate, but not to the maximum electron transportation rate, ratio of electron partitioned to carboxylation in Calvin cycle or sink leaf strength.
Subject(s)
Droughts , Triticum , Acclimatization , Carbon Dioxide , Photosynthesis , Plant LeavesABSTRACT
We used an OTC (open top chamber) system to study the effects of elevated CO2 concentration (atmospheric CO2 concentration + 200 #x03BC;mol·mol-1) on the growth and photosynthetic physiology of Hylotelephium erythrostictum. Elevated CO2 concentration decreased the leaf stomatal density of the upper and lower epidermis of H. erythrostictum by 16.1% and 16.7%, respectively. Elevated CO2 concentration increased the vascular bundle in leaves and the cell volume near the upper epidermis. Elevated CO2 concentration significantly increased the photosynthetic pigments content, net photosynthetic rate, stomatal conductance and transpiration rate of H. erythrostictum at night. In the evening of initial flowering stage, elevated CO2 concentration significantly reduced the malic acid content by 64.0%, while increased cellulose content by 20.8%. In the morning of full flowering stage, elevated CO2 concentration significantly increased the malic acid content by 27.0%, but had no effect on carbohydrate content. Elevated CO2 concentration increased the number of branches per plant, stem mass and total biomass of H. erythrostictum. Elevated CO2 concentration was beneficial to the growth of H. erythrostictum.
