|XU, GUANGLI - Sichuan University|
|SINGH, SHARDENDU - University Of Maryland Eastern Shore (UMES)|
|LI, TAN - Sichuan University|
Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2016
Publication Date: 8/20/2016
Citation: Xu, G., Singh, S., Reddy, V., Barnaby, J.Y., Sicher Jr, R.C., Li, T. 2016. Soybean grown under elevated CO2 benefits the most at low temperature than at high temperature stress: varying response of photosynthetic limitations, leaf metabolites, growth, and seed yield. Journal of Plant Physiology. 205:20-32. doi: 10.1016j.jplph.2016.08.003.
Interpretive Summary: A low or high temperature often results in the loss of crop yield due to limitations to photosynthesis, reduced vegetative and reproductive growth. The episodes of heat and cold stresses are predicted to increase due to the projected changes in the climatic conditions. Temperature stresses, especially when they coincide with the reproductive stages of soybean growth, will minimize the beneficial effect of high atmospheric carbon dioxide (CO2), which is projected to double from the current level of 400 ppm by the end of the 21st century. Results showed that compared to the optimum temperature the limitation to photosynthesis was always greater at temperature stresses and elevated CO2 had no significant effect. Soybean growth and yield declined more at high than low temperature. Elevated CO2 did over-compensate the negative effect of temperature stress for biomass production, but only partially compensated for seed yield. The results will be of interest among researchers and agronomists attempting to enhance crop tolerance to temperature stress conditions at current and future atmospheric carbon dioxide concentration.
Technical Abstract: To evaluate the combined effects of temperature and CO2 on photosynthetic processes, leaf metabolites and growth, soybean (Glycine max (L.) Merr.) was grown under controlled environment at low (22/18°C, LT), optimum (28/24°C, OT) and high (36/32°C HT) temperatures during reproductive stages at ambient (400 µmol mol-1; aCO2) or elevated (800 µmol mol-1; eCO2) CO2 concentrations. In general, stomatal (gs) and mesophyll (gm) conductance, quantum yield of photosystem II, maximum carboxylation (VCmax) and rate of electron transport (J) increased with temperature across CO2. However, compared to OT, the percentage increase at HT was smaller than the observed decline at LT. Photosynthetic limitations at LT or OT was primarily caused by photo-biochemical processes (49-58%, Lb) followed by stomatal (27-32%, Ls) and mesophyll (15-19%, Lm) limitations. Whereas at HT it was primarily caused by Ls (41%) followed by Lb (33%) and Lm (26%). The differences in the dominance of a specific limitation appeared to be associated with the accumulation of non-structural carbohydrates (e.g. starch) and several organic acids in leaves at lower temperatures. Whereas this accumulation did not occur at HT indicating increased metabolic activities. Compared to OT, biomass and seed yield declined more at HT than LT. The eCO2 over compensated the effect of temperature stresses for biomass but only partially compensated for seed yield at high temperature. Photosynthetic acclimation at eCO2 was revealed by accumulation of non-structural carbohydrates and insignificant effect or decrease in the gs, gm, VCmax or J resulting in the lack of CO2 effect on photosynthetic limitations across temperature regimes. Thus, photosynthetic limitations were mainly temperature dependent and primarily influenced by the alteration in photo-biochemcial processes and metabolic activities.