Co-regulation of photosynthetic processes under potassium deficiency across CO2 levels in soybean: mechanisms of limitations and adaptations

Authors: SINGH, SHARDENDU - University Of Maryland Eastern Shore (UMES); Reddy, Vangimalla

Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2018
Publication Date: 2/24/2018
Citation: Singh, S., Reddy, V. 2018. Co-regulation of photosynthetic processes under potassium deficiency across CO2 levels in soybean: mechanisms of limitations and adaptations. Photosynthesis Research. https://doi.org/10.1007/s11120-018-0490-3.
DOI: https://doi.org/10.1007/s11120-018-0490-3

Interpretive Summary: Coordinated functions of plants photosynthesis-related traits are essential to capture light and atmospheric carbon dioxide (CO2) and to adjust metabolic processes for maximum photosynthesis. The rising CO2 often benefits, but potassium (K) deficiency adversely affects plant photosynthetic processes. Since photosynthesis contributes to the majority of plant biomass, understanding the mechanisms of limitations and adaptations under K deficiency are critical to enhancing crop productivity. To investigate this, soybean was grown under controlled environment with adequate and deficient levels of K supply under ambient and elevated CO2. Results showed a well coordinated regulation of photosynthesis traits such as CO2 diffusion in leaves, chlorophyll pigments, leaf absorption of light, photorespiration, and several metabolic processes with either a sustained rate of photosynthesis (amid ˜50% lower leaf K concentration) or with a down-regulated photosynthesis (when leaf K concentration further declined ˜85%). These results are useful to researchers and farmers to understand soybean photosynthesis response to the combination of K and CO2, highlight the importance of adequate soil K supply to minimize losses in crop yields, and provide insight to improve photosynthetic potential in K limited environment.

Technical Abstract: Plants photosynthesis-related traits are often co-regulated to capture light and CO2 to optimize the rate of CO2 fixation (A) via photo-biochemical processes. However, potassium (K) limitations and adaptations strategies of photosynthetic processes across CO2 levels are not well understood. To evaluate this, soybean plants were grown under controlled conditions with an adequate (control, 5.0 mM) and two deficient (0.50 and 0.02 mM) K levels under ambient (aCO2; 400 µmol mol-1) and eCO2 (800 µmol mol-1). Results showed that under 0.02 mM K, pigments, leaf absorption, processes of light and dark reactions, and CO2 diffusion (DL) through stomata (Ls) and mesophyll (Lm) were down co-regulated with A while light compensation point, photorespiration, alternative electron fluxes, and respiration were up-regulated. However, under 0.5 mM, these traits were well co-regulated with the sustained A with no apparent limitations amid ˜50% reduction in leaf K level. Primary (>50%) mechanisms of K limitation to A under control and 0.5 mM K was biochemical processes (Lb) while under 0.02 mM K was the DL with greater impacts of Lm than Ls. The eCO2 increased DL while lessened the Lb under K deficiency. Adaptation strategies under severe K deficiency (0.02 mM K) were reductions of photosynthetic pigments and light absorption and the down-regulation of photochemical quenching while up-regulation of photorespiration and electron fluxes to alternative sinks, and by optimizing metabolic processes to enhance K utilization efficiency (KUE). The eCO2 stimulated A and KUE when K deficiency was not severe. Thus, plant responded to K deficiency by a coordinated regulation of photosynthetic processes to optimize A and eCO2 failed to alleviate the DL in the severely K-deficient plants.