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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Adaptive Cropping Systems Laboratory » Research » Publications at this Location » Publication #312382
Title: Methods of mesophyll conductance estimation: its impact on key biochemical parameters and photosynthetic limitations in phosphorus-stressed soybean across CO2

Author
item SINGH, SHARDENDU - University Of Maryland Eastern Shore (UMES)
item Reddy, Vangimalla

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2015
Publication Date: 3/16/2016
Citation: Singh, S.K., Reddy, V. 2016. Methods of mesophyll conductance estimation: its impact on key biochemical parameters and photosynthetic limitations in phosphorus-stressed soybean across CO2. Physiologia Plantarum. 157(2):234-254.

Interpretive Summary: Phosphorus as a primary nutrient exerts major control over plant photosynthesis response to rising atmospheric carbon dioxide concentration in soybean. One of the main limitations to plant photosynthesis is caused by restricted diffusion of carbon dioxide from atmospheric to interior of leaves. This study examines various limitations to photosynthesis in soybean grown at phosphorus sufficient and deficient conditions under ambient and elevated carbon dioxide concentrations. Results showed that photosynthesis was highly limited under phosphorus deficient condition but elevated carbon dioxide partially decreased this limitation. The results will be of interest to researchers attempting to enhance soybean photosynthesis and yield in phosphorus-deficient soils under future atmospheric carbon dioxide concentration.

Technical Abstract: Photosynthetic potential in C3 plants is largely limited by CO2 diffusion through stomata (Ls) and mesophyll (Lm) and photo-biochemical (Lb) processes. Accurate estimation of mesophyll conductance (gm) using gas exchange (GE) and chlorophyll fluorescence (CF) parameters of the photosynthetic processes is critical for the partitioning of these limitations. Phosphorus (P) deficiency decreases photosynthetic capacity but rising CO2 concentration is suggested to partly negate this effect. To test this idea and to evaluate the methods of gm estimation, soybean plants were grown in controlled environment with three levels of phosphorus (P) (0.50, 0.10 and 0.01 mM) each at ambient (aCO2, 400 µmol mol-1) and elevated (eCO2, 800 µmol mol-1) CO2 concentration. Both the GE and CF parameters declined with tissue P concentration, whereas eCO2 stimulated some of these parameters such as light saturated CO2 assimilation and quantum efficiency of photosystems. Maximum rate of electron transport (Jmax), trios phosphate utilization, Lm and Lb were unaffected by the methods of gm estimation. Despite the significant effect of methods on gm and maximum rate of carboxylation (VCmax), mostly common patterns of lower gm and VCmax in response to P and CO2 emerged. However, their magnitude and the VCmax response to CO2 varied among the methods. For instance, VCmax was highly inconsistent among methods when it was compared against the VCmax if determined assuming infinite gm. The decline in photosynthetic potential was mainly caused by Lb followed by Ls than Lm across phosphorus nutrition. The CO2 enrichment lessened the limitation caused by Lb but Ls and Lm remained largely unaffected. Acclimation/downregulation of soybean photosynthetic capacity at eCO2 was revealed due to reduction of gm, VCmax and Jmax. The results showed that photosynthetic limitation in P deficient soybean is primarily caused by photo-biochemical processes regardless of the methods used for gm estimation. However, the effect of methods on the extent of gm and VCmax might be a concern, especially when their absolute values are discussed to explain the underlying processes of photosynthesis.