|SINGH, SHARDENDU - University Of Maryland Eastern Shore (UMES)|
Submitted to: Photosynthetica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2016
Publication Date: 9/6/2016
Citation: Singh, S.K., Reddy, V., Fleisher, D.H., Timlin, D.J. 2016. Relationship between photosynthetic pigments and chlorophyll fluorescence in soybean under varying phosphorus nutrition at ambient and elevated CO2. Photosynthetica. 55:421-433. doi.org/10.1007/s11099-016-0657-0.
Interpretive Summary: Photosynthetic pigments such as chlorophylls and carotenoids capture solar energy that is used in photosynthetic processes in green leaves. The excess energy absorbed by chlorophyll molecules is harmful to photosynthetic apparatus and often reemitted as chlorophyll fluorescence and dissipated as heat. Phosphorus deficiency and elevated atmospheric carbon dioxide concentration (CO2) often have opposite effects on photosynthesis and their interaction might alter the leaf nutrient composition consecutively affecting the concentration of photosynthetic pigments and chlorophyll fluorescence emission. Although photosynthetic pigments and chlorophyll fluorescence are widely used to assess the relative impact of environmental stresses on the photosynthetic properties, studies evaluating their relationships are limited. A controlled environment experiment was conducted using a range of phosphorus nutrition under current and elevated CO2 to investigate the relationship between photosynthetic pigments and chlorophyll fluorescence in soybean. The chlorophyll concentration decreased under phosphorus-stress, but carotenoids concentration was stable indicating its possible role to protect photosynthetic apparatus from excess energy. It was also supported by the strongest correlation of chlorophyll fluorescence with chlorophyll/carotenoids ratio. This relationship was not affected by growth CO2 conditions. The results will benefit researchers by emphasizing the quantification of both chlorophyll and carotenoids concentrations in leaves to understand the photochemistry and underlying mechanisms of excess energy dissipation.
Technical Abstract: Photosynthetic pigments such as chlorophyll (Chl) a, Chl b and carotenoids concentration, and chlorophyll fluorescence (CF) have widely been used as indicators of stress and photosynthetic performance in plants. Although photosynthetic pigments and CF are partly interdependent due to absorption and re-remittance of solar energy in green leaves, studies on their relationships are limited. To assess the relationship between photosynthetic pigments and CF, soybean plants were grown in controlled environments at three levels of phosphorus (P) treatments (0.50, 0.10, 0.01 mM) under ambient and elevated CO2 (aCO2, 400 and eCO2, 800 µmol mol-1, respectively). A significant effect of treatments (P and CO2) on soybean was confirmed by the decrease in plant height, mainstem node number, and leaf area associated with reductions in the rates of stem elongation, node addition, and leaf area expansion under P deficiency. However, eCO2 stimulated these growth parameters. Under P deficiency, the estimated CF parameters, total Chl, Chl a, and Chl b concentrations decreased but carotenoids concentration was fairly stable indicating its possible role in photo protection in soybean. The CF parameters showed a good relationship with chlorophyll concentration but a relatively poor correlation with Chl a/b ratio or carotenoids. However, TChl/Carotenoids ratio showed the strongest linear relationship with CF parameters such as efficiency of energy harvesting by photosystem II reaction centers (r2 = 0.70) and photochemical quantum yield (r2 = 0.60). This relationship was not affected by growth CO2 conditions. The high correlation between TChl/Carotenoids emphasized the importance of the quantification of both chlorophyll and carotenoids concentrations to understand the photochemistry and underlying processes of minimizing photo protection mechanisms in a given environmental conditions.