|Rascher, Uwe -|
|Biskup, Bernhard -|
|Leakey, Andrew D B -|
|Mcgrath, Justin -|
Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2010
Publication Date: July 1, 2010
Citation: Rascher, U., Biskup, B., Leakey, A.D.B., McGrath, J.M., Ainsworth, E.A. 2010. Altered Physiological Function, Not Structure, Drives Increased Radiation-Use Efficiency of Soybean Grown at Elevated CO2. Photosynthesis Research. 105(1):15-25. Interpretive Summary: The effects of elevated carbon dioxide on canopy structure and subsequent radiation use effiency were measured in a soybean canopy under open air conditions. Three dimensional maps of the soybean canopy were monitored during the day to investigate how carbon dioxide affected diurnal leaf movements and leaf orientation. Leaf level measurements of photosynthetic physiology were made concurrently. The results indicated that elevated carbon dioxide had little effect on leaf orientation and canopy structure, but significantly increased the rates of photosynthetic electron transport, thereby improving radiation use efficiency. This study provided a proof of concept for quantifying structure-function relationships in 3-dimensional canopies, and modeling the contribution of both leaf-level and canopy-level effects on energy conversion.
Technical Abstract: Previous studies of elevated carbon dioxide concentration ([CO2]) on crop canopies have found that radiation-use efficiency is increased more than radiation-interception efficiency. It is assumed that increased radiation-use efficiency is due to changes in leaf-level physiology; however, canopy structure can affect radiation-use efficiency if leaves are displayed in a manner that optimizes their physiological capacity, even though the canopy intercepts the same amount of light. In order to determine the contributions of physiology and canopy structure to radiation-use and radiationinterception efficiency, this study relates leaf-level physiology and leaf display to photosynthetic rate of the outer canopy. We used a new imaging approach that delivers three-dimensional maps of the outer canopy during the growing season. The 3D data were used to model leaf orientation and mean photosynthetic electron transport of the outer canopy to show that leaf orientation changes did not contribute to increased radiation-use; i.e. leaves of the outer canopy showed similar diurnal leaf movements and leaf orientation in both treatments. Elevated [CO2] resulted in an increased maximum electron transport rate (ETRmax) of light reactions of photosynthesis and increased capacity of nonphotochemical energy dissipation at high light. Modeling of canopy light interception showed that stimulated leaf-level electron transport at elevated [CO2], and not alterations in leaf orientation, was associated with stimulated radiation-use efficiency and biomass production in elevated [CO2]. This study provides proof of concept of methodology to quantify structure-function relationships in combination, allowing a quantitative estimate of the contribution of both effects to canopy energy conversion under elevated [CO2].