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Title:The maximum quantum efficiency of CO2 assimilation declines with depth in the canopies of the C4 crops Miscanthus x giganteus and Zea mays
Author(s):Pignon, Charles
Advisor(s):Long, Stephen P.
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):light distribution
C4 photosynthesis
Miscanthus x giganteus
CO2 leakage
Abstract:Leakage of CO2 from bundle sheath cells of C4 plants (φ) could limit their productivity. φ is thought to increase at low light in the C4 crop Miscanthus x giganteus (M. x giganteus) (Kromdijk et al., 2008). This should reduce photosynthetic light use efficiency (PLUE) in the lower canopy. Zea mays (Z. mays), a close relative, may share this problem. Measurements were taken on healthy upper and lower canopy leaves of M. x giganteus and Z. mays, and isolated aging leaves of M. x giganteus. The maximum quantum yield of CO2 assimilation (ΦCO2, max) was derived from the initial linear slope of the responses of leaf CO2 uptake (A) to photon flux (Q) corrected for leaf fractional light absorptance (α) measured in an integrating sphere. In addition, dark-adapted maximum quantum yield of photosystem II (PSII; ΦPSII, max), operating yields of CO2 assimilation (ΦCO2), and PSII photochemistry (ΦPSII) were determined. These allowed calculation and analysis of electron transport rate (J) and the proportion of maximal PSII capability used during light exposure (qP). In both species, A is greater in the upper canopy at all light levels and ΦCO2,max in the lower canopy leaves is significantly less despite minor variations in ΦPSII, max and an increase in α in M. x giganteus. The inverse of the slope of A* to J at low light is greater in the lower canopy, showing that more electrons are needed to assimilate CO2 here, which could result from alternative electron sinks such as increased φ. When leaves are artificially maintained in high light, even at 60 days there is no decrease in ΦCO2, max, showing that this loss is not the result of aging, but attributable to a developmental response to the altered light quality and quantity as they transition to the lower canopy. While this appears to be a maladaptation in both crops, the impact on overall carbon gain at the canopy level is shown to be small.
Issue Date:2013-05-24
Rights Information:Copyright 2013 Charles Pignon
Date Available in IDEALS:2013-05-24
Date Deposited:2013-05

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