The low-light reduction in the quantum yield of photosynthesis: potential errors and biases when calculating the maximum quantum yield |
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Authors: | Johnson Zackary Barber Richard T |
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Institution: | (1) MIT Department of Civil and Environmental Engineering, 48-336A, Cambridge, MA 02139, USA;(2) Nicholas School of the Environment Marine Laboratory, Duke University, 135 Duke Marine Lab Rd, Beaufort, NC 28516, USA |
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Abstract: | Photosynthesis-irradiance (P-E) curves are widely used to describe photosynthetic efficiency and potential. Contemporary models assume maximal photosynthetic quantum yield ( ) at low irradiances. But P-E observations made with both oxygen evolution and carbon uptake techniques show that this is not always the case. Using new and published data in conjunction with modeling exercises, we demonstrate that regardless of the mechanism there can be reductions in at low irradiances that are not readily observable using conventional P-E analyses. We also show that analytical errors, such as inaccurate estimation of dark oxygen consumption or carbon uptake, can markedly affect the structure of -E curves with negligible effect on P-E curve structure. Whether from respiration `corrections' or other mechanisms, these deviations in at low light levels from the maximum quantum yield of photosynthesis ( max) can lead to significant errors (> 50%) in the estimation of the linear portion of the P-E curve and ultimately max. Non-linear models of P-E, such as the rectangular hyperbola, quadratic, exponential and hyperbolic tangent that are commonly used to estimate the initial slope ( ) of the P-E curve assume that is maximal at low light levels and therefore can err in the estimation of max when is reduced at low light levels. Using a diverse data set of 622 P-E curves with a total of 7623 points, we show that although model skills are high (r
2 = 0.96 ± 0.05, 0.97 ± 0.04, 0.97 ± 0.04 and 0.97 ± 0.04, respectively), a large fraction of the model-predicted max differ by greater than 10% from true max values (91%, 50%, 82% and 46%, respectively). Data from these observations and modeling exercises lead us to suggest that max be determined by directly estimating the true maximum of a -E curve rather than using the more conventional methodology employing the initial slope of the P-E curve.This revised version was published online in October 2005 with corrections to the Cover Date. |
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Keywords: | Emerson enhancement models P-E P-I photosynthetic quantum yield quantum efficiency |
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