Extrapolating gross primary productivity from leaf to canopy scale in a winter wheat crop

Loss of photosynthetic efficiency in the shade. An Achilles heel for the dense modern stands of our most productive C4crops?

“…While these changes fit with expectations of shade acclimation (Boardman, 1977; Givnish, 1988; Björkman, 1981), loss of 14–29% of efficiency of photosynthesis in low light $({\Phi }_{{\text{CO}}_{\text{2}}\text{max,abs}})$ does not. A loss of low-light photosynthetic efficiency in shaded leaves was not seen in field crops in two separate studies of wheat (Hoyaux et al , 2008; Beyschlag et al , 1990). This parallels studies of non-crop plants.…”

“…${\Phi }_{{\text{CO}}_{\text{2}}\text{max,app}}$ was constant in all green leaves irrespective of leaf position and canopy depth in two independent studies of photosynthesis in field stands of modern cultivars of wheat ( Triticum aestivum L.) (Beyschlag et al , 1990; Hoyaux et al , 2008). Similarly, ${\Phi }_{{\text{CO}}_{\text{2}}\text{max,app}}$ did not vary with depth into the canopy in wild oats ( Avena fatua L.) growing in a wheat crop (Beyschlag et al , 1990), and did not vary in grapevine ( Vitis vinifera L.) leaves throughout the canopy (Cartechini and Palliotti, 1995).…”

Mesoscale modelling of the CO<sub>2</sub> interactions between the surface and the atmosphere applied to the April 2007 CERES field experiment

“…A probable reason for the underestimation of the NEE by the model is that the simulated assimilation depends on the LAI and does not take into account the assimilation by the total Photosynthetic Area Index (PAI) (including stems, ears, leaves...). In fact, a recent study, by Hoyaux et al (2008) shows that for winter crops the stem assimilation rate equal to 63% of the leaf assimilation. The comparisons at the surface fluxes stations are also difficult because of the spatial variability of the ecosystem and the problem of representativeness of a 8 km grid cell.…”

Carbon balance assessment of a Belgian winter wheat crop (Triticum aestivum L.)

“…GPP and TER were inferred from these measurements. At the leaf scale, leaf net assimilation was measured once a week and scaled up to provide a second GPP assessment (Hoyaux et al , in press). At the soil plot scale, soil respiration (SR) was measured every half hour with an automatic system and once a week with a manual system.…”