Enhancement of crop photosynthesis by diffuse light: quantifying the contributing factors

Abstract

Diffuse light enhanced crop photosynthesis. A more uniform horizontal PPFD distribution played the most important role in this enhancement, and a more uniform vertical PPFD distribution and higher leaf photosynthetic capacity contributed more to the enhancement of crop photosynthesis than did higher values of LAI.

Excess Diffuse Light Absorption in Upper Mesophyll Limits CO2 Drawdown and Depresses Photosynthesis

“…When canopy-level extinction coefficients were relatively high (i.e. 1.06 and 0.82 for diffuse and direct light, respectively; Li et al, 2014), we predicted that deeper diffuse light penetration into the canopy of sun-grown leaves dominated the photosynthetic benefit of direct light within the upper canopy (Fig. 9).…”

“…This resulted from a strong mismatch between the absorption profile, which peaked in the upper portion of the palisade mesophyll, and the chlorophyll distribution profile, which peaked in the spongy mesophyll. Such a mismatch would lead to a high level of excess absorption in the upper palisade and a substantial underutilization of j max in the lower palisade Li et al (2014), the top left graph shows the light availability at various cumulative LAI values from the upper to lower canopy when the extinction coefficient (k) is 1.06 and 0.82 for direct light (solid lines) and diffuse light (dashed lines), respectively. Canopylevel light availability at 0.25*k is shown in the bottom left graph.…”

“…In our first scenario (Fig. 9), we assumed that direct and diffuse light have canopy-level extinction coefficients of 1.06 and 0.82, respectively (Li et al, 2014). Using our modeled leaflevel light response curves for sun-and shade-grown leaves under diffuse versus direct light (Fig.…”

“…Deeper diffuse light penetration along canopy depth has been suggested as the primary mechanism underlying the corresponding increases of canopy-level LUE (Urban et al, 2007;Li et al, 2014). This mechanism is further supported by observations of increasing LUE with higher leaf area index (LAI; Greenwald et al, 2006;Alton et al, 2007), which varies with genotype/species differences in leaf morphology, orientation, and distribution.…”

“…Whether increases in LUE under diffuse light result in higher primary productivity, however, is unclear, as lower total surface irradiance tends to accompany diffuse light conditions (Kanniah et al, 2012). Moreover, a lack of consideration for plant phenology associated with seasonal changes in LAI and photosynthetic capacity has confounded most previous studies (for exceptions, see Li et al, 2014;Williams et al, 2014), potentially leading to a substantial overestimation of diffuse light photosynthetic enhancement at the canopy level (Williams et al, 2016).…”