Light reacclimatization of lower leaves in C₄maize canopies grown at two planting densities

Abstract

C4 plants have high photosynthetic capacity but are inefficient under low light. In a canopy, lower leaves developed under high light are progressively shaded. To elucidate how lower leaves in a C4 canopy reacclimatize to low light, we investigated maize canopies differing in light environment grown at standard and low planting densities (SPD, LPD). Although upper leaves at SPD and both upper and lower leaves at LPD had light-response curves of photosynthesis of sun leaves, lower leaves at SPD had that of shade leaves. All leaves at both densities had anatomical framework of sun leaves, but the chloroplast content in mesophyll and bundle-sheath cells of lower leaves at SPD was greatly reduced to reacclimatize to low light. This study demonstrates that lower leaves at SPD reacclimatize to low light by adjusting their physiological and chloroplast traits while maintaining anatomical framework, whereas those at LPD behave as sun leaves.

Canopy development, leaf traits and yield in high-altitude Andean maize under contrasting plant densities in Argentina

“…Increased light penetration in the canopy could explain the thicker leaves at ERO, whereas, at HOR, increased shading resulted in higher specific leaf area (Yabiku et al. , 2020) further augmented by high plant density (Table 1) in line with other works (Yang et al. , 2022).…”

“…Consistent with this, specific leaf area is decreased in leaves developed at low T (Riva-Roveda et al, 2016;Zhou et al, 2020) and in maize lines from cool temperate regions compared with lines from warmer origin (Verheul et al, 1996). Increased light penetration in the canopy could explain the thicker leaves at ERO, whereas, at HOR, increased shading resulted in higher specific leaf area (Yabiku et al, 2020) further augmented by high plant density (Table 1) in line with other works (Yang et al, 2022). Other factors could also be involved, such as increased leaf sugar accumulation and decreasing specific leaf area which has been reported in leaves developed under lower T (Riva-Roveda et al, 2016).…”

Artificial selection for grain yield has increased net CO2 exchange of the ear leaf in maize crops

“…Net CO 2 exchange rate at a PAR of 2000 μmol m −2 s −1 (close to the maximum attainable midday PAR at the latitude of the experiments) decreased with high PP (P<0.001; Fig. 5B), indicating that mutual shading reduced the photosynthetic potential of the ear leaf (see also Dwyer et al, 1991;Pignon et al, 2017;Yabiku et al, 2020) but showed no correlation with YOR. The net CO 2 exchange rate at a PAR of 0 μmol m −2 s −1 equates to the rate of respiration, and it was notable that this decreased at high PP (Fig.…”

“…The net CO 2 exchange rate at a PAR of 0 μmol m −2 s −1 equates to the rate of respiration, and it was notable that this decreased at high PP (Fig. 6A; see also Pignon et al, 2017;Yabiku et al, 2020) and with YOR, and an interaction was observed (PP×YOR, P=0.012). We confirmed the trend between respiration and YOR in a set of experiments with plants grown in pots (Fig.…”

“…In crops grown at commercial PPs, shaded leaves may approach saturation at relatively low PAR values (Yabiku et al, 2020), raising the question as to whether the ear leaf could take advantage of extra PAR interception. Here, we showed that in commercial crops the average PAR levels reaching the ear leaf are limiting for photosynthesis even at midday, as the increased PAR interception of the ear-leaf stratum with the year of release (YOR) (Fig.…”