Photosynthesis in the fleeting shadows: an overlooked opportunity for increasing crop productivity?

Abstract

Summary Photosynthesis measurements are traditionally taken under steady‐state conditions; however, leaves in crop fields experience frequent fluctuations in light and take time to respond. This slow response reduces the efficiency of carbon assimilation. Transitions from low to high light require photosynthetic induction, including the activation of Rubisco and the opening of stomata, whereas transitions from high to low light require the relaxation of dissipative energy processes, collectively known as non‐photochemical quenching (NPQ). Previous attempts to assess the impact of these delays on net carbon assimilation have used simplified models of crop canopies, limiting the accuracy of predictions. Here, we use ray tracing to predict the spatial and temporal dynamics of lighting for a rendered mature Glycine max (soybean) canopy to review the relative importance of these delays on net cumulative assimilation over the course of both a sunny and a cloudy summer day. Combined limitations result in a 13% reduction in crop carbon assimilation on both sunny and cloudy days, with induction being more important on cloudy than on sunny days. Genetic variation in NPQ relaxation rates and photosynthetic induction in parental lines of a soybean nested association mapping (NAM) population was assessed. Short‐term NPQ relaxation (<30 min) showed little variation across the NAM lines, but substantial variation was found in the speeds of photosynthetic induction, attributable to Rubisco activation. Over the course of a sunny and an intermittently cloudy day these would translate to substantial differences in total crop carbon assimilation. These findings suggest an unexplored potential for breeding improved photosynthetic potential in our major crops.

Variation in photosynthetic induction between rice accessions and its potential for improving productivity

“…Improving its photosynthetic efficiency has become a focus, in particular by introducing C 4 photosynthesis (Kajala et al, 2011). Breeding for increased speeds of induction might provide a more immediate and complementary means to increase photosynthetic efficiency (Wang et al, 2020).…”

Coordinated Systemic Stomatal Responses in Soybean

“…S1). Taken together, our findings reveal that rapid and coordinated systemic stomatal responses occur in a crop plant such as soybean and could be involved in the acclimation of soybean to rapid changes in light conditions, humidity, and temperature occurring in the field as a result of sunflecks and/or other rapid changes in environmental conditions (Pearcy, 1990;Kollist et al, 2019;Papanatsiou et al, 2019;Wang et al, 2020).…”

“…The change in light intensity was limited to one leaf and conducted within the portable photosynthesis system chamber. Young, fully expanded source leaves, at the same relative position, of same-age and developmental-stage plants (4-week-old) were used, and light intensities used were based on measured intensities at different heights within the soybean canopy under field conditions (Wang et al, 2020).…”

Variation in relaxation of non-photochemical quenching in a soybean nested association mapping panel as a potential source for breeding improved photosynthesis

“…Taking the slowest, fastest and average short term relaxation rates of the NAM parents in 2019, and inputting them into a soybean canopy photosynthesis model suggested the difference between the slowest and average could result in a small but substantial (1.3 %) increase in carbon assimilation on a cloudy day (Wang et al, 2020). However, it remained unclear to what extent this variation in soybean is heritable, information which is required to estimate the ease with which variation in NPQ could be selected for in a conventional breeding program.…”