Photosynthetic induction describes the transient increase in leaf CO 2 uptake with an increase in light. During induction, efficiency is lower than at steady state. Under field conditions of fluctuating light, this lower efficiency during induction may cost > 20% of potential crop assimilation. Accelerating induction would boost photosynthetic and resource-use efficiencies.Variation between rice accessions and potential for accelerating induction was analysed by gas exchange. Induction during shade to sun transitions of 14 accessions representing five subpopulations from the 3000 Rice Genome Project Panel (3K RGP) was analysed.Differences of 109% occurred in the CO 2 fixed during the first 300 s of induction, 117% in the half-time to completion of induction, and 65% in intrinsic water-use efficiency during induction, between the highest and lowest performing accessions. Induction in three accessions with contrasting responses (AUS 278, NCS 771 A and IR64-21) was compared for a range of [CO 2 ] to analyse limitations. This showed in vivo capacity for carboxylation at Rubisco (V c,max ), and not stomata, as the primary limitation to induction, with significant differences between accessions.Variation in nonsteady-state efficiency greatly exceeded that at steady state, suggesting a new and more promising opportunity for selection of greater crop photosynthetic efficiency in this key food crop.

Several breeding initiatives have sought to improve flag leaf performance as its health and physiology are closely correlated to rice yield. Previous studies have described natural variation of photosynthesis for flag leaves; however, none have examined their performance under the non-steady-state conditions that prevail in crop fields. Photosynthetic induction is the transient response of photosynthesis to a change from low to high light. Rice flag leaf photosynthesis was measured in both steady- and non-steady-state conditions to characterize natural variation. Between the lowest and highest performing accession there was a 152% difference for average CO2 assimilation during induction (Ā300), a 77% difference for average intrinsic water-use efficiency during induction (iWUEavg), and a 185% difference for the speed of induction (IT50), indicating plentiful variation. No significant correlation was found between steady- and non-steady-state photosynthetic traits. Additionally, neither measures of steady-state or non-steady-state photosynthesis of flag leaves correlated with the same measures of leaves in the vegetative growth stage, with the exception of iWUEavg. Photosynthetic induction was measured at six [CO2], to determine biochemical and diffusive limitations to photosynthesis in vivo. Photosynthetic induction in rice flag leaves was limited primarily by biochemistry.

Despite significant advances to harvest index and interception efficiency, photosynthesis has remained largely unimproved through conventional breeding approaches. However, increasing photosynthetic efficiency is a key method for enhancing crop productivity, yield, and sustainability. In this study, photosynthetic and morphological traits were characterized in indica rice to examine natural variation and the potential for hybridization in the future. Additionally, broad‐sense heritability (H2) was calculated for photosynthetic traits, including, for the first time, biochemical limitations to photosynthesis. Heritability was high for CO2 assimilation in saturating light and [CO2] (Amax; H2 = .65), the maximum rate of carboxylation (Vc,max; H2 = .63), the maximum rate of electron transport (Jmax; H2 = .68), and triosephosphate utilization (TPU; H2 = .73). Genetic advances of up to 17.7% were estimated, suggesting that it would be possible to not only select for the improvement of biochemical components of photosynthesis but also achieve significant gains in one generation. Heritability was low for CO2 assimilation at ambient [CO2] in saturating light (Asat; H2 = .22), suggesting that rising [CO2] may increase heritability for photosynthesis in rice.

Source traits are currently of great interest for the enhancement of yield potential, for example much effort is being expended to find ways of modifying photosynthesis. However, photosynthesis is but one component of crop regulation so sink activities and the coordination of diverse processes throughout the crop must be considered in an integrated, systems approach. A set of ‘Wiring Diagrams’ has been devised as a visual tool to integrate the interactions of component processes at different stages of wheat development. They enable the roles of chloroplast, leaf and whole canopy processes to be seen in the context of sink development and crop growth as a whole. In this review, we dissect source traits both anatomically (foliar, non foliar) and temporally (pre- and post-anthesis) and consider the evidence for their regulation at local and whole plant/crop levels. We consider how the formation of a canopy creates challenges (self occlusion) and opportunities (dynamic photosynthesis) for components of photosynthesis. Lastly, we discuss the regulation of source activity by feedback regulation. The review is written in the framework of the Wiring Diagrams which, as integrated descriptors of traits underpinning grain yield, are designed to provide a potential workspace for breeders and other crop scientists that, along with high-throughput and precision phenotyping data, genetics and bioinformatics, will help build future dynamic models of trait and gene interactions to achieve yield gains in wheat and other field crops.

Wild rice species are a source of genetic material for improving cultivated rice (Oryza sativa) and a means to understand its evolutionary history. Renewed interest in non‐steady‐state photosynthesis in crops has taken place due its potential in improving sustainable productivity. Variation was characterized for photosynthetic induction and relaxation at two leaf canopy levels in three rice species. The wild rice accessions had 16%–40% higher rates of leaf CO2 uptake (A) during photosynthetic induction relative to the O. sativa accession. However, O. sativa had an overall higher photosynthetic capacity when compared to accessions of its wild progenitors. Additionally, O. sativa had a faster stomatal closing response, resulting in higher intrinsic water‐use efficiency during high‐to‐low light transitions. Leaf position in the canopy had a significant effect on non‐steady‐state photosynthesis, but not steady‐state photosynthesis. The results show potential to utilize wild material to refine plant models and improve non‐steady‐state photosynthesis in cultivated rice for increased productivity.

Empirical evidence shows complementarity between maize and soybean as a sustained agricultural system across North and South America as well as Eastern Europe. The potential application to sub-Saharan Africa motivates this literature review. Maize is one of the most important crops on the African subcontinent, accounting for over half of daily caloric intake in some regions. However, continuous cropping of maize has led to extensive degradation of soil and decrease in crop productivity and endangers household food and nutritional security. The cultivation of soybean holds great promise in improving agricultural systems in sub-Saharan Africa. Introducing soy into rotation with maize is a method to diversify diets, better nutritional status, reduce abiotic and biotic stresses, and improve soil fertility, while enhancing crop productivity and generating more income for farmers. However, limited access to extension services and other sources of technical support constrains adoption of the more complex rotation cropping system involving a new crop, soybean. Rotating soybean with maize too challenges farmers as there is not a specific prescription that can guide farmers operating across Africa’s diverse agroecological environments. Finally, soybean is an input-intensive crop requiring significant investment at planting, which may not allow small holders with limited resources and no access to credit.

In this study, four tobacco transformants with the overexpression of inorganic carbon transporter B (ictB) were screened for photosynthetic performance relative to wild-type (WT) in field-based conditions. The WT and transgenic tobacco plants were evaluated for photosynthetic performance to determine the maximum rate of carboxylation (Vc,max), maximum rate of electron transport (Jmax), the photosynthetic compensation point (Γ*), quantum yield of photosystem II (ΦPSII), and mesophyll conductance (gm). Additionally, all plants were harvested to compare differences in above-ground biomass. Overall, transformants did not perform better than WT on photosynthesis, biomass, and leaf composition related traits. This is in contrast to previous studies that have suggested significant increases in photosynthesis and yield with the overexpression of ictB, although not widely evaluated under field conditions. These findings suggest that the benefit of ictB is not universal and may only be seen under certain growth conditions. While there is certainly still potential benefit to utilizing ictB in the future, further effort must be concentrated on understanding the underlying function of the gene and in which environmental conditions it offers the greatest benefit to crop performance. As of now, it is possible that ictB overexpression may be largely favorable in controlled environments, such as greenhouses.

Water deficit currently acts as one of the largest limiting factors for agricultural productivity worldwide. Additionally, limitation by water scarcity is projected to continue in the future with the further onset of effects of global climate change. As a result, it is critical to develop or breed for crops that have increased water-use efficiency and that are more capable of coping with water-scarce conditions. However, increased intrinsic water-use efficiency (iWUE) typically comes with a trade-off to CO2 assimilation as all gas exchange is mediated by stomata, through which CO2 enters the leaf while water vapor exits. Previously, promising results were shown about using guard-cell targeted overexpression of hexokinase to increase iWUE without incurring a penalty to photosynthetic rates or biomass production. Here, two homozygous transgenic lines expressing AtHXK1 constitutively (35SHXK2 and 35SHXK5) and a line that had guard-cell targeted overexpression of AtHXK1 (GCHXK2) were evaluated relative to wild type (WT) for traits related to photosynthesis and yield. In this study significantly better iWUE was found in GCHXK2 relative to WT without negatively impacting CO2 assimilation, although results were dependent upon leaf age and proximity of precipitation event to gas exchange measurement.