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Leaf-level gas exchange data support the mechanistic understanding of plant fluxes of carbon and water. These fluxes inform our understanding of ecosystem function, are an important constraint on parameterization of terrestrial biosphere models, are necessary to understand the response of plants to global environmental change, and are integral to efforts to improve crop production. Collection of these data using gas analyzers can be both technically challenging and time consuming, and individual studies generally focus on a small range of species, restricted time periods, or limited geographic regions. The high value of these data is exemplified by the many publications that reuse and synthesize gas exchange data, however the lack of metadata and data reporting conventions make full and efficient use of these data difficult. Here we propose a reporting format for leaf-level gas exchange data and metadata to provide guidance to data contributors on how to store data in repositories to maximize their discoverability, facilitate their efficient reuse, and add value to individual datasets. For data users, the reporting format will better allow data repositories to optimize data search and extraction, and more readily integrate similar data into harmonized synthesis products. The reporting format specifies data table variable naming and unit conventions, as well as metadata characterizing experimental conditions and protocols. For common data types that were the focus of this initial version of the reporting format, i.e., survey measurements, dark respiration, carbon dioxide and light response curves, and parameters derived from those measurements, we took a further step of defining required additional data and metadata that would maximize the potential reuse of those data types. To aid data contributors and the development of data ingest tools by data repositories we provided a translation table comparing the outputs of common gas exchange instruments. Extensive consultation with data collectors, data users, instrument manufacturers, and data scientists was undertaken in order to ensure that the reporting format met community needs. The reporting format presented here is intended to form a foundation for future development that will incorporate additional data types and variables as gas exchange systems and measurement approaches advance in the future. The reporting format is published in the U.S. Department of Energy's ESS-DIVE data repository, with documentation and future development efforts being maintained in a version control system.

Miscanthus holds a promise as a biocrop due to its high yield, perenniality and ability to grow on infertile soils. However, the current commercial biomass production of Miscanthus is mostly limited to a single sterile triploid clone of M. × giganteus. Nevertheless, parental species of M. × giganteus, Miscanthus sacchariflorus and Miscanthus sinensis contain vast genetic diversity for crop improvement. With M. sacchariflorus having a natural geographic distribution in cold‐temperate northeast China and eastern Russia, we hypothesised that it has substantial variation in physiological response to chilling. Using a semi‐high‐throughput method, we phenotyped 209 M. sacchariflorus genotypes belonging to six genetic groups for non‐photochemical quenching (NPQ) and photosystem II efficiency (ΦPSII) kinetics under warm and chilling treatments in three growing seasons. In response to the chilling treatment, all genetic groups exhibited an increase in NPQ induction rate indicating faster activation of NPQ in light. Notably, under chilling, the Korea/NE China/Russia 2x and N China 2x groups stood out for the highest NPQ rate in light and the highest steady‐state NPQ in light. This NPQ phenotype may contribute adaptation to chilling during bright, cold mornings of spring and early autumn in temperate climates, when faster NPQ would better protect from oxidative stress. Such enhanced adaptation could expand the growing season and thus productivity at a given location or expand the range of economically viable growing locations to higher latitudes and altitudes. A genome‐wide association study identified 126 unique SNPs associated with NPQ and ΦPSII traits. Among the identified candidate genes were enzymes involved in the ascorbate recycle and shikimate pathway, gamma‐aminobutyric acid and cation efflux transporters. Identifying natural variation and genes involved in NPQ and ΦPSII kinetics considerably enlarges the toolbox for breeding and/or engineering Miscanthus with optimised photosynthesis under warm and chilling conditions for sustainable feedstock production for bioenergy. Chilling affects the productivity and geographical distribution of most crops. Using a semi‐high‐throughput approach to investigate photosynthesis‐related traits, we characterised variation existing in the bioenergy crop Miscanthus under chilling and warm conditions and identified potential genes associated with it. Under chilling, two genetic groups from the northern edge of Miscanthus distribution stood out for faster activation of photoprotection. This trait may contribute adaptation to chilling in temperate climates, when faster photoprotection would better defend from oxidative stress. Enhanced chilling adaptation could expand the growing season and thus productivity or enlarge the range of growing locations. [ABSTRACT FROM AUTHOR]

Mesophyll conductance (gm ) describes the efficiency with which CO2 moves from substomatal cavities to chloroplasts. Despite the stipulated importance of leaf architecture in affecting gm , there remains a considerable ambiguity about how and whether leaf anatomy influences gm . Here, we employed nonlinear machine‐learning models to assess the relationship between 10 leaf architecture traits and gm . These models used leaf architecture traits as predictors and achieved excellent predictability of gm . Dissection of the importance of leaf architecture traits in the models indicated that cell wall thickness and chloroplast area exposed to internal airspace have a large impact on interspecific variation in gm . Additionally, other leaf architecture traits, such as leaf thickness, leaf density and chloroplast thickness, emerged as important predictors of gm . We also found significant differences in the predictability between models trained on different plant functional types. Therefore, by moving beyond simple linear and exponential models, our analyses demonstrated that a larger suite of leaf architecture traits drive differences in gm than has been previously acknowledged. These findings pave the way for modulating gm by strategies that modify its leaf architecture determinants. Summary Statement: We demonstrated that systematic training and testing of random forest regression models using a comprehensive data set, covering different plant functional types, can pinpoint leaf structural and anatomical traits that determine mesophyll conductance. [ABSTRACT FROM AUTHOR]

Insufficient water availability for crop production is a mounting barrier to achieving the 70% increase in food production that will be needed by 2050. One solution is to develop crops that require less water per unit mass of production. Water vapor transpires from leaves through stomata, which also facilitate the influx of CO2 during photosynthetic assimilation. Here, we hypothesize that Photosystem II Subunit S (PsbS) expression affects a chloroplast-derived signal for stomatal opening in response to light, which can be used to improve water-use efficiency. Transgenic tobacco plants with a range of PsbS expression, from undetectable to 3.7 times wild-type are generated. Plants with increased PsbS expression show less stomatal opening in response to light, resulting in a 25% reduction in water loss per CO2 assimilated under field conditions. Since the role of PsbS is universal across higher plants, this manipulation should be effective across all crops.

Optimal stomatal regulation is important for plant adaptation to changing environmental conditions and for maintaining crop yield. The guard cell signal γ-aminobutyric acid (GABA) is produced from glutamate by glutamate decarboxylase (GAD) during a reaction that generates CO2 as a by-product. Here, we investigated a putative connection between GABA signalling and the more clearly defined CO2 signalling pathway in guard cells. The GABA-deficient mutant Arabidopsis lines gad2-1 , gad2-2 , and gad1/2/4/5 were examined for stomatal sensitivity to various CO2 concentrations. Our findings show a phenotypical discrepancy between the allelic mutant lines gad2-1 and gad2-2 —a weakened CO2 response in gad2-1 (GABI_474_E05) in contrast to a wild-type response in gad2-2 (SALK_028819) and gad1/2/4/5. Through transcriptomic and genomic investigation, we traced the response of gad2-1 to a deletion of full-length Mitogen-activated protein kinase 12 (MPK12) in the GABI-KAT line, thereafter renamed as gad2-1 *. Guard cell-specific complementation of MPK12 in gad2-1* restored the wild-type CO2 phenotype, which confirms the proposed importance of MPK12 in CO2 sensitivity. Additionally, we found that stomatal opening under low atmospheric CO2 occurs independently of the GABA-modulated opening channel ALUMINIUM-ACTIVATED MALATE TRANSPORTER 9 (ALMT9). Our results demonstrate that GABA has a role in modulating the rate of stomatal opening and closing, but not in response to CO2 per se. [ABSTRACT FROM AUTHOR]

The stomatal response to red light appears to link stomatal conductance (g s) with photosynthetic rates. Initially, it was suggested that changes in intercellular CO2 concentration (C i) provide the main cue via a C i - dependent response. However, evidence for C i-independent mechanisms suggests an additional, more direct relationship with photosynthesis. While both C i-dependent and -independent mechanisms clearly function in stomatal red light responses, little is known regarding their relative contribution. The present study aimed to quantify the relative magnitude of C i-dependent and -independent mechanisms on the stomatal red light response, to characterize their interplay and to assess the putative link between plastoquinone redox state and C i-independent stomatal responses. Red light response curves measured at a range of C i values for wild-type Arabidopsis (Col-0) and the CO2 hyposensitive mutant ca1ca4 allowed deconvolution of C i-dependent and -independent pathways. Surprisingly, we observed that both mechanisms contribute equally to stomatal red light responses, but C i-independent stomatal opening is suppressed at high C i. The present data are also consistent with the involvement of the plastoquinone redox state in coordinating the C i - independent component. Overall, it seems that while C i-independent mechanisms are distinct from responses to C i, interplay between these two pathways is important to facilitate effective coordination between g s and photosynthesis. [ABSTRACT FROM AUTHOR]

The growing demand for global food production is likely to be a defining issue facing humanity over the next 50 years. To tackle this challenge, there is a desire to bioengineer crops with higher photosynthetic efficiencies, to increase yields. Recently, there has been a growing interest in engineering leaves with higher mesophyll conductance (gm), which would allow CO2 to move more efficiently from the substomatal cavities to the chloroplast stroma. However, if crop yield gains are to be realised through this approach, it is essential that the methodological limitations associated with estimating gm are fully appreciated. In this review, we summarise these limitations, and outline the uncertainties and assumptions that can affect the final estimation of gm. Furthermore, we critically assess the predicted quantitative effect that elevating gm will have on assimilation rates in crop species. We highlight the need for more theoretical modelling to determine whether altering gm is truly a viable route to improve crop performance. Finally, we offer suggestions to guide future research on gm, which will help mitigate the uncertainty inherently associated with estimating this parameter. Summary statement: This review outlines the uncertainties and assumptions that can affect the estimation of mesophyll conductance gm and critically assesses the predicted quantitative effect that elevating gm will have on assimilation rates in crop species. [ABSTRACT FROM AUTHOR]

Gas exchange measurements enable mechanistic insights into the processes that underpin carbon and water fluxes in plant leaves which in turn inform understanding of related processes at a range of scales from individual cells to entire ecosytems. Given the importance of photosynthesis for the global climate discussion it is important to (a) foster a basic understanding of the fundamental principles underpinning the experimental methods used by the broad community, and (b) ensure best practice and correct data interpretation within the research community. In this review, we outline the biochemical and biophysical parameters of photosynthesis that can be investigated with gas exchange measurements and we provide step‐by‐step guidance on how to reliably measure them. We advise on best practices for using gas exchange equipment and highlight potential pitfalls in experimental design and data interpretation. The Supporting Information contains exemplary data sets, experimental protocols and data‐modelling routines. This review is a community effort to equip both the experimental researcher and the data modeller with a solid understanding of the theoretical basis of gas‐exchange measurements, the rationale behind different experimental protocols and the approaches to data interpretation. Summary statement: This review outlines the fundamental principles underpinning photosynthetic gas exchange and gives guidance on best practice for obtaining and correctly interpreting measurements. It is meant to provide a solid foundation in gas exchange techniques to the novice and act as a point of reference for the experienced researcher. [ABSTRACT FROM AUTHOR]

Crop leaves in full sunlight dissipate damaging excess absorbed light energy as heat. When sunlit leaves are shaded by clouds or other leaves, this protective dissipation continues for many minutes and reduces photosynthesis. Calculations have shown that this could cost field crops up to 20% of their potential yield. Here, we describe the bioengineering of an accelerated response to natural shading events in Nicotiana (tobacco), resulting in increased leaf carbon dioxide uptake and plant dry matter productivity by about 15% in fluctuating light. Because the photoprotective mechanism that has been altered is common to all flowering plants and crops, the findings provide proof of concept for a route to obtaining a sustainable increase in productivity for food crops and a much-needed yield jump.

Summary: γ‐Aminobutyric acid (GABA) accumulates rapidly under stress via the GABA shunt pathway, which has been implicated in reducing the accumulation of stress‐induced reactive oxygen species (ROS) in plants.γ‐Aminobutyric acid has been demonstrated to act as a guard‐cell signal in Arabidopsis thaliana, modulating stomatal opening. Knockout of the major GABA synthesis enzyme Glutamate Decarboxylase 2 (GAD2) increases the aperture of gad2 mutants, which results in greater stomatal conductance and reduces water‐use efficiency compared with wild‐type plants.Here, we found that the additional loss of GAD1, GAD4, and GAD5 in gad2 leaves increased GABA deficiency but abolished the more open stomatal pore phenotype of gad2, which we link to increased cytosolic calcium (Ca2+) and ROS accumulation in gad1/2/4/5 guard cells. Compared with wild‐type and gad2 plants, glutamate was ineffective in closing gad1/2/4/5 stomatal pores, whereas lowering apoplastic calcium, applying ROS inhibitors or complementation with GAD2 reduced gad1/2/4/5 guard‐cell ROS, restored the gad2‐like greater stomatal apertures of gad1/2/4/5 beyond that of wild‐type.We conclude that GADs are important contributors to ROS homeostasis in guard cells likely via a Ca2+‐mediated pathway. As such, this study reveals greater complexity in GABA's role as a guard‐cell signal and the interactions it has with other established signals. [ABSTRACT FROM AUTHOR]