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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.

In this study, Zea mays L. was grown in indoor controlled environment chambers with a uniform daytime temperature of 30°C, and night-time temperatures of 30, 25, 20, or 15°C. Responses of net photosynthesis (PN) of mature leaves at high PPFD to intercellular CO2 concentrations (Ci) were measured at 20, 25, and 30°C using a new method that generates a complete PN vs. Ci curve in less than four minutes. Results indicated that photosynthesis measured at both Ci values of 25 and 150 µmol mol-1 increased strongly with measurement temperature in plants grown with night temperatures of 25 and 30°C, but there was a much smaller change in photosynthesis with temperature in plants grown with night temperatures of 15 or 20°C. These results indicate that the acclimation of photosynthesis to temperature in this C4 species is substantially affected by night temperature. [ABSTRACT FROM AUTHOR]

We hypothesized that decreased stomatal conductance ( g) at elevated CO might decrease transpiration ( E), increase leaf water potential (Ψ), and thereby protect net photosynthesis rate ( P) from heat damage in maize ( Zea mays L) seedlings. To separate long-term effects of elevated CO, plants grew at either ambient CO or elevated CO. During high-temperature treatment (HT) at 45°C for 15 min, leaves were exposed either to ambient CO (380 μmol mol) or to elevated CO (560 μmol mol). HT reduced P by 25 to 38% across four CO combinations. However, the g and E did not differ among all CO treatments during HT. After returning the leaf temperature to 35°C within 30 min, g and E were the same or higher than the initial values. Leaf water potential (Ψ) was slightly lower at ambient CO, but not at elevated CO. This study highlighted that elevated CO failed in protecting P from 45°C via decreasing g and Ψ. [ABSTRACT FROM AUTHOR]

Experiments were performed to determine if growth at elevated partial pressure of CO2 altered the sensitivity of leaf water vapour conductance and rate of CO2 assimilation to the leaf-to-air difference in the partial pressure of water vapour (Δw). Comparisons were made between plants grown and measured at 350 and 700 μPa Pa-1 partial pressures of CO2 for amaranth, soybean and sunflower grown in controlled environment chambers, soybean grown outdoors in pots, and orchard grass grown in field plots. In amaranth, soybean and orchard grass, both the absolute and the relative sensitivity of conductance to Δw at the leaf surface were less in plants grown and measured at the elevated CO2. In sunflower, there was no change in the sensitivity of conductance to Δw for the two CO2 partial pressures. Tests in soybeans and amaranth showed that the change in sensitivity resulted from elevated CO2 during the measurement of the Δw response. Assimilation rate of CO2 was not altered by Δw in amaranth, which has C4 metabolism. In sunflower, the assimilation rate of plants grown and measured at elevated CO2 was insensitive to Δw, consistent with the response of assimilation rate to intercellular CO2 partial pressure in the prevailing range. In soybean, the sensitivity of assimilation rate to Δw was not different between CO2 treatments, in contrast to what would be expected from the response of assimilation rate to intercellular CO2 partial pressure. [ABSTRACT FROM AUTHOR]

Leaf area expansion, photosynthetic carbon dioxide uptake and leaf dry mass accumulation were compared for expanding leaves of well-watered soybean (Glycine max [L.] Merr.) plants, mildly dehydrated plants and well-watered plants treated with abscisic acid (ABA). Both ABA treatment and dehydration reduced area expansion in the light and over a 24 h period without decreasing the photosynthetic rates of expanding leaves. Dry mass accumulation during the light was less in ABA-treated and water-stressed leaves than in control leaves, with no differences among treatments in leaf mass per unit of area. ABA treatment and water stress both increased export of carbon from expanding leaves in the light. ABA applied near the end of the light period also increased export of carbon during the following dark period. However, it is unlikely that decreased availability of photosynthate caused slow expansion in the ABA and dehydration treatments, because expansion rates were not slowed in plants kept in dim light, even though photosynthetic rates and dry mass accumulation rates were greatly reduced. The data suggest that ABA may mediate the effects of mild dehydration on leaf area expansion and partitioning of photosynthate. [ABSTRACT FROM AUTHOR]