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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.

The temperature response of photosynthesis is one of the key factors determining predicted responses to warming in global vegetation models (GVMs). The response may vary geographically, owing to genetic adaptation to climate, and temporally, as a result of acclimation to changes in ambient temperature. Our goal was to develop a robust quantitative global model representing acclimation and adaptation of photosynthetic temperature responses. We quantified and modelled key mechanisms responsible for photosynthetic temperature acclimation and adaptation using a global dataset of photosynthetic CO2 response curves, including data from 141 C3 species from tropical rainforest to Arctic tundra. We separated temperature acclimation and adaptation processes by considering seasonal and common-garden datasets, respectively. The observed global variation in the temperature optimum of photosynthesis was primarily explained by biochemical limitations to photosynthesis, rather than stomatal conductance or respiration. We found acclimation to growth temperature to be a stronger driver of this variation than adaptation to temperature at climate of origin. We developed a summary model to represent photosynthetic temperature responses and showed that it predicted the observed global variation in optimal temperatures with high accuracy. This novel algorithm should enable improved prediction of the function of global ecosystems in a warming climate.

Climate change is expected to be most pronounced at high latitudes, but we have little data on how dominant boreal tree species will respond to rising temperatures and C[O.sub.2] concentrations ([C[O.sub.2]]). We review the mechanisms through which elevated growth temperatures and atmospheric C[O.sub.2] alter tree physiology and growth, focusing on the dominant species in northern forests. Water and nutrient availability, as well as day length, are likely to constrain the ability of these forests to respond positively to warmer, potentially longer growing seasons and higher C[O.sub.2] levels. We also analyze published tree responses to future climate scenarios for key boreal tree species and show that (i) high [C[O.sub.2]] increases biomass and net photosynthetic rates compared with ambient [C[O.sub.2]], under both current temperatures and warmer climates; (ii) increases in temperature above current levels have little effect on growth or carbon gain; and (iii) the combination of elevated [C[O.sub.2]] and elevated temperatures increases plant biomass, but this effect appears to have a threshold above a 5°C increase in growth temperatures. While rising temperatures and [C[O.sub.2]], therefore, have the potential to increase the productivity of northern forest species (based on experiments that supply ample water and fertilizer), this response is likely to be limited by these soil resources and the photoperiod in the field, and may not occur under the more extreme warming conditions predicted for the future in this region. Key words: carbon sequestration, climate warming, conifers, global change, photosynthetic capacity. On s'attend que les changements climatiques soient plus prononces a des latitudes elevees, mais il n'existe que peu de donnees sur la facon dont des especes dominantes d'arbres de la foret boreale repondront a l'accroissement des temperatures et des concentrations de C[O.sub.2] ([C[O.sub.2]]). Les auteurs passent en revue les mecanismes par lesquels les temperatures de croissance elevees et le [C[O.sub.2]] atmospherique modifient la physiologie et la croissance des arbres, en se concentrant sur les especes dominantes des forets du Nord. La disponibilite en eau et en nutriments de meme que la duree du jour limiteront probablement la capacite de ces forets a repondre positivement a des saisons de croissance plus chaudes et potentiellement plus longues et a des niveaux de C[O.sub.2] plus eleves. Les auteurs ont aussi analyse les donnees publiees sur la reponse aux scenarios climatiques futurs des especes cles d'arbres de la foret boreale et ils ont montre que (i) des niveaux eleves de C[O.sub.2] augmentent la biomasse et les taux nets de photosynthese comparativement au [C[O.sub.2]] ambiant, tant aux temperatures actuelles que sous des climats plus chauds; (ii) les augmentations de temperature au-dessus des niveaux actuels ont peu d'effets sur la croissance ou le gain en carbone, et (iii) la combinaison de [C[O.sub.2]] eleve et de temperatures elevees augmente la biomasse vegetale, mais cet effet semble avoir un seuil inferieur a une augmentation de 5°C des temperatures de croissance. Alors que l'augmentation des temperatures et du [C[O.sub.2]] pourrait ainsi avoir la potentiel d'augmenter la productivite des especes des forets du Nord (selon des experiences ou l'apport en eau et en fertilisants est suffisant), cette reponse sera probablement limitee par ces ressources du sol et la photoperiode de la zone, et pourrait ne pas se produire avec le rechauffement le plus extreme predit dans cette region, dans le futur. Mots-cles: sequestration du carbone, rechauffement climatique, coniferes, changement global, capacite photosynthetique., Introduction Atmospheric C[O.sub.2] concentrations ([C[O.sub.2]]) are projected to reach 730-1020 ppm by the year 2100, mainly due to anthropogenic fossil fuel burning and land use change (Meehl et al. 2007). [...]

Projected rises in atmospheric CO2 concentration and minimum night-time temperatures may have important effects on plant carbon metabolism altering the carbon balance of the only two vascular plant species in the Antarctic Peninsula. We assessed the effect of nocturnal warming (8/5 °C vs. 8/8 °C day/night) and CO2 concentrations (400 ppm and 750 ppm) on gas exchange, non-structural carbohydrates, two respiratory-related enzymes, and mitochondrial size and number in two species of vascular plants. In Colobanthus quitensis, light-saturated photosynthesis measured at 400 ppm was reduced when plants were grown in the elevated CO2 or in the nocturnal warming treatments. Growth in elevated CO2 reduced stomatal conductance but nocturnal warming did not. The short-term sensitivity of respiration, relative protein abundance, and mitochondrial traits were not responsive to either treatment in this species. Moreover, some acclimation to nocturnal warming at ambient CO2 was observed. Altogether, these responses in C. quitensis led to an increase in the respiration-assimilation ratio in plants grown in elevated CO2. The response of Deschampsia antarctica to the experimental treatments was quite distinct. Photosynthesis was not affected by either treatment; however, respiration acclimated to temperature in the elevated CO2 treatment. The observed short-term changes in thermal sensitivity indicate type I acclimation of respiration. Growth in elevated CO2 and nocturnal warming resulted in a reduction in mitochondrial numbers and an increase in mitochondrial size in D. antarctica. Overall, our results suggest that with climate change D. antarctica could be more successful than C. quitensis, due to its ability to make metabolic adjustments to maintain its carbon balance. [ABSTRACT FROM AUTHOR]