The importance of species-specific and temperature-sensitive parameterisation of A/Ci models: A case study using cotton (Gossypium hirsutum L.) and the automated 'OptiFitACi' R-package

The heat is on: scaling improvements in photosynthetic thermal tolerance from the leaf to canopy to predict crop yields in a changing climate

Crop production must increase to sustain a growing global population, and this challenge is compounded by increased growing season temperatures and extreme heat events that are already causing significant yield losses in staple crops. Therefore, there is an urgent need to develop strategies to adapt crops to withstand the impacts of a warmer climate. Temperature-sensitive vegetative processes fundamentally related to yield, like photosynthesis, will be impacted by warming throughout the growing season, thus strategies to enhance their resilience hold promise to future-proof crops for a warmer world. Here, we summarize three major strategies to enhance C3 photosynthesis above the thermal optimum: enhanced rubisco activation, modified photorespiration and increased rates of ribulose bisphosphate regeneration. We highlight recent experimental evidence demonstrating the efficacy of these strategies, and then use a mechanistic modelling approach to predict the benefit of these engineering strategies on leaf-level carbon assimilation and soybean yield at elevated temperatures. Our approach highlights that these three engineering targets, particularly when combined, can enhance photosynthetic rates and yield under both ambient and elevated temperatures. By targeting multiple aspects of photosynthetic metabolism, we can develop crops that are better equipped to withstand the challenges of a warming climate and contribute to future food security.This article is part of the theme issue 'Crops under stress: can we mitigate the impacts of climate change on agriculture and launch the 'Resilience Revolution'?'.

Carbon assimilation dynamics in Pontederia crassipes in response to light intensity and CO2 levels

Pontederia crassipes Mart. is an aquatic macrophyte native to South America, tolerant to high intensity of sunlight and has spread to various countries worldwide. This study aimed to investigate the photosynthetic characteristics of P. crassipes leaves under different light intensities and CO2 concentrations by analyzing net photosynthetic response, Rubisco activity, and related photosynthetic parameters. The plants were acclimated in a greenhouse under natural light conditions at a temperature of 25 ± 5 °C. The light response curve was measured using a portable infrared gas exchange system, coupled with the 6400-40 Leaf Chamber Fluorometer. The response of net photosynthesis to intercellular CO2 concentration was determined at 1500 µmol m-2 s-1 of photosynthetic active radiation (PAR). P. crassipes demonstrated a remarkable capacity for adaptation to varying light intensities and CO2 concentrations, exhibiting strong photosynthetic efficiency, as indicated by its net CO2 assimilation rate in response to PAR, sustained electron transport rate up to 1000 µmol photons m-2 s-1, a positive correlation between φPSII and φCO2, and a high net CO2 assimilation rate in response to C i .

PhotoGEA: An R Package for Closer Fitting of Photosynthetic Gas Exchange Data With Non-Gaussian Confidence Interval Estimation

Fitting mechanistic models, such as the Farquhar-von-Caemmerer-Berry model, to experimentally measured photosynthetic CO2 response curves (A-Ci curves) is a widely used technique for estimating the values of key leaf biochemical parameters and determining limitations to photosynthesis in vivo. Here, we present PhotoGEA, an R package with tools for C3 A-Ci, C3 Variable J and C4 A-Ci curve fitting. In contrast to existing software, these automated tools use derivative-free optimizers to ensure close fits and they calculate non-Gaussian confidence intervals to indicate which parameter values are most reliable. Results from PhotoGEA's C3 A-Ci curve fitting tool are compared against other available tools, where it is found to achieve the closest fits and most reasonable parameter estimates across a range of curves with different characteristics. PhotoGEA's C3 Variable J and C4 A-Ci fitting tools are also presented, demonstrating how they can provide insights into mesophyll conductance and the processes limiting C4 photosynthesis at high CO2 concentrations. PhotoGEA enables users to develop data analysis pipelines for efficiently reading, processing, fitting and analysing photosynthetic gas exchange measurements. It includes extensive documentation and example scripts to help new users become proficient as quickly as possible.

Cotton under heat stress: a comprehensive review of molecular breeding, genomics, and multi-omics strategies

Cotton is a vital fiber crop for the global textile industry, but rising temperatures due to climate change threaten its growth, fiber quality and yields. Heat stress disrupts key physiological and biochemical processes, affecting carbohydrate metabolism, hormone signaling, calcium and gene regulation and expression. This review article explores cotton's defense mechanism against heat stress, including epigenetic regulations and transgenic approaches, with a focus on genome editing tools. Given the limitations of traditional breeding, advanced omics technologies such as GWAS, transcriptomics, proteomics, ionomics, metabolomics, phenomics and CRISPR-Cas9 offer promising solutions for developing heat-resistant cotton varieties. This review highlights the need for innovative strategies to ensure sustainable cotton production under climate change.

Changes in the Responses of Leaf Gas Exchange to Temperature and Photosynthesis Model Parameters in Four C3 Species in the Field

Substantial variation in the temperature dependence of parameters of the Farquhar, von Caemmerer, and Berry C3 photosynthesis model, as well as those of in vitro Rubisco kinetic characteristics, have been observed in controlled conditions but have seldom been systematically examined in the field. In this work, A vs. Ci curves were measured over a 15 or 20 °C range of temperature in four C3 species growing outdoors on two occasions about three weeks apart early in the growing season and also once near mid-season when air temperatures were more stable. The two early season occasions were chosen for having contrasting temperatures for 3 to 4 days preceding the measurements. Low temperatures (mean maximum/minimum temperatures of 19/11 °C) resulted in higher values of the VCmax of Rubisco and Jmax at a given measurement temperature in most species compared with higher temperatures (max/min 31/25 °C). The apparent activation energy of VCmax of Rubisco ranged from 56 to 82 kJ mol-1, and that of electron transport (Jmax) ranged from 28 to 56 kJ mol-1 across species and temperatures. In three of the four species, the activation energy of VCmax decreased and that of Jmax increased after the cooler temperatures. Stomatal conductance measured at 20 and 25 °C increased strongly with the prior warm temperatures in all species. Measurements made near mid-season, after a period of relatively stable temperatures (mean maximum/minimum temperatures of 27/18 °C), also indicated a wide range of values of the activation energies of VCmax and Jmax among these species.

The thermal optimum of photosynthetic parameters is regulated by leaf nutrients in neotropical savannas

Global warming significantly threatens species in the Cerrado, the world's largest savannah. Therefore, understanding how plants respond to temperature change, particularly in relation to leaf-level photosynthetic capacity, is crucial to understanding the future of Cerrado vegetation. Here, we determined the optimum temperature of the maximum rate of RuBP-carboxylation and maximum electron transport rate (TOptV and TOptJ, respectively) of 12 tree species in two opposite borders (northeastern and southeastern) of the Cerrado with distinct temperature regimes. We focused on four widespread species found in both sites, four restricted to the northeast, and four to the southeast. We compared TOptV and TOptJ between regions and between widespread species (co-occurring in both sites) and species restricted to each ecoregion. Additionally, we also explored the relationship between TOptV and TOptJ with leaf nitrogen (N), phosphorus (P) and potassium (K). As a result, we found that TOptV and TOptJ values were similar across species, regardless of the study region or species distribution range. The similarity of TOpt values among species suggests that photosynthetic performance is optimized to current temperatures. Additionally, we also observed that the TOptV and TOptJ were similar to the local maximum ambient temperatures. Therefore, if these species do not have enough plasticity, the increasing temperature predicted for this region may reduce their photosynthetic performance. Finally, the studied species exhibited general relationships between the TOptV and TOptJ and foliar key nutrients, particularly with P, suggesting the nutrient availability has an important role in the thermal acclimation of leaves. These findings offer valuable insights into physiological and ecological mechanisms in photosynthesis performance present in the Cerrado species.