Two Inexpensive and Non-destructive Techniques to Correct for Smaller-Than-Gasket Leaf Area in Gas Exchange Measurements

A guide to photosynthetic gas exchange measurements: Fundamental principles, best practice and potential pitfalls

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.

Characterization of physiological and antioxidant responses in Run1Ren1 Vitis vinifera plants during Erysiphe necator attack

Grapevine is a fruit crop of major significance worldwide. Fungal attacks are one of the most relevant factors affecting grapevine yield and fruit quality, and powdery mildew caused by Erysiphe necator is one of the most harmful fungal diseases for this fruit-bearing species. Incorporating resistance genes such as Run1 and Ren1 in new vine selections offers a sustainable alternative to control the disease. These combined loci produce an immune response that prevents the development of the disease. However, to date studies are lacking concerning whether this response generates alterations in the physiological and antioxidant parameters of resistant plants in the presence of the fungus or if it has an associated energy cost. Therefore, the main goal of our research was to determine if Run1Ren1 plants present alterations in their physiological and biochemical parameters in the presence of the fungus. To achieve this target, a previously characterized resistant Run1Ren1 genotype and the susceptible Carménère cultivar were analyzed. We evaluated photochemical parameters (Fv'/Fm', ΦPSII and ETR), net photosynthesis (Pn), photosynthetic pigments, transpiration (E), stomatal conductance (g_s ), oxidative stress parameters (MDA), antioxidant activity, and phenols. Our results show that the physiological parameters of Run1Ren1 plants were not negatively affected by the fungus at 10 days post-inoculation, contrasting with alterations observed in the susceptible plants. Therefore, we propose that the resistance response triggered by Run1Ren1 is physiologically and biochemically advantageous to grapevines by preventing the development of powdery mildew infection.

Challenging the water stress index concept: Thermographic assessment of Arabidopsis transpiration

Water stress may greatly limit plant functionality and growth. Stomatal closure and consequently reduced transpiration are considered as early and sensitive plant responses to drought and salinity stress. An important consequence of stomatal closure under water stress is the rise of leaf temperature (T_leaf ), yet T_leaf is not only fluctuating with stomatal closure. It is regulated by several plant parameters and environmental factors. Thermal imaging and different stress indices, incorporating actual leaf/crop temperature and reference temperatures, were developed in previous studies toward normalizing for effects unassociated to water stress on T_leaf , aiming at a more efficient water stress assessment. The concept of stress indices has not been extensively studied on the model plant Arabidopsis thaliana. Therefore, the aim of this study was to examine the different indices employed in previous studies in assessing rosette transpiration rate (E) in Arabidopsis plants grown under two different light environments and subjected to salinity. After salinity imposition, E was gravimetrically quantified, and thermal imaging was employed to quantify rosette (T_rosette ) and artificial reference temperature (T_wet, T_dry ). T_rosette and several water stress indices were tested for their relation to E. Among the microclimatic growth conditions tested, RWSI₁ ([T_rosette  - T_wet ]/[T_dry  - T_wet ]) and RWSI₂ ([T_dry  - T_rosette ]/[T_dry  - T_wet ]) were well linearly-related to E, irrespective of the light environment, while the sole use of either T_wet or T_dry in different combinations with T_rosette returned less accurate results. This study provides evidence that selected combinations of T_rosette , T_dry , and T_wet can be utilized to assess E under water stress irrespective of the light environment.

Photosynthesis, Yield and Quality of Soybean (Glycine max (L.) Merr.) under Different Soil-Tillage Systems

Due to current climate changes and drought periods, it is recommended to cultivate soybean in no-plowing tillage systems. The conducted research is to contribute to a partial explanation of the course of photosynthesis processes in soybean plants, which may facilitate the decision making before sowing this species in a given tillage system. The aim of the study was to assess the dependence of photosynthesis on the yield and variable hydrothermal conditions of tillage systems, as well as their impact on the productivity and quality of soybean. A field experiment was carried out using soybean cv. Merlin, between 2017 and 2019 in Boguchwała, Poland. The plant tested was soybean cv. Merlin. The tillage systems—conventional (CT), reduced (RT) and no-tillage (NT)—were the experimental factors. The use of CT and RT influenced growth in leaf area index (LAI) and soil plant analysis development (SPAD) and improved the photosynthesis process, which increased the values of the maximal quantum yield of the photolysis system of the donor side of PSII (Fv/F0), and performance index of PS II (PI) and net photosynthetic rate (PN), stomatal conductance (gs) parameters, compared to NT. CT treatment increased the yield of soybean plants to significantly higher compared with NT treatment, and seeds treated with the CT treatment contained more protein. The content of fat and phosphorus (P) were significantly higher in the NT system and the content of potassium (K) from RT. In 2017, under drought conditions (the June–September period), the seed yield of NT was similar to the yield of CT and significantly higher than the yield of RT. The higher value of hydrothermal coefficients in 2019 resulted in an increase in photosynthesis parameters, seed yield as well as the content of fat and elements P and K.

Higher Photochemical Quenching and Better Maintenance of Carbon Dioxide Fixation Are Key Traits for Phosphorus Use Efficiency in the Wheat Breeding Line, RAC875

Maintaining carbohydrate biosynthesis and C assimilation is critical under phosphorus (P) deficiency as inorganic P (Pi) is essential for ATP synthesis. Low available P in agricultural soils occurs worldwide and fertilizer P sources are being depleted. Thus, identifying biosynthetic traits that are favorable for P use efficiency (PUE) in crops is crucial. This study characterized agronomic traits, gas exchange, and chlorophyll traits of two wheat genotypes that differ in PUE. RAC875 was a P efficient genotype and Wyalkatchem was a P inefficient genotype. The plants were grown in pots under growth room conditions at two P levels; 10 mg P kg^-1 soil (low P) and 30 mg P kg^-1 soil (adequate P) and gas exchange and chlorophyll fluorescence were measured at the vegetative and booting stages using a portable photosynthesis system (LI-6800, LI-COR, United States). Results showed significant differences in some agronomic traits between the two wheat genotypes, i.e., greater leaf size and area, and a higher ratio of productive tillers to total tillers in RC875 when compared with Wyalkatchem. The CO₂ response curve showed Wyalkatchem was more severely affected by low P than RAC875 at the booting stage. The relative ratio of the photosynthetic rate at low P to adequate P was also higher in RAC875 at the booting stage. Photochemical quenching (qP) in RAC875 was significantly higher when compared with Wyalkatchem at the booting stage. Maintaining CO₂ fixation capacity under low P and higher qP would be associated with P efficiency in RAC875 and measuring qP could be a potential method to screen for P efficient wheat.