Understanding the distribution of plant moisture during the seedling stage of greenhouse crops is challenge in developing scientific irrigation strategies and proposing effective cooling methods. This study investigated the effects of different soil moisture contents [W1: 25-35 % (severe drought), W2: 35-45 % (mild drought), W3: 45-55 % (suitable moisture), and W4: 55-65 % (excess moisture)] on tomato seedlings under summer greenhouse thermic extremes. Furthermore, thermal infrared imaging and chlorophyll fluorescence multi-dimensional digital image sensors were used to determine differences in tomato seedling morphology and plant physiology. The increase in canopy area under W1 and W4 soil moisture content was smaller than that of W2 and W3, and the canopy area of the W1 group decreased as the high temperature condition continued. The average canopy temperature of each treatment generally increased first, and then plateaued. From high to low, average temperatures were 28.15 degrees C in W1, 27.73 degrees C in W4, 26.67 degrees C in W2, and 25.72 degrees C in W3. The canopy temperature gradually decreased from the middle to the edge of the leaf (stem temperature > leaf base temperature > leaf vein temperature > leaf edge temperature). The F-v/F-m ratio in the chlorophyll fluorescence index qualitatively expresses the degree of water stress. phi PSII, non-photochemical quenching (NPQ), and qP values were used as indicators to quantitatively analyze stress in leaves of different maturity. A preliminary mathematical relationship between the canopy and NPQ was established. This study quantitatively characterized the morphological and physiological changes of tomato seedlings in the greenhouse during summer, visualized the process of canopy temperature changes, and provided a theoretical basis for mitigating heat-induced damage.

Heatwaves and soil droughts are increasing in frequency and intensity, leading many tree species to exceed their thermal thresholds, and driving wide-scale forest mortality. Therefore, investigating heat tolerance and canopy temperature regulation mechanisms is essential to understanding and predicting tree vulnerability to hot droughts. We measured the diurnal and seasonal variation in leaf water potential (Psi), gas exchange (photosynthesis A(net) and stomatal conductance g(s)), canopy temperature (T-can), and heat tolerance (leaf critical temperature T-crit and thermal safety margins TSM, i.e., the difference between maximum T-can and T-crit) in three oak species in forests along a latitudinal gradient (Quercus petraea in Switzerland, Quercus ilex in France, and Quercus coccifera in Spain) throughout the growing season. Gas exchange and Psi of all species were strongly reduced by increased air temperature (T-air) and soil drying, resulting in stomatal closure and inhibition of photosynthesis in Q. ilex and Q. coccifera when T-air surpassed 30 degrees C and soil moisture dropped below 14%. Across all seasons, T-can was mainly above T-air but increased strongly (up to 10 degrees C > T-air) when A(net) was null or negative. Although trees endured extreme T-air (up to 42 degrees C), positive TSM were maintained during the growing season due to high T-crit in all species (average T-crit of 54.7 degrees C) and possibly stomatal decoupling (i.e., A(net) 0). Indeed, Q. ilex and Q. coccifera trees maintained low but positive g(s) (despite null A(net)), decreasing Psi passed embolism thresholds. This may have prevented T-can from rising above T-crit during extreme heat. Overall, our work highlighted that the mechanisms behind heat tolerance and leaf temperature regulation in oak trees include a combination of high evaporative cooling, large heat tolerance limits, and stomatal decoupling. These processes must be considered to accurately predict plant damages, survival, and mortality during extreme heatwaves.

Penstemon, with more than 250 species native to North America, holds signi fi cant aesthetic and ecological value in Utah, supporting diverse pollinators. Despite their signi fi cance, the survival of penstemon is threatened by challenges such as habitat loss, climate change, and Utah ' s naturally high soil salinity. To address these challenges and understand their adaptability, this study evaluated the salt tolerance of two penstemon species [ Penstemon davidsonii (Davidson ' s penstemon) and Penstemon heterophyllus (foothill penstemon)] under controlled greenhouse conditions. The aim was to develop baseline information for nursery production and landscape use that utilize reclaimed water for irrigation. Plants were irrigated weekly with a nutrient solution at an electrical conductivity (EC) of 1.0 dSm - 1 as control or a saline solution at an EC of 2.5, 5.0, 7.5, or 10.0 dSm - 1 for 8 weeks. Half of the plants were harvested after four irrigation events, and the remaining plants were harvested after eight irrigation events. At harvest, visual rating (0 = dead and 5 = excellent without foliage salt damage), plant width, number of shoots, leaf area, shoot dry weight, leaf greenness [Soil Plant Analysis Development (SPAD)], stomatal conductance, and canopy temperature were collected to assess the impact of salinity stress. In both species, salt damage was dependent on the salinity levels and length of exposure. After four irrigation events, both species exhibited foliage damage that increased in severity with rising EC. The most severe damage was observed in plants receiving saline solution at an EC of 10.0 dSm - 1 . After eight irrigation events, P. davidsonii exposed to a saline solution with an EC of 10.0 dSm - 1 received a visual rating of 0, whereas P. heterophyllus had a visual rating of 0.4. Both species exhibited salinity -induced effects, with variations observed in the speci fi c parameters and the degree of response. Penstemon davidsonii exhibited signi fi - cant salinity stress, as indicated by reduced leaf area, shoot dry weight, SPAD reading, and stomatal conductance with increasing EC of the saline solution. In addition, in both species, at both harvests, canopy temperatures increased either linearly or quadratically by 8% to 36% as the EC levels of the saline solution increased. These results indicate that P. davidsonii was more sensitive to salinity stress than P. heterophyllus .

Introduction Plant responses to drought stress are influenced by various factors, including the lateral root angle (LRA), stomatal regulation, canopy temperature, transpiration rate and yield. However, there is a lack of research that quantifies their interactions, especially among different cotton varieties.Methods This experiment included two water treatments: well-watered (75 +/- 5% soil relative water content) and drought stress (50 +/- 5% soil relative water content) starting from the three-leaf growth stage.Results The results revealed that different LRA varieties show genetic variation under drought stress. Among them, varieties with smaller root angles show greater drought tolerance. Varieties with smaller LRAs had significantly increased stomatal opening by 15% to 43%, transpiration rate by 61.24% and 62.00%, aboveground biomass by 54% to 64%, and increased seed cotton yield by 76% to 79%, and decreased canopy temperature by 9% to 12% under drought stress compared to the larger LRAs. Varieties with smaller LRAs had less yield loss under drought stress, which may be due to enhanced access to deeper soil water, compensating for heightened stomatal opening and elevated transpiration rates. The increase in transpiration rate promotes heat dissipation from leaves, thereby reducing leaf temperature and protecting leaves from damage.Discussion Demonstrating the advantages conferred by the development of a smaller LRA under drought stress conditions holds value in enhancing cotton's resilience and promoting its sustainable adaptation to abiotic stressors.