With the expansion of cucumber cultivation, many growers continue to experience extreme weather and environmental issues. This study aimed to examine and model the effects of low temperature (LT) and poor light (PL) stresses on cucumber growth. The experiment was designed as an orthogonal experiment that analyzed temperature, light, and duration. The daily maximum/minimum temperatures of the experiment were set as per the following four levels: 13 °C/3 °C, 16 °C/6 °C, 19 °C/9 °C, 22 °C/12 °C, and the control at 28 °C/18 °C. The light was divided into two levels: 200 μmol∙m⁻²∙s⁻¹ and 400 μmol∙m⁻²∙s⁻¹, with 800 μmol∙m⁻²∙s⁻¹ as the control. Treatment duration was set at 2, 5, 8, and 11 days. Stress with different LT, PL, and duration was expressed using the stress effect (0–1), which decreased with an increase in stress level. Meanwhile, treatment with a temperature of 3 °C and light of 400 μmol∙m⁻²∙s⁻¹ for 11 days had the smallest effect on stress, which was only 67% of that of the control following 50 days of recovery, and had the most severe effect on cucumber growth. The proportion of dry weight allocated to leaves and stems decreased with increasing low temperatures and poor light stress, but the proportion allocated to fruit increased. The highest percentage of fruit distribution was found in the treatment with temperature of 9 °C, light of 200μmol∙m⁻²∙s⁻¹, and 11 days duration, being 3.57 times higher than the control. In order to better investigate the effects of LT and PL stress on cucumber growth, light and temperature effect (LTE), growing degree days (GDD), and product of thermal effectiveness and PAR (TEP) models were developed based on temperature and light. The root mean square error (RMSE) of the LTE model was found to be 4.214 g∙plant⁻¹, 36.3% of that of the GDD model and 78.8% of that of the TEP model, better simulating the above-ground dry weight of cucumber plants.

High temperatures have become a severe factor limiting growth and yield for tomatoes (Lycopersicon esculentum Mill.) due to unfavorable, above-optimum temperatures. Temperature and nitrogen application were the main regulatory factors in tomato plant cultivation. This research was undertaken to evaluate the effects of nitrogen application and high temperature on tomato morphology, dry matter accumulation and distribution, root vitality and nitrogen content of the above ground. Tomato variety “Jinfen No. 1” was planted and exposed to 4 day/night temperature levels (25 °C/15 °C as control CKT; 30 °C/20 °C, lightly high-temperature LHT; 35 °C/25 °C, moderate high-temperature MHT; 40 °C/30 °C, severe high temperature SHT) for 7 days after five nitrogen supply levels (N1–N5: 0, 1.3, 1.95, 2.6 and 3.75 g/plant, respectively; 2.6 g/plant is the recommended nitrogen-application rate, as control CKTN4). Within conditions, there was an extremely significant difference (p < 0.01) in all tomato plant parameters and an extremely significant interaction (p < 0.01) between high temperatures and nitrogen supply levels, except for plant height sampling on the 1st day in the recovery period. Dry matter accumulation decreased, and the accumulation rate slowed down. Dry matter accumulation under low nitrogen treatment was higher than in high nitrogen treatment. The proportion of dry matter in leaves decreased, the proportion of dry matter in stems increased and the difference in dry matter accumulation and proportion of dry matter between different nitrogen treatments decreased. Under LHT, the root activity of the tomato was increased under all nitrogen levels, while under MHT and SHT, high nitrogen and low nitrogen supply significantly inhibited root activity. Lightly high-temperature stress can increase root activity, and LHTN4 can increase by 5.15% compared with CKTN4. Appropriate nitrogen application can alleviate the damage caused by high-temperature stress on tomato plants and enhance the resistance of tomato plants, while excessive nitrogen application will aggravate the damage degree of tomato plants. In this study, the optimal nitrogen application rates under CKT-SHT treatment were 2.6, 2.6, 1.95 and 1.3 g/plant, respectively.

To study the impact of nitrogen application on the photosynthetic structure and photosystem activity of tomato (Lycopersicon esculentum Mill.) leaves during the recovery stage after heat stress, the OJIP curve and JIP parameters were determined through a control experiment in an artificial climate chamber. The tomato variety was “Jinfen No. 1”. Four day/night temperature levels (25 °C/15 °C as control CKT; 30 °C/20 °C, lightly high-temperature LHT; 35 °C/25 °C, moderate high-temperature MHT; 40 °C/30 °C, severe high-temperature SHT) were set for a duration of 7 days. Five nitrogen supply levels (N1–N5: 0, 1.3, 1.95, 2.6 and 3.75 g/plant, respectively; 2.6 g/plant is the recommended nitrogen application rate, CKTN4) were applied. The results showed that the O, K, J, I and P phases on the chlorophyll a fluorescence curve were significantly affected by different nitrogen treatments in heat stress recovery. Compared with CKT, with the increase in nitrogen supply, the fluorescence intensity of SHTN2-SHTN5 treatment increased significantly at P, I and J phases, while that of MHTN1-MHTN4 treatment decreased. The fluorescence intensity of SHTN5 and SHTN3 increased by 13.27% and 10.10% in the P phase, 13.52% and 12.1% in the I phase and 20.16% and 26.18% in the J phase, respectively. There were highly significant differences (p < 0.01) in the impact of high temperatures and nitrogen levels on the fluorescence parameters. On the 1st day after short-term heat stress, N had no significant effect on ${\mathrm{F}}_{\mathrm{v}}/{\mathrm{F}}_{\mathrm{M}}$, ${\mathrm{F}}_{\mathrm{v}}$, ${\mathrm{F}}_{\mathrm{o}}$ and ${\mathrm{F}}_{\mathrm{M}}$; however, their interaction was significant (p < 0.05). On the 8th day, there were no significant interaction effects between HT and N for ${\mathrm{F}}_{\mathrm{v}}/{\mathrm{F}}_{\mathrm{o}}$, ABS/RC and ${\mathrm{D}\mathrm{I}}_{\mathrm{o}}/\mathrm{R}\mathrm{C}$. ${\mathrm{F}}_{\mathrm{v}}/{\mathrm{F}}_{\mathrm{o}}$ proved to be sensitive to the application of both high temperatures and nitrogen. Under all five nitrogen applications, temperature played a significant role in increasing ${\mathrm{D}\mathrm{I}}_{\mathrm{o}}/\mathrm{R}\mathrm{C}$, especially for N2 and N3. The results indicated that decreasing the nitrogen application under SHT resulted in a higher number of active $\mathrm{R}\mathrm{C}\mathrm{s}$ and an increased value of specific energy flux ($\mathrm{A}\mathrm{B}\mathrm{S}/\mathrm{R}\mathrm{C}$, ${\mathrm{T}\mathrm{R}}_{\mathrm{o}}/\mathrm{R}\mathrm{C}$ and ${\mathrm{D}\mathrm{I}}_{\mathrm{o}}/\mathrm{R}\mathrm{C}$), indicating the enhanced ability of $\mathrm{R}\mathrm{C}$ to reduce plastoquinone. The study provides a reference for the diagnosis of nitrogen nutrition under high-temperature stress using chlorophyll fluorescence methods.

Chilling injury can adversely affect strawberry bud differentiation, pollen vitality, fruit yield, and quality. Photosynthesis is a fundamental process that sustains plant life. However, different strawberry varieties exhibit varying levels of cold adaptability. Quantitatively evaluating the physiological activity of the photosynthetic system under low-temperature chilling injury remains a challenge. In this study, we investigated the effects of different levels of chilling stress on twenty photosynthetic fluorescence parameters in strawberry plants, using short-day strawberry variety “Toyonoka” and day-neutral variety “Selva” as representatives. Three dynamic chilling treatment levels (20/10 °C, 15/5 °C, and 10/0 °C) and three durations (3 days, 6 days, and 9 days) were applied to each variety. WUE, LCP, Y(II), qN, ${\mathrm{S}\mathrm{I}\mathrm{F}}_{{\mathrm{O}}_2-\mathrm{B}}$ and ${\mathrm{r}\mathrm{S}\mathrm{I}\mathrm{F}}_{{\mathrm{O}}_2-\mathrm{B}}$ were selected as crucial indicators of strawberry photosynthetic physiological activity. Subsequently, we constructed a comprehensive score to assess the strawberry photosynthetic system under chilling injury and established a hyperspectral inversion model for stress quantification. The results indicate that the short-day strawberry “Toyonoka” exhibited a recovery effect under continuous 20/10 °C treatment, while the day-neutral variety “Selva” experienced progressively worsening stress levels across all temperature groups, with stress severity higher than that in “Toyonoka”. The BPNN model for the comprehensive assessment of the strawberry photosynthetic system under chilling injury showed optimal performance. It achieved a stress level prediction accuracy of 71.25% in 80 validation samples, with an R² of 0.682 when fitted to actual results. This study provides scientific insights for the application of canopy remote sensing diagnostics of strawberry photosynthetic physiological chilling injury in practical agricultural production.

Heat stress is a serious threat to tomato production. The ultrastructure and element mapping of tomato chloroplast were investigated under different nitrogen levels to explore the regulatory effect of nitrogen on tomato chloroplast under heat stress. Experiments design two temperature treatments (25°C/15°C, as control, 40°C/30°C, as severe high-temperature, SHT ) and four nitrogen levels (0.0 kg hm-2, N1; 187.5 kg hm-2, N2; 250 kg hm-2, N3, as recommended nitrogen-application; 312.5kg hm-2 , N4) for a duration of 5 days in artificial climate chamber. The results showed that heat stress led to obvious damage to the ultrastructure of tomato chloroplast, including thylakoid stacking disorder, granum destruction, and starch grain aggregation and degradation. With the increase of nitrogen level, the ratio of long and short axes of tomato chloroplasts increased, the differentiation of chloroplasts was strengthened, the number of plastoglobuli was increased and aggregated, and the degree of damage to the ultrastructure of chloroplasts was reduced. The regulatory effect of nitrogen on the ultrastructure of tomato chloroplasts under heat stress was mainly reflected in the phosphorylation degradation process of starch granules in chloroplasts. There are obvious segmentation lines of Ca, P and Cl on both sides of the inner and outer chloroplasts, and enriched in the chloroplasts, which can outline the boundary of the chloroplasts. Element mapping analysis revealed that heat stress significantly increased the contents of calcium, phosphorus and chlorine in the chloroplast of tomato leaves, while the contents of potassium was decreased. The application of nitrogen fertilizer could significantly regulate the element distribution of tomato chloroplast under heat stress, especially the regulation of phosphorus, chlorine, calcium, magnesium. These results provide new insight into the role of nitrogen using TEM-EDX mapping in the protection of tomato chloroplast under heat stress and the mechanism of heat stress tolerance in plants.