It is of great importance to study the changes in reference evapotranspiration (ET₀) and the factors that influence it to ensure sustainable and efficient water resource utilization. Daily ET₀ data calculated using the Penman–Monteith method from 37 meteorological stations located within Guangdong Province in the humid zone of southern China from 1960 to 2020 were analyzed. The trend analysis and Mann–Kendall test were used to analyze the time series changes in ET₀ and major climatic factors (air temperature (T), relative humidity (RH), sunshine duration (SD), and wind speed (u₂)) for over 61 years. Sensitivity and contribution analyses were used to evaluate the driving factors of ET₀. The main findings of the study are as follows: (1) the trend in average annual ET₀ time series in Guangdong slightly increased at a trend rate of 1.61 mm/10a over the past 61 years, with most stations experiencing an increase in ET₀. During the same period, air temperature significantly increased, while RH and SD decreased; u₂ also decreased. (2) Sensitivity analysis showed that ET₀ was more sensitive to RH and T than SD and u₂, with ET₀ being most sensitive to RH in spring and winter and T in summer and autumn. (3) The contribution analysis showed that T was the dominant factor for ET₀ variation in Guangdong, followed by SD. SD was found to be the dominant factor in ET₀ changes in areas where the “evaporation paradox” occurred, as well as in spring and summer. The study concludes that the climate in Guangdong became warmer and drier over the past 61 years, and if the current global warming trend continues, it will lead to higher evapotranspiration and drought occurrence in the future.

Selections of drought-tolerant cultivars and drought-stress diagnosis are important for sugarcane production under seasonal drought, which becomes a crucial factor causing sugarcane yield reduction. The main objective of this study was to investigate the differential drought-response strategies of drought-resistant (‘ROC22’) and -susceptible (‘ROC16’) sugarcane cultivars via photosynthetic quantum efficiency (Φ) simulation and analyze photosystem energy distribution. Five experiments were conducted to measure chlorophyll fluorescence parameters under different photothermal and natural drought conditions. The response model of Φ to photosynthetically active radiation (PAR), temperature (T), and the relative water content of the substrate (rSWC) was established for both cultivars. The results showed that the decreasing rate of Φ was higher at lower temperatures than at higher temperatures, with increasing PAR under well-watered conditions. The drought-stress indexes (ε_D) of both cultivars increased after rSWC decreased to the critical values of 40% and 29% for ‘ROC22’ and ‘ROC16’, respectively, indicating that the photosystem of ‘ROC22’ reacted more quickly than that of ‘ROC16’ to water deficit. An earlier response and higher capability of nonphotochemical quenching (NPQ) accompanied the slower and slighter increments of the yield for other energy losses (Φ_NO) for ‘ROC22’ (at day5, with a rSWC of 40%) compared with ‘ROC16’ (at day3, with a rSWC of 56%), indicating that a rapid decrease in water consumption and an increase in energy dissipation involved in delaying the photosystem injury could contribute to drought tolerance for sugarcane. In addition, the rSWC of ‘ROC16’ was lower than that of ‘ROC22’ throughout the drought treatment, suggesting that high water consumption might be adverse to drought tolerance of sugarcane. This model could be applied for drought-tolerance assessment or drought-stress diagnosis for sugarcane cultivars.

Heat stress severely impairs normal plant growth and yield, which significantly limits the horticultural and productive application of most Rhododendron species. In contrast, Rhododendron hainanense exhibits considerable heat tolerance due to its unique growing environment; however, the molecular mechanisms underlying its response to heat stress remain poorly understood. In this study, R. hainanense plants were subjected to heat stress treatment. Combined transcriptomic and metabolomic analyses identified 5454 differentially expressed genes and 152 differential metabolites. The results demonstrated that heat stress significantly induced the accumulation of flavonoids in R. hainanense. Notably, derivatives of myricetin, quercetin, and kaempferol were abundantly accumulated, suggesting their potential role in aiding plant defense against heat stress. The significant up-regulation of specific Rh4CL and RhFLS genes under high-temperature stress, coupled with the substantial accumulation of their flavonoid products (myricetin, quercetin, and kaempferol), indicates a potential role for these metabolites in the thermotolerance of Rhododendron hainanense. These findings provide novel insights into the heat stress response and flavonoid biosynthesis regulation in R. hainanense, highlighting the critical role of flavonoids in plant adaptation to heat stress. This study offers valuable references for the genetic improvement of Rhododendron cultivars with high stress resistance.

Elucidating nutrient requirements is crucial for the fertilization management of fruit trees. The current study explored the nutrient uptake and allocation patterns of macro- (N, P, K, Ca and Mg) and micro- (Fe and Zn) elements during the vegetative and reproductive periods of 15-year-old ‘Keitt’ mango trees in Southwest China. The contents of N, P, K, Ca, and Mg were significantly higher in young organs than in perennial organs, while Fe and Zn exhibited the highest accumulation in perennial branches. For yielding 100 kg of fruit in each mango tree, the annual total uptake of N, P, K, Ca, Mg, Fe, and Zn was 601.32, 93.45, 275.74, 541.50, 88.68, 21.22, and 1.35 g, respectively. Nutrient allocation showed element-specific patterns during the annual growth cycle. Nutrient losses from pruning and fallen flowers and fruits accounted for 27.74–38.94% of the total nutrient uptake of each tree. The harvested fruits contained 3.79–32.89% of the total nutrient uptake of each tree; furthermore, K and Mg were the two highest amounts in the fruit. The Ca requirement was significantly higher than those of P and K in mango trees; however, only 2% of the total Ca in each tree was distributed in the fruit. These findings can contribute to in-season fertilization strategies for mature mango orchards according to nutrient uptake per tree and fruit yield.