Research on plant photosynthetic characteristics and regulation mechanisms in photovoltaic greenhouses under fluctuating solar radiation

Development of photovoltaic greenhouses is constrained by the challenge of matching crop photosynthetic responses with environmental regulation under fluctuating light and thermal conditions. Although environmental regulation of crop circadian rhythms can be achieved under natural light, the impacts of light-thermal fluctuations on photosynthesis and the associated high energy consumption of environmental control remain unresolved. This study focused on strawberries to investigate the characteristics of temperature and humidity variations within PV greenhouses and their relationship with photosynthetic rate. Air enthalpy was introduced as a comprehensive regulatory indicator to analyze its variation patterns in the greenhouse and its influence on crop photosynthesis. Results showed a significant antagonistic effect between temperature and humidity, with more pronounced regulatory effects when temperature exceeded 24 °C. The critical enthalpy value for photosynthesis initiation was identified as 75 kJ/kg, and the photosynthetic rate peaked within an enthalpy range of 85–90 kJ/kg. Latent heat in the air was found to be a key factor affecting environmental and energy exchange in PV greenhouses. Based on the relationship between enthalpy and photosynthetic rate, a dynamic regulation strategy was proposed using the critical enthalpy value as a threshold. By adjusting temperature and humidity in stages, this strategy achieves dynamic matching between environmental conditions and crop physiological needs. Compared to conventional temperature-based control, the proposed approach reduces energy consumption by 21.81 %–32.05 %, providing theoretical and empirical support for efficient and energy-saving environmental regulation in PV greenhouses under fluctuating natural light.