Effect of micro–spray on plant growth and chlorophyll fluorescence parameter of tomato under high temperature condition in a greenhouse

Abstract

Micro–spray is usually used to improve plant growth environment to avoid growth inhibiting and yield decreasing due to the high temperature inside the greenhouses in summer. To investigate the effect of micro–spray on plant growth and physiological properties, a combined irrigation method of micro–spray and drip irrigation (MSDI) was applied to tomato plants growing in a Venlo–type greenhouse for two seasons. The plant growth and physiological parameters of tomatoes grown under MSDI were compared with them under drip irrigation (DI). The running time of micro–spray was set based on the timing of high air temperature (Ta) appeared. The micro–spray was opened (7.5 L/h for each nozzle) for 1 min for each time point at 9:00, 10:00, 11:00, 12:00, 13:00 and 14:00 when the Ta was higher than 30 °C. The MSDI had a positive effect on plants growth (18% increased in stem diameter compared to DI) and the leaf temperature (Tl) decreased around 3–6 °C when the micro–spray was operated, and the cooling effect can be sustained for 10–30 min. Water use efficiency (WUE) under MSDI was similar to it under DI by comparing yield and total water consumption of tomato plants, and the total soluble solids (TSS) of tomato under two irrigation methods were similar (5.4% under DI and 5.5% under MSDI) during 2021.The results shown that the photosynthetically active radiation (PAR) and Ta were represented a negative correlation with chlorophyll fluorescence parameter (the effective quantum yield of PSII, ФPSII). The ФPSII value of tomato under MSDI was higher than it under DI during the micro–spray operating period, and it was more stable during the high Ta period. The improvement rate of ФPSII at different intensity of PAR (at 9:30, 10:30, 11:30, 12:30, 13:30 and 14:30) was varied, and it had a unified decline at 12:30 at the highest Tl during two seasons. Short time (1minute) micro–spray application did not have a remarkable effect on the adjusting of the damage caused by heat stress once temperature over 35 °C. Applying MSDI for tomato plants grown in greenhouse is recommended to reduce the severe effect on plant growth and physiology by high temperature. In addition, the result of this study provides a scientific guide for the development of intellectualization irrigation systems.