LAUSR

Abstract Recent trends in global warming have restricted the cropping periods in Japan, as ambient temperature during summer often rises above 35 °C and concomitantly, the air temperature inside a greenhouse can reach up to 50 °C. In this study, we investigated a strategy for reducing heat stress for sustainable greenhouse cultivation of spinach. Generally, this species is not cultivated during hot seasons due to heat-induced inhibition of growth. We compared the growth of spinach with and without a micro-mist system that produced mist with an average particle size of 10 μm. Our system effectively reduced the temperature in the greenhouse by as much as 4.3 °C through the evaporation of mist. Additionally, when temperature in the control area peaked at 37.4 °C, the temperature in the micro-mist area was 3.7 °C lower. Furthermore, average soil temperature decreased maximum average soil-temperature by 0.7 °C and average daily humidity was approximately 5 % higher. Consequently, crop yield increased by 30 %. Finally, spinach mineral content with/without micro-mist in the hot season did not differ from that measured in spinach grown conventionally, while spinach grown in the hot season with the micro-mist system had 1.4-fold greater lutein content than spinach grown conventionally. Altogether, our results demonstrate that spinach can be cultivated even during hot seasons in greenhouses equipped with a micro-mist system, without any significant decrease in mineral or lutein content.