Effects of Short-Term High Temperature on Gas Exchange in Kiwifruits (Actinidia spp.)

SIMPLE SUMMARY: Climate changes occurring today require detailed research of the effects of increasing temperatures on photosynthesis in different species and cultivars. In addition, it is very important to determine how different Actinidia species growing in the temperate climate zone will respond to global climate change and increasing temperatures. Temperature variability is a crucial determinant of the yield and quality of plants, particularly when high-temperature episodes coincide with their growth and fruit development. Species and cultivars that can adapt to extreme temperatures and are least affected by these temperatures should be determined and used for high-quality and profitable production in the coming years. In this study, the effects of environmental factors on photosynthetic activity and gas exchange in Actinidia species with different ploidy levels were evaluated. Tetraploids showed higher high-temperature resistance, while hexaploids had the highest net photosynthetic rate. Our research showed that the high-temperature tolerance of kiwifruits existed not only in different species but also among cultivars. As a result, it was determined that high temperatures have important effects on the photosynthetic activities of kiwifruit plants with different ploidy levels, and that these effects can significantly change their development according to how they differ among different species/cultivars. ABSTRACT: Climate changes occurring today require detailed research of the effects of increasing temperatures on photosynthesis in different species and cultivars. Temperature variability is a crucial determinant of the yield and quality of plants, particularly when high-temperature episodes coincide with their growth and fruit development. The effect of high temperature (HT) on higher plants primarily concerns photosynthetic functions, but the sensitivity of photosynthesis to high temperature is not well-understood in kiwifruits. In this study, we designed a new environmental monitoring system to evaluate the effects of environmental factors on the photosynthetic physiology of different kiwifruit species and cultivars. A significant positive correlation was determined between the main photosynthetic indices of kiwifruits, such as transpiration rate and net photosynthetic rate. The net photosynthetic rate of commercial kiwifruit cultivars was strongly inhibited when the temperature exceeded 44.5 °C, and the leaves of kiwifruits were irreversibly damaged when the temperature increased to 52 °C. Kiwifruit cultivars with different ploidy levels (diploid, tetraploid and hexaploid) were found to be sensitive to high temperature, whereas tetraploids had higher HT resistance and hexaploids had the highest net photosynthetic rate. Further research showed that the HT tolerance of kiwifruits existed not only between species but also among cultivars. A. eriantha had the highest net photosynthetic rate at more than 44.7 °C, but those of A. deliciosa and A. arguta declined sharply as the temperature exceeded 43.5 °C. As a result, it was determined that high temperatures have important effects on the photosynthetic activities of kiwifruit plants with different ploidy levels, and that these effects can significantly change their development according to how they differ among different species/cultivars.