Abstract
In grape, high temperatures and low humidity prolong midday depression of foliar photosynthesis and dramatically reduce fruit yield. In this study, we explored the effects of various mist micro-spray treatments on grape photosynthesis at a test site in Shanshan County (N, 42.91°; E, 90.30°), Turpan, Xinjiang, China. We tested four different mist micro-spray durations including 1 h (WP1), 2 h (WP2), 3 h (WP3), and 0 h (CK). WP1, WP2, and WP3 affected canopy air temperature and humidity for 5 h, 7 h, and 9 h, respectively. At 12:30, WP1, WP2, and WP3 had the strongest cooling effect and altered temperature by −5.12 °C, −5.09 °C, and −5.17 °C respectively. The relative chlorophyll content was higher in the upper than the lower canopy leaves. There were no differences in the same leaf layers across treatments. The net photosynthesis and transpiration rates and stomatal conductance were higher for the upper than the lower canopy leaves. Compared with CK, the mist micro-spray treatments mitigated “midday depression” in the upper leaves and eliminated it altogether in the lower leaves. Mist micro-spray for 1 h d-1 most effectively improved grape leaf photosynthesis. The findings of the present study lay an empirical foundation for improving grape leaf photosynthesis and fruit yield.
Highlights
Photosynthesis provides energy for crop growth and determines harvest yield and quality (Rubio et al, 2003; Garnier et al, 2004)
The maximum difference in canopy air temperature between were applied for 1 h (WP1) and CK, between WP2 and CK, and between WP3 and CK were -5.12 °C, -5.09 °C, and -5.17 °C, respectively
The mist micro-spray only prevented stomatal limitation in the upper leaves. We propose that it was excessively high leaf temperature caused by non-stomatal-restricted active light radiation and not excessively high air temperature that caused "midday depression" in the upper leaves
Summary
Photosynthesis provides energy for crop growth and determines harvest yield and quality (Rubio et al, 2003; Garnier et al, 2004). Undesirable noontime environmental conditions such as excessive photosynthetically active radiation (Wu et al, 2019; Zhang et al, 2018), high or low air temperature (Zuo et al, 2017), and low relative humidity (Yuan et al, 2020) may induce "midday depression" in photosynthesis that can result in negative photosynthetic rate, lower photosynthetic efficiency, and significantly reduce crop yield. Various measures were proposed to increase photosynthesis including shading (Tang et al, 2019), air temperature control (Yang et al, 2018), air humidity (Wei et al, 2019) in order to prevent "midday depression". The effects of these modalities on field crops are unknown
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