Abstract
The role of a proposed micro-fog system in regulating greenhouse environments and enhancing tomato (Solanum lycopersicum L.) productivity during summer season was studied. Experiments were carried out in a multi-span glass greenhouse, which was divided into two identical compartments involving different environments: (1) without environment control and (2) with a micro-fog system operating when the air vapor pressure deficit (VPD) of greenhouse was higher than 0.5 KPa. The micro-fog system effectively alleviated heat stress and evaporative demand in the greenhouse during summer season. The physiologically favourable environment maintained by micro-fog treatment significantly enhanced elongation of leaf and stem, which contributed to a substantial elevation of final leaf area and shoot biomass. These improvements in physiological and morphological traits resulted in around 12.3% increase of marketable tomato yield per plant. Relative growth rate (RGR) of micro-fog treatment was also significantly higher than control plants, which was mainly determined by the substantial elevation in net assimilation rate (NAR), and to a lesser extent caused by leaf area ratio (LAR). Measurement of leaf gas exchange parameters also demonstrated that micro-fog treatment significantly enhanced leaf photosynthesis capacity. Taken together, manipulation of VPD in greenhouses by micro-fog systems effectively enhanced tomato growth and productivity via improving photosynthesis during summer season.
Highlights
In the northern China, high temperature and heat stress are currently observed in greenhouses during summer, especially around midday
Inhibition of photosynthesis caused by the high temperature and low humidity can limit plant growth and dry matter accumulation, and reduce yield, which already became a major constrain for the sustainable greenhouses vegetable production in northern China during summer season [6]
Spatial distribution of droplet size was not uniform: percentage of larger droplets increased from ground to nozzles (S2 Fig)
Summary
In the northern China, high temperature and heat stress are currently observed in greenhouses during summer, especially around midday. By regulating stomatal aperture and the transpiration water loss, plant can attempt to minimize water deficit. This regulation has an adaptive significance in protecting plant vascular systems from dysfunction, but the reduction in stomatal aperture is accompanied by depressing effects on stomatal conductance for CO2 diffusion, leading to a sharp decline in photosynthesis rate [2,3,4,5]. Inhibition of photosynthesis caused by the high temperature and low humidity (high vapor pressure deficit, VPD) can limit plant growth and dry matter accumulation, and reduce yield, which already became a major constrain for the sustainable greenhouses vegetable production in northern China during summer season [6]
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