Abstract
Vapor pressure deficit (VPD) is considered to be one of the major environmental factors influencing stomatal functions and photosynthesis, as well as plant growth in crop and horticultural plants. In the greenhouse cultivation, air temperature and relative air humidity are regulated by switching on/off the evaporative systems and opening/closing the roof windows, which causes VPD fluctuation. However, it remains unclear how VPD fluctuation affects photosynthetic and growth performance in plants. Here, we examined the effects of the VPD fluctuation on the photosynthetic and growth characteristics in lettuce (Lactuca sativa L.). The parameters for gas exchange and chlorophyll fluorescence and biomass production were evaluated under the conditions of drastic (1.63 kPa for 6 min and 0.63 for 3 min) or moderate (1.32 kPa for 7 min and 0.86 kPa for 3 min) VPD fluctuation. The drastic VPD fluctuation induced gradual decrease in stomatal conductance and thus CO2 assimilation rate during the measurements, while moderate VPD fluctuation caused no reduction of these parameters. Furthermore, data showed moderate VPD fluctuation maintained leaf expansion and the efficiency of CO2 diffusion across leaf surface, resulting in enhanced plant growth compared with drastic VPD fluctuation. Taken together, fine regulation of VPD can be crucial for better plant growth by maintaining the photosynthetic performance in lettuce. The present work demonstrates the importance of VPD control during plant cultivation in plant factories and greenhouses.
Highlights
Natural resource availability has been a limitation of agricultural industry throughout human history; agricultural production has been greatly threatened by water and nutrition shortage and insufficient available land for centuries
The fluctuating vapor pressure deficit (VPD) condition in the environmentally controlled chamber of portable photosynthesis system induced the fluctuation of a stomatal conductance, CO2 assimilation rate, electron transport rate (ETR) I and ETR II, the amplitude of the fluctuation was much larger in the stomatal conductance and CO2 assimilation rate than electron transport rate through PSI (ETR I) and ETR II (Figure 1)
The remaining activity of PSI showed no difference between two VPD conditions, that of PSII was significantly lower under drastic VPD fluctuation than moderate VPD fluctuation (Figure 2), suggesting that more photodamage at PSII would be accumulated under drastic VPD fluctuation
Summary
Natural resource availability has been a limitation of agricultural industry throughout human history; agricultural production has been greatly threatened by water and nutrition shortage and insufficient available land for centuries. Most plants would grow well at vapor pressure deficit (VPD) between 0.5 and 0.8 kPa (Bakker, 1991). The reduction of transpiration rate at high VPD is observed in most crop species (> 2.0 kPa; Gholipoor et al, 2010; ZamanAllah et al, 2011). Atmosphere water deficit can suppress the photosynthetic performance by directly impairing metabolic activities including the enzyme activity of Calvin-Benson cycles (Farquhar et al, 1989) and leads to the loss of biomass production throughout the crop growing period (Tibbitts, 1979; Grange and Hand, 1987; Bakker, 1991; Marsden et al, 1996; Leuschner, 2002; Codarin et al, 2006)
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