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This study was conducted to investigate the effect of atmosphere-leaf vapor pressure deficit (VPD) in Allium microdictyon Prokh, and Allium ochotense Prokh. The vapor pressure deficit (VPD) was rapidly increased with increasing temperature and decreasing relative humidity. Taken as a whole, the stomatal transpiration reaction was slightly late with increading of VPD. Maximum photosynthetic rate at high-VPD condition was 5.98μmol CO₂· m-2 s-1 in Allium microdictyon, which was a little lower than 6.59umol CO₂· m-2 · s-1 in Allium ochotense, respectively. After 2p.m, stomatal transpiration of Allium microdictyon at the high VPD condition were rapidly decreased, Ci/Ca began to decline sharply at 8a.m and showed the lowest value at 2p.m, The results showed that Ci/Ca decreased with being used CO₂ in the mesophyll intercellular space for photosynthesis, In high VPD condition, The water potential values showed the highest at 5a.m, and the lowest at 1p.m in high VPD condition. The water saturation deficits (WSD) in high VPD condition showed about 1.5 times higher than in low VPD condition, The results indicated that physiological activities in Allium microdictyon is more limited from high VPD conditions.
Lee et al. (Sat,) studied this question.