Effects of rising VPD on the nutrient uptake, water status and photosynthetic system of tomato plants at different nitrogen applications under low temperature

In winter and spring, the low-temperature and high-humidity environment of greenhouses in China and some locations are not suited for the development of tomatoes, which is sensitive to cold. At low temperature circumstances, the plant growth is slow, and the water transpiration ability is weak. The study tried to increase the vapor pressure deficit (VPD) by decreasing the humidity to observe if it can promote plant transpiration, which in turn facilitates nutrient absorption conveyed by the water, or it directly influences plant development through the alteration of the plant morphological structure. Two VPD levels (high VPD, HVPD; low VPD, LVPD) and three N supply gradients (low N level, LN; normal N level, NN; high N level, HN) were set in a climate chamber for 30 days test. We observed the physiological alterations of plants. The results revealed that biomass of low nitrogen, normal nitrogen and high nitrogen of HVPD plants decreased by 22.54%, 40.75% and 10.31%, respectively, compared with LVPD-treated plants. The palisade/spongy tissue ratio in leaves of HVPD plants decreased at normal and high nitrogen levels. Under HVPD conditions, the stomatal length and width increased, but its density decreased; the electron transfer and photochemical efficiency of the photosystem reaction center reduced. At low, normal and high nitrogen concentration, the photosynthetic rate of HVPD plants was 17.29%, 30.18% and 15.15% lower than that of LVPD plants. For HVPD plants, compared with LVPD plants, K+ absorption under LN increases significantly; nutritional absorption with HN treatment reduced significantly; the absorption of trace elements was also lower than LVPD plants. It revealed that even within the theoretically suitable VPD range for plant growth, rising VPD cannot achieve the purpose of improving nutrient absorption and stimulating growth. It needed to be examined according to certain environmental circumstances. In addition, the promotion impact of increasing N fertilizer was restricted, and it may not be favorable to plant development. At low nitrogen, LVPD treated plants thrived nicely, compared with HVPD treated plants. The investigation revealed that the optimal growth treatment at low temperature was LVPD+NN treatment.