Response of photosynthesis, transpiration and different scales of water use efficiency to water and nitrogen in greenhouse tomato at three growth stages in Northeastern China

Abstract

Elucidating the physiological mechanisms underlying crop responses to water and nitrogen availability can help optimize the irrigation and fertilization of greenhouse−cultivated tomatoes. This study aimed to determine how photosynthetic and transpiration characteristics and water use of greenhouse−cultivated tomatoes in Northeast China respond to water and nitrogen treatments under different growth stages. Three irrigation levels (W1−W3) were controlled using the upper and lower irrigation limits, which were 75±5%θfc ,85±5%θfc and 95±5%θfc respectively; and the lower limits were 65±5%θfc, 75±5%θfc and 85±5%θfc respectively (where θfc is the field holding capacity). Three levels of N application were used: N1 (180 kg hm−2 soil), N2 (240 kg hm−2 soil) and N3 (360 kg hm−2 soil). The results showed that tomatoes at flowering and fruiting stage (Stage 1) were not suitable for water deficiency (W1) and high N application (N3), and leaf instantaneous water use efficiency (WUEins) and yield were more significantly correlated. The fruiting stage (Stage 2) was the growth stage with the weakest negative correlation (R2=0.24−0.49) between water use efficiency (leave scale and plant scale) and yield, and the water−nitrogen interaction started to show positive regulation of all indicators in tomato, so it was the best growth stage to appropriately improve water use efficiency and save water. At ripening stage (Stage 3), irrigation water use efficiency (WUEi) and yield were more significantly correlated. N3 supply could compensate or improve photosynthesis, transpiration index and WUE in the early and mid−growth stages. Water and nitrogen had a significant time−scale effect on the correlation between net photosynthetic rate (Pn) and stem flow rate, but the fit results were good (R2=0.92–0.40) for developing their fitting models under various growth stages. The increase in Pn and chlorophyll content (SPAD) under the W2N2 treatment was not accompanied by an excessive increase in transpiration rate (Tr) and stomatal conductance (Gs), and response of Pn to stem flow rate was minimized by the time scale effect (R2=0.90–0.74), and the water use efficiency and yield at all scales at a superior level. As a result, W2N2 is suggested as the best water and nitrogen treatment for use in greenhouse tomatoes in Northeastern China. The findings of this study can serve as a foundation for smart water and nitrogen management strategies for various greenhouse tomato growth stages in Northeastern China.