Moisture and short-term UV-B radiation effect on nitrate and photosynthesis in Spinacia oleracea

Abstract

The objective of this study was to evaluate the effects of substrate moisture and short-term UV-B irradiation on spinach’s (Spinacia oleracea) nitrate ion assimilation and photosynthesis intensity. Experiment was conducted in growth chambers of controlled environment at the Institute of Horticulture, Lithuanian Research Centre for Agriculture and Forestry. Three separate chambers (24 m2each) were used for the study. Seeds of spinach plant were sown in120 ml vessels (one seed per vessel) in peat substrate (Durpeta, Lithuania). Plants were placed at 18/13⁰C day/night thermo period and 12/12h day/night photoperiod. High pressure sodium lamps (SON-T Agro, Philips) were used for illumination (photon flux density 150 μ mol m-2 s-1). Plants were grown in those conditions 21 days before the experiment started. Plants were grown in peat substrate at two moisture regimes: well watered (̴ 40 %) and mild water deficiency (̴ 25 %) substrate moisture. After 7 days effect of substrate moisture plants were exposed to 0 kJm-2day-1, 1 kJm-2day-1 and 2 kJm-2 day-1 UV-B for 1 day. The results showed that UV-B radiation, independently of dosage, resulted in decrease of nitrate ion content in spinaches grown in well-watered substrate. When spinaches were exposed to1 kJm-2day-1 UV-B radiation, nitrate ion content determined 1.58 times lower and when plants were exposed to 2 kJm-2day-1 – it was 1.42 times lower as compared to UV-B untreated plants. Statistically reliable effect of UV-B dosage on nitrate ion content in plants grown in mild water deficiency was not identified. Photosynthesis intensity also decreases under UV-B exposure in spinaches grown in both moisture conditions. Plants affected by UV-B radiation and grown in well-watered substrate showed significantly lower photosynthesis intensity decrease. [...].