Impact of nitrogen deficiency on biomass production, leaf gas exchange, and betacyanin and total phenol concentrations in red beet (Beta vulgaris L. ssp. vulgaris) plants - G. Salahas; A. Papasavvas; E. Giannakopoulos; T. Tselios; H. Konstantopoulou; D. Savvas (European Journal of Horticultural Science)