1Hellenic Sugar Industry SA, Larissa factory, Department of Experimentation, 411 10 Larissa, Hellas, Greece
2Hellenic Sugar Industry SA, Agronomic Research Service, 574 00 Sindos, Hellas, Greece
The seasonal changes of leaf physiological traits and its relationship with abiotic factors (photosynthetic active radiation-PAR, leaf temperature-Tleaf, air temperature-Tair, Tleaf- Tair- ΔT) were studied on sugar beets grown under the semi-arid conditions of central Greece. Sugar beet (Betavulgaris L.) cv Rizor was established in a Randomised Complete Block design experiment for two years (2004-2005). From early June till the end of October, 11 determinations of leaf physiological traits (intracellular to ambient CO2 concentration-ci, transpiration rate-E, stomatal conductance-gs, net photosynthesis-A, instantaneous water use efficiency-A/E, photosynthetic water use efficiency-A/gs, chlorophyll content-SPAD, carbon isotope discrimination- Δ, N concentration and specific leaf area-SLA) took place. Temperatutes (Tleaf and Tair) and ΔT were higher in 2004 when water budget (WB, precipitation + irrigation – evapotranspiration) was more negative. Also, seasonal mean of carbon isotope discrimination (Δ) and net photosynthesis (A) were lower in 2004 to compare to 2005. A gradual decline with the progress of the growing season was found for A, Δ, gs, E, SLA and leaf N concentration while the adverse trend was evident for water use efficiencies (WUE, A/E and A/gs). PAR was positively related with gs and E and negatively with A/E. Temperatures (Tair and Tleaf) had a positive effect on E and a negative one on A/E. High temperatures (35-37 ºC) degraded leaf chlorophyll but temperatures higher than 37 ºC tended to increase chlorophyll content. ΔT (transpirational cooling) was negatively related with gs, E, and A and positively with A/E and A/gs. Both E and A were regulated by gs which was kept higher or slightly lower than 0.10 mol m-2 s-1, a limit indicative of severe drought in C3 species. Positive relationships were found between A, leaf N concentration and SLA. SLA is an indicator of resource-use strategy and can provide useful information about abiotic factor effects on sugar beet physiology and yield. Δ was negatively related with A/gs showing that it can be an indirect assessment of WUE at leaf level.