Leaf carbon isotope discrimination relationships to element content in soil, roots and leaves of sugar beets grown under Mediterranean conditions

In a 2-year experiment (2002-2003), we aimed to study the trends and relationships between leaf carbon isotope discrimination (A) and elemental concentration in leaves (N, K, Na, Ca, Mg), roots (K, Na, alpha-amino N) and soil (total N, NO3-N, K, Na) of sugar beet grown under semi-arid, irrigated conditions on non-saline, non-sodic soils of Central Greece. In both years, 10 samplings (leaves, roots, soils) took place from mid-June till November. Seasonal mean A was higher in 2002 due to the higher rainfall occurred from the end of July till the end of the season. Strong positive relationships were found between A and leaf N but A was inversely related with leaf Na in both years. Increased Na accumulation in leaves had probably detrimental effects on photosynthesis and stomatal conductance lowering A. Reduced A values have been also reported for plants grown under saline or drought conditions. Increased Na accumulation caused an increase of total salinity in leaves since leaf Ca and Mg had analogous to Na effects on A. On contrary, K was positively related to A indicating a positive role of this element on stomata functioning. Our data showed that sugar beet root is an active sink accumulating large amounts of elements regardless of the soil nutrient and water status. In 2003, when soil Na concentration was lowest, element antagonistic phenomena were evident since negative relationships between soil Na and leaf K or between soil K and leaf Mg concentration were found. Also, element concentrations in roots affected leaf nutrients but the effects were year specific. In 2002, root K was negatively related to leaf Na concentration while in 2003, a negative relationship between root Na and leaf K or Ca was evident. (c) 2006 Elsevier B.V. All rights reserved.