Impacts of drought on mineral macro- and microelements in provenances of beech (Fagus sylvatica L.) seedlings.

Beech seedlings originating from 11 German provenances with different climatic conditions were grown in pots and cultivated in a greenhouse. The composition of macro- and microelements in roots, axes and leaves was measured after half of the seedlings were subjected to a simulated summer drought. The recently described sensitivity of these provenances to drought was compared with drought-mediated changes in the elemental and ionic composition in organs of the seedlings; in addition, partitioning between roots and shoots was evaluated. A number of element concentrations were decreased in roots due to drought (K 94% of control, Mg 94%, Mn 75% and Zn 85%). However, chloride concentration increased in all organs (115-125%) and was the only element affected in leaves. Some changes in ionome can be related to sensitivity of provenances, but it is difficult to decide whether these changes are a result of, or a reason for, drought tolerance or sensitivity. Observed increases in chloride concentration in all plant parts of drought-treated beech seedlings can be explained by its function in charge balance, in particular since the level of phosphate was reduced. As a result of chloride accumulation, the sum of added charges of anions (and cations) in water extracts of leaf and root material was similar between drought and control plants. Since only the partitioning of Ca and Al (both only in axis) as well as Mn was affected and other elements (together with previously observed effects on C, N, S and P) remained unaffected by drought in all provenances, it can be concluded that direct effects by means of mass flow inhibition in xylem and phloem are unlikely. Secondary effects, for example on the pH of transport sap and the apoplastic space, cannot be excluded from the present study. These effects may affect partitioning between the apoplast and symplast and therefore may be significant for drought sensitivity.