The effect of drought on C and N stable isotopes in different fractions of leaves, stems and roots of sensitive and tolerant beech ecotypes

Beech seedlings from 11 German climatic provenances were exposed to a realistically timed drought treatment in a greenhouse experiment. The stable isotope composition of carbon (C) and nitrogen (N) was analysed in pooled bulk material of roots, stems and leaves, as well as in the aqueous extracts and starch fractions. The delta(13)C values increased in bulk samples (BS) of roots, stems and leaves by drought, although no leaf growth occurred during the experimental period. A clear drought effect on delta(13)C in aqueous extracts was detected in leaves. In aqueous extracts of stems and roots as well as in starch fractions of all organs, abundance of delta(13)C also tended to be increased by drought, but this effect was not statistically significant. For both delta(13)C and delta(15)N, enrichment was observed from the site of uptake/ source to the site of use/sink. A gradient for delta(13)C in all fractions from leaves (-29.49,-28.89 and -27.85 parts per thousand) to stems (-28.8.1, -27.48 and -26.98 parts per thousand) and to roots (-27.60, -26.37 and -26.48 parts per thousand) was detected in BS, aqueous extracts and starch, respectively. An opposite gradient for delta(15)N was found in BS: 1.59 parts per thousand, 1.84 parts per thousand and 3.05 parts per thousand in roots, stems and leaves, respectively. delta(15)N was neither affected by drought in the BS nor in aqueous extracts, but an effect of provenance was observed. Particularly in roots and stems, drought-sensitive provenances showed the strongest shifts in delta(13)C induced by drought and the lowest delta(15)N values. In the present experiment, delta(13)C values were more affected by the environmental factor drought, while delta(15)N values were more affected by the genetic factor provenance.