Genetic variation in responses to different soil water treatments in Quercus robur L.

The effect of soil water content on growth and growth cessation was studied in 18 provenances from northern Europe and 20 Danish open-pollinated families of Quercus robur in a greenhouse experiment. The objective was to study the genotypic responses, phenotypic plasticity and genotype by environment interactions, with regards to growth and to different levels of soil water content. The aim was to increase the knowledge on the genetic and adaptive potential of Q. robur to grow under different water stress conditions. Knowledge on genetic and adaptive potential can be used for practical seed zone management. Differences in growth between provenances were strongly related to latitude. Provenances of southernmost origin reacted vigorously to irrigation compared with Scandinavian provenances. For growth, the rank of provenances was the same at high and medium soil water treatments. Increased growth correlated with a higher number of secondary shoots and a prolonged growing season. Low soil water content initiated early growth cessation in all provenances. Root biomass was affected by soil water treatment and the highest root biomass was observed with medium and high soil water treatments. The results demonstrated a large evolutionary potential in relation to water treatment. The southernmost genotypes responded more strongly in growth to increased soil water level, but the local material showed a large variation and was less prone to early frost damage. The growth of Danish provenances of Q. robur was not reduced with high soil water treatment, in contrast to a study using Danish Fagus sylvatica provenances, indicating that Q. robur is well adapted to high soil water conditions.