Clone-specific responses in leaf phenolics of willows exposed to enhanced UVB radiation and drought stress

The effects of enhanced UVB radiation and drought stress on willow secondary phenolics were studied using the leaves of 8-week-old micropropagated plantlets from interspecific hybrids (Salix myrsinites L. xS. myrsinifolia Salisb.) and pure species (S. myrsinifolia). The plantlets were subjected for 4 weeks to two levels of UVB radiation (ambient, enhanced) and two levels of watering (well-watered, drought-stressed) according to a 2 x 2 factorial design. Enhanced UVB radiation increased the total concentration of flavonoids and phenolic acids in all plantlets, while the total concentration of salicylates remained unaffected. Drought stress reduced the total concentration of salicylates and phenolic acids in S. myrsinifolia plantlets, while in hybrids only phenolic acids were affected. The response of phenolic acids to enhanced UVB in drought-stressed plantlets was different from that in well-watered ones, indicating that drought stress limited the accumulation of phenolic acids under enhanced UVB radiation. Flavonoids increased in response to enhanced UVB radiation in drought-stressed plantlets, although drought caused serious physiological stress on growth. There were significant differences between hybrid and S. myrsinifolia plantlets with respect to the composition of phenolics and between families and clones with respect to their concentration. In addition, the response of salicylates, flavonoids and phenolic acids to enhanced UVB and drought stress was clone-specific, which may indicate that climatic changes will alter the genetic composition of northern forests.