Effects of drought stress on spring bud development in poplar and willow clones

Understanding spring bud phenology is important for predicting tree responses to changing cli­mates and selecting the clones appropriate for various regions. This study assessed how summer drought affects bud development in six poplar and three willow clones. Experimental plants were grown in pots under three levels of water deficiency – 75%, 50%, and 25% moisture by volume compared to the control (light, moderate, and severe stress) throughout the growing season, preceded by monitoring of spring phenology. Bud assessments of one-year-old plants started nine months after initiating the drought treatment. Bud development was observed for 45 days using a six-score scale, which measures developmental stages ranging from dormancy (0) to full leaf expansion (6). Under control watering, poplar buds developed faster than willow buds. Additionally, drought had no sig­nificant effect on willow buds, so we focused on the impact of drought on poplar bud development, which was affected by moderate and severe stress. Plant survivability in both poplars and willows decreased under severe drought, whereas moderate and light stress had no impact. In terms of bud development, poplar clones ‘Gulliver’, ‘Novoberlinska-3’, and ‘Slava Ukrainy’ coped with stress faster than others, while ‘Volos­ystoplidna’ was the most drought-sensitive. The studied tree clones can survive under 50% of water shortage in the pots, but such severe drought conditions delayed bud development. We suppose that the most actively growing clones might be more sensitive to water shortage. Contrastingly, less productive clones were more drought-tolerant, as their bud development “recovered” faster. Therefore, such clones, even being less productive, could survive severe drought compared to clones, that are highly productive under optimal conditions. Our findings provide in­sights into clone selection for drought-prone environments. They also advance the understanding of woody plant responses to a changing climate.