Drought-induced plasticity in daily stem radius fluctuations and relationships with xylem hydraulics in hybrid poplars

National audience; Radial stem variations are a great source of tree physiological and ecological information. Time series of stem radius fluctuations using point dendrometers can provide information about radial stem growth and tree water relations with unprecedented quality and high temporal resolution. It is well known that climatic drivers such as the evaporative demand or water availability exert a strong control over the daily fluctuation patterns. The extent of within-species variations and the interaction with the environment remains however poorly documented. Here, we present stem radius fluctuations among eight 3-year-old Populus deltoides × Populus nigra genotypes grown in a common garden under two distinct water regimes. Daily patterns were analysed for one growing season. From daily patterns, we extracted the maximum daily shrinkage (MDS) which is mostly related to the capacitive discharge of outer bark elastic tissues and the day-to-day difference in stem radius over time (dR) which is mostly related to cambial growth. The duration of each daily cycle and individual phase (stem contraction, stem expansion and stem radius increment) were also estimated. Differences among genotypes, genotype × drought interactions, and relationships with other aspects of tree water/carbon relations such as xylem vulnerability to cavitation, growth and water-use efficiency will be presented and discussed in line with potential implications for poplar cultivation.