Comparisons of biomass, water use efficiency and water use strategies across five genomic groups ofPopulusand its hybrids

Abstract

AbstractGenetic improvement and hybridization in thePopulusgenus have led to the development of genotypes exhibiting fast growth, high rooting ability and disease resistance. However, while large biomass production is important for bioenergy crops, efficient use of resources including water is also important in sites lacking irrigation and for maintaining ecosystem water availability. In addition, comparison of water use strategies across a range of growth rates and genetic variability can elucidate whether certain strategies are shared among the fastest growing and/or most water use efficient genotypes. We estimated tree water use throughout the second growing season via sapflow sensors of 48 genotypes from fivePopulustaxa;P. deltoidesW. Bartram ex Marshall × P. deltoides(D × D),P. deltoides × P. maximowicziiA. Henry (D × M),P. deltoides × P. nigraL. (D × N),P. deltoides × P. trichocarpaTorr. & Gray (D × T) andP. trichocarpa × P. deltoides(T × D) and calculated average canopy stomatal conductance (GS). We regressedGSand atmospheric vapor pressure deficit (VPD) wherein the slope of the relationship represents stomatal sensitivity to VPD. At the end of the second growing season, trees were harvested, and their dry woody biomass was used to calculate whole tree water use efficiency (WUET). We found that D × D and D × M genotypes exhibited differing water use strategies with D × D genotypes exhibiting high stomatal sensitivity while retaining leaves while D × M genotypes lost leaf area throughout the growing season but exhibited low stomatal sensitivity. Across measured taxa, biomass growth was positively correlated with WUET, and genotypes representing each measured taxa except D × N and T × D had high 2‐year dry biomass of above 6 kg/tree. Overall, these data can be used to selectPopulusgenotypes that combine high biomass growth with stomatal sensitivity and WUETto limit the negative impacts of bioenergy plantations on ecosystem water resources.