Mechanisms of Drought Resistance in Populus Deltoides and P. × Canadensis Clones to Possible Situations of Water Restriction in Irrigated Systems in Drylands

We have identified poplar clones suitable for dryland forestry, which stand out for their resistance to cavitation, level of anisohydrism, adjustment of cellular water relations and high water use efficiency. In drylands, such as the arid western region of Argentina, poplar afforestation depends on intermittent furrow irrigation, subjecting the plantations to variable water availability both in time and space. Our objective was to study stem biomass production and drought resistance responses of eight poplar clones, to explore whether there are more suitable varieties for forestry in drylands than those currently cultivated, i.e. the hybrid Populus × canadensis clones ‘Conti’ 12 and ‘Guardi’. We conducted a pot experiment with three levels of water availability (control, moderate stress and severe stress), studying four clones of P. × canadensis, ‘Conti 12’, ‘Guardi’, ‘I-214’ and ‘I45/51’, as well as four clones of the Populus deltoides species, ‘Stoneville 67’, ‘Catfish 2’, ‘Dvina’ and ‘Australiano 129/60’. We found that the clones that were more productive under water stress, ‘I-214’ and ‘I45/51’, were also the most resistant to cavitation. However, these clones were not very productive under high water availability. The ‘Guardi’ and ‘Australiano 129/60’ clones performed best in this situation, showing moderately high productivity under water stress. These clones exhibited the highest degree of anisohydrism, high water use efficiency and ‘Australiano 129/60’ stood out for its low water potential at the point of wilting due to osmotic adjustment. The currently most cultivated variety in Cuyo region, ‘Conti 12’, was less productive, did not make cellular adjustments and had low water use efficiency. These results suggest that other available clones may be more suitable for poplar forestry in drylands and should be evaluated in field trials.