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The genotype ’Neva’ under high plant density showed the highest biomass yield and optimal physiological strategies and could be the most suitable choice under semi-arid environment

The poplars (Populus spp.) are the most sensitive plants to water deficit conditions among the woody species utilized for biomass production for energetic purposes; their productivity is associated with water availability in the soil. In the Mediterranean environment, crops are mainly limited by evapotranspirative demand that is not balanced by rainfall supply. As new hybrids with high growth rates and resistance to water stress are selected, the use of poplar as an energy crop may increase in Southern regions of Mediterranean Europe. The growth dynamics and physiological characteristics of poplar hybrid genotypes have been monitored for 2 years at a site with a Mediterranean climate, Apulia region, that could be used for energy crops. Unrooted cuttings of three recently selected genotypes of poplar (’Neva’, ’Dvina’ and ’Lena’) and two "traditional" genotypes (’Luisa Avanzo’ and ’Bellini’) were planted in the spring of 2010 at two different densities: (a) low plant density = 1,667 cuttings ha(-1) (LPD); (b) high plant density = 6,667 cuttings ha(-1) (HPD). The genotypes ’Lena’ and ’Dvina’ showed the lowest survival rates and the poorest growth among the hybrid poplar tested. The genotype ’Bellini’ had low stomatal sensitivity to soil water content and a moderate productive performance. The genotypes ’Luisa Avanzo’ and ’Neva’ had a good degree of rooting and sprouting, high values of leaf relative water content (RWCl) and low values of stomatal conductance (g (s)) during the summer months. In "Neva", these characteristics were associated with the best yields (4 t ha(-1)) in HPD.