Survival and juvenile-age performance of Salicaceae clones for biomass

The adaptability of three Salicaceae clones selected for biomass (Salix x ‘Terra Nova’, Populus x ‘AF-18’ and Populus x ‘AF-8’) was tested in the first year of growth at nursery in comparison with a poplar cultivar for wood production (Populus x ‘I-214’). An experimental plantation was established in April 2020 with standard hardwood cuttings on 0.2 ha of nursery land along the Danube River in Central Northern Bulgaria. Principal leaf gas exchange parameters were measured. Diameter increment, height growth and increment, and normalized difference vegetation index were monitored on representative samples of plants. The influence of the genotype was analyzed, and correlations with main climate parameters were sought. The willow clone showed early increment culmination and a sharp decline in growth and viability with the suspension of watering. It had the lowest net photosynthetic rate (8.312 ± 0.107 μmol (CO2)·m-2·s-1), low biomass growth (0.098 ± 0.01 kg DM) and a high survival rate. Unlike the other poplar genotypes, ‘I-214’ showed rapid growth at the beginning of the summer, a high transpiration rate (1.222 ± 0.034 mmol (H2O)·m-2·s-1) and a stronger dependence on moisture. Clones ‘AF-8’ and ‘AF-18’ had high photosynthetic (10.238 ± 0.231 and 11.480 ± 0.193 μmol (CO2)·m-2·s-1, respectively) and low transpiration (0.672 ± 0.024 and 0.682 ± 0.015 mmol (H2O)·m-2·s-1, respectively) rates, and their growth was positively affected by the temperatures. The water use efficiency of the poplar biomass clones was the highest. ‘AF-8’ genotype showed the best diameter and biomass (0.194 ± 0.036 kg DM per plant) growth, while the ‘AF-18’ genotype grew best in height.