Growth performance and nitrogen use efficiency of two Populus hybrid clones (P. nigra × P. maximowiczii and P. trichocarpa × P. maximowiczii) in relation to soil depth in a young plantation Dejuan Euring It is a challenge to produce woody crops on marginal land. The goal of this study was to examine growth responses and nitrogen use efficiency of different poplar species on shallow soil. Typical biomass poplar clones of Max1 (P. nigra × P. maximowiczii) and H275 (P. trichocarpa × P. maximowiczii) were planted on a marginal site where a gradient in soil depth was present. The growth, biomass production, and nitrogen uptake rate as well as nitrogen use efficiency of Max1 and H275 were determined for three consecutive years. Both poplar clones showed decreased growth and biomass production in the shallow soil. Max1 showed better adaptation to shallow soil with higher survival rate and more biomass production than H275. Max1 had lower nitrogen use efficiency on shallow soil than H275. The results suggest that higher nitrogen uptake of poplar species might be an important adaptation to maintain productivity under unfavorable soil conditions. Keywords: Biomass, Nitrogen Use Efficiency, Poplar, Shallow Soil IntroductionWoody biomass is considered as a sustainable alternative source of energy for fossil fuels (Pleguezuelo et al. 2015). Short rotation woody crops such as poplar trees (Populus spp.) are well suited for woody biomass production because they are highly productive and can be managed using agronomic techniques (Kauter et al. 2003). To avoid competition for fertile land with food production, poplar plantations are expected to be established on marginal land which is less suitable for agriculture because of limited water and nutrient availability (Shortall 2013). Since the productivity of a poplar plantation depends on the proper selection of genotypes (Zalesny et al. 2011), research is needed to identify poplar cultivars with high survival rates, high biomass productivity and high disease resistance for cultivation on marginal soil ).Shallow soil with limited rooting depth, low drainage and high stone content are typical features of marginal land (Jiang et al. 2014). Rooting depth is an important determinant for the successful establishment and production of woody biomass (Burgess et al. 2015). N storage and cycling are vital processes for growth, adaptation and productivity of poplar trees (Millard & Grelet 2010). N storage and remobilization are particularly important to meet the N demand of forest trees for continuous growth (Rennenberg et al. 2010). Poplar species differ in the way they take up and assimilate N (Luo et al. 2013, Gan et al. 2015, which may impact their competitive ability for soil nutrients and resistance to environmental stresses (Castro-Rodríguez et al. 2015, Molina-Rueda & Kirby 2015. Several studies have focused on identifying and quantifying the best management practices to successfully establish hybrid poplar plantations under different nitrogen regimes (Lee & Jose 2003, Euring et al....