Soil nutrient availability and microclimate are influenced more by genotype than by planting stock type in hybrid poplar bioenergy buffers on farmland

Bioenergy buffers planted with fast-growing woody crops such as hybrid poplars (Populus spp.) are increasingly integrated into agricultural land to enhance the provision of ecosystem services. Genotype and planting stock type selection may influence buffer establishment success and soil properties, which may affect buffer functions such as soil nutrient removal, hydrological regulation (i.e. soil dewatering) or local climate regulation (i.e. temperature reduction). This farm-scale study tested the effects of two unrelated hybrid poplar genotypes (P. deltoides × P. nigra, genotype D × N-3570 and P. maximowiczii × P. balsamifera, genotype M × B-915311) and two planting stock types (unrooted whips and bare-root stocks) on biomass growth, soil nutrient availability and soil microclimate in 15 m wide bioenergy buffers located downslope of hayfields in the cold temperate region of southern Québec, Canada. Poplar genotype had an important effect on biomass growth, soil microclimate and the supply rates of several macronutrients and micronutrients, while planting stock type had little effect on these variables. The P. maximowiczii × P. balsamifera genotype produced the highest biomass and had generally lower nutrient availability in the soil, but not for soil NO3, which was less available under the P. deltoides × P. nigra genotype. Compared to the hayfield soils, only the P. maximowiczii × P. balsamifera genotype maintained a lower supply rate of available P in the buffer soil. Compared to the hayfield soils, NH4 supply rates were lower in the buffers for both genotypes, while NO3 supply rates were similar or higher. Both genotypes had the capacity to maintain cooler soil temperatures and lower moisture content in the soil of the buffer compared to the adjacent hayfields, but this capacity was greater for the P. maximowiczii × P. balsamifera genotype. Because plant-soil interactions are strongly affected by hybrid poplar genetics, genotype selection is an important consideration in the design of multifunctional agricultural buffers. In temperate agroecosystems, future studies should try to identify productive poplar genotypes that would decrease topsoil NO3 and P availability and reduce soil water content in order to minimize potential N and P losses from buffer soils during runoff events.