Polyclonal plantings of Populus deltoides are expected to display increased site resource use, productivity, and tolerance to stress through plasticity changes leading to niche differentiation (i.e changes to crown/canopy structures). In the present study, P. deltoides Clones S7C8, 110412, and polyclonal plots were tested for differentially expressed genes and enriched biological pathways between planting schemes. Transcriptomic analysis of leaves revealed upregulation of an active growth gene and gene family members that play important roles in plant stress and stress tolerance in polyclonal plantings. A gene associated with oxidative stress was upregulated in polyclonal plantings across all treatments. Secondary metabolic pathways including arginine and proline metabolism were upregulated in monoclonal plantings and downregulated in polyclonal plantings. Phenotypic results displayed greater aboveground biomass in polyclonal plantings. Results suggested a potential increased tolerance in polyclonal plantings to water and heat stress, including increased productivity and resource usage.