Biochar in growing media influences ponderosa pine seedling growth and morphological traits

Ponderosa pine forests are experiencing large-scale mortality and inadequate natural regeneration across the American Southwest. High-quality nursery-grown ponderosa pine ( Pinus ponderosa Douglas ex C. Lawson) seedlings for reforestation are needed to compensate for these losses. The standard growing media used operationally for producing these seedlings includes a combination of peat moss, vermiculite, and perlite, which are subject to supply chain and cost issues. Additionally, each of these components is a nonrenewable resource extracted through mining, leading to their use for large-scale reforestation operations being unsustainable. In this study, we tested the effects of different proportions of biochar (0% (Control), 25%, 50%, 75%, and 100%) as a substitute for the standard media mix on germination, survival, growth, and a suite of morphological traits. Varying levels of biochar influenced seedling growth rate, biomass, and leaf area, but had no effect on germination rates or seedling survival. Results indicate a general decline in shoot:root and growth rate as biochar levels increased. This can inform biochar’s potential use as a locally sourced growing media component for producing tree seedlings. Although biochar amendment may limit post-germination seedling growth, these plants also exhibit some morphological characteristics which may be better adapted to a warmer and drier climate.