Abstract
Plants are colonized by numerous microorganisms serving important symbiotic functions that aid in plant growth and success. Populus deltoides (Eastern Cottonwood) and Populus trichocarpa (Black Cottonwood) are potential biofuel crops that rely on microbial symbionts to complete essential tasks, such as nitrogen fixation. Often, in agricultural and biofuel production, exogenous nitrogen is added to soils, since nitrogen availability is the limiting factor for plant growth. However, these additions may alter the soil microbial communities and result in unintentional consequences if excess nitrogen escapes the setting. We sought to determine how nitrogen fertilization alters the microbial communities within the soil, roots, and leaves of two cottonwoods. We grew P. deltoides and P. trichocarpa in a greenhouse with and without added nitrogen fertilizer, in two soil types. The soils were from Oregon and West Virginia and had distinctive chemical properties and different initial soil microbial communities. We hypothesized that the abundance of diazotrophs within the soils would increase as nitrogen became limiting. Over the 2-month study, we assessed plant growth characteristics for over 160 Populus plants. We investigated the root, leaf, and soil microbiomes of selected plants using 16S rRNA gene and ITS2 PCR amplicon DNA sequencing. We then used bioinformatics tools to evaluate the composition and diversity of these microbiomes. The microbiomes differed significantly across all three experimental factors - nitrogen addition, Populus species, and soil type.
