Increasing Biomass Production with Reduced Inputs in Non-Legume Crops Using N-Fixing Endophytes of Poplar

The use of symbiotic microorganisms rather than chemical fertilizers could offer a more environmentally sustainable means of increasing agriculture and biomass production.  Poplar and willow are early-successional pioneer plant species that thrive in N-limited environments across the Northern hemisphere.  Their ability to grow in low-nutrient substrates is usually attributed to nitrogen use efficiency (NUE); however, when there is little to no organic material available, NUE cannot account for the rapid growth rates and high biomass attained by poplar. We previously reported the presence of endophytic Rhizobium tropici from hybrid poplar grown in greenhouses.  A variety of diazotrophic (N₂ fixing) endophytes were subsequently isolated from wild poplar at a natural riparian area dominated by cobble.  These endophytes were shown to be mutualistic symbionts by adding them to other plant species, including turfgrasses, corn, rice, and a variety of other agronomically-important plants for improved growth and health in nutrient-limited conditions.  Increased yields of bell pepper and tomato fruits were achieved using the endophytes as a bio-fertilizer.  When the endophytes from wild poplar were added to hybrid poplars under greenhouse conditions, there was a significant increase in nitrogen fixation.  We will report the first definitive evidence of N₂ fixation within poplar plants from a natural stand of riparian poplar.  Not only do the endophytes from wild poplar fix N₂, they also produce plant hormones, solubilize phosphate, and increase drought tolerance.  By using symbiosis with natural microbial endophytes, substantial increases in plant biomass and yields could be attained with reduced inputs.