Enhancing the productivity of hybrid poplar (Populus × hybrid) and switchgrass (Panicum virgatum L.) by the application of beneficial soil microbes and a seaweed extract

This study investigates the use of Azospirillum brasilense N8, Penicillium bilaii, Variovorax paradoxus JM63, and a seaweed (Ascophyllum nodosum) extract (ANE) on growth and nutrient content of three clones of hybrid poplars (Populus x cv. 'Hill'; P. x cv. 'Okanese' and P. x cv. 'Walker') and two cultivars of switchgrass (Panicum virgatum L. wild-type (WT) and cv. 'Cave-In-Rock'). Biomass accumulation in the poplar clones 'Okanese' and 'Walker' grown under both greenhouse and field conditions was significantly enhanced in treatments with either A. brasilense N8 or P. bilaii by up to 23% and 26%, respectively. There is also evidence of ANE increasing second-year growth of the clone 'Walker' by 16%. With one exception, there were no treatments effects on biomass accumulation in the poplar clone 'Hill,' thereby indicating a genotype-specific effect. In switchgrass, there was an 18% increase in shoot biomass in cv. 'Cave-In-Rock' inoculated with either A. brasilense N8 or P. bilaii in the greenhouse trials, but there were no significant increases in the field trials. None of the treatments had significant effects on biomass accumulation in the WT switchgrass, again indicating a genotype-specific effect. Treatment effects on nutrient content of the plant tissues suggest a relationship between microbial-facilitated nutrient acquisition by the plants and the biomass enhancements. These results indicate that application of certain beneficial soil microbes and plant-growth promoting substances such as ANE could be used in certain genotypes of biomass feedstock crops to improve sustainable production of these crops.