Poplar trees have been reported as one of the fast-growing trees that can be harnessed as a biofuel feedstock for cellulose ethanol production. As with other potential biofuel feedstocks under investigation, strategies for  sustainable cultivation are being studied. One of these "sustainable" strategies is the utilization of marginal soils for the cultivation of biofuel feedstocks. Increasing the ability of biofuel feedstocks to thrive in marginal soils is an active area of study. Recently, scientists from the Brookhaven National Laboratory of the United States Department of Energy (US-DOE) and their colleagues from Hasselt University (Belgium) identified "plant-associated microbes that can improve plant growth on marginal land". They identified some "endophytic bacteria" (bacteria residing within plant hosts without causing disease symptoms) from poplar and willow which had beneficial effects on plant growth. Poplar cuttings inoculated with Enterobacter sp. 638 and Burkholderia cepacia BU72, repeatedly showed the highest increase in biomass production by as much as 50%. The production of plant-growth-promoting hormones by endophytic bacteria which stimulates poplar growth in marginal soils, is seen as a possible mechanism. The results of their study are reported in the journal, Applied and Environmental Microbiology. Further investigations are underway, with the objective of improving biomass production and the carbon sequestration potential of poplar trees when grown in marginal soil..