Can naturally-occurring endophytic nitrogen-fixing bacteria of hybrid white spruce sustain boreal forest tree growth on extremely nutrient-poor soils?
Probiotics are regarded as a sustainable and environment-friendly way to support plant growth through various mechanisms, including biological nitrogen fixation. Biological nitrogen fixation is a process by which atmospheric N2 gas is converted into a plant-usable form (NH3) by certain bacteria. In natural ecosystems like boreal forests, such bacteria could be a potent source of nitrogen nutrition for trees growing on nutrient-poor soils.
West Chilcotin is a secluded region located in central-interior BC where cold climate and low annual precipitation have resulted in dry and weakly developed soils lacking essential plant nutrients, particularly nitrogen. This region is commonly affected by disturbances like forest fires and timber harvesting, which has led to the gradual loss of nitrogen from soils. Yet, hybrid white spruce (Picea glauca x engelmannii) trees thrive on such nitrogen-limited soils, raising a crucial question regarding their nitrogen sources. One of the sources could be biological nitrogen fixation by bacteria living inside the tissues of spruce trees growing in this region. We evaluated such bacteria under nitrogen-poor conditions in a year-long greenhouse trial with their original host (i.e. hybrid white spruce). In a different year-long trial, we also tested these bacteria with another host native to this West Chilcotin region (i.e. lodgepole pine) to examine their interaction with a foreign host. We found that these bacteria can fix significant amounts of nitrogen from the atmosphere in spruce and pine (17–56% of the total plant nitrogen). In addition, bacteria-inoculated spruce and pine seedlings were considerably longer (up to 50%) and accumulated significantly more biomass (up to 475%) than non-inoculated controls.
Therefore, our results suggest that such bacteria harboured by hybrid spruce trees can sustain their growth on nitrogen-limited soils via biological nitrogen fixation. These bacteria can also provide similar benefits to a foreign host – lodgepole pine, indicating their wide-range ecological applications in improving the N-supply of forest stands in this region and beyond. In addition, such bacteria may sustain the tree growth for years and could act as an environment-friendly and cost-effective solution to offset/reduce the need to periodically apply chemical fertilizers to forest stands in BC.
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