Inoculation with in vitro promising plant growth-promoting bacteria isolated from nitrogen-limited boreal forest did not translate to in vivo growth promotion of agricultural plants

Abstract Many yet undiscovered plant growth-promoting bacteria are proposed to be harboured in the nitrogen-limited boreal forest. These bacteria are suggested to increase plant growth not only due to their ability to fix nitrogen but also through other growth-promoting properties. Therefore, this study looked at the plant growth promotion potential of endophytic bacteria isolated from boreal forest conifer Scots pine ( Pinus sylvestris ) needles. Seven assays were used to measure the potential plant growth-promoting abilities of two newly isolated bacteria in this study and seven additionally selected bacteria isolated in our previous study. The three best-performing bacteria were used, either individually or in a consortium, to assess growth promotion on four common crop species. The greenhouse study included the presence of native soil and seed microbiota and used naturally nutrient-abundant soil. The results showed that while all bacteria were capable of multiple plant growth-promoting properties in the in vitro assays, they did not promote plant growth in the in vivo experiment as inoculated plants had similar or decreased chlorophyll content, root and shoot length and dry biomass compared to control plants. Our results show that bacterial plant growth-promoting potential does not always translate into successful plant growth increase in in vivo conditions and highlight the need for a better understanding of plant-bacteria interaction for the future establishment of successful bacterial bioinoculants.