Colonization of naïve roots fromPopulus tremula x albainvolves successive waves of fungi and bacteria with different trophic abilities

Abstract

Through their roots, trees interact with a highly complex community of microorganisms belonging to various trophic guilds and contributing to tree nutrition, development and protection against stresses. Tree roots select for specific microbial species from the bulk soil communities. The root microbiome formation is a dynamic process but little is known on how the different microorganisms colonize the roots and how the selection occurs. To decipher if the final composition of the root microbiome is the product of several waves of colonization by different guilds of microorganisms, we planted sterile rooted cuttings of Gray Poplar obtained from plantlets propagated in axenic conditions in natural soil taken from a poplar stand. We analyzed the root microbiome at different time points between 2 and 50 days of culture by combining high-throughput Illumina MiSeq sequencing of fungal rDNA ITS and bacterial 16S rRNA amplicons with Confocal Laser Scanning Microscope observations. The microbial colonisation of poplar roots took place in three stages but the dynamic was different between bacteria and fungi. Root bacterial communities were clearly different from the soil after two days of culture. By contrast, if fungi were also already colonizing roots after two days, the initial communities were very close to the one of the soil and were dominated by saprotrophs. Those were slowly replaced by endophytes and ectomycorhizal fungi. The replacement of the most abundant fungal and bacterial community members observed in poplar roots along time suggest potential competition effect between microorganisms and/or a selection by the host.

Plant Growth-Promoting Rhizobacteria (PGPR) with Microbial Growth Broth Improve Biomass and Secondary Metabolite Accumulation of Cannabis sativa L.

“…slow-growing PGPR take longer to colonize the host but can be present for a longer time. 57 Our hypothesis proposed that the presence of microbial growth medium could improve the efficiency of PGPR colonization of cannabis roots. In the previous study, we evaluated the effects of the bacterial cells suspended in magnesium chloride (a nutrient-free matrix) on cannabis growth and reported that the slow-growing PGPR Mucilaginiabcter sp.…”

“…56 In the field, the relative ineffectiveness of PGPR could be influenced by a range of factors including the requirement for specific signals from host plants and an inhospitable rhizosphere environment. Some genera, for example, Bacteroidota, Verrucomicrobiota, and Acidobacteriota, colonize host plant roots rapidly, while species within the genus Mucilaginibacter take a longer time to dominate in roots, 57 suggesting that growth speed could be one of the main reasons for differences in the successful colonization of PGPR. 58 King's B medium is a general type of nutrient-rich microbiological medium, containing proteose peptone, which provides carbonaceous and nitrogenous compounds for the growth of bacteria.…”