Microbial activity in coniferous forest topsoils is habitat-specific and shows seasonality

Link To Share This Poster: https://cdmcd.co/nQ7mZB
Live Discussion Link: https://cdmcd.co/v9DZw5

Zander R. Human, Tomáš Větrovský, Martina Štursová, Rubén López Mondéjar and Petr Baldrian, Laboratory of Environmental Microbiology, Institute of Microbiology of the Czech Academy of Sciences, Prague, Czech Republic, Alonso R. Serrano, Simon Law, Nathaniel R. Street and Vaughan Hurry, Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, Umeå, Sweden, Lucas Auer and Francis Martin, INRAE, UMR 1136, Interactions Arbres/Microorganismes (IAM), Centre INRAE GrandEst ‐ Nancy, Université de Lorraine, Champenoux, France, Adina C. Howe, Agricultural and Biosystems Engineering, Iowa State University, Ames, IA, Christa Pennachio and Igor V. Grigoriev, U.S. Department of Energy Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, Igor V. Grigoriev, Department of Plant and Microbial Biology, University of California Berkeley, Berkeley, CA, Håvard Kauserud, Section for Genetics and Evolutionary Biology, University of Oslo, Oslo, Norway

Background/Question/Methods
Coniferous forests are globally important due to the large land area that they cover and their role as global carbon sink. Coniferous forest soils play an important role in carbon fixation and nutrient supply to trees and can broadly be divided into different habitats, based on physical and chemical properties and the accompanying microbiome. Roots are the hotspots of interactions between trees and symbiotic ectomycorrhizal (ECM) fungi, while in the rhizosphere microbial activity is also high due to the abundance of root exudates. Bulk soil is dominated by bacteria although also containing large quantities of ECM mycelia. Litter consists largely of recalcitrant plant material, which is decomposed by saprotrophic fungi. In this study, we analysed metatranscriptomes from P. abies roots, rhizosphere, bulk soil and litter in March, June, September and December. Our aims were to determine microbiome function in different forest soil habitats, such as N and C cycling. Furthermore, we test the hypothesis that seasonality in forest soil habitats are driven by spruce root activity and ECM symbiosis and thus the extent of seasonality depends on the degree of influence of root activity.
Results/Conclusions
Roots and litter had the highest proportion of unique transcripts while rhizosphere and bulk soil shared the majority of transcripts, although bulk soil had more unique functions. Carbon cycling in roots and litter was mainly directed towards plant cell wall polymers such as lignin and cellulose, while in rhizosphere and soil, CAZymes targeted mostly α-glucans and biopolymers contained in bacterial and fungal biomass. Ammonia assimilation was the most transcribed function related to N-cycling overall, and highest in litter and roots, while nitrification was the most transcribed in soil and rhizosphere. Expression was most seasonal in roots, followed by rhizosphere and bulk soil, while litter was the least seasonal. Early summer (June) was the season most differentiated from other seasons, and had the highest expression of root-growth associated transcripts. ECM symbiosis-related gene expression was higher in June and September compared to December and March. Seasonality of transcription was evident in taxonomic profiles of total transcription and ribosomal proteins in all habitats, with copiotrophic taxa most active in June and oligotrophic bacteria most active in December and March. Together, our results show that microbial activity in forest topsoil largely reflects substrate quality and content, and that root-derived compounds are likely the largest source of this seasonality.