Seminar – Martin Hartmann

A seminar by Dr. Martin Hartmann, Swiss Federal Research Institute for Forest, Snow and Landscape Research WSL, Birmensdorf (Switzerland), entitled :

Consequences of long-term drought for the structure and function of a forest soil microbiome

will take place on Thursday, 16 November 2017, from 1.30 pm in Conference room, Centre INRA Grand Est – Nancy, Champenoux


The impact of climate change on forests potentially alters the nutrient and energy flows through terrestrial ecosystems. In semi-arid environments, water availability is a major constraint on biogeochemical cycling due to the combination of high summer temperatures and low rainfall. By setting up an inverse climate change field experiment in the central European Alps, we explored how long-term irrigation of a drought-affected pine forest altered the soil microbiome and associated ecosystem functioning. A decade of irrigation stimulated primary production resulting in higher crown cover, larger yearly increments of tree biomass, increased litter fall, and greater root biomass. Greater amounts of plant-derived carbon inputs through litter and rhizodeposits in the irrigated forest stands stimulated soil microbial activity coupled to pronounced structural shifts in the microbiome from largely oligotrophic to more copiotrophic lifestyles. These structural shifts were accompanied by profound changes in the functional capacity encoded in the underlying metagenome, showing shifts in carbon and nitrogen metabolism as well as regulatory processes protecting from starvation. Microbial groups benefitting from increased resource availabilities thrived under irrigation, leading to enhanced soil organic matter mineralization and carbon respired from irrigated soils. However, the loss of soil carbon due to increased microbial activity under irrigation was contrasted by higher primary production and enhanced carbon sequestration to the extent that it fully compensated for the increased soil organic matter decomposition. Based on all these observations, we further hypothesized that plant litter decomposition – an important process for carbon turnover in forest ecosystems – will be different between the drought-affected and irrigated forest soils. However, decomposition of root litter as well as specific degradation of cellulose and lignin were not different between the sites, although different communities colonized the root litter and different microbial taxa were involved in degradation of lignin and cellulose as determined by stable isotope probing. This unique long-term study provides new insights into the impact of precipitation changes on the soil microbiome and associated ecosystem functioning in a drought-prone pine forest ecosystem and improves our understanding of the persistency of long-term soil carbon stocks in a changing climate.