Periodic Reporting for period 1 - MYCOMOSS (Mosses as a gateway of nitrogen into northern ecosystems)
Période du rapport: 2018-03-01 au 2020-02-29
Mosses are primitive plant and are a major component of high latitude and high elevation ecosystems where they often cover most of the ground. Mosses are known to be important contributors to primary production and through their insulation and water retention capacity they control soil biogeochemical processes such as decomposition of soil organic matter. However, mosses are also key players for N input to terrestrial ecosystems as they readily take up nutrients entering the ecosystem from deposition through the cell walls of their thin leaves and through their association with bacteria fixing atmospheric N2. In this way, mosses work as a gateway and conduit for new N to enter these N-limited ecosystems. Mosses are considered efficient in holding on to newly incorporated N in the short term and old moss tissue is highly recalcitrant and therefore decomposing slowly. However, mosses may loose N via leakage e.g. upon drying and re-wetting , while old parts of the moss shoot eventually die and turn into litter, which then becomes subject to decomposition. Mosses thus likely play a two-faced role in the cycling of N but the mechanisms of and extent to which N bound in mosses becomes available to the decomposer sub-system and to vascular plants is largely unknown, despite the crucial role of N in these ecosystems.
The overall objective of MYCOMOSS was to develop mechanistic and quantitative understanding of the role of mosses as providers of new nitrogen to nitrogen-limited ecosystems under climate change.
As nitrogen is highly limiting for growth in cold ecosystems, it is possible that other organisms, eg. plants and fungi, will try to get hold of nitrogen entering the ecosystem via mosses. To describe fungal community composition in the moss layer, I collected moss shoots from 2 experiments in Sweden. One in Boreal and one in subarctic forest. I analysed shoots for 15N and 13C content and for fungal community composition and total fungal biomass. Fungal community analysis revealed that plant-associated fungi are present all the way up into the living moss tissue. These results are currently being remade with some methodological adjustments. The planned manuscript is therefore still under preparation.
To directly trace nitrogen from the moss into the rest of the ecosystem, I used labeled N (15N) added to the moss. I created 144 controlled mini-ecosystems containing soil, one of two plant species and moss covering the soil. Soil and plants were separated from the moss with one of 3 meshes of varying sizes. In this way, 15N in mosses could enter the soil-plant compartment 1) only through free water transport, 2) through both water transport and mycorrhizal colonisation of the moss or 3) through any mechanism also including plant roots growing into the moss layer. Plants established well but did not grow as fast as anticipated. I therefore decided to postpone the planned harvest of pots in 2019 to 2020. Instead, in 2019 preliminary samples of plant leaves were taken and analysed for 15N. These showed that we could trace 15N which confirms that the concentrations added are sufficient for our purpose. However, after only one year we did not see any difference in plant 15N concentration between plant with different access to moss N. This year I and MSc will finalise the project. She will include the results in her MSc thesis and I will synthesise the result in a manuscript for publication.