PRIMO

Priming effects of moss leachates on soil organic matter dynamics

 

Drying-rewetting cycles of bryophytes cause pulses of labile substrates leached from forest floor moss layers. In the PRIMO-project we investigate how moss leachates influence soil microbial activity and ecosystem carbon and nutrient cycling

 

The poikilohydric life style of bryophytes implies that active phases in moist state alternate with inactive phases in desiccated state, which requires a range of physiological adaptations, like the accumulation of sugars, polyols and antioxidants. Despite such adaptations, re-wetting of desiccated mosses causes considerable leakage of intracellular metabolites due to membrane restructuring and damage of cell membranes. The ecosystem implication of these drying-rewetting cycles of mosses is that major rain events following intermittent periods of dry weather cause pulses of labile carbon-rich substrates leached from the moss layer, which are subsequently washed into the soil. The impact of this C-flush on soil microbial activity is, however, yet unknown.

In this project we address two main research questions:

(1) Does the pulse of low molecular weight organic compounds in moss leachates stimulate soil microbial activity and enhance microbial decomposition processes of soil organic matter?

(2) Does the effect of moss leachates on soil microbial activity differ between moss species and are such differences linked to the concentration of leached DOC or to the chemical quality of the organic compounds contained in moss leachates?

We investigate this by a mesocosm experiment using soils from two spruce forests to which leachates of four forest floor moss species will be added. We will determine effects on soil microbial processes, soil C and N pools and soil microbial community composition, and we will link these effects to the chemical composition of the moss leachates. The mesocosm experiment will be complemented by in-situ moss leachate collections in two spruce forests over one growing season, elucidating the relationship between moss leaching intensity and climatic conditions.

By interlinking plant physiological, soil microbiological and biogeochemical aspects, the PRIMO project will improve our understanding of the role of bryophytes in the functioning of montane forest ecosystems and thus help to refine models of C and nutrient cycling in moss-rich ecosystems under climate change.

 

Project duration: 2022 – 2026

Funded by the Austrian Science Fund (FWF, project nr. P35514-B)

 

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Spruce forest in Kalkalpen National Park (Photo: M. Koranda)

Hylocomium splenders (Photo: M. Koranda)