Effects of moss leachates on soil organic matter dynamics

Bryophytes, which occur in many ecosystems worldwide, are fundamentally distinct from higher plants in various respects. E.g., many bryophyte species are able to survive dry periods in desiccated, inactive state, which requires special physiological adaptations, such as the accumulation of sugars and antioxidants. Despite these adaptations, strong rain events following intermittent dry periods lead to membrane damage of mosses and cause substantial leakage of moss metabolites, which are subsequently washed into the soil. Our project aims at elucidating how soil microorganisms (i.e., fungi and bacteria) react to these substances leached from mosses. a topic, which has never been investigated so far. Do soil microbes use the sugar-rich moss leachates for growth? Or do they use them as energy source for synthesis of enzymes and enhanced degradation of soil organic matter, in order to gain additional nutrients from soil? Both processes are crucial for regulating soil carbon storage and thus the CO2-concentration in the atmosphere. Furthermore, we investigate if bryophyte species differ in their effects on soil microbes and if such differences are related to the amount or the chemical composition of the moss leachates. Bryophytes are characterized by a high diversity of metabolites, which may also have antimicrobial or antifeedant properties. The effect of these substances on soil microbes is, however, yet unknown. In order to address these research questions, we collect leachates from mosses which have been labelled with stable carbon isotopes, by simulating a rain event in the laboratory, and we subsequently apply the moss leachates to soil cores. We then measure the reaction of the soil microbial processes and microbial community composition; we trace the moss metabolites in the soil and analyse the chemical composition of the moss leachates. Furthermore, we perform a field experiment at two forest sites in Upper and Lower Austria, where we continuously measure the amount of solutes leached from mosses over one growing season and relate these data to the weather data at the field sites. The results of these experiments will yield new insights into carbon and nutrient cycling in moss-rich ecosystems.