Mosses reduce soil nitrogen availability in a subarctic birch forest via effects on soil thermal regime and sequestration of deposited nitrogen

Abstract

1. In high-latitude ecosystems bryophytes are important drivers of ecosystem functions. Alterations in abundance of mosses due to global change may thus strongly influence carbon (C) and nitrogen (N) cycling and hence cause feedback on climate. The effects of mosses on soil microbial activity are, however, still poorly understood. Our study aims at elucidating how and by which mechanisms bryophytes influence microbial decomposition processes of soil organic matter and thus soil nutrient availability. 2. We present results from a field experiment in a subarctic birch forest in northern Sweden, where we partly removed the moss cover and replaced it with an artificial soil cover for simulating moss effects on soil temperature and moisture. We combined this with a fertilization experiment with 15 N-labelled N for analysing the effects of moss N sequestration on soil processes. 3. Our results demonstrate the capacity of mosses to reduce soil N availability and retard N cycling. The comparison with artificial soil cover plots suggests that the effect of mosses on N cycling is linked to the thermal insulation capacity of mosses causing low average soil temperature in summer and strongly reduced soil temperature fluctuations, the latter also leading to a decreased frequency of freezethaw events in autumn and spring. Our results also showed, however, that the negative temperature effect of mosses on soil microbial activity was in part compensated by stimulatory effects of the moss layer, possibly linked to leaching of labile substrates from the moss. Furthermore, our results revealed that bryophytes efficiently sequester added N from wet deposition and thus prevent effects of increased atmospheric N deposition on soil N availability and soil processes. 4. Synthesis. Our study emphasizes the important role of mosses in carbon and nutrient cycling in high-latitude ecosystems and the potential strong impacts of reductions in moss abundance on microbial decomposition processes and nutrient availability in subarctic and boreal forests. K E Y W O R D S bryophytes, extracellular enzyme activities, microbial communities, microbial processes, moss, nitrogen availability, nitrogen cycling, soil temperature This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Plant functional types drive spatial and temporal variation in soil microbial community composition and extracellular enzyme activities in a tundra heath

“…Contrary to rst hypothesis, soils at moss-grown sites exhibited relatively high microbial biomass N, dissolved N and potential enzyme activities (Fig. 4 and Table 3), which contrasts with ndings of our previous study in a nearby birch forest, where we observed a negative effect of the moss layer on soil N availability (Koranda and Michelsen 2021). This apparent discrepancy shows that the in uence of mosses on soil microbial processes and nutrient cycling is context-speci c, depending on the factors most strongly regulating soil microbial activity in the respective ecosystem: While in the birch forest, characterized by a homogenous understorey and SOM quality, the insulating effect of the moss layer was a crucial factor for soil microbial activity (Koranda and Michelsen 2021), in tundra heath the high spatial variability in plant traits, SOM quality and soil pH mainly determined microbial community structure and nutrient availability, whereas soil temperature was comparatively less relevant.…”

“…Potential hydrolytic enzyme activities were estimated by microplate assays using uorescent substrates, as described in detail in Koranda and Michelsen (2021). Soil slurries were prepared using Na-acetate buffer (pH 5.7).…”

Microbial function regulates the effect of vegetation restoration on the contribution of biocrusts to soil respiration in drylands

“…Biocrusts are ecosystem engineers at the atmosphere–soil interface, and they regulate a wide range of ecosystem functions, including C budgets (Dacal et al, 2020; García‐Palacios et al, 2018), nitrogen (N) cycles (Koranda & Michelsen, 2021; Maier et al, 2021), phosphorus (P) cycles (Kurth et al, 2021), hydrological processes (Eldridge et al, 2020), soil thermal properties (Xiao, Ma, et al, 2019) and soil stability (Algayer et al, 2014). Specifically, biocrusts regulate soil CO 2 flux not only directly through photosynthesis (Li, Hui, et al, 2021) and respiration (Guan et al, 2021, 2022) but also indirectly by altering the soil temperature (Xiao, Ma, et al, 2019), moisture (Eldridge et al, 2020), N availability (Koranda & Michelsen, 2021) and microbial community and functional structure (Wang, Wang, et al, 2021). For example, soil respiration at microsites with high biocrust coverage is significantly higher than that at microsites with low biocrust coverage (Escolar et al, 2015; Maestre et al, 2013) or in bare soils (Morillas et al, 2017; Yao et al, 2020), and biocrusts can contribute to more than 40% of CO 2 flux via soil respiration (Castillo‐Monroy et al, 2011).…”

“…As structural components of drylands, biocrusts are soil surface communities dominated by cyanobacteria, algae, lichens and mosses (Belnap et al, 2016), and they cover ~30% of the dryland soil surface (Rodriguez‐Caballero et al, 2018). Biocrusts are ecosystem engineers at the atmosphere–soil interface, and they regulate a wide range of ecosystem functions, including C budgets (Dacal et al, 2020; García‐Palacios et al, 2018), nitrogen (N) cycles (Koranda & Michelsen, 2021; Maier et al, 2021), phosphorus (P) cycles (Kurth et al, 2021), hydrological processes (Eldridge et al, 2020), soil thermal properties (Xiao, Ma, et al, 2019) and soil stability (Algayer et al, 2014). Specifically, biocrusts regulate soil CO 2 flux not only directly through photosynthesis (Li, Hui, et al, 2021) and respiration (Guan et al, 2021, 2022) but also indirectly by altering the soil temperature (Xiao, Ma, et al, 2019), moisture (Eldridge et al, 2020), N availability (Koranda & Michelsen, 2021) and microbial community and functional structure (Wang, Wang, et al, 2021).…”

Biological nitrogen fixation, diversity and community structure of diazotrophs in two mosses in 25 temperate forests

“…Mosses are a species‐rich clade found in almost all terrestrial ecosystems from the Arctic to the tropics (Geffert et al, 2013), with an often large impact on the carbon (C) and nitrogen (N) cycle (Elbert et al, 2012; Koranda & Michelsen, 2021). They live on soils, rocks and bark of living or dead trees under sometimes extreme climatic and nutrient‐poor conditions (Dierssen, 2001; Müller et al, 2020).…”