Bryophytes dominate plant regulation of soil microclimate in alpine grasslands

Abstract

Soil temperature and moisture are important regulators of a broad range of biotic and abiotic processes in terrestrial ecosystems. Vegetation can, in turn, play a role in regulating soil microclimate, which creates potential for powerful and interactive feedbacks from soil and vegetation on the atmosphere. Although the regulatory effect of vegetation on soil microclimatic conditions has been quite extensively and empirically assessed, most studies have determined the net effect of intact woody vegetation versus bare ground. However, for other plant functional groups we lack a clear understanding of their role and any climate‐context dependency in controlling microclimatic conditions.We investigated the role of three major plant functional groups – graminoids, forbs and bryophytes – in regulating soil microclimate in semi‐natural alpine grasslands. Using a fully factorial above‐ground biomass removal experiment, we assessed the role of these plant functional groups in regulating soil temperature amplitude, soil moisture, and number of freezing days. The experiment was replicated across orthogonal temperature and precipitation gradients in Norway to assess whether the effects of functional group abundance varied with climate.The effect of plant biomass on soil microclimate varied among functional groups across the climatic gradients. Bryophytes reduced growing season soil temperature, whereas graminoids and forbs did not (0.5ºC compared to 0ºC), and with a stronger effect in colder climates at higher elevations and on days with high solar radiation. Bryophyte biomass further reduced the number of soil freezing days at boreal and sub‐alpine sites. Finally, graminoid biomass partly explained variation in soil moisture: soils dried more under graminoids at drier sites.Our findings highlight that functional group identity plays a key role in regulating soil microclimate in alpine grasslands across seasons. The strong effect of bryophytes on soil temperature points to their importance in the plant community for a variety of ecosystem functions, some of which may be indirectly vulnerable to future warming via biomass reductions of bryophytes.

Moss Matters: Unravelling the intricate web of interactions between mosses, microclimate, and seed germination in New Zealand's alpine ecosystems

“…Soil moisture and water availability also appear to influence how well P. officinarum is able to establish in grasslands; hawkweeds are more abundant in moister sites, and are predicted to establish at those first during invasions (Duncan et al, 1997) and irrigation increases the production of stolons and daughter rosettes (Lamoureaux et al, 2003). Soil moisture and temperature are known to be influenced by bryophyte cover in tussock grasslands (Jaroszynska et al, 2023;Michel et al, 2012;Soudzilovskaia et al, 2013).…”

“…Water retention ability was calculated as the number of hours for a specimen to dry to 50 % of its saturated capacity (𝑡 50 ) (Elumeeva et al, 2011;Jaroszynska et al, 2023;Michel et al, 2012). I used the above data on drying time and extrapolated 𝑡 50 from the intervals at which I weighed the specimens.…”

“…The insulative ability of mosses is related to their volume and density (O'Donnell et al, 2009); large, low density mosses provide good insulation with many trapped air pockets and increase temperature minima within and below them, while those with a high capacity for water act to reduce extreme maxima through evaporative cooling. A study in Norwegian grasslands demonstrated, through factorial removal of plant functional groups, that mosses decrease soil temperatures and increase moisture, particularly on sunny days and at higher elevations (Jaroszynska et al, 2023). Soudzilovskaia et al (2013) showed greater soil temperature fluctuations when mosses were removed across a range of ecosystems in Norway.…”

“…I examined microclimate effects at a very small spatial scale not often achieved in tussock grasslands, but my analysis of temperature and moisture variation was temporally coarse. Other studies have analysed vegetation effects on daily temperatures (Davis et al, 2019;Jaroszynska et al, 2023;Kašpar et al, 2021), while my models used averages across 137 days. For example, if solar radiation were measured (requiring a separate sensor) and sunny days (those with a high level of solar radiation due to lower cloud cover) were considered separately from cloudy days the effect of moss, tussock, or topography may be more pronounced.…”

“…Quantifying shading directly would require photospectrum measurements within different moss canopies under controlled light conditions. Microclimate effects might also be better delimited through vegetation removal trials, such as those of Jaroszynska et al (2023), rather than my opportunistic placements. An ideal study would use controlled removal of different vegetation types (including mosses) over a regular gradient of a climate variable, such as precipitation (or an analogue, such as elevation, longitude, or aspect), with confounding variables controlled for or tested as factors in their own right.…”