Bryophyte species differ widely in their growth and N₂-fixation responses to temperature

Abstract

Bryophytes are abundant in tundra ecosystems, where they affect carbon and nitrogen cycling through primary production and associations with N2-fixing bacteria. Bryophyte responses to climate warming are inconclusive, likely because species-specific responses are poorly understood. Here we investigated how warming affects growth and nitrogenase activity of ten tundra bryophyte species in two tundra landscapes. Collected bryophyte samples were grown in temperature-controlled growth chambers for 12 weeks at five temperatures from 3 to 18 °C. We measured growth, N concentration, δ15N and δ13C after 3 months and nitrogenase activity after 5 and 12 weeks. Bryophyte growth and associated nitrogenase activity generally increased with temperature, but species differed in their optima. Bryophyte N concentration and δ15N indicated that, for some species, increased N2-fixation could not compensate for growth-induced N limitation. High landscape coverage and large positive warming effects on feather mosses and Sphagnum species highlight their competitive advantages, confirm earlier field observations, and contribute with mechanistic understanding of differential bryophyte growth in response to warming. We suggest that indirect effects of climate change, such as surface drying and shrub expansion, are likely main threats to slow-growing bryophytes across the Arctic, with consequences for biodiversity and C balance.

Moss species and precipitation mediate experimental warming stimulation of growing season N2 fixation in subarctic tundra

“…Importantly, species-specific estimates of moss cover at the landscape scale are missing at large (but see Rzepczynska et al, 2022;Stewart et al, 2011;Stuart, Pederson, et al, 2020).…”

“…While species‐specific in situ N 2 fixation rates are relatively easy to obtain, moisture and temperature conditions in the moss layer may change across the growing season and point measurements of N 2 fixation might not fully describe N 2 fixation cumulative rates. Further, species‐specific cover estimates at a scale larger than the plot or site scale are few and difficult to obtain as mosses are difficult to identify to species and notoriously overlooked (but see Rzepczynska et al., 2022). Modelled rates combined with high temporal resolution field microclimate data can resolve this issue and provide estimates of seasonal N input.…”

“…Moss density and shoot δ 13 CTop layer (green part of the moss shoots) δ 13 C, which reflect past moisture conditions in the moss tissue during moss carbon acquisition(Deane-Coe et al, 2015;Rzepczynska et al, 2022), was generally decreased by warming (Figure4b; Table…”

Scale‐dependent effects of herbivory on moss communities in Arctic wetlands: A 25‐year experiment

“…Mosses constitute a significant component of peatland ecosystems, including in Arctic wetlands used by foraging snow geese (Gauthier et al., 1996 , 2004 ). Mosses can structure plant diversity, contribute to carbon sequestration and nitrogen fixation, and account for a substantial proportion of net primary production in the Arctic (Jägerbrand et al., 2006 ; Rzepczynska et al., 2022 ; Turetsky et al., 2012 ). Although snow geese do not typically consume mosses (Audet et al., 2007 ; Gauthier, 1993 ), they disrupt the moss layer due to their digging behavior when they forage on graminoid rhizomes, a behavior known as grubbing (Jasmin et al., 2008 ).…”

Differentially abundant bacteria drive the N2-fixation of a widespread moss in the forest-tundra transition zone

“…Nonetheless, acrocarpous or erect-growing mosses also provide N 2 input into northern ecosystems, including Racomitrium spp., Dicranum spp., Aulacomnium spp. and Polytrichum spp., but the information is almost restricted to boreal zones with scatter information from arctic environments (Calabria et al 2020;Stuart et al 2021;Holland-Moritz et al 2021;Rzepczynska et al 2022;Klarenberg et al 2023). These acrocarpic mosses are particularly abundant in the forest-tundra ecotone compared to feather mosses and sphagnum spp., forming large mats (Gordon et al 2001;Cutler 2011) and, thus, may represent an essential entry of N 2 through their associated diazotrophic bacteria.…”