Arctic mosses govern below-ground environment and ecosystem processes

Abstract

Mosses dominate many northern ecosystems and their presence is integral to soil thermal and hydrological regimes which, in turn, dictate important ecological processes. Drivers, such as climate change and increasing herbivore pressure, affect the moss layer thus, assessment of the functional role of mosses in determining soil characteristics is essential. Field manipulations conducted in high arctic Spitsbergen (78 degrees N), creating shallow (3 cm), intermediate (6 cm) and deep (12 cm) moss layers over the soil surface, had an immediate impact on soil temperature in terms of both average temperatures and amplitude of fluctuations. In soil under deep moss, temperature was substantially lower and organic layer thaw occurred 4 weeks later than in other treatment plots; the growing season for vascular plants was thereby reduced by 40%. Soil moisture was also reduced under deep moss, reflecting the influence of local heterogeneity in moss depth, over and above the landscape-scale topographic control of soil moisture. Data from field and laboratory experiments show that moss-mediated effects on the soil environment influenced microbial biomass and activity, resulting in warmer and wetter soil under thinner moss layers containing more plant-available nitrogen. In arctic ecosystems, which are limited by soil temperature, growing season length and nutrient availability, spatial and temporal variation in the depth of the moss layer has significant repercussions for ecosystem function. Evidence from our mesic tundra site shows that any disturbance causing reduction in the depth of the moss layer will alleviate temperature and moisture constraints and therefore profoundly influence a wide range of ecosystem processes, including nutrient cycling and energy transfer.

Effects of bryophyte and lichen cover on permafrost soil temperature at large scale

“…Our finding is consistent with various field experiments as well as modelling studies at site level, which confirm the important role of bryophytes and lichens for reducing heat exchange between atmosphere and soil at high latitudes (Beringer et al, 2001;Gornall et al, 2007;Jorgenson et al, 2010). Our results suggest that the insulating effect of the bryophyte and lichen ground cover should be taken into account in largescale modelling studies which focus on feedbacks between permafrost soil and atmospheric CO 2 under climatic change.…”

“…Blok et al (2011) show that the experimental removal of moss leads to increased ground heat flux and increased soil evaporation. Gornall et al (2007) observe higher soil temperatures in summer with decreasing thickness of the moss cover on the ground and lower soil temperatures in winter. In a modelling study, Bonan (1991) perform simulations with a local energy balance model for 20 forest stands in central Alaska to estimate the effect of moss removal on soil temperature.…”

Towards a more detailed representation of high-latitude vegetation in the global land surface model ORCHIDEE (ORC-HL-VEGv1.0)

“…Furthermore, the total living biomass simulated in the 2000s (around 100 gC m −2 in Fig. 11) is in accordance with the estimates given by Bond-Lamberty and Gower (2007) and Gornall et al (2007). For the introduction of boreal shrubs, a new allometry had to be defined (compared to trees) in order to simulate a realistic vegetation height, which is further used to describe the interactions of shrubs with snow, and in particular increased snow accumulation and density decrease near shrubs (Sect.…”

“…Bryophytes and lichens (NVPs) have a rather small amount of living biomass, around 200 g m −2 (Bond-Lamberty and Gower, 2007;Gornall et al, 2007), but with significant dead organic matter beneath. In contrast, in boreal and tundra ecosystems, where mosses compose a small fraction of total ecosystem biomass, their net primary productivity (NPP) can be up to 50 % of total annual NPP (Viereck et al, 1986;Beringer et al, 2001) corresponding to approximately 1-6 % of the global terrestrial NPP (Ito, 2011;Porada et al, 2013).…”

Uptake and recovery of soil nitrogen by bryophytes and vascular plants in an alpine meadow

“…Thick layers of live and dead bryophytes control the hydrology of vast peatland areas (Beringer et al 2001;Blok et al 2011), and preserve permafrost through their temperature-insulating capacity (Gornall et al 2007;Blok et al 2011). N (N) is the most limiting nutrient to net primary productivity in many terrestrial ecosystems, particularly in temperate and boreal regions (Chapin 1980;Vitousek and Howarth 1991;Elser et al 2007;LeBauer and Treseder 2008).…”