Freeze–thaw cycles have minimal effect on the mineralisation of low molecular weight, dissolved organic carbon in Arctic soils

Abstract

Warmer winters in Arctic regions may melt insulating snow cover and subject soils to more freezethaw cycles. The effect of freeze-thaw cycles on the microbial use of low molecular weight, dissolved organic carbon (LMW-DOC) is poorly understood. In this study, soils from the Arctic heath tundra, Arctic meadow tundra and a temperate grassland were frozen to -7.5°C and thawed once and three times. Subsequently, the mineralisation of 3 LMW-DOC substrates types (sugars, amino acids and peptides) was measured over an 8-day period and compared to controls which had not been frozen. This allowed the comparison of freeze-thaw effects between Arctic and temperate soil and between different substrates. The results showed that freeze-thaw cycles had no significant effect on C mineralisation in the Arctic tundra soils. In contrast, for the same intensity freeze-thaw cycles, a significant effect on C mineralisation was observed for all substrate types in the temperate soil although the response was substrate specific. Peptide and amino acid mineralisation were similarly affected by FT, whilst glucose had a different response. Further work is required to fully understand microbial use of LMW-DOC after freeze-thaw, yet these results suggest that relatively short freeze-thaw cycles have little effect on microbial use of LMW-DOC in Arctic tundra soils after thaw.

Dissolved organic carbon in permafrost regions: A review

“…Soil properties Aitkenhead and McDowell, 2000;Petrone et al, 2006Petrone et al, , 2007Prokushkin et al, 2009;Kindler et al, 2011;Kicklighter et al, 2013 Groundwater table Moore et al, 1998;Strack et al, 2008 Soil temperature and moisture contents Freeman et al, 2004;Kicklighter et al, 2013 Proportion of wetlands/peatlands Koprivnjak and Moore, 1992;Moore et al, 1998;Xenopoulos et al, 2003 Vegetation (NPP) De March, 1975;Meybeck, 1981;Moore, 1997;Judd and Kling, 2002;Freeman et al, 2004;Kicklighter et al, 2013;Abbott et al, 2016 Wildfires Schindler et al, 1997;Petrone et al, 2007;Betts and Jones Jr, 2009;Kicklighter et al, 2013;Larouche et al, 2015;Vonk et al, 2015 Atmospheric CO 2 level e.g., Freeman et al, 2004Elevation Sommaruga et al, 1999Xenopoulos et al, 2003 Permafrost degradation Prokushkin et al, 2007;Walvoord and Striegl, 2007;Prokushkin et al, 2009;O′Donnell et al, 2012;Larouche et al, 2015;Thompson et al, 2015;Ewing et al, 2015 Freeze-thaw cycles Yu et al, 2010;Foster et al, 2016 Atmospheric deposition chemistry Hope et al, 1994;Moore, 1997;…”

Inhibitory effects of climate change on the growth and extracellular enzyme activities of a widespread Antarctic soil fungus

“…It is possible that the 33% reduction in the number of freeze–thaw events in OTCs compared with control plots at Mars Oasis might have led to lower microbial mineralization of organic C and N, limiting nutrient availability in chambered, glycine‐, or TSB‐amended soils, and resulting in restricted growth of P. roseus . However, experiments on High Arctic tundra and montane soils indicate that freeze–thaw events with minimum temperatures of −9.0°C and −7.5°C have no effects on the microbial mineralization of C from glucose and amino acids, including glycine (Foster et al, 2016; Lipson & Monson, 1998). Given these observations, it seems unlikely that freeze–thaw events at Mars Oasis, during which soil temperatures fell to between −0.7°C and −4.7°C, would have affected the mineralization of nutrients from glycine and TSB in OTCs, with consequent impacts on the growth of P. roseus in soil.…”

“…Freeze-thaw is a significant factor for polar and montane soils, with the process reducing microbial biomass and leading to increased soil C and N availability following spring thaw (Grogan et al, 2004;Schimel et al, 2007). However, the extent of freeze-thaw effects depends on the severity of the freezing treatment and on the environment in which the experiments take place, with less pronounced effects in permanently cold soils (Matzner & Borken, 2008 (Foster et al, 2016;Lipson & Monson, 1998). Given these observations, it seems unlikely that freeze-thaw events at Mars Oasis, during which soil temperatures fell to between −0.7°C and −4.7°C, would have affected the mineralization of nutrients from glycine and TSB in OTCs, with consequent impacts on the growth of P. roseus in soil.…”

“…A consistent feature of the fungi, and other microbes, inhabiting cold regions is their adaptation to growth at low temperatures. A rich literature, predominantly derived from the Arctic, has accumulated about the metabolism of cold-adapted microbes at temperatures close to freezing point (e.g., Foster et al, 2016;McMahon et al, 2009;Mikan et al, 2002;Schimel et al, 2007). These organisms, referred to as psychrophiles and psychrotrophs, are able to grow at, or below, 0°C and typically have growth temperature optima at <15°C and <20°C, respectively (Morita, 1975;Russell, 1990).…”

Five decades of terrestrial and freshwater research at Ny-Ålesund, Svalbard

“…Changes to winter precipitation, especially the incidence of rainfall and the cover, depth and density of snow, have major effects on Arctic vegetation. For instance, studies using snow fences on Brøggerhalvøya and also in Adventdalen indicate major consequences for vegetation and nutrient cycling of increased snow depth (e.g., Rieley et al 1995;Morgner et al 2010;Foster et al 2016). These include altered leaf traits and delayed phenology (Rieley et al 1995;Cooper et al 2011;Semenchuk, Gillespie et al 2016), higher leaf and whole plant N contents (Semenchuk et al 2015;Mörsdorf et al 2019) and changes in plant community composition, with, for instance, loss of dwarf shrub dominance in some areas (Cooper et al 2019).…”