Decomposition in differing snow regimes in high Arctic Svalbard

Abstract

Rapidly rising temperatures are having great effects on the high arctic ecosystem, historically characterized by long, cold winter periods, and cold dry summers. Due to the length of the winter season, arctic soils have been an important carbon sink, but may now be facing increased microbial activity due to increasing temperatures. Temperature, moisture, and litter quality play important roles in decomposition processes, where winter temperature, summer moisture, and plant community composition is strongly influenced by the amount of accumulated snow during the winter period. Increased winter snow depth has been found to increase winter soil temperatures, therefore increasing microbial activity and decomposition in the winter period. Decomposition of green and rooibos tea bags was studied in a long-term experiment in Adventdalen, Svalbard, where snow was manipulated behind snow fences to create Ambient, Medium, and Deep regimes. Open top chambers (OTCs) were used to measure simulated warmer summer temperatures on tea bag decomposition. Decomposition was measured for an annual term (September 2017-August 2018), a winter term (September 2017-June 2018), and a summer term (June 2018-August 2018, inside and outside of open top chambers). Temperature loggers recorded soil surface temperature hourly throughout the study period. Enhanced snow depth increased winter temperatures in the Deep and Medium snow regimes compared to Ambient. The Deep regime had delayed snowmelt compared to the Ambient and Medium regimes, and was coolest regime during the summertime. The Medium regime was the warmest regime during summer, by visual observation. Soil moisture decreased in all snow regimes over the course of the summer period, and soil moisture measured inside of OTCs was lower than outside of OTCs. Green tea and rooibos tea demonstrated different patterns of decomposition under the varying snow depth regimes. Annual decomposition was lowest in the Deep regime for both substrates. Annual decomposition was highest in Medium for green tea and highest in Ambient for rooibos tea. Decomposition was lower inside of OTCs than outside of OTCs for both types of tea. These results demonstrate the complexity of the processes driving decomposition in Arctic soils. Increased snow cover may cause lower decomposition in long-term studies where plant and microbial community composition may have changed over time, suggesting that winter soil temperatures alone may not be as important in these changing ecosystems.