Dear Colleagues,

Mean temperatures in many polar regions are warming at unprecedented rates, in association with a suite of other environmental changes. Critically, this is not just increasing the heat input for terrestrial ecosystems, it is also shifting the balance of when and where melting occurs and the form of precipitation (rain vs. snow), which dramatically changes the seasonal cycle of water availability. The indigenous soil fauna in the Arctic and Antarctic are uniquely adapted to cope with long chronically cold winters within often frozen (and thus dry) microhabitats. ‘Milder’ winters create the challenges of depleting energy reserves more quickly during dormancy, exposure to more frequent freeze–thaw cycles and increased risk of inoculative freezing in wet habitats. Somewhat counter-intuitively, increased snow melt can also leave certain terrestrial habitats exposed to more severe winter cold and icing events by removing/depleting the insulating blanket of snow. Because winter conditions are currently warming faster than other seasons, an in-depth knowledge of soil fauna species cold stress physiology is critical to accurately predict the ecological consequences of climate change.

Changing summer conditions also present many important challenges, with normally short, cool summers being extended and instances of record warm air temperatures being experienced, e.g., 18.3 °C on 6 February 2020 on the Antarctic Peninsula, and 38 °C in the Russian Arctic on the 29 June 2020. While these longer growing seasons may permit more rapid development and thus population growth of soil organisms, the impacts are not uniform across all species, resulting in sometimes quite dramatic changes in community structure. Longer, warmer summers can also disrupt phenology, resulting in the ‘wrong’ developmental stages overwintering with associated consequences on winter survival, or loss of synchrony, e.g., in plant–insect or predator–prey interactions. Furthermore, extreme warm (and drying) events during summer may be pushing some polar soil organisms beyond their physiologcal stress limits.

In combination with all the abiotic environmental changes brought about by climate warming comes the biotic threat of competition from alien species whose distribution ranges have either naturally extended into higher latitudes, or have been introduced in association with increasing human movement. Where extreme winter cold and/or brief cool growing seasons were once a barrier to establishment, warmer conditions have opened the door enabling some alien species to become invasive. Just one species introduction within these often very simple ecosystems can shift the entire balance of soil communities, especially if the species introduces a new ecological function such as a novel threat of predation, or shifts rates/patterns of nutrient cycling. Here, there are important differences, and thus comparisons to be made, between the Arctic and Antarctic due to differences in the complexity of native communities and their accessibility to alien species as well as differences in rates of environmental change.

This Special Issue provides a syntheisis of studies investigating the ecology, physiology and molecular biology of the native soil fauna of the Antarctic and Arctic. Collectively, these studies will advance our understanding of species adaptations to extreme environments, as well as identifying winners and losers in the face of challenges posed by climate change. Combining this understanding with historic and future scenario microclimate data will, in turn, allow us to address key knowledge gaps in the capacity of these species to shift their distributions in response to advancing warming conditions. In turn, equivalent studies of alien species with distribution ranges currently at the edge of polar zones, in combination with assessment of the risks posed by increased human movement in these regions, will allow us to determine future invasion threats and how polar soil communities will change in future.

Dr. Scott Hayward
Dr. Peter Convey
Dr. Nicholas M. Teets
Guest Editors

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• arctic
• antarctic
• climate change
• physiology
• phenology
• terrestrial
• invertebrate
• extreme environment
• overwintering
• soil fauna
• communities