High arctic heath soil respiration and biogeochemical dynamics during summer and autumn freeze‐in – effects of long‐term enhanced water and nutrient supply

• Published in: Global Change Biology
• Main Authors: Christiansen, Casper T., Svendsen, Sarah H., Schmidt, Niels M., Michelsen, Anders
• Other Authors: Danish National Research Foundation, Danish Council for Independent Research
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2012
• Subjects: Greenland; Tundra; Zackenberg
• Online Access: http://dx.doi.org/10.1111/j.1365-2486.2012.02770.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-2486.2012.02770.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2486.2012.02770.x; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/j.1365-2486.2012.02770.x

Abstract In High Arctic NE Greenland, temperature and precipitation are predicted to increase during this century, however, relatively little information is available on the role of increased water supply on soil CO 2 efflux in dry, high arctic ecosystems. We measured soil respiration (R soil ) in summer and autumn of 2009 in combination with microbial biomass and nutrient availability during autumn freeze‐in at a dry, open heath in Zackenberg, NE Greenland. This tundra site has been subject to fully factorial manipulation consisting of increased soil water supply for 14 years, and occasional nitrogen (N) addition in pulses. Summer watering enhanced R soil during summer, but decreased R soil in the following autumn. We speculate that this is due to intensified depletion of recently fixed plant carbon by soil organisms. Hence, autumn soil microbial activity seems tightly linked to growing season plant production through plant‐associated carbon pools. Nitrogen addition alone consistently increased R soil , but when water and nitrogen were added in combination, autumn R soil declined similarly to when water was added alone. Despite several freeze‐thaw events, the microbial biomass carbon (C) remained constant until finally being reduced by ~60% in late September. In spite of significantly reduced microbial biomass C and phosphorus (P), microbial N did not change. This suggests N released from dead microbes was quickly assimilated by surviving microbes. We observed no change in soil organic matter content after 14 years of environmental manipulations, suggesting high ecosystem resistance to environmental changes.