Semenchuk, Philipp R.3; Elberling, Bo5; Amtorp, Cecilie4; Winkler, Judith4; Rumpf, Sabine3; Michelsen, Anders6; Cooper, Elisabeth J.3
1 Geography, Department of Geosciences and Natural Resource Management, Faculty of Science, Københavns Universitet2 Terrestrial Ecology, Department of Biology, Faculty of Science, Københavns Universitet3 UiT The Arctic University of Norway4 University Center in Svalbard5 Geography, Department of Geosciences and Natural Resource Management, Faculty of Science, Københavns Universitet6 Terrestrial Ecology, Department of Biology, Faculty of Science, Københavns Universitet
Nitrogen (N) mineralization, nutrient availability, and plant growth in the Arctic are often restricted by low temperatures. Predicted increases of cold-season temperatures may be important for plant nutrient availability and growth, given that N mineralization is also taking place during the cold season. Changing nutrient availability may be reflected in plant N and chlorophyll content and lead to increased photosynthetic capacity, plant growth, and ultimately carbon (C) assimilation by plants. In this study, we increased snow depth and thereby cold-season soil temperatures in high Arctic Svalbard in two vegetation types spanning three moisture regimes. We measured growing-season availability of ammonium (NH4 (+)), nitrate (NO3 (-)), total dissolved organic carbon (DOC) and nitrogen (TON) in soil; C, N, delta N-15 and chlorophyll content in Salix polaris leaves; and leaf sizes of Salix, Bistorta vivipara, and Luzula arcuata at peak season. Nutrient availability was significantly higher with increased snow depth in the two mesic meadow vegetation types, but not in the drier heath vegetation. Nitrogen concentrations and delta N-15 values of Salix leaves were significantly higher in all vegetation types, but the leaf sizes were unchanged. Leaves of Bistorta and Luzula were significantly larger but only significantly so in one moist vegetation type. Increased N and chlorophyll concentrations in leaves indicate a potential for increased growth (C uptake), supported by large leaf sizes for some species. Responses to cold-season soil warming are vegetation type- and species-specific, with potentially stronger responses in moister vegetation types. This study therefore highlights the contrasting effect of snow in a tundra landscape and has important implications for projections of whole tundra responses to climate change.