Plant Performance and Soil Nitrogen Mineralization in Response to Simulated Climate Change in Subarctic Dwarf Shrub Heath

Changes in Tree Growth, Biomass and Vegetation Over a 13-Year Period in the Swedish Sub-Arctic

“…Black circles denote clusters on the north side of the lake in 1997, and red circles denote clusters on the south-side of the lake in 1997. Arrows denote the change in biomass between 1997 and 2010 It has been suggested that increased nutrient availability associated with higher soil temperatures, and a longer growing season could underpin increased tree and shrub abundance and biomass in the Arctic (e.g., Chapin 1983;Weih and Karlsson 1997;Hartley et al 1999;Tape et al 2006). Kammer et al (2007) on the other hand, suggest that the observed increase may merely be a delayed re-expansion of shrubs and trees following the ''Little Ice-age'' that ended in the early twentieth century (Grubb 2008; see discussion in Rundqvist et al 2011, this issue).…”

Two Decades of Experimental Manipulations of Heaths and Forest Understory in the Subarctic

“…However, in situ buried bag studies suggest that the soil temperature increase by 1-2°C as in the passive warming Ruess et al 1999) does not significantly increase the microbial net N mineralization (Robinson et al 1995;Schmidt et al 2002;Jonasson et al 2006;Rinnan et al 2007b). When soil warming by 5°C was accomplished by heating cables buried 5 cm below the soil surface, seasonal net mineralization was transiently doubled after 2 years, but the difference disappeared after 5 years (Hartley et al 1999). Hence, fertilization treatments at high doses, intended to mimic the expected higher soil nutrient availability in response to warming, do not therefore reflect long-term effects of climate warming but rather they serve as a means to study effects of alleviated nutrient limitation.…”

“…1b), higher altitude dry heat, meadow and tussock tundra (Björk et al 2007;Molau 2010) and a peat bog (Dorrepaal et al 2009) and typically lead to 1-2°C soil warming, and to 3-4°C air warming above ambient summer temperature. By placing heating cables in the soil, additional soil warming in forest understory has been achieved (Hartley et al 1999), also in an experiment which included combined treatment with elevated CO 2 . OTCs have furthermore been erected in late autumn and early spring to increase the frequency of freeze-thaw cycles in order to examine how these cycles affect microbes, soil arthropods, and nutrient availability (Konestabo et al 2007).…”

Microtopography and Plant-Cover Controls on Nitrogen Dynamics in Hummock Tundra Ecosystems in Siberia

“…Although many studies, especially those utilizing experimental approaches, have demonstrated that temperature (Hartley et al, 1999;Hobbie, 1996;Oberbauer et al, 1991) and soil-moisture content (Johnson et al, 1996) are major determinants on nutrient-cycling rates of Arctic soils, increasing evidence also indicates that other topographic patterns are controlling nutrient turnover. For example, an incubation study with Arctic soils at different sites along a toposequence revealed that the overall effect of quality of soil organic matter was more important in controlling C-and N-mineralization rates than temperature .…”