Coupled long-term summer warming and deeper snow alters species composition and stimulates gross primary productivity in tussock tundra

Abstract

Climate change is expected to increase summer temperature and winter precipitation throughout the Arctic. The long-term implications of these changes for plant species composition, plant function, and ecosystem processes are difficult to predict. We report on the influence of enhanced snow depth and warmer summer temperature following 20 years of an ITEX experimental manipulation at Toolik Lake, Alaska. Winter snow depth was increased using snow fences and warming was accomplished during summer using passive open-top chambers. One of the most important consequences of these experimental treatments was an increase in active layer depth and rate of thaw, which has led to deeper drainage and lower soil moisture content. Vegetation concomitantly shifted from a relatively wet system with high cover of the sedge Eriophorum vaginatum to a drier system, dominated by deciduous shrubs including Betula nana and Salix pulchra. At the individual plant level, we observed higher leaf nitrogen concentration associated with warmer temperatures and increased snow in S. pulchra and B. nana, but high leaf nitrogen concentration did not lead to higher rates of net photosynthesis. At the ecosystem level, we observed higher GPP and NEE in response to summer warming. Our results suggest that deeper snow has a cascading set of biophysical consequences that include a deeper active layer that leads to altered species composition, greater leaf nitrogen concentration, and higher ecosystem-level carbon uptake.

Leaf anatomy, BVOC emission and CO2exchange of arctic plants following snow addition and summer warming

“…This may be due to a higher proportion of diffuse relative to direct solar radiation in OTCs (Leadley and Drake, 1993), which enhances photosynthetic efficiency in Arctic plant canopies (Williams et al, 2014). The observed higher P G is in agreement with B. pendula having greater photosynthesis at an elevated temperature (Riikonen et al, 2009;Hartikainen et al, 2012), but in contrast with a lack of OTC effects on B. nana net photosynthesis at saturating light after a 20-year-long experimental manipulation (Leffler et al, 2016). Evergreens seem even less responsive.…”

Long‐term deepened snow promotes tundra evergreen shrub growth and summertime ecosystem net CO2 gain but reduces soil carbon and nutrient pools

“…In contrast, evergreen and sedge cover declined after 8 years of deepened snow treatment in a nearby moist acidic tussock tundra site. This differential effect was attributed to shading by increased deciduous shrub cover (Wahren et al., ), and was sustained even after 20 years of snow manipulation (Leffler, Klein, Oberbauer, & Welker, ). However, snow depth in those sites was increased up to 3 m, whereas our increase was from ~0.3 (ambient) up to a maximum of 1 m, suggesting that our conclusions are likely more realistic in terms of both inter‐annual and landscape‐scale spatial variation in low Arctic tundra snow depths, as well as climate predictions (Bintanja & Van Der Linden, ).…”

Delayed herbivory by migratory geese increases summer‐long CO2 uptake in coastal western Alaska

“…Flux of CO 2 for NEE and ER was determined with a nonlinear curve fit of chamber CO 2 over time between 30 and 120 s following chamber closure with the slope of the curve at the time of chamber closure as the instantaneous flux; GPP was calculated from NEE and ER (Rogers et al, 2011;Leffler et al, 2016). Each plot was measured ca.…”

“…Finally, herbivores can affect soil respiration through changes to the physical environment by reducing shading, which warms and dries soils (Köster, Köster, Berninger, Heinonsalo, & Pumpanen, 2018;Welker, Fahnestock, Bilbrough, & Piper, 2004); warmer soils often promote greater N availability (Leffler, Klein, Oberbauer, & Welker, 2016).…”