Complex carbon cycle responses to multi‐level warming and supplemental summer rain in the high Arctic

Abstract

The Arctic has experienced rapid warming and, although there are uncertainties, increases in precipitation are projected to accompany future warming. Climate changes are expected to affect magnitudes of gross ecosystem photosynthesis (GEP), ecosystem respiration (ER) and the net ecosystem exchange of CO2 (NEE). Furthermore, ecosystem responses to climate change are likely to be characterized by nonlinearities, thresholds and interactions among system components and the driving variables. These complex interactions increase the difficulty of predicting responses to climate change and necessitate the use of manipulative experiments. In 2003, we established a long-term, multi-level and multi-factor climate change experiment in a polar semidesert in northwest Greenland. Two levels of heating (30 and 60 W m(-2) ) were applied and the higher level was combined with supplemental summer rain. We made plot-level measurements of CO2 exchange, plant community composition, foliar nitrogen concentrations, leaf δ(13) C and NDVI to examine responses to our treatments at ecosystem- and leaf-levels. We confronted simple models of GEP and ER with our data to test hypotheses regarding key drivers of CO2 exchange and to estimate growing season CO2 -C budgets. Low-level warming increased the magnitude of the ecosystem C sink. Meanwhile, high-level warming made the ecosystem a source of C to the atmosphere. When high-level warming was combined with increased summer rain, the ecosystem became a C sink of magnitude similar to that observed under low-level warming. Competition among our ER models revealed the importance of soil moisture as a driving variable, likely through its effects on microbial activity and nutrient cycling. Measurements of community composition and proxies for leaf-level physiology suggest GEP responses largely reflect changes in leaf area of Salix arctica, rather than changes in leaf-level physiology. Our findings indicate that the sign and magnitude of the future High Arctic C budget may depend upon changes in summer rain.

Environmental Humidity Regulates Effects of Experimental Warming on Vegetation Index and Biomass Production in an Alpine Meadow of the Northern Tibet

“…Although several previous studies found that experimental warming-induced changes in biomass production may be related to warming magnitudes in alpine regions [2,23,28,50,58,59], the change magnitudes in NDVI, GNDVI, SAVI, AGB and GPP caused by experimental warming were not correlated with those in T s , T a , SM and VPD in the current study (S1 Fig). Experimental warming-induced change magnitudes in T s and T a in 2014 was not different from those in 2015.…”

“…Field warming experiments can reduce and even exclude the disturbance of human activities on the vegetation indices. Few studies have analyzed the response of ground-based vegetation indices to warming at field experimental site scale [14,22,23]. Therefore, it remains unclear how climatic warming will affect vegetation index and more field warming experiments should focus on this issue.…”

Rates and radiocarbon content of summer ecosystem respiration in response to long‐term deeper snow in the High Arctic of NW Greenland

“…The study was carried out in prostrate dwarf-shrub tundra in the High Arctic of northwest Greenland near Thule Air Base (76°32′N, 68°50′W; 200-350 m above sea level) [Sullivan et al, 2008;Sharp et al, 2013]. Mean annual air temperature is À11.3 ± 1.3°C, with 122.6 ± 45.4 mm of mean annual precipitation .…”

Plant genetic effects on soils under climate change

“…Climate change is shaping species responses in terms of C flux in a wide range of ecosystems (e.g. Asner et al 2003;Sharp et al 2013). For example, plants are allocating C to roots at deeper soil profiles under elevated atmospheric [CO 2 ] in forested ecosystems possibly leading to a shift in soil development, root morphology and C storage (Norby and Zak 2011).…”