Though one of the most vulnerable terrestrial ecosystems, wetlands provide multiple ecosystem services, most notably storing carbon. It is now widely recognized that climate change could have a large impact on high-latitude wetlands. A key question is how climate change will affect the distribution pattern of wetland plant communities, and to what extent the transitions among different wetland plant communities respond to regional warming? To answer this question, we estimated the total SOC storage with 139 soil profiles in the Xing'anling Mountains and performed ensemble species distribution modelling for 11 dominant wetland plant communities by using numerous vegetation plots. Results show that 4.5-23.8% of the high-latitude wetlands in the study area would be lost following widespread thawing of permafrost under different climate warming scenarios by the end of this century. The total wetland SOC in the Xing'anling Mountains is estimated to be 1.58 Pg, about 25.5-29.3% of the total of China's wetlands, however, predicted wetland loss could put 5.4-20.5% (0.08-0.32 Pg C) of the total SOC storage at risk of instability. Our results also predicted a significant northward migration of southern Deyeuxia angustifolia communities driven by future climate changes. This wetland succession could profoundly reduce future carbon sequestration capacity of wetlands in the study area. The findings presented here are helpful for both current reserve management and future conservation planning of wetlands in the study area.

Warming in the Arctic accelerates top-soil decomposition and deep-soil permafrost thaw. This may lead to an increase in plant-available nutrients throughout the active layer soil and near the permafrost thaw front. For nitrogen (N) limited high arctic plants, increased N availability may enhance growth and alter community composition, importantly affecting the ecosystem carbon balance. However, the extent to which plants can take advantage of this newly available N may be constrained by the following three factors: vertical distribution of N within the soil profile, timing of N-release, and competition with other plants and microorganisms. Therefore, we investigated species- and depth-specific plant N uptake in a high arctic tundra, northeastern Greenland. Using stable isotopic labelling (N-15-NH4+), we simulated autumn N-release at three depths within the active layer: top (10 cm), mid (45 cm) and deep-soil near the permafrost thaw front (90 cm). We measured plant species-specific N uptake immediately after N-release (autumn) and after 1 year, and assessed depth-specific microbial N uptake and resource partitioning between above- and below-ground plant parts, microorganisms and soil. We found that high arctic plants actively foraged for N past the peak growing season, notably the graminoidKobresia myosuroides. While most plant species (Carex rupestris,Dryas octopetala,K. myosuroides) preferred top-soil N, the shrubSalix arcticaalso effectively acquired N from deeper soil layers. All plants were able to obtain N from the permafrost thaw front, both in autumn and during the following growing season, demonstrating the importance of permafrost-released N as a new N source for arctic plants. Finally, microbial N uptake markedly declined with depth, hence, plant access to deep-soil N pools is a competitive strength. In conclusion, plant species-specific competitive advantages with respect to both time- and depth-specific N-release may dictate short- and long-term plant community changes in the Arctic and consequently, larger-scale climate feedbacks.

Aims: This paper focuses on quantifying the distribution patterns of plant communities along the permafrost thaw depth gradient, in order to develop a framework for predicting the response of vegetation characteristics in cold high latitude ecosystems to permafrost degradation as a result of climate warming. Study area: Great Hing'an Mountains of northeastern China. Methods: Thirty plots were selected in a west slope region of the Great Hing'an Mountain Valleys to study the relationship between the depth of the active layer of permafrost and characteristics of plant communities. Results: The distribution of plant communities strongly correlated with the permafrost thaw depth. With increasing depth of the active layer, important species showed an obvious transition and plant strategies shifted gradually from helophilous to hygrophilous to mesophilous. Both biodiversity and the total biomass of understory vegetation decreased significantly along this gradient. Conclusions: The response of the vegetation characteristics varied considerably with the depth of the active layer throughout the permafrost degradation. Our results show implications for vegetation in the face of climate change as rising temperatures directly affect permafrost, and in many areas the depth of the active layer is increasing.

1. The polar desert biome of the Canadian high Arctic Archipelago is currently experiencing some of the greatest mean annual air temperature increases on the planet, threatening the stability of ecosystems residing above temperature-sensitive permafrost. 2. Ice wedges are the most widespread form of ground ice, occurring in up to 25% of the world's terrestrial near-surface, and their melting (thermokarst) may catalyse a suite of biotic and ecological changes, facilitating major ecosystem shifts. 3. These unknown ecosystem shifts raise serious questions as to how permafrost stability, vegetation diversity and edaphic conditions will change with a warming high Arctic. Ecosystem and thermokarst processes tend to be examined independently, limiting our understanding of a coupled system whereby the effect of climate change on one will affect the outcome of the other. 4. Using in-depth, comprehensive field observations and a space-for-time approach, we investigate the highly structured landscape that has emerged due to the thermokarst-induced partitioning of microhabitats. We examine differences in vegetation diversity, community composition and soil conditions on the Fosheim Peninsula, Ellesmere Island, Nunavut. We hypothesize that (i) greater ice wedge subsidence results in increased vegetation cover due to elevated soil moisture, thereby decreasing the seasonal depth of thaw and restricting groundwater outflow; (ii) thermokarst processes result in altered vegetation richness, turnover and dispersion, with greater microhabitat diversity at the landscape scale; and (iii) shifts in hydrology and plant community structure alter soil chemistry. 5. We found that the disturbance caused by melting ice wedges catalysed a suite of environmental and biotic effects: topographical changes, a new hydrological balance, significant species richness and turnover changes, and distinct soil chemistries. Thermokarst areas favour a subset of species unique from the polar desert and are characterized by greater species turnover (beta-diversity) across the landscape. 6. Synthesis. Our findings suggest that projected increases of thermokarst in the polar desert will lead to the increased partitioning of microhabitats, creating a more heterogeneous high arctic landscape through diverging vegetation communities and edaphic conditions, resulting in a wetland-like biome in the high Arctic that could replace much of the ice-rich polar desert.

How the greening of Arctic landscapes manifests as a change in ecosystem structure and function remains largely unknown. This study investigates the likely implications of plant community change on ecosystem function in tundra near Barrow, Alaska. We use structural data from marked plots, established in 1972 and resampled in 1999, 2008 and 2010 to assess plant community change. Ecosystem functional studies were made close to peak growing season in 2008 and 2010 on destructive plots adjacent to marked plots and included measurement of land-atmosphere CH4 and CO2 exchange, hyperspectral reflectance, albedo, water table height, soil moisture, and plant species cover and abundance. Species cover and abundance data from marked and destructive plots were analyzed together using non-metric multi-dimensional scaling (NMS) ordination. NMS axis scores from destructive plots were used to krig ecosystem function variables in ordination space and produce surface plots from which time series of functional attributes for resampled plots were derived. Generally, the greatest functional change was found in aquatic and wet plant communities, where productivity varied and soil moisture increased, increasing methane efflux. Functional change was minimal in moist and dry communities, which experienced a general decrease in soil moisture availability and appeared overall to be functionally more stable through time. Findings suggest that the Barrow landscape could have become less productive and less responsive to change and disturbance over the past few decades. This study is a contribution to the International Polar Year-Back to the Future Project (512).