Warming of subarctic tundra increases emissions of all three important greenhouse gases – carbon dioxide, methane, and nitrous oxide

Abstract

Rapidly rising temperatures in the Arctic might cause a greater release of greenhouse gases (GHGs) to the atmosphere. To study the effect of warming on GHG dynamics, we deployed open-top chambers in a subarctic tundra site in Northeast European Russia. We determined carbon dioxide (CO ), methane (CH ), and nitrous oxide (N O) fluxes as well as the concentration of those gases, inorganic nitrogen (N) and dissolved organic carbon (DOC) along the soil profile. Studied tundra surfaces ranged from mineral to organic soils and from vegetated to unvegetated areas. As a result of air warming, the seasonal GHG budget of the vegetated tundra surfaces shifted from a GHG sink of -300 to -198 g CO -eq m to a source of 105 to 144 g CO -eq m . At bare peat surfaces, we observed increased release of all three GHGs. While the positive warming response was dominated by CO , we provide here the first in situ evidence of increasing N O emissions from tundra soils with warming. Warming promoted N O release not only from bare peat, previously identified as a strong N O source, but also from the abundant, vegetated peat surfaces that do not emit N O under present climate. At these surfaces, elevated temperatures had an adverse effect on plant growth, resulting in lower plant N uptake and, consequently, better N availability for soil microbes. Although the warming was limited to the soil surface and did not alter thaw depth, it increased concentrations of DOC, CO and CH in the soil down to the permafrost table. This can be attributed to downward DOC leaching, fueling microbial activity at depth. Taken together, our results emphasize the tight linkages between plant and soil processes, and different soil layers, which need to be taken into account when predicting the climate change feedback of the Arctic.

Increased nitrous oxide emissions from Arctic peatlands after permafrost thaw

“…Field studies show that the presence of vegetation reduces N 2 O emissions (16)(17)(18), also observed here, by lowering the mineral N supply in the rooting zone of vascular plants (Fig. 3 B and C).…”

“…In previous studies, we identified patches of bare peat in permafrost peatlands as hot spots for N 2 O emissions in subarctic tundra (16,17). Furthermore, an increase in growing season temperature without causing permafrost thaw not only increases N 2 O emissions from these hot spots, but also triggers N 2 O emissions from vegetated tundra peatlands (18), which cover large areas of the Arctic. This highlights the important role that peatlands may play in promoting Arctic N 2 O emissions in the future.…”

“…So far, soil moisture, soil organic matter (SOM) content, C/N ratio, and plant growth have been identified as the key regulators of Arctic N 2 O emissions (17,18). The great unknown, however, is how permafrost thaw will affect N 2 O emissions by potentially unlocking the vast N stocks currently stored in Arctic soils (10).…”

On Upscaling of Soil Microbial Processes and Biogeochemical Fluxes From Aggregates to Landscapes

“…We used ranked correlated surfaces to visualize the synthetic maps for visualization purposes (Schrenk et al, ). The chemical and physical properties including organic matter content, respiration rate, C:N ratios, and bulk density were extracted from literature data on field measurements (Gil et al, ; Repo et al, ; Voigt et al, ) and mapped as shown in Table S1 (and Figure S5 for respiration rates from different ecosystems). The upscaled biophysical model is linked to hydrologic and thermal modules to estimate soil water content and temperature profiles (see supporting information Figure S2 and Ebrahimi & Or, ).…”

土壤含水量调控高寒草原生态系统n2o排放对增温的响应

“…Overall, these results demonstrate that soil moisture regulates the responses of N 2 O emissions to experimental warming, highlighting the necessity to consider the warming-induced drying effect when estimating the magnitude of N 2 O emissions under future climate warming. Key words climate warming; nitrous oxide; ammonia-oxidizing archaea; ammonia-oxidizing bacteria; QinghaiXizang Plateau Wang GQ, Li F, Peng YF, Chen YL, Han TF, Yang GB, Liu L, Zhou GY, Yang YH (2018 (Mosier, 2008;Shi et al, 2012;Voigt et al, 2016), 然而, 也有少数研究发 现增温会抑制土壤N 2 O的排放 或者 未造成显著影响 (Ward et al, 2013;徐冰鑫等, 2014), 计算: Chapin III et al, 2011) …”