Soil ecosystem responses to experimental warming in northern Mongolia

Background/Question/Methods

A recent study in the Lake Hövsgöl region of northern Mongolia has shown that mean annual air temperature has increased by 1.8 ^oC over the last 40 years, greater than global average temperature increases. Although it is hypothesized that projected warmer temperatures in the future will cause higher soil CO₂ efflux, responses of soil efflux to climate change may differ among ecosystems due to response variations of controlling factors. The objectives of our study were (1) to examine the environmental responses (soil temperature and moisture) to experimental warming and (2) to test responses of soil CO₂ efflux to experimental warming, in three different ecozones.
The experimental site is located in Dalbay Valley, on the eastern shore of Lake Hövsgöl in northern Mongolia (51° 01.405' N 100° 45.600' E; 1670 m elevation). Replicate plots with ITEX-style open-top passive warming chambers and non-warmed control areas were installed in three different ecosystems: (1) semi-arid grassland on the south-facing slope not underlain by permafrost, (2) riparian zone and (3) larch forest on the north-facing slope underlain by permafrost. Aboveground air temperature was recorded for each treatment (control and OTC) by HOBO dataloggers, and belowground soil temperature and moisture (10 and 20 cm) by ECH₂O sensors. Soil CO₂ efflux was measured periodically using an infra-red gas analyzer with an attached soil respiration chamber.

Results/Conclusions

Passive warming chambers increased air temperatures during nighttime consistently; 0.1-0.2 °C in forest, 0.2-0.5 °C in riparian area, 0.8-1.5 °C in grassland. Increases in daytime air temperatures ranged 0.3-1.6 °C in the grassland, but did not appear to be significant in the riparian and forest areas. Similar results were observed for soil temperatures at 10 and 20 cm depths. The chamber effect on soil moisture at 10 and 20 cm depths was not consistent in forest and riparian areas, and was highly dependent on initial conditions; however in most plots chamber had slight drying effect. In warmed plots in the grassland, soil moisture contents at 10 cm and 20 cm depths were lower by 3-12% and 1-6%, respectively. Measured soil CO₂ efflux rates were 0.90 g C m^-2 h^-1 in forest, 1.10 g C m^-2 h^-1 in riparian area, and 0.60 g C m^-2 h^-1 in grassland. Initial results of soil efflux measurements suggest that the warming treatment had little effect on soil respiration.

Overall, our preliminary results suggest that responses to experimental warming differed significantly among the three ecozones of Dalbay Valley.