Changing climate in northern regions is causing permafrost to thaw with major implications for the global mercury (Hg) cycle. We estimated Hg in permafrost regions based on in situ measurements of sediment total mercury (STHg), soil organic carbon (SOC), and the Hg to carbon ratio (RHgC) combined with maps of soil carbon. We measured a median STHg of 43 ± 30 ng Hg g soil−1 and a median RHgC of 1.6 ± 0.9 μg Hg g C−1, consistent with published results of STHg for tundra soils and 11,000 measurements from 4,926 temperate, nonpermafrost sites in North America and Eurasia. We estimate that the Northern Hemisphere permafrost regions contain 1,656 ± 962 Gg Hg, of which 793 ± 461 Gg Hg is frozen in permafrost. Permafrost soils store nearly twice as much Hg as all other soils, the ocean, and the atmosphere combined, and this Hg is vulnerable to release as permafrost thaws over the next century. Existing estimates greatly underestimate Hg in permafrost soils, indicating a need to reevaluate the role of the Arctic regions in the global Hg cycle.

Abstract. The current Northern Circumpolar Soil Carbon Database did not include organic carbon storage in permafrost regions on the Qinghai–Xizang (Tibetan) Plateau (QXP). In this study, we reported a new estimation of soil organic carbon (SOC) pools in the permafrost regions on the QXP up to 25 m depth using a total of 190 soil profiles. The SOC pools were estimated to be 17.3 ± 5.3 Pg for the 0–1 m depth, 10.6 ± 2.7 Pg for the 1–2 m depth, 5.1 ± 1.4 Pg for the 2–3 m depth and 127.2 ± 37.3 Pg for the layer of 3–25 m depth. The percentage of SOC storage in deep layers (3–25 m) on the QXP (80%) was higher than that (39%) in the yedoma and thermokarst deposits in arctic regions. In total, permafrost regions on the QXP contain approximately 160 ± 87 Pg SOC, of which approximately 132 ± 77 Pg (83%) stores in perennially frozen soils and deposits. Total organic carbon pools in permafrost regions on the QXP was approximately 8.7% of that in northern circumpolar permafrost region. The present study demonstrates that the total organic carbon storage is about 1832 Pg in permafrost regions on northern hemisphere.

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The response of dissolved organic carbon (DOC) flux to permafrost degradation is one of the major sources of uncertainty in predicting the permafrost carbon feedback. We investigated DOC export and properties over two complete flow seasons in a catchment on the northern Qinghai‐Tibetan Plateau. DOC concentration and biodegradability decreased systematically as thaw depth increased through the season, attributable to changing carbon sources and degree of microbial processing. Increasing DOC aromaticity and δ13C‐DOC indicated shifts toward more recalcitrant carbon sources and greater residence time in soils prior to reaching the stream network. These strong and consistent seasonal trends suggest that gradual active layer deepening may decrease DOC export and biodegradability from permafrost catchments. Because these patterns are opposite observations from areas experiencing abrupt permafrost collapse (thermokarst), the overall impact of permafrost degradation on DOC flux and biodegradability may depend on the proportion of the landscape experiencing gradual thaw versus thermokarst.

Small heat shock proteins (smHSPs) play important and extensive roles in plant defenses against abiotic stresses. We cloned a gene for a smHSP from the David Lily (Lilium davidii (E. H. Wilson) Raffill var. Willmottiae), which we named LimHSP16.45 based on its protein molecular weight. Its expression was induced by many kinds of abiotic stresses in both the lily and transgenic plants of Arabidopsis. Heterologous expression enhanced cell viability of the latter under high temperatures, high salt, and oxidative stress, and heat shock granules (HSGs) formed under heat or salinity treatment. Assays of enzymes showed that LimHSP16.45 overexpression was related to greater activity by superoxide dismutase and catalase in transgenic lines. Therefore, we conclude that heterologous expression can protect plants against abiotic stresses by preventing irreversible protein aggregation, and by scavenging cellular reactive oxygen species.

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Quercetin is a flavonoid ubiquitously found in nature. The therapeutic effect of quercetin on human hepatoma cell line (HepG2) was evaluated in this study. Various groups were incubated with different doses of quercetin for 12-, 24-, 48- and 72-h time duration and compared with control groups. Dose- and time-dependent inhibition in HepG2 proliferation was found with quercetin treatment. At 48 h of incubation, 61.78% of the cells were arrested at G(1) phase with 25 microM/l quercetin while 89.62% were arrested at G(1) phase with 50 microM/l quercetin. Furthermore, the results indicate that quercetin increased the content of Cdk inhibitor p21 protein, which was correlated with the elevation in p53 levels during 12 h of incubation. In addition, quercetin also increased the level of Cdk inhibitor p27 protein during 24 h of incubation. From our results it can be concluded that quercetin blocks cell cycle progression at G(1) phase and exerts its growth-inhibitory effect through the increase of Cdk inhibitors p21 and p27 and tumor suppressor p53 in HepG2.

Important unknowns remain about how abrupt permafrost collapse (thermokarst) affects carbon balance and greenhouse gas flux, limiting our ability to predict the magnitude and timing of the permafrost carbon feedback. We measured monthly, growing‐season fluxes of CO2, CH4, and N2O at a large thermokarst feature in alpine tundra on the northern Qinghai‐Tibetan Plateau (QTP). Thermokarst formation disrupted plant growth and soil hydrology, shifting the ecosystem from a growing‐season carbon sink to a weak source but decreasing feature level CH4 and N2O flux. Temperature‐corrected ecosystem respiration from decomposing permafrost soil was 2.7 to 9.5‐fold higher than in similar features from Arctic and Boreal regions, suggesting that warmer and dryer conditions on the northern QTP could accelerate carbon decomposition following permafrost collapse. N2O flux was similar to the highest values reported for Arctic ecosystems and was 60% higher from exposed mineral soil on the feature floor, confirming Arctic observations of coupled nitrification and denitrification in collapsed soils. Q10 values for respiration were typically over 4, suggesting high‐temperature sensitivity of thawed carbon. Taken together, these results suggest that QTP permafrost carbon in alpine tundra is highly vulnerable to mineralization following thaw, and that N2O production could be an important noncarbon permafrost climate feedback. Permafrost collapse altered soil hydrology, shifting the ecosystem from a carbon sink to carbon source but decreasing CH4 and N2O flux. Little to no vegetation recovery after stabilization suggests potentially large net carbon losses. High N2O flux compared to Arctic and Boreal systems suggests noncarbon permafrost climate feedback.