The impact of permafrost on carbon dioxide and methane fluxes in Siberia: A meta-analysis.

There are serious concerns associated with greenhouse gases (GHG) fluxes in high latitude ecosystems and how the permafrost thawing may potentially affect the global climate, through the alteration of carbon (C) dioxide (CO2) and methane (CH4) emissions. We performed a meta-analysis of 3002 observations from 104 published studies on CO2 and CH4 fluxes in Siberia (Russian Federation). Siberia is a vast region characterized by a large C-rich permafrost region, which is already degrading due to escalating climate change, and also large wetland areas, also regarded as a source of CH4. GHG fluxes were strongly controlled by location (Western, Central, Eastern, and Far East Siberia), permafrost presence and season. Maximum CO2 fluxes, in the permafrost zone, were observed in Central and Eastern Siberia. In the non-permafrost zone, maximum CO2 fluxes were found in Western Siberia. According to our analyses, CH4 fluxes in the permafrost zone were significantly different in all parts of Siberia. Thus, permafrost has a more profound effect on CH4 than on CO2 flux. The rank order of increase of CH4 emissions among the various Siberian regions is as follows: Central < Eastern < Western < Far East. In the non-permafrost area, CH4 fluxes in Western Siberia are higher than those in the Central part. Soil temperature was the only significant predictor of soil CO2 flux in the permafrost area. CH4 fluxes were well correlated with temperature and soil water content in the permafrost zone, but only dependent on temperature in the non-permafrost area. In this meta-analysis, we established several statistically significant temporal trends of long-term changes of GHG fluxes over three decades (1984-2017): an increasing trend of soil CO2 fluxes in the non-permafrost area of Western Siberia and a declining trend in the non-permafrost area of Central Siberia. There was also a significant increasing trend of CH4 fluxes in the permafrost area of Eastern Siberia, and its decreasing trend in the non-permafrost area of Western Siberia.

Intraseasonal carbon sequestration and allocation in larch trees growing on permafrost in Siberia after 13C labeling (two seasons of 2013-2014 observation).

This research is an attempt to study seasonal translocation patterns of photoassimilated carbon within trees of one of the high latitudes widespread deciduous conifer species Larix gmelinii (Rupr. Rupr). For this purpose, we applied whole-tree labeling by 13CO2, which is a powerful and effective tool for tracing newly developed assimilates translocation to tissues and organs of a tree. Experimental plot has been established in a mature 105-year-old larch stand located within the continuous permafrost area near Tura settlement (Central Siberia, 64°17'13″N, 100°11'55″E, 148 m a.s.l.). Measurements of seasonal photosynthetic activity and foliage parameters (i.e., leaf length, area, biomass, etc.), and sampling were arranged from early growing season (June 8, 2013; May 14, 2014) until yellowing and senescence of needles (September 17, 2013; September 14, 2014). Labeling by 13C of the tree branch (June 2013, for 3 branch replicates in 3 different trees) and the whole tree was conducted at early (June 2014), middle (July 2014), and late (August 2013) phase of growing season (for different trees in 3 replicates each time) by three pulses [(CO2)max = 3000-4000 ppmv, 13CO2 (30 % v/v)]. We found at least two different patterns of carbon translocation associated with larch CO2 assimilation depending on needle phenology. In early period of growing season (June), 13C appearing in newly developed needles is a result of remobilized storage material use for growth purposes. Then approximately at the end of June, growth processes is switching to storage processes lasting to the end of growing season.

Fossil mosses are emitting methane after maritime Antarctic glacier retreat.

In the extraordinary weather conditions of the austral summer of 2023, fossil mosses thawed out from under the Bellingshausen Ice Dome, King George Island, Southern Shetland Archipelago of maritime Antarctica. At the end of the austral summer, we directly measured greenhouse gas fluxes (CH4 and CO2) from the surface of fossil mosses. We showed that fossil mosses were strong emitters of CH4 and weak emitters of CO2. The real-time measured CH4 emissions reached 0.173 µmol m-2 s-1, which is comparable to CH4 efflux in water bodies or wet tundra in the Arctic.

Mixed-power scaling of whole-plant respiration from seedlings to giant trees.

The scaling of respiratory metabolism with body mass is one of the most pervasive phenomena in biology. Using a single allometric equation to characterize empirical scaling relationships and to evaluate alternative hypotheses about mechanisms has been controversial. We developed a method to directly measure respiration of 271 whole plants, spanning nine orders of magnitude in body mass, from small seedlings to large trees, and from tropical to boreal ecosystems. Our measurements include the roots, which have often been ignored. Rather than a single power-law relationship, our data are fit by a biphasic, mixed-power function. The allometric exponent varies continuously from 1 in the smallest plants to 3/4 in larger saplings and trees. Therefore, our findings support the recent findings of Reich et al. [Reich PB, Tjoelker MG, Machado JL, Oleksyn J (2006) Universal scaling of respiratory metabolism, size, and nitrogen in plants. Nature 439:457-461] and West, Brown, and Enquist [West GB, Brown JH, Enquist BJ (1997) A general model for the origin of allometric scaling laws in biology. Science 276:122 -126.]. The transition from linear to 3/4-power scaling may indicate fundamental physical and physiological constraints on the allocation of plant biomass between photosynthetic and nonphotosynthetic organs over the course of ontogenetic plant growth.

Soil contamination by diesel fuel destabilizes the soil microbial pools: Insights from permafrost soil incubations.

Arctic contamination by diesel fuel (DF) is of great concern because of the uncertain feedback of permafrost carbon (C) and soil microbiota to DF in the context of climate change in high latitudes. We conducted a laboratory incubation experiment with a gradient of DF addition ratios to examine the responses of the soil microbiota of the typical permafrost soils in the tundra ecosystems of the Norilsk region (Siberia). The study revealed initial heterogeneity in the microbial activity of the studied soils (Histic Gleyic Cryosols (CR-hi,gl), Turbic Cryosols (CR-tu), Turbic Spodic Folic Cryosols (CR-tu,sd,fo), Gleyic Fluvisols (FL-gl)). We applied the two-pool model for evaluation of the effect of DF on the proportions of C pools and revealed significant differences between soil types in the fast and slow C pools in response to DF addition. The results showed that DF addition treatments had varying effects on the fast and slow C pools, microbial activity, and microbial community structure in the studied soils. For minor exceptions, DF dramatically accelerated C loss from the slow C pool in all soil types. We assume that differences in C pool and microbiota responses to DF addition were caused by soil texture and changes in microbial community structure. We isolated Serratia proteamaculans, S. liquefaciens, S. plymuthica, Rhodococcus erythropolis, Pseudomonas antarctica, P. libanensis, P. brassicacearum, and P. chlororaphis from the DF-polluted soils. These species are recommended for bioremediation to mitigate the DF contamination of permafrost soils, especially regarding climate change and the sustainable well-being of Arctic ecosystems.