D. V. Karelin

CO2 flux measurements in Russian Far East tundra using eddy covariance and closed chamber techniques

The objective of this study was to estimate the CO2 exchange of a tundra ecosystem in the Russian Far East using the eddy covariance technique using closed-chamber measurements as a reference. An eddy covariance tower was placed near the Lavrentiya settlement (Chukotskiy Peninsula, Russia, 65° 36′N, 171°04′W) within a typical tundra landscape. During the 85 d of continuous measurements [Julian days (JD) 205–289, 2000] the CO2 exchange of the studied ecosystem was found to be close to equilibrium (a carbon sink at 10.2 gC m−2). In the late summer period (JD 205–240) the ecosystem sequestered 32.1 gC m−2, whereas in autumn (JD 241–289), it was functioning as a carbon source of 21.9 gC m−2. Model-based estimates of ecosystem respiration and gross primary production were obtained over the period of observations. These are the first eddy covariance-based measurements performed in the Russian tundra.

Androgen Receptor Gene Polymorphism, Aggression, and Reproduction in Tanzanian Foragers and Pastoralists.

The androgen receptor (AR) gene polymorphism in humans is linked to aggression and may also be linked to reproduction. Here we report associations between AR gene polymorphism and aggression and reproduction in two small-scale societies in northern Tanzania (Africa)—the Hadza (monogamous foragers) and the Datoga (polygynous pastoralists). We secured self-reports of aggression and assessed genetic polymorphism of the number of CAG repeats for the AR gene for 210 Hadza men and 229 Datoga men (aged 17–70 years). We conducted structural equation modeling to identify links between AR gene polymorphism, aggression, and number of children born, and included age and ethnicity as covariates. Fewer AR CAG repeats predicted greater aggression, and Datoga men reported more aggression than did Hadza men. In addition, aggression mediated the identified negative relationship between CAG repeats and number of children born.

Sensitivity of tundra carbon balance to ambient temperature.

Summer field observations in thenorth-east European region of Russia (1995–1996) proved thatnatural local and temporal warming could cause similarreversible changes of carbon (C) balance pattern ofsouth tundra ecosystems. Thirty-six diurnal chambermeasurements of carbon dioxide fluxes at two differentsites (67°57′N, 64°40′E; 67°20′N,63°44′E) in 4 main types of ecosystems werestudied. Wide magnitude of ambient mean diurnal airtemperature (from +4.1 to +20.2 °C) allowed toobtain significant linear relationship between thisparameter and variation in ecosystems C net flux (from–2.6 (sink) to +2.0 (source) gC m-2 d-1, R2 = 0.769). In the midst ofthe vegetative season, an increase of mean diurnal airtemperature in the plant canopy over the criticalvalue of +14 °C lead to a change in the C netflux from sink to source. This can revert with atemperature decreases below the critical value. Theabove-mentioned effect is mostly due to thetemperature influenced increase of gross ecosystemrespiration. The summer temperature induced changesmay result in positive (C source) annual C balance insome studied ecosystems. The annual C loss ofshrub-dwarf shrub community in 1996 was estimated at45 gC m-2 yr-1. We consider ourresults to be another evidence of possible positivefeed-back between climate warming and C emission tothe atmosphere on short-term and regional scales.

Aggression and polymorphisms in AR, DAT1, DRD2, and COMT genes in Datoga pastoralists of Tanzania

The aim of this study was to analyse the relationships between polymorphisms in four candidate genes (AR, DAT1, DRD2, and COMT) and aggression in men from a traditional society of East African pastoralists, the Datoga. Buss and Perrys Aggression Questionnaire was used to measure aggression. The number of CAG repeats in the AR gene was negatively correlated with physical aggression, anger, and hostility. Among the genes of the dopaminergic system, a significant single-gene effect was detected only for DRD2 with regard to anger. At the level of a two-gene model, a significant effect for DRD2 and a tendency for DAT1 were observed for the DAT1-DRD2 gene pair regarding hostility, and two tendencies were observed for the interaction effect of the DAT1-COMT pair regarding anger and hostility. These data suggest a probable link between physical aggression and direct fitness caused by strong sexual selection in Datoga men.

Factors of spatiotemporal variability of CO2 fluxes from soils of southern taiga spruce forests of Valdai

Factors determining the spatiotemporal variability of carbon dioxide emission from soil on various scales (from hours and days to seasons of the year and multiple years, and from microbiotopes to mesobiotopes) were identified using the results of a five-year study in the southern taiga spruce forest at Valdai highlands (Novgorod oblast). The air temperature close to the soil and that of the top layer of the soil, the humidity of the top layer of the soil, the precipitation during the preceding period, the litter thickness, the minimal distance to the trunks of dead standing and fallen spruce trees, and the coefficient of enhancement of microbial respiration were among the most significant factors. The soil temperature at a depth of 1 cm was the only variable of significance for both spatial and temporal distribution. The necessity of taking both spatial and temporal factors into account upon the prediction of the estimated value of CO2 emission by the soil has been demonstrated.

Changes in soil respiration in the course of the postagrogenic succession on sandy soils in the southern taiga zone

The dynamics of the CO2 emission from sandy soils in the course of the postagrogenic succession in the southern taiga zone were studied. We measured total emission from the soil surface and, separately, respiration from the litter and mineral soil horizons during the warm (snowless) seasons of 2010 and 2011 on differently aged fallow plots: 0 years (cropland) and 7, 23, 55, 100, and 170 years. It was demonstrated that changes in the CO2 emission in the course of the succession have a nonlinear pattern: the emission sharply increases in the first decade, then somewhat decreases, and then gradually increases again up to the maximum values. This is explained by the dependence of the rate of the emission on the soil carbon pools (humus + litter + underground phytomass) that are also subjected to nonlinear changes. Initially, the emission is mainly due to mineralization of labile organic substances added to the plowed soils in the form of organic fertilizers. Then, in parallel with a gradual increase in the pools of litter and underground phytomass, the total pool of soil organic carbon increases, and its role in the emission becomes more pronounced. The seasonal dynamics of the soil respiration are mainly controlled by the soil temperature; the soil moistening plays an important role only during the initial meadow stage of the succession.

Experimental studies and physically substantiated model of carbon dioxide emission from the exposed cultural layer of Velikii Novgorod

The results of quantitative assessment and modeling of carbon dioxide emission from urban pedolithosediments (cultural layer) in the central part of Velikii Novgorod are discussed. At the first stages after the exposure of the cultural layer to the surface in archaeological excavations, very high CO2 emission values reaching 10–15 g C/(m2 h) have been determined. These values exceed the normal equilibrium emission from the soil surface by two orders of magnitude. However, they should not be interpreted as indications of the high biological activity of the buried urban sediments. A model based on physical processes shows that the measured emission values can be reliably explained by degassing of the soil water and desorption of gases from the urban sediments. This model suggests the diffusion mechanism of the transfer of carbon dioxide from the cultural layer into the atmosphere; in addition, it includes the equations to describe nonequilibrium interphase interactions (sorption–desorption and dissolution–degassing of CO2) with the first-order kinetics. With the use of statistically reliable data on physical parameters—the effective diffusion coefficient as dependent on the aeration porosity, the effective solubility, the Henry constant for the CO2 sorption, and the kinetic constants of the CO2 desorption and degassing of the soil solution—this model reproduces the experimental data on the dynamics of CO2 emission from the surface of the exposed cultural layer obtained by the static chamber method.

Active-Layer Monitoring in Northeast Russia: Spatial, Seasonal, and Interannual Variability

This paper focuses on regional analysis of results from a program of active-layer monitoring at three active CALM (Circumpolar Active Layer Monitoring program) sites in northeast Russia. The length of the observation period varied between 3 and 9 years at different sites. Thaw depth was measured mechanically on 100 × 100 m grids with 1-4 replications at each grid node, 1-4 times per thawing season. Additional parameters, depending on site, were volumetric soil moisture, thickness of the organic layer, thickness of the moss cover, absolute elevation of nodes, surface disturbance and quality of microhabitats, and density of vegetation cover. There were no evident trends in end-of-season thaw depth at our sites in northeast Russia during the 1994-2002 period. Water tracks, surface disturbances, soil moisture, and organic soil horizon thickness are major controls over spatial variations of end-of-season thaw depth. The influence of different factors on the thawing process is seasonally specific. Temporal variation of thaw depths is strongly temperature dependent.

Changes in the carbon dioxide emission from soils in the course of postagrogenic succession in the Chernozems forest-steppe

The CO2 emission from soils in the course of the long-term postagrogenic succession on Calcic Chernozems under meadow-steppe vegetation was studied. Seasonal dynamics of the emission at different stages of the restoration of natural vegetation and long-term changes in the main pools of carbon in the soils and phytomass were examined. These data were used to create a regression model of the CO2 emission on the basis of data on the soil water content and temperature with a temporal resolution of 3 h. The results were compared with an analogous study of the postagrogenic succession on sandy Agropodzols of southern taiga. It was found that the long-term pattern of the CO2 emission has a bimodal character. The first maximum corresponds to the early stages of the succession (2–8 years) and is ensured by a sharp intensification of respiration in the organomineral soil horizons under the impact of plant species typical of these stages, active growth of their underground parts, and, probably, activation of microbiota in the rhizosphere. The second maximum of the emission is observed at the final stages of the succession and is mainly ensured by the increasing pool of steppe litter. A decrease in the soil temperature because of the thermal insulation of the soil surface by the accumulating litter and organic substances in the topsoil horizons leads to a temporary decrease in the emission intensity at the middle stages of the succession, when the litter pool is still not vary large. The restoration of the initial level of the CO2 emission typical of the natural cenoses is achieved in about 80–100 years after the abandoning of the cultivated fields, i.e., considerably faster than that in the southern taiga zone (150–170 years). The results of modeling suggest that this is caused by the considerable accumulation of steppe litter, organic substances, and phytomass in the topsoil horizons rather than by the somewhat increased heat supply owing to longer duration of vegetation season.

Interannual changes in PAR and soil moisture during warm season may be more important than temperature fluctuations in directing annual carbon balance in Tundra

The results of 16-year instrumental monitoring (1996–2011) of the state of permafrost, soils, and vegetation influenced by environmental factors in the shrub tundra subzone of northeastern European Russia (Bol’shezemel’skaya Tundra) are described. The field measurement data for CO2 fluxes in 1996 and 1998–1999 have been used to construct regression equations and to simulate intraanual carbon fluxes with a step of 3 h. Over the observation period, the average annual and summer air temperatures have been considerably elevated relative to the local climate norms as of a climatically stable period of 1980–1996. According to our instrumental observations, the average winter and annual temperatures, total number of positive degree days, the input of photosynthetically active radiation (PAR), and average seasonal soil moisture increased during the next period (1996–2011). Correspondingly, the average annual depth of seasonal soil thawing, and seasonal maximum of vascular leaf phytomass stock also increased considerably. According to the model, the net ecosystem exchange of carbon (NEE) increased from an equilibrium state in 1996–2002 to a considerable elevation in the carbon stock in 1998–2011. Thus, the total stock over the 16-year period amounted to 109 g C m−2. An independent confirmation of the effect assumed by the model is an increase in the aboveground stocks of the live and dead organic matter in ecosystem. A statistical analysis of the model has demonstrated that, in addition to an increase in PAR and temperature, acting over the long-term period in the observed range in a mode of mutual compensation relative to NEE, the main reason underlying the observed increase in long-term carbon stock is the amount of vascular plant leaf stock, which has emerged as a major predictor for NEE and, correspondingly, acts as an independent parameter of the carbon balance. This increase is most likely determined by an increase in soil moisture.