Plant-soil-microbial interactions mediate vegetation succession in retreating glacial forefields.

Global warming is accelerating glacial retreat and leaving open areas for vegetation succession on young developing soils. Soil microbial communities interact with plants affecting vegetation succession, but the specific microbial groups controlling these interactions are unclear. We tested whether plant-soil-microbial interactions explain plant primary succession in the Gongga Mountain glacial retreat chronosequence. The direction and intensity of plant-soil-microbial interactions were quantified by comparing the biomass of one early-, two mid- and two late-succession plant species under sterilized vs. live, and inter- vs. intra-specific competition. The performance of most plant species was negatively affected by soil biota from early habitats (5-10 yr), but positively by soil biota from mid- (30-40) and late-succession (80-100) habitats. Two species of Salicaceae from middle habitats, which are strong competitors, developed well on the soils of all successional stages and limited the establishment of later serial plant species. The strongest microbial drivers of plant-microbial interactions changed from i) saprophytic fungal specialists during the early stage, to ii) generalists bacteria and arbuscular mycorrhizal fungi in the middle stage, and finally to iii) ectomycorrhizal fungal specialists in the late stage. Microbial turnover intensified plant-soil-microbial interactions and accelerated primary succession in the young soils of the glacial retreat area.

Effects of plastic film mulch biodegradability on nitrogen in the plant-soil system.

The application of biodegradable film mulching (BFM) instead of non-biodegradable film mulching (NBFM) is a promising way to mitigate the negative impacts of residual film in agricultural mulching systems. But the effects of BFM on soil mineral nitrogen (N) are not known. To investigate the effects of BFM on N mineralization, nitrate (NO3-) accumulation and leaching, and plant N uptake, we conducted two-year field experiment with five treatments: no-mulching (No-M), white non-biodegradable film mulching (White-NotBioM), black non-biodegradable film mulching (Black-NotBioM), white biodegradable film mulching (White-BioM), and black biodegradable film mulching (Black-BioM). The net N mineralization in NBFM was greater than that in BFM due to the disintegration of biodegradable films in the middle and late stages of maize growth, resulting in a decrease in soil water content under BFM. Higher net N mineralization caused a higher NO3- accumulation in the topsoil (0-20 cm) under NBFM. The NO3- accumulation in the topsoil in Black-NotBioM was 23-88% higher than that in Black-BioM; while in White-NotBioM it was 16-63% higher than that in White-BioM. After two years of cropping, the NO3- accumulation in 100-180 cm (defined as N leaching in deep layers, NLD) in NBFM was 52-63% higher than that in BFM, implying that the higher NO3- accumulation in the topsoil in NBFM caused more N leaching. The yields and plant N uptake were similar between NBFM and BFM, but BFM had higher N harvest index values. Compared with NBFM, BFM showed less NO3- accumulation in the topsoil and less NLD, whereas yield, plant N uptake and net economic benefits were not reduced. Therefore, BFM, especially Black-BioM, could be an alternative to NBFM in maize production on the Loess Plateau. However, the higher N accumulation in root soil layer (0-100 cm) under Black-BioM should be accounted for in N fertilizer management.

Post-fire vegetation succession in the Siberian subarctic tundra over 45 years.

Wildfires are relatively rare in subarctic tundra ecosystems, but they can strongly change ecosystem properties. Short-term fire effects on subarctic tundra vegetation are well documented, but long-term vegetation recovery has been studied less. The frequency of tundra fires will increase with climate warming. Understanding the long-term effects of fire is necessary to predict future ecosystem changes. We used a space-for-time approach to assess vegetation recovery after fire over more than four decades. We studied soil and vegetation patterns on three large fire scars (>44, 28 and 12 years old) in dry, lichen-dominated forest tundra in Western Siberia. On 60 plots, we determined soil temperature and permafrost thaw depth, sampled vegetation and measured plant functional traits. We assessed trends in Normalized Difference Vegetation Index (NDVI) to support the field-based results on vegetation recovery. Soil temperature, permafrost thaw depth and total vegetation cover had recovered to pre-fire levels after >44 years, as well as total vegetation cover. In contrast, after >44 years, functional groups had not recovered to the pre-fire state. Burnt areas had lower lichen and higher bryophyte and shrub cover. The dominating shrub species, Betula nana, exhibited a higher vitality (higher specific leaf area and plant height) on burnt compared with control plots, suggesting a fire legacy effect in shrub growth. Our results confirm patterns of shrub encroachment after fire that were detected before in other parts of the Arctic and Subarctic. In the so far poorly studied Western Siberian forest tundra we demonstrate for the first time, long-term fire-legacies on the functional composition of relatively dry shrub- and lichen-dominated vegetation.

Trace elements composition of surface snow in the polar zone of northwestern Siberia: the impact of urban and industrial emissions.

In order to evaluate the level of atmospheric pollution in the north of Western Siberia, we studied the composition of urban snow in the vicinity of the Tazovsky settlement as well as in the area of Zapolyarnoye-the largest natural gas field in Russia in terms of a total extraction volume. Our results indicate that anthropogenic activities have caused an increase in electric conductivity and pH values of meltwaters. Concentrations of dissolved and particulate forms of trace elements (Fe, Mn, Ni, Cr, Cu, Pb, Zn, and Cd) were determined using atomic absorption spectroscopy. Dissolved forms of Cd, Zn, and Mn and particulate forms of Cu, Fe, and Ni prevailed in meltwaters of background territories. Human-affected territories were characterized by a predominance of particulate forms of trace elements (except Cd), which indicated increased dust deposition rates. For Cu, Mn, and Fe, mean values of contamination factor (CF) exceeded background levels by 4.4, 4.7, and 6.6 times, respectively. At some sampling sites, concentrations of trace elements exceeded background levels by 10-111 times. The concentration of Zn in our study area was higher than those in other oil and gas fields located in polar and boreal regions. The Cd concentration in the vicinity of the Tazovsky settlement was higher than those in other cities of Western Siberia. The data obtained in the present study on concentrations of soluble and particulate forms of trace elements in snow will be valuable for environmental protection in Russia's Arctic territory.

Improving dialogue among researchers, local and indigenous peoples and decision-makers to address issues of climate change in the North.

The Circumpolar North has been changing rapidly within the last decades, and the socioeconomic systems of the Eurasian Arctic and Siberia in particular have displayed the most dramatic changes. Here, anthropogenic drivers of environmental change such as migration and industrialization are added to climate-induced changes in the natural environment such as permafrost thawing and increased frequency of extreme events. Understanding and adapting to both types of changes are important to local and indigenous peoples in the Arctic and for the wider global community due to transboundary connectivity. As local and indigenous peoples, decision-makers and scientists perceive changes and impacts differently and often fail to communicate efficiently to respond to changes adequately, we convened a meeting of the three groups in Salekhard in 2017. The outcomes of the meeting include perceptions of how the three groups each perceive the main issues affecting health and well-being and recommendations for working together better.