Increased Soil Temperature Research Articles

Response Mechanism of cbbM Carbon Sequestration Microbial Community Characteristics in Different Wetland Types in Qinghai Lake.

Carbon-sequestering microorganisms play an important role in the carbon cycle of wetland ecosystems. However, the response mechanism of carbon-sequestering microbial communities to wetland type changes and their relationship with soil carbon remain unclear. To explore these differences and identify the main influencing factors, this study selected marsh wetlands, river wetlands and lakeside wetlands around Qinghai Lake as research subjects. High-throughput sequencing was employed to analyze the functional gene cbbM of carbon-sequestering microorganisms. The results revealed that the alpha diversity of cbbM carbon-sequestering microorganisms mirrored the trend in total carbon content, with the highest diversity observed in marsh wetlands and the lowest in lakeside wetlands. The dominant bacterial phylum was Proteobacteria, with prevalent genera including Thiothrix, Acidithiobacillus, and Thiodictyon. Acidithiobacillus served as a biomarker in lakeside wetlands, while two other genera were indicative of marsh wetlands. The hierarchical partitioning analysis indicated that the diversity of cbbM carbon-fixing microorganisms was primarily influenced by the total nitrogen content, while the community structure was significantly affected by the soil total carbon content. Moreover, an increased soil temperature and humidity were found to favor the carbon fixation processes of Thiomicrospira, Thiomonas, Polaromonas, and Acidithiobacillus. In summary, changes in wetland types seriously affected the characteristics of cbbM carbon sequestration in microbial communities, and a warm and humid climate may be conducive to wetland carbon sequestration.

Energy Compensation for Crop Growth under Plastic Mulching: Theories, Models, and Limitations

Plastic film mulching (PM) is a useful agronomic means to adapt to the environmental conditions of dryland agriculture and improve crop production. To improve the theoretical framework of PM technology, this study focuses on the interaction between the soil temperature change caused by PM and crop growth. The definition, action mechanism, and simulation of the compensatory effect of PM on growing degree days are introduced to reveal the effect of soil temperature under PM on crop development and growth. Our summary shows that the strength of the warming effect changes with the growth and development of crops, strengthening during the early stage of crop growth and gradually weakening as a crop canopy develops. Generally, the warming effect has a good promotion effect on crop growth, but the crop growth is hampered even with a yield reduction when the increased soil temperature caused by PM exceeds the tolerant temperature for plant growth. Moreover, the compensatory effect of PM could be used to quantify the growth and development of crops under PM and has been widely applied to cotton, corn, winter wheat, and rice. The compensation coefficient is larger in the early stage of crop growth than in the later stage. The compensation coefficient has certain differences for the same crop because of the influence of climate factors, soil moisture content, and soil microtopography. In future research, the theoretical integration of the safety period of PM and the time threshold of the compensatory effect could be theoretically interpreted, and the construction of the compensatory effect module in the crop models will also be an important issue.

Effects of biochar versus film mulching on soil hydrothermal properties and wheat crop performance in semi‐arid loess

AbstractFilm mulching and biochar have been applied as effective measures for increasing crop yields in arid and semi‐arid areas for many years. However, the effects of the temporal and spatial distributions of soil hydrothermal properties on crop yields are still unclear under film mulching and biochar addition. Thus, we conducted a field experiment with winter wheat on the Loess Plateau of China for two years (2020–2022) with three treatments: control, film mulching, and biochar. The results demonstrated that film mulching and biochar addition increased the average soil temperature in the 0–50 cm soil depth throughout the whole growth period and the influence depth exceeded 50 cm. Biochar addition only significantly increased soil temperature in the overwintering stage (p < 0.05). Film mulching increased the maximum and minimum temperatures in the 0–50 cm soil depth at seedling stage. Film mulching and biochar increased average ≥10°C accumulated soil temperature by increasing the ≥10°C accumulated soil temperature in the daytime and nighttime, and the number of days with a daily soil temperature ≥10°C during the whole growth period. Film mulching improved soil water storage in the 0–300 cm soil depth in each growth stage during both years, and also increased the wheat grain yield, aboveground biomass, and water use efficiency. Biochar addition increased the wheat grain yield and aboveground biomass of two years compared with control, but the increases were not significant (p > 0.05). In addition, correlation analysis showed that adequate temperatures in the 0–50 cm soil depth during the seedling and overwintering stages, and suitable soil moisture conditions in the 0–300 cm soil depth before sowing, jointing, and filling stages were important factors for increasing wheat grain yields under film mulching. In summary, film mulching mainly regulated the soil temperature in the 0–50 cm soil depth and moisture conditions in the 0–300 cm soil depth during different growth stages to increase grain yields. Film mulching has more obvious effects on moisture regulation, temperature regulation, and yield increases than biochar addition. Some environmentally friendly measures (such as conservation agriculture) with the same yield improving effect as mulching are also recommended to explore and promote in theLoess Plateau region.

Optimized decomposition of fresh tomato remnants in facility soil

To return vegetable remnants to soil in situ and understand parameters that determine their decomposition efficiency, the tomato remnant length, soil moisture, soil temperature and dosage of a microbial decomposer (MD) have been evaluated through a laboratory experiment using a nylon mesh bag in this study. The results showed that the residual remnant weight, and total carbon content increased 28.49 % and 32.65 %, respectively with two different remnant lengths (∼0.5 cm and ∼2.5 cm), while the decay rate and organic carbon breakdown rate decreased by 6.14 % and 7.48 %, respectively. When the relative water content in soil increased, the residual remnant weight and total carbon content first decreased and then increased, while the trend of the decay rate (16.94 % with 80 % soil water content) and organic carbon breakdown rate (9.96 % with 60 % soil water content) were opposite. At a high MD dosage (7 % or 9 % of the total compost weight), both rates of remnants were greater than those at the low dosage (1 %), with an increase of 38.63 % or 36.19 % and 15.89 % or 15.78 %, respectively. With an increase in soil temperature, both residual remnant weight and total carbon content decreased first and then increased, while both decomposition rate and organic carbon breakdown rate increased first and then decreased by 27.35 % and 22.78 %, respectively at 45 °C, compared with those at 30 °C. It was concluded that the decomposition rate was significantly correlated with the remnant length and the MD dosage, while the organic carbon breakdown rate was significantly associated with all four parameters evaluated. The optimal decomposing efficiency was achieved through cutting tomato remnants to a length of ∼0.5 cm, maintaining soil relative moisture content at 89 %, keeping soil temperature at 50 °C, and adding 7 % microbial decomposer MD to chopped tomato cuttings.

Deepened snow cover accelerates litter decomposition by stimulating microbial degradation

Changing precipitation patterns and global warming have greatly changed winter snow cover, which can affect litter decomposition process by altering soil microenvironment or microbial biomass and activity. However, it remains unknown how and to what extent snow cover affects litter decomposition during winter and over longer periods of time. Here, we conducted a meta-analysis to synthesize litter decomposition studies under different levels of snow cover. Overall, deepened snow significantly enhanced litter decomposition rate and mass loss by 17% and 3%, respectively. Deepened snow enhanced litter carbon loss by 7% but did not impact the loss of litter nitrogen or phosphorus. Deepened snow increased soil temperature, decreased the frequency of freeze-thaw cycles, and stimulated microbial biomass carbon and bacterial biomass during winter, but had no effect on these parameters in summer. The promoting effect of deepened snow cover on litter decomposition in winter is mainly due to its positive effect on microbial decomposition by increasing soil temperature and reducing freeze-thaw cycles exceeded its negative effect on physical fragmentation of litter by reducing freeze-thaw cycles. Our findings indicate that the changes in winter snow cover under global change scenarios can greatly impact winter litter decomposition and the associated carbon cycling, which should be taken into consideration when assessing the global carbon budget in modeling.

Drought effects on soil greenhouse gas fluxes in a boreal and a temperate forest

AbstractChanging water regimes (e.g. drought) have unknown long-term consequences on the stability and resilience of soil microorganisms who determine much of the carbon and nitrogen exchange between the biosphere and atmosphere. Shifts in their activity could feedback into ongoing climate change. In this study, we explored soil drought effects on soil greenhouse gas (GHG; CO2, CH4, N2O) fluxes over time in two sites: a boreal, coniferous forest in Finland (Hyytiälä) and a temperate, broadleaf forest in Austria (Rosalia). Topsoil moisture and topsoil temperature data were used to identify soil drought events, defined as when soil moisture is below the soil moisture at the permanent wilting point. Data over multiple years from automated GHG flux chambers installed on the forest floor were then analyzed using generalized additive models (GAM) to study whether GHG fluxes differed before and after drought events and whether there was an overall, multiyear temporal trend. Results showed CO2 and N2O emissions to be more affected by drought and long-term trends at Hyytiälä with increased CO2 emission and decreased N2O emissions both following drought and over the entire measurement period. CH4 uptake increased at both sites both during non-drought periods and as an overall, multiyear trend and was predominantly affected by soil moisture dynamics. Multiyear trends also suggest an increase in soil temperature in the boreal forest and a decrease in soil moisture in the temperate forest. These findings underline forests as an important sink for CH4, possibly with an increasing rate in a future climate.

Assessment of CH4 flux and its influencing drivers in the rice-wheat agroecosystem of the Huai River Basin, China

To understand the CH4 flux variations and their climatic drivers in the rice-wheat agroecosystem in the Huai River Basin of China, the CH4 flux was observed by using open-path eddy covariance at a typical rice-wheat rotation system in Anhui Province from November 2019 to October 2021. The variations and their drivers were then analyzed with the Akaike information criterion method. CH4 flux showed distinct diurnal variations with single peaks during 9:00~13:00 local time. The highest peak was 2.15 µg m-2 s-1 which occurred at 11:00 in the vegetative growth stage in the rice growing season (RGS). CH4 flux also showed significant seasonal variations. The average CH4 flux in the vegetative growth stage in the RGS (193.8±74.2 mg m-2 d-1) was the highest among all growth stages. The annual total CH4 flux in the non-rice growing season (3.2 g m-2, 11.8%) was relatively small compared to that in the RGS (23.9 g m-2, 88.2%). CH4 flux increased significantly with increase in air temperature, soil temperature, and soil water content in both the RGS and the non-RGS, while it decreased significantly with increase in vapor pressure deficit in the RGS. This study provided a comprehensive understanding of the CH4 flux and its drivers in the rice-wheat rotation agroecosystem in the Huai River Basin of China. In addition, our findings will be helpful for the validation and adjustment of the CH4 models in this region.

Heterogeneity of soil CO2 efflux from local parks across an urban landscape

ContextThe soil-atmosphere carbon exchange is an important component of the carbon cycle; however, dynamics of CO2 fluxes from urban landscapes are particular complicated and poorly understood due their heterogeneity.ObjectivesThe objectives of this study were to examine the total and temporal variation in CO2 flux from wooded and turfgrass areas of local parks in different part of town and identify the biophysical characteristics and landscape level factors that contribute to CO2 flux spatiotemporal variance in urban greenspaces.MethodsWe characterized the soil CO2 fluxes, temporal variation, and response to soil temperature from five parks under uniform management of a medium-sized town in southwestern Virginia, USA. We measured site scale characteristics (soil properties, tree cover) as well as the urbanicity of the surrounding land (land cover composition, population).ResultsSoil total nitrogen, soil temperature, and bulk density explained approximately 70% variation in the annual CO2 flux across the five parks. Diurnal, weekly, and seasonal CO2 fluxes were primarily related to changing soil temperature and differed between the turfgrass and wooded areas. Contrary to predictions that increased urbanicity around parks would increase soil temperature and CO2 fluxes, both CO2 and soil temperature of turfgrass were higher at parks located on town edges compared to parks in the center.ConclusionsIn sum, this study indicates that soil nitrogen and compaction, urbanicity, and the resulting site-scale structure of vegetation have a strong influence on temperature dependent biogeochemical processes like CO2 efflux.

Influence of tillage methods on carbon dioxide emissions in spring wheat crops

The agriculture intensification is associated with an increase in anthropogenic load on arable soils. Tillage leads to disruption of the natural process of soil formation in connection with which the soil biota activity changes and the carbon cycle is disrupted. The purpose of the study is to establish the effects of the tillage method on the carbon dioxide emission in spring wheat crops. The emission of carbon dioxide during the growing season of spring wheat varies significantly depending on the soil processing method and temperature. At the beginning of spring wheat development, the daily emission of carbon dioxide during the dump and subsurface tillage method does not exceed 36.0 and 36.2 CO2 kg/ha using zero technology provides a reduction in production CO2 production to 27.8 kg/ha*day. With an increase in soil temperature by July 24, the daily emission increases on a dump and subsurface background to 105.5 and 106.0 CO2 kg/ha*day, on a zero background to 95.4 CO2 kg/ha*day. In the future, it decreases. The total carbon losses during the dump and subsurface tillage methods are 2829 and 2793 kg/ha, the use of zero tillage technology reduces carbon losses in grain agrocenosis by 18%.

An empirical and a dynamic-empirical model for the estimation of maize seedbed temperature

Soil temperature is the main factor in determining the germination of maize seeds and the emergence time of the crop. It controls the rate of phenological development while the meristem is underground, which is until the V6 (six leaf collar) stage of maize. The research performed by the authors aimed to model maize seedbed temperatures at sowing depth (soil temperature at 5 cm depth) during the sowing-emergence-early development period. The research is based on measurements in ploughed plots of the maize experiments at the Látókép Experiment Site of the University of Debrecen (Eastern Hungary) in two growing seasons of 2021–2022. Two types of empirical models were established, a multilinear regression model (M1) and a dynamic-empirical model (M2), where the daily increase and decrease of soil temperature are determined by multilinear regression. Candidates for input variables for both models were various, easily available daily meteorological parameters. M2 model performed better than M1 when applied to an independent database of 2022. This is particularly valid for the maximum and minimum soil temperatures. It was found that both M1 and M2 can be used to predict the soil temperature of the maize seedbed before shading by the plants. For daily mean temperature, M1 and M2 give a similarly good estimation, while the dynamic-empirical model has to be preferred for the maximum and minimum temperatures. M2, which is based on daily temperature, global radiation and wind speed data, predicts the daily mean (RMSE = 1.4 °C), maximum (RMSE = 2.2 °C), and minimum (RMSE = 1.6 °C) of seedbed temperature not worse than many earlier soil temperature models do, even hybrid or mechanistic ones with a large number of parameters.

Eight-year warming might induce a shift toward forbs in an alpine meadow community of the Qinghai-Tibetan Plateau by increasing the soil temperature and nitrogen content

Plant biomass reveals the productivity and stability of a biotic community and is extremely sensitive to climate warming in permafrost regions, such as the Qinghai-Tibetan Plateau (QTP) in China. However, the response of the plant biomass of different functional groups to rising temperatures in such alpine zones remains unclear. Here, infrared radiators were used to simulate year-round warming on the QTP from 2011 to 2018. During the 8-year warming experiment, air temperature increased by 0.16 °C, while humidity tended to increase by 0.27 % at 20 cm above the ground. However, the rate of the increase in air temperature declined with an increasing number of years. Soil temperature and moisture increased by 1.28 °C and 3.61 %, respectively, on average from 0 to 100 cm below the ground, and the increment of soil moisture tended to rise with increasing depth. At the depths from 0 cm to 20 cm below the ground, soil organic carbon and total phosphorus tended to decrease by 0.79 g/kg and 0.04 g/kg, respectively, while soil total nitrogen tended to increase by 0.04 g/kg. Plant biomass had non-significant responses to warming, but the variation among different plant functional groups was greatest for forbs with the increment being 12.50, 147.97, and 160.47 g/m2 for plants aboveground, belowground, and total biomass, respectively. The ratios of plant total biomass tended to decrease by 2.29 %, increase by 0.60 %, and increase by 1.70 % for grasses, sedges, and forbs, respectively, so warming greatly decreased the proportion of grasses and increased the proportion of forbs in community. Warming weakened the positive correlation of grass biomass with soil temperature and enhanced the negative correlation of grass biomass with soil N and P content, along with weakening the positive correlation of sedge biomass with soil moisture and N content, while enhancing the negative correlation between sedge biomass and soil temperature. Meanwhile, forb biomass was greatly increased by soil temperature in the effects of warming. In conclusion, the 8-year warming produced negative effects on grasses and sedges by increasing soil temperature and N content and thus promoted the growth of forbs, which might induce a shift toward forbs in this community.

Evaluating Soil Carbon Efflux Responses to Soil Moisture and Temperature Variations in Brazilian Biomes

Changes in soil moisture and temperature can directly influence soil carbon emissions, which can add carbon to the atmosphere and make the greenhouse effect more intense. In this sense, research is needed that contributes to this knowledge and that simulates future scenarios, allowing actions to be taken in advance. Thus, an experiment was set up in which carbon dioxide efflux was collected over a period of one year in three Brazilian biomes, Cerrado, Pantanal, and Cerrado-Amazonian Ecotone, and to verify the influence of soil moisture, leaf area index and litter, multiple regression models were carried out. Correlation analyses were performed, and subsequently, sensitivity analyses were conducted for possible efflux increase sowing to 2ºC and 10% decreases or increases in soil temperature and moisture, respectively, simulating possible climate change scenarios. The results showed that of the three study areas, the Cerrado forest was most resistant to changes in these variables, and the correlation between the carbon efflux and the variables, soil temperature and moisture, were positive and significant for Cerrado and Pantanal.

Divergent rhizosphere and non-rhizosphere soil microbial structure and function in long-term warmed steppe due to altered root exudation.

While there is an extensive body of research on the influence of climate warming on total soil microbial communities, our understanding of how rhizosphere and non-rhizosphere soil microorganisms respond to warming remains limited. To address this knowledge gap, we investigated the impact of 4 years of soil warming on the diversity and composition of microbial communities in the rhizosphere and non-rhizosphere soil of a temperate steppe, focusing on changes in root exudation rates and exudate compositions. We used open top chambers to simulate warming conditions, resulting in an average soil temperature increase of 1.1°C over a span of 4 years. Our results showed that, in the non-rhizosphere soil, warming had no significant impact on dissolved organic carbon concentrations, compositions, or the abundance of soil microbial functional genes related to carbon and nitrogen cycling. Moreover, soil microbial diversity and community composition remained largely unaffected, although warming resulted in increased complexity of soil bacteria and fungi in the non-rhizosphere soil. In contrast, warming resulted in a substantial decrease in root exudate carbon (by 19%) and nitrogen (by 12%) concentrations and induced changes in root exudate compositions, primarily characterized by a reduction in the abundance in alcohols, coenzymes and vitamins, and phenylpropanoids and polyketides. These changes in root exudation rates and exudate compositions resulted in significant shifts in rhizosphere soil microbial diversity and community composition, ultimately leading to a reduction in the complexity of rhizosphere bacterial and fungal community networks. Altered root exudation and rhizosphere microbial community composition therefore decreased the expression of functional genes related to soil carbon and nitrogen cycling. Interestingly, we found that changes in soil carbon-related genes were primarily driven by the fungal communities and their responses to warming, both in the rhizosphere and non-rhizosphere soil. The study of soil microbial structure and function in rhizosphere and non-rhizosphere soil provides an ideal setting for understanding mechanisms for governing rhizosphere and non-rhizosphere soil carbon and nitrogen cycles. Our results highlight the distinctly varied responses of soil microorganisms in the rhizosphere and non-rhizosphere soil to climate warming. This suggests the need for models to address these processes individually, enabling more accurate predictions of the impacts of climate change on terrestrial carbon cycling.

Addition of biochar decreased soil respiration in a permanent no-till cover crop system for organic soybean production

The increase in soil carbon sequestration under long-term no-till (NT) and cover crop management has been shown to form part of a sustainable agricultural management practice system. Along with the increase in soil organic carbon (SOC), soil respiration in this system was also enhanced by the increased soil temperature through the decomposition that causes carbon loss from the soil. To overcome this issue, biochar can be applied. However, the addition of biochar into this system is not well studied. Therefore, the aim of this study was to investigate the effect of this system on soil respiration. The experiment was conducted at the Center for International Field Agriculture Research & Education, Ibaraki University. Long-term tillage practices, such as NT and moldboard plowing (MP), cover crops such as rye (RY) and fallow (FA), and biochar application such as with biochar (WB) and no biochar (NB) were applied to a split–split plot in a randomized complete block design with four replications. The daily CO2 flux was measured every week at 9:00–11:00 a.m. The daily soil respiration was affected by tillage and cover crop with NT practice had significantly higher daily CO2 flux than that of MP (23.8%–107.4% and 38.0%–107.8%), while RY had higher flux than that of FA (11.9%–81.2% and 34.9%–65.4%) in 2020 and 2021 soybean growing season, respectively. Additionally, in the 2020 cover crop growing season RY also increased daily CO2 flux approximately 41.8%–88.2% compared to FA. Biochar addition significantly reduced soil respiration in soybean and cover crop seasons compared to NB by 24.0%–50.7% and by 25.9%–48.3%, respectively. This reduction in soil respiration by the biochar decreased annual CO2 emissions by 17.6% and 13.0% in 2020 and 2021. The values of these emissions ranged from 9.6 Mg ha−1 for MP FA WB to 18.9 Mg ha−1 for MP RY NB in 2020 and from 7.5 Mg ha−1 for MP FA WB to 13.7 Mg ha−1 for NT FA NB in 2021. This study highlights the crucial role of biochar in reducing soil respiration and enhancing SOC sequestration. The addition of biochar into this system was able to reduce soil respiration by regulating the soil temperature, soil moisture, and protect the SOC from decomposition. Biochar addition also increased the SOC and decreased the soil bulk density, which improves soil porosity. Therefore, these findings would be very useful to be included within the global scenario of soil organic matter management.

Alternate row mulching optimizes soil temperature and water conditions andimproves groundnut yield in rainfed farming

Half mulching coverage within alternate rows (HM) increased soil temperature in the early growth stage and prolonged time of warming compared with full mulching coverage within all rows (FM). Moreover, the magnitude of the warming effect in the early stages under mulching conditions was greater than that of cooling effect in the late stages.

Effect of Mulching on Soil Temperatures and Its Impact on Plasmodiophora brassicae and Clubroot.

Clubroot caused by Plasmodiophora brassicae is a serious soilborne disease on cruciferous crops worldwide. Agricultural practice is a preferable clubroot management strategy because of its low investment requirement and environmental safety. Among the agricultural practices, solarization has been widely applied in the integrated management of other soilborne diseases. However, only few reports exist on the effect of solarization on clubroot management. In this study, we measured the effect of plastic mulching on soil temperature at different depths and on clubroot incidence and severity under greenhouse and field conditions. The pathogen density in the soil after solarization was measured by quantitative PCR analysis. Results indicated that the mulching treatment increased soil temperature especially in the soil layer ranges of 0 to 20 cm. Solarization with mulching also effectively reduced the incidence and severity of clubroot in the greenhouse assay and the field trial by decreasing the P. brassicae population in the soil. This study suggested that solarization with mulching can impair clubroot development and thus contribute to the sustainable management of clubroot.

Effects of simulated warming on soil microbial community diversity and composition across diverse ecosystems

Soil warming can directly affect the microbial community, or indirectly affect the microbial community by affecting soil moisture, nutrient availability, vegetation growth, etc. However, the response of microorganisms to soil warming is complex, and there is no uniform conclusion on the impact and mechanism of warming on microbial diversity. As the global climate gradually warms, a comprehensive assessment of warming on soil microbial community changes is essential to understand and predict the response of microbial geochemical processes to soil warming. Here, we perform a meta-analysis of studies to investigate changes in soil microbial communities along soil warming gradients and the response of soil microbes to elevated temperature in different ecosystems. We found that the α diversity index of soil microorganisms decreased significantly with the increase in temperature, and the β diversity altered with the increase in soil temperature and the shifts in ecosystem. Most bacteria only alter when the temperature rises higher. Compared to the non-warming condition, the relative abundance of Acidobacteria, Proteobacteria, Bacteroidetes, Planctomycetes and Verrucomicrobia decreased by 19 %, 11 %, 19 %, 8 % and 6 %, respectively, and the relative abundance of Firmicutes increased by 34 %. Compared to farmland, forest, grassland and tundra ecosystems, soil microorganisms in wetland ecosystems were more sensitive to temperature increase, and the changes in bacteria were consistent with the overall alterations. This meta-analysis revealed significant changes in the composition of microbial communities on soil warming. With the decrease in biodiversity under increasing temperature conditions, these dominant microbiomes, which can grow well under high-temperature conditions, will play a stronger role in regulating nutrient and energy flow. Our analysis adds a global perspective to the temperature response of soil microbes, which is critical to improving our understanding of the mechanisms of how soil microbes change in response to climate warming.

Climate change impacts on streamflow, sediment load and carbon fluxes in the Lena River delta

Water and sediment supply are essential to the health of deltaic ecosystems. Diverse datasets were integrated to better understand how climate change is shifting the supply of water and sediment to the largest polar distributary channel pattern – the Lena River Delta. Here the increase in warming rate from an average air temperature is from 4.1 °C for the period 1950–99 to 6.1 °C during 2000–21, which is higher than in the adjacent polar regions. Streamflow and sediment yield entering the Lena Delta have increased since 1988 by 56.3 km3 and 6.1×106 t, respectively; meanwhile, the Lena River’s increases in water temperature in June, July–August and September were found to be as much as 1.1, 0.6 and 0.05 °C. These changes have a pronounced effect on sediment regimes in particular parts of the delta. Based on analyses of correlations between various hydroclimatic drivers and sediment concentration changes across particular distributaries of the Lena Delta extracted from Landsat datasets, bank degradation driven by thermal erosional processes (which are in turn related to air and soil temperature increases) is proved to be the primary factor of the sediment regime in the delta. The study also highlights that sediment load changes are sensitive to wind speed due to remobilization of bottom sediment. Sums of daily air temperature and wind speed over 3 days are correlated with sediment concentration changes in the delta. The results also indicate that carbon transport across the delta (both POC and DOC) depends on sediment transport conditions and water discharge and might increase by up to 10 %. We conclude that the Lena Delta can be recognized as the global hot spot in terms of the hydrological consequences of climate change, which is altering sediment regimes, stream hydromorphology and carbon transport.

ELECTROPERSULFATE TREATMENT OF OIL PRODUCTION WASTE

A study on the possibility of implementing electropersulfate treatment of waste from the oil industry has been conducted. The dynamics of the volt-ampere characteristics during the transmission of electric current through the soil containing reservoir water and oil, with the introduction of persulfate salt, has been studied.The experiment made it possible to give a preliminary assessment of the possibility of using electropersulfate cleaning. The fairly high rate of electrophysical and electrochemical processes is associated, among other things, with the ability of potassium persulfate to actively oxidize components in the treated environment. The presence of formation water in the soil, which increases the humidity and the amount of salts dissociated into ions, and accordingly increases the conductivity of the soil, can accelerate the process. In addition, the use of iron electrodes promotes the activation of potassium persulfate, as does an increase in soil temperature during electrical treatment. In general, the presented experience allowed us to conclude that soil purification by electrical cleaning using potassium persulfate is suitable. At the same time, an important task for future research is to determine the optimal parameters of the minimum reasonable (in terms of time, amount of charge passed through the medium, dose of introduced persulfate) treatment using electroactivated persulfate salts.

Contrasting impacts of plastic film mulching and nitrogen fertilization on soil organic matter turnover

Plastic film mulching and nitrogen (N) fertilization are two important field management practices used to increase crop yields in rain-fed agriculture in arid and semi-arid areas. These two practices, however, can have opposing effects on soil organic carbon (SOC) stock and turnover. To clarify and analyze the combined effects of these practices, we conducted a 7-year continuous maize cultivation experiment with four treatments: (1) no plastic film mulching without N fertilization (Control), (2) plastic film mulching without N fertilization (PFM), (3) N fertilization without plastic film mulching (N), and (4) plastic film mulching with N fertilization (PFM + N). The 13C natural abundance of in the light and heavy fractions of organic carbon (LFOC and HFOC) was used to differentiate “old” (>7 years) and “new” (<7 years) C in the soil after C3 to C4 vegetation change. PFM increased soil temperature and moisture content over 7 years and led to a 150 % and 108 % increase in the above-ground and root biomass of maize, respectively. Hot and wet conditions under PFM accelerated the decomposition of both labile C (i.e., LFOC) and persistent C (i.e., HFOC), as measured by CO2 efflux from the soil. PFM decreased the LFOC and HFOC pools due to the fast decomposition of “old” C and inadequate stabilization of “new” C. Furthermore, PFM accelerated HFOC decomposition to a greater extent than that of LFOC. The Q10 values of SOC decomposition remained similar both in the presence and absence of PFM. Nitrogen fertilization increased the aboveground and root biomass of maize by 54 % and 40 %, respectively. In the control soil, microorganisms decomposed organic N owing to limited availability of mineral N and in the absence of any from replenishment by fertilizer N. Thus, the increase in LFOC content under N fertilization, was primarily attributed to the reduced decomposition of “old” C. The use of N fertilization produced a similar HFOC content as that of the control soil, while also accelerating the decomposition of “old” C and promoting the stabilization of “new” C, resulting in a faster turnover rate. Consequently, the impact of N fertilization on SOC turnover was negligible owing to the contrasting effects on LFOC and HFOC. The application of N fertilization resulted in a reduction of the Q10 value as compared to control. The combination of PFM and N fertilization accelerated the decomposition of HFOC and SOC, while having absent effect on SOC, labile C and persistent C contents. This indicates that 7 years weren’t long enough to trigger a response to the combination of PFM and N fertilization from SOC and HFOC contents. In summary, PFM led to a decline in the SOC content by accelerating the decomposition of both LFOC and HFOC. Conversely, N fertilization maintained SOC content by inhibiting LFOC decomposition and enhancing HFOC decomposition.