The impact of global climate change and human-induced nitrogen (N) deposition on winter weather patterns will have consequences for soil N cycling and greenhouse gas emissions in temperate deserts. Biological soil crusts (referred to as biocrusts) are crucial communities in soil and significant sources of nitrous oxide (N2O) emission in desert ecosystems and are sensitive to environmental changes. The contribution of bacteria and fungi to N2O production in drylands has been acknowledged. However, the effect of changes in snow cover and N deposition on the N2O production of different microbial groups of microorganisms is not yet clear. In this study, we examine the responses of fungi and bacteria mediated pathways involved in soil N2O production from biocrusts to longterm snow cover manipulation and N addition experiments in the Gurbantunggut Desert. These soils were incubated and subjected to biocide treatments (such as cycloheximide and streptomycin, and fungal and bacterial inhibitors), after which rates of potential nitrification and N2O production were measured. Compared with controls, snow removal treatments from bare sand, lichen crust and moss crust reduced background rates of N2O production by 29.41 %, 26.21 % and 20.49 %, respectively; N2O production rates were 1.53-fold higher in bare sand, 1.38-fold higher in lichen crust, and 1.56-fold higher in moss crust after N addition. The addition of streptomycin significantly reduced the potential nitrification rates of bare sand and biocrusts, indicating that bacteria may be important sources of NO3- production in biocrusts rather than fungi. Conversely, fungi were main sources of N2O production in biocrusts. Additionally, fungi also played a major role in N2O production in biocrusts after snow cover manipulation and N addition. Both snow cover manipulation and N addition treatment indirectly affected the N2O production in biocrusts by considerably affecting the content of substrate N and the abundance of microbial groups. Our research suggests that fungi are main contributors for denitrification in biocrusts, and that snow cover changes (removal snow and double snow) and N addition alter the contribution of biotic pathways responsible for N cycling.

Aviation emissions are the only direct source of anthropogenic particulate pollution at high altitudes, which can form con-trails and contrail-induced clouds, with consequent effects upon global radiative forcing. In this study, we develop a pre-dictive model, called APMEP-CNN, for aviation non-volatile particulate matter (nvPM) emissions using a convolutional neural network (CNN) technique. The model is established with data sets from the newly published aviation emission databank and measurement results from several field studies on the ground and during cruise operation. The model also takes the influence of sustainable aviation fuels (SAFs) on nvPM emissions into account by considering fuel properties. This study demonstrates that the APMEP-CNN can predict nvPM emission index in mass (EIm) and number (EIn) for a number of high-bypass turbofan engines. The accuracy of predicting EIm and EIn at ground level is significantly improved (R2 = 0.96 and 0.96) compared to the published models. We verify the suitability and the applicability of the APMEP-CNN model for estimating nvPM emissions at cruise and burning SAFs and blend fuels, and find that our predictions for EIm are within & PLUSMN;36.4 % of the measurements at cruise and within & PLUSMN;33.0 % of the measurements burning SAFs in av-erage. In the worst case, the APMEP-CNN prediction is different by -69.2 % from the measurements at cruise for the JT3D-3B engine. Thus, the APMEP-CNN model can provide new data for establishing accurate emission inventories of global aviation and help assess the impact of aviation emissions on human health, environment and climate.Synopsis: The results of this paper provide accurate predictions of nvPM emissions from in-use aircraft engines, which im-pact airport local air quality and global radiative forcing.

Under the condition of warming and wetting trend on Qinghai-Tibet Plateau due to climate change, summer rainfall infiltration alters the change of the hydrothermal state and may impact the cooling performance of crushed-rock interlayer embankment. Herein, two experimental models with the 1.4-m-thickness (M1) and 0.6m-thickness (M2) crushed-rock layer (CRL) were conducted in an environmental simulator experiencing the freezing and thawing cycles. The hydrothermal response to rainfall events was investigated and quantified by analyzing the variations of measured soil temperatures, volumetric water contents, and heat fluxes. Thermal observations show that rainfall infiltration caused heat advection and resulted in step change of soil temperature at depth. Rainfall infiltration reduced the surface temperature of the CRL, but warmed the soil layer at depth by up to 2.13 degrees C. The average temperature of the base soil layer under the action of concentrated rainfall basically showed an increasing trend. In particular, the CRL with a smaller thickness (M2) had a more significant thermal response to rainfall event. In addition, the moisture pulse, experiencing a step increase and following a gradual decrease caused by rainfall water infiltration, appeared several hours earlier than the temperature pulse. Moreover, infiltrated water produced an additional energy to warm the soil at depth, with maximum heat flux of 12.13 W/m2 and 79.90 W/m2 for the M1 and M2, respectively. The infiltrated water accumulated at the top of base soil significantly delayed the refreezing processes in cold period due to the latent heat effect. The net founding of this study provide an insight into improving the design crushed-rock embankment in permafrost regions.

The Mongolian Plateau is located in the permafrost transitional zone between high-altitudinal and high-latitudinal permafrost regions in the Northern Hemisphere. Current knowledge of the thermal state and changes in the permafrost on the Mongolian Plateau is limited. This study adopted an improved calculation method of the Mongolian Plateau air freezing and thawing index using the monthly air temperature reanalysis dataset from the Climate Research Unit (CRU). The spatial and temporal variation characteristics from 1901 to 2019 were further assessed by the Mann-Kendall (M-K) test and spatial interpolation methods. The results indicate that the spatial distributions of the freezing and thawing index show clear latitudinal zonality. Over the study period, the air freezing index decreased by 4.1 degrees C center dot d/yr, and the air thawing index increased by 2.3 degrees C center dot d/yr. The change point in the air thawing index appeared in 1995 (p < 0.05) based on the M-K method, in contrast to the so-called hiatus in global warming. Our results reveal rapid warming on the Mongolian Plateau, especially in the permafrost region, and are useful for studying permafrost changes on the Mongolian Plateau.

The Mongolian Plateau is located in the permafrost transitional zone between high-altitudinal and high-latitudinal permafrost regions in the Northern Hemisphere. Current knowledge of the thermal state and changes in the permafrost on the Mongolian Plateau is limited. This study adopted an improved calculation method of the Mongolian Plateau air freezing and thawing index using the monthly air temperature reanalysis dataset from the Climate Research Unit (CRU). The spatial and temporal variation characteristics from 1901 to 2019 were further assessed by the Mann-Kendall (M-K) test and spatial interpolation methods. The results indicate that the spatial distributions of the freezing and thawing index show clear latitudinal zonality. Over the study period, the air freezing index decreased by 4.1 degrees C center dot d/yr, and the air thawing index increased by 2.3 degrees C center dot d/yr. The change point in the air thawing index appeared in 1995 (p < 0.05) based on the M-K method, in contrast to the so-called hiatus in global warming. Our results reveal rapid warming on the Mongolian Plateau, especially in the permafrost region, and are useful for studying permafrost changes on the Mongolian Plateau.

The relationship between soil temperature and its variations with different types of land cover are critical to understanding the effects of climate warming on ecohydrological processes in frozen soil regions such as the Qinghai-Tibet Plateau (QTP) of China. Biological soil crusts (biocrusts), which cover approximately 40% of the open soil surface in frozen soil regions, exert great impacts on soil temperatures. However, little attention has been given to the potential effects of biocrusts on the temperature characteristics, dynamics and freezing duration of soil in frozen soil regions. To provide more insight into this issue, an automatic system was used to monitor soil temperatures and dynamics at depths of 5, 30, 50 and 100 cm beneath bare soil and two types of biocrustal soils (soils covered with two types of biocrusts) on the QTP of China. The results showed that biocrusts play an important role in controlling the dynamics of soil temperatures. Biocrusts cause a 0.6-1 degrees C decrease in the mean annual temperature of soils down to a depth of 100 cm. The extent of the decrease in soil temperature was dependent on biocrust type, and dark biocrust showed a greater reduction in soil temperature than light biocrust. In addition, reductions in soil temperatures of biocrusts mainly occurred in daytimes of the thawing period, and this prolonged the freezing duration in the top 100 cm by approximately 10-20 days. The results of this study indicate that biocrusts maintain lower temperatures in the thawing period and slow the thawing of frozen soil in the spring, which helps to maintain the stability of the frozen soil. This information may aid understanding of the function of biocrusts in the frozen soil regions under global warming conditions.

Spring, especially the freeze-thaw season, is considered the key period for the growth and carbon sequestration of desert mosses. It is not clear how the change in environment water and temperature affects the physiological characteristics of desert mosses in freeze-thaw season. In this study, the effects of water and freeze-thaw cycles on the physiological characteristics of Syntrichia caninervis were assessed by manipulating the increase or removal of 65% snow and changes in the freeze-thaw cycles. The results showed that the changes in snow depth, freeze-thaw cycles, and their interaction significantly affected the plant water content, osmoregulatory substances content, antioxidant substance, and antioxidant enzyme activities. The contents of free proline, soluble sugar, ascorbic acid (AsA), reduced glutathione (GSH), and malondialdehyde (MDA), and superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities increased significantly with the decrease in snow depth and freeze-thaw cycles. POD and free proline were the most sensitive to the snow depth and freeze-thaw cycles, while SOD and CAT were the least sensitive. Therefore, compared with the increase in freeze-thaw cycles, the reduction in freeze-thaw cycles weakened the physiological sensitivity of S. caninervis to snow depth changes.

Fire severity is increasing across the boreal forest biome as climate warms, and initial post-fire changes in tree demographic processes could be important determinants of long-term forest structure and carbon dynamics. To examine soil burn severity impacts on tree regeneration, we conducted experimental burns in summer 2012 that created a gradient of residual post-fire soil organic layer (SOL) depth within a mature, sparse-canopy Cajander larch (Larix cajanderi Mayr.) forest in the Eastern Siberian Arctic. Each fall from 2012 to 2016, we added larch seeds to plots along the burn severity gradient. We tracked density of new larch germinants and established seedlings (alive >= 1 year) during subsequent growing seasons, along with changes in seedbed conditions (permafrost thaw depth, moisture, and temperature). Over the study, a cumulative total of 17 and 18 new germinants m(-2) occurred in high and moderate severity treatments, respectively, while germinants were rare in unburned and low severity treatments ( 50%) germinated in summer 2017, following a mast event in fall 2016, suggesting safe sites for germination were not fully occupied in previous years despite seed additions. By 2017, established seedling density was similar to 5 times higher on moderate and high severity treatments compared to other treatments. Cumulative total density of new germinants and established seedlings increased linearly with decreasing residual SOL depth, as did thaw depth, soil moisture, and soil temperature. Our findings suggest that increased soil burn severity could improve seedbed conditions and increase larch recruitment, assuming seed sources are available. If these demographic changes persist as stands mature, a climate-driven increase in soil burn severity could shift forest structure from sparse-canopy stands, which dominate this region of the Siberian Arctic, to high density stands, with potential implications for carbon, energy, and water cycling.