Latitudinal permafrost in Northern Northeast (NNE) China is located in the southern margin of the Eurasian continent, and is very sensitive to climatic and environmental change. Numerical simulations indicate that air temperature in the permafrost regions of Northeast China has been on the rise since the 1950s, and will keep rising in the 21^st century, leading to extensive degradation of permafrost. Permafrost degradation in NNE China has its own characteristics, such as northward shifts in the shape of a "W" for the permafrost southern boundary (SLP), discontinuous permafrost degradation into island-like frozen soil, and gradually disappearing island permafrost. Permafrost degradation leads to deterioration of the ecological environment in cold regions. As a result, the belt of larch forests dominated by Larix gmelinii has shifted northwards and wetland areas with symbiotic relationships with permafrost have decreased significantly. With rapid retreat and thinning of permafrost and vegetation change, the CO₂ and CH₄ flux increases with mean air temperature from continuous to sporadic permafrost areas as a result of activity of methanogen enhancement, positively feeding back to climate warming. This paper reviews the features of permafrost degradation, the effects of permafrost degradation on wetland and forest ecosystem structure and function, and greenhouse gas emissions on latitudinal permafrost in NNE China. We also put forward critical questions about the aforementioned effects, including: (1) establish long-term permafrost observation systems to evaluate the distribution of permafrost and SLP change, in order to study the feedback of permafrost to climate change; (2) carry out research about the effects of permafrost degradation on the wetland ecosystem and the response of Xing'an larch to global change, and predict ecosystem dynamics in permafrost degradation based on long-term field observation; (3) focus intensively on the dynamics of greenhouse gas flux in permafrost degradation of Northeast China and the feedback of greenhouse gas emissions to climate change; (4) quantitative studies on the permafrost carbon feedback and vegetation carbon feedback due to permafrost change to climate multi-impact and estimate the balance of C in permafrost regions in the future.

In recent years, the desertification of alpine meadows has become a serious ecological problem and has gradually become a threat to regional economic activities in Maqu County. To reveal the mechanism for sandy desertification of alpine meadows, we conducted wind tunnel experiments on aeolian processes over sandy alpine meadows. Results show that the sand-flux profile of mix-sized sediment decays exponentially with increasing height. However, the profile pattern of a group of uniform-sized particles depends on the experimental wind speeds. The profile pattern of all the groups studied can be expressed by exponential decay functions when the wind speed is less than or equal to 16 m/s. while that for all the groups studied can be expressed by a Gaussian distribution function when the wind speed is above 16 m/s. The average saltation heights of mixed sands at wind speeds of 12 m/s, 16 m/s, 20 m/s, and 24 m/s were 2.74, 4.19, 5.28, and 6.12 cm, respectively. The mean grain size basically first decreases and then increases with increasing height under different wind speeds. The sorting improves with increasing wind speed, while the kurtosis and skewness show relationships with only the characteristics of the parent soil.

Yanchi County is located in the agro-pastoral ecotone and belongs to the ecologically fragile area of Northwest China. It is important to study the evolution of landscape pattern to curb its environmental degradation. In order to intuitively show how the landscape pattern of the study area changes over time, Landsat Thematic Mappers (TM) and Landsat Operational Land Imager (OLI) data of 1991, 2000, 2010 and 2017 were used. This paper attempts to apply niche theories and methods into landscape ecology, and constructs a niche model of landscape components by using "n-dimentional hypervolume niche theory" and landscape pattern indices. By evaluating the spatial and temporal evolution of niche from the perspective of two-dimensional space to reflect the changes of landscape pattern in the study area over the past 26 years, new theories and methods were introduced for the characterization of landscape pattern. The results indicate that: 1) The larger the attribute and dominance value of landscape components, the higher the ecological niche and the stronger the control effect on the overall landscape. 2) The ecological niche of each landscape component was significantly different, just as its control effect on the overall landscape. 3) The dynamic change of the ecological niche of each landscape component was different, with grassland, unused land and arable land always in a high dominant position, although the ecological niche of construction land and water area was always low. In general, the introduction of niche theory into the landscape ecology provided a new method to study the changes in regional landscape pattern.

Landscapes of the mountainous regions in northwestern China comprise a unique pattern of vegetation, consisting of a mosaic of grassland and shrub-forest. Forests generally self-organize into ordered structures and coalesce into blocks on north-facing slopes or stripes along southeast-facing slopes, with Picea crassifolia being the most representative and dominant tree species. We investigated the tree-water status and soil-moisture dynamics at a forest site (Guantan) of the Qilian Mountains in northwest China. The 30-minute-interval measurements of tree-sap flow during the growing season of 2008 are presented, and the potential functional relations between tree transpiration and environmental factors are evaluated. Soil moisture and solar energy were identified as the most influential factors, explaining more than 70% of the variance in sap flow. Based on field measurements obtained at the forest site, a stochastic model of soil-moisture dynamics was tested; and the steady-state probability density functions (PDFs) of the long-term soil-moisture dynamics and static tree-water stress were estimated using the validated model and parameters. We found that the model reproduced measured soil moisture well, despite all the simplifying assumptions. The generated PDF of long-term soil moisture was relatively open, with middle to low average values; and the calculated density of the static tree-water stress at the forest site was largely concentrated between 0 and 0.6, suggesting a moderate water-stress situation in most cases. We argue that both water and energy are limiting factors for vegetation at the forest site. In addition, the tradeoff between reduced evapotranspiration (ET) from limited solar energy and increased soil-moisture availability may create a stressed but tolerable environment and, in turn, produce a relatively constant ecological niche favorable to Picea crassifolia growth.

Microbes inhabiting the desert respond sensitively to environmental changes and may be an indicator for changes in the desert ecosystem. Hypolithic microbial communities in the desert play a vital role in ecosystem processes such as soil formation and organic matter accumulation. This study investigated and compared the culturable bacterial community structure and diversity in hypolithic and peripheral soils, and the interaction between bacteria and environmental factors. The bacteria were isolated using four different kinds of media and identified by 16S rRNA gene-sequence analysis. The numbers of culturable bacteria in the hypolithic and peripheral soils ranged from 3.0×10⁴ to 3.6×10⁵ CFU/g and from 6.5×10⁴ to 5.3×10⁵ CFU/g, respectively, indicating that the bacteria number in peripheral soil was higher than that in hypolithic soil. A total of 98 species belonging to 34 genera were identified, among which Arthrobacter, Bacillus,and Streptomyces were found dominantly and widely distributed. The community of culturable bacteria had obvious sample specificity, and the diversity in hypolithic soil was higher than that in peripheral soil. On the regional scale, the distribution of culturable bacteria and the environmental factors showed regular changes. On the local scale, the high heterogeneity of the hypolithic environment determined the specificity of the number and species of culturable bacteria.