Forest soil microorganisms determine the energy flow and material cycle of forest ecosystems, and their community structure and influencing factors are significant to maintain ecosystem stability and respond to global climate change. Phospholipid fatty acids (PLFAs) can be used as biomarkers to directly reflect the biomass and community structure of different microbial communities in soil because they only exist in living microorganisms. This study focuses on soil microorganisms and uses the PLFA method to analyze the community structure, biomass, and physicochemical properties of microorganisms in natural forest soils from all six climate types in China. The main factors affecting the microbial community structure were analyzed using correlation analysis and redundancy analysis methods. The analysis results indicate that there are significant differences in soil density, soil pH, soil litter carbon content, soil organic carbon content, soil total nitrogen content, soil carbon nitrogen ratio, and soil total phosphorus content among the six climate types. There are significant differences in fungal community biomass among the six climate types, with a trend of first increasing and then decreasing as the climate types change from cold zone to temperate zone to tropical zone. The ratio of fungi to bacteria in warm temperate soil is the highest (0.7), significantly higher than that in subtropical and tropical soils (0.4-0.5). The ratio of Gram positive to negative bacteria in tropical and alpine soils is significantly higher than that in other climate types (1.3-1.5), with the lowest in subtropical soils (0.7). The climate (annual average temperature, annual precipitation) and soil physicochemical properties (soil pH, soil density, soil total nitrogen content and soil organic carbon content) are significantly correlated with the soil microbial biomass and community structure represented by PLFAs content (P<0.01). This study summarizes that there is no significant difference in the overall microbial biomass represented by total PLFAs among six climate types, but there are significant differences in soil physicochemical properties and microbial community structure. The main influencing factors of forest soil microbial community structure are annual mean temperature, annual mean precipitation and soil pH value. This study reveals the characteristics of forest soil microbial communities in China as a whole, and providing a basis for us to reveal the response of soil microbial communities to climate change in space.

Rice is an important part of the food system in China and the world. It is of great significance to study the life cycle carbon footprint of rice food system from the perspective of food system for low-carbon transformation and green development. Based on statistics from 22 major rice-producing provinces in China in 2018, the cradle-to-market carbon footprint of Rice food systems in China, including its structural composition, regional differences and rice type differences was calculated and analyzed by using the life cycle assessment (LCA) method and the CF-Rice rice carbon footprint calculation tool developed by the International Rice Research Institute (IRRI). The results showed that 1) when comparing carbon footprint per unit production (CO₂ eq), the carbon footprint was in the order of late indica rice (2.31 kg?kg^-1), middle indica rice (1.32 kg?kg^-1), japonica rice (1.13 kg?kg^-1) and early indica rice (1.08 kg?kg^-1). When comparing carbon footprint per unit area (CO₂ eq), the carbon footprint was in the order of late indica rice (9.15×10³ kg?hm^-2), middle indica rice (6.34×10³ kg?hm^-2), japonica rice (5.56×10³ kg?hm^-2) and early indica rice (4.16×10³ kg?hm^-2); 2) Methane (CH₄) in paddy field was the most important component of the carbon footprint of rice food system, accounting for 36.2%-71.5%, followed by fertilization (8.69%-20.0%), harvest (8.41%-18.5%) and prenatal (4.97%-12.1%). Mechanical operations, storage, processing, packaging and transportation, although only accounting for less than 10%, were also significant sources of emissions; 3) early indica rice, middle indica rice and late indica rice showed no obvious spatial distribution pattern, while the main producing areas of japonica rice had a large spatial span and showed an increasing trend of carbon footprint from north to south, specifically as follows: except for Shandong, the carbon footprint of japonica rice in Northeast (Heilongjiang, Jilin, Liaoning) and North China (Inner Mongolia, Hebei) was lower than that in East (Anhui, Jiangsu, Zhejiang), central (Henan, Hubei) and southwestern China (Yunnan); 4) from the perspective of the composition of greenhouse gases, the contribution rate of CH₄ to the carbon footprint of rice food system was the highest, reaching 20.1%-76.4%, followed by that of CO₂ (21.1%-72.3%), and that of N₂O (1.76%-10.7%) was the lowest. The regional and type differences of rice food system carbon footprint were mainly related to climatic conditions, planting management measures and emission factors. Hence, in order to reduce the carbon emissions of rice food system, it is necessary to take overall consideration to reduce the CH₄ emission of rice field, improve water and fertilizer management, reduce energy consumption, and decrease food loss and waste.

Rice production is the main source of carbon emissions. Liaoning Province is a major production area of high-quality rice in China. Exploring the potential of carbon sequestration and emission reduction in rice fields is very important for achieving carbon peak and carbon neutralization. Following the basic framework and requirements of IPCC, we estimated the potential of carbon sequestration and emission reduction of rice fields in Liaoning Province. The results showed that the methane emission (CO₂-eqv) from rice fields in Liaoning Province was 2.13-3.39 Tg·a^-1, and the direct or indirect N₂O emission (CO₂-eqv) was 0.37-0.40 Tg·a^-1 or 0.08-0.09 Tg·a^-1, respectively. The total carbon emission (CO₂-eqv) of conventional fertilization was 2.61 Tg·a^-1. Optimized fertilization could reduce carbon emission (CO₂-eqv) by 0.03 Tg·a^-1. Organic fertilization and straw returning increased carbon emission (CO₂-eqv) by 0.42 Tg·a^-1 and 1.36 Tg·a^-1, respectively. The carbon emission intensity per unit area and per unit yield of rice field were the highest in straw returning, which were 49.96%-52.68% and 50.30%-52.46% higher than those of conventional fertilization. The carbon emission (CO₂) intensity per unit area of rice field in Liaohe Delta was the highest, which was 5.17-8.08 t·hm^-2·a^-1; the carbon emission (CO₂) intensity of unit yield in southeast area of Liaoning Province was the highest, which was 0.66-1.01 t·t^-1·a^-1. Liaohe Delta rice area had the largest carbon emission (CO₂-eqv) reduction potential, which was 5.50-14.20 million tons per annum. Among nutrients, the carbon emission (CO₂-eqv) reduction from nitrogen fertilizer was the largest, which was 0.18-12.00 million tons of per annum; among fertilization methods, organic-inorganic combined fertilization showed the greatest reduction, which was 3.78-14.2 million tons of per annum. The amounts of carbon sequestration (CO₂-eqv) in soil with organic-inorganic combined fertilization and straw returning were 0.10-0.28 Tg·a^-1 and 0.22-0.65 Tg·a^-1, respectively, and the offset ratios of carbon sequestration to soil by increased carbon emission were 56.68%-82.52% and 89.34%-99.03%, respectively. Therefore, organic-inorganic combined fertilization is the best nutrient management measure for carbon emission reduction in rice production in Liaoning Province.

Owing to the interactions between environmental factors, different conclusions can be drawn about the relationships among soil microbial biomass carbon, nitrogen, and their influencing factors. Thus, it is important to increase research in different ecosystems. To explore the dynamics of soil microbial biomass during the growing season in the Qinghai alpine grassland and the relative contribution of water and heat factors to spatial changes in soil microbial biomass, we conducted studies on the plots set up by the Sanjiangyuan Grassland Ecosystem National Observation and Research Station. The results showed that: (1) The alpine steppes located in the central and western regions of Qinghai Province, especially the Hoh Xil region, had the lowest microbial biomass, while there was relatively high microbial biomass in alpine meadow, alpine meadow steppe, and warm steppe. (2) The seasonal dynamics of soil microbial biomass carbon and nitrogen varied in different regions, and the central western and eastern regions of Qinghai Province exhibited significantly different trends. (3) Using an enhanced regression tree model to quantitatively evaluate the relative contributions of water (soil water content, relative humidity of air, precipitation, and evapotranspiration) and heat (soil temperature, air temperature, and net radiation) factors to microbial biomass changes, it was found that, compared with other water and heat factors, the soil water content (P=0.000) and soil temperature (P=0.000) had the greatest impact on microbial biomass carbon and nitrogen, and both were positively correlated. On the vertical gradient of the soil, the influence of the water factor (63.58%-76.62%) on the change of microbial biomass was greater than that of the heat factor (23.38%-36.42%), but its contribution decreased with depth in the soil layer. Over the whole region, the heat factor (52.11%-81.84%) contributed most to the variation in microbial biomass in the eastern and central regions, while the water factor (66.33%-95.19%) controlled the variation in microbial biomass in the western regions. We conclude that the soil microbial biomass of alpine meadow, alpine meadow steppe, and temperate steppe was significantly higher than that of alpine steppe in Qinghai. The soil water content and soil temperature were the main factors controlling variations in soil microbial biomass. The impact of the factors on the variation of soil microbial biomass across the region showed a transition from the heat factor in the east to the water factor in the west. This study provides a reference for exploring the soil carbon nitrogen cycle and its influencing factors in Qinghai alpine grassland in the context of climate change.

The freeze-thaw cycle (FTC) is an important factor that affects the physicochemical and biological properties of alpine grassland soils. The deposition and degradation of grazing livestock dung during freeze-thaw period may also be affected by the complex and significant effects of FTCs. However, the effects and mechanisms of FTCs on dung degradation and nutrient changes in alpine grassland remain unclear. In this study, a 30-day indoor freeze-thaw simulation experiment was conducted by using yak and Tibetan sheep dung collected from the seasonal freeze-thaw alpine grassland in the northern Tibetan plateau. Dung samples were collected to analyze the physicochemical properties and nutrient concentration after 0, 5, 15, and 30 days of FTCs, respectively, so as to investigate the detailed influences of repeated FTCs on dung degradation and major nutrient dynamics. The results showed that 1) the moisture content and dry matter content of yak dung significantly decreased during the first 15 days of FTCs (P<0.05), and the moisture content of sheep dung decreased by 82.6% in the first 5 days of FTCs. This decrease could be attributed to the repeated FTCs of fresh dung that easily damage the physical structure of dung pats at the initial stage and therefore accelerate the loss of moisture content and dry matter content. 2) The concentration of ammonium nitrogen (NH₄⁺-N) of yak dung reached its maximum after 5 days FTCs (415 mg·kg⁻¹), while the nitrate nitrogen (NO₃⁻-N) concentration of yak and sheep dung significantly decreased across the first 15 days FTCs (P<0.05). The increased organic nitrogen mineralization and enhanced denitrification rate at the early stage of FTCs may be the primary reasons for the brief increase in NH₄⁺-N concentration and sustained decrease in NO₃⁻-N concentration. 3) The concentration of AP in yak dung significantly decreased by 21.2% (P<0.05) from 15 to 30 days of FTCs, while the concentration of AP in Tibetan sheep dung fluctuated throughout the entire experimental period, indicating that yak dung pat AP was variously influenced by later-stage FTCs, whereas particulate sheep dung AP was subject to more complex and variable influences from FTCs across the whole experiment. In summary, repeated FTCs tend to induce changes in the block structure, physicochemical properties, and microbial characteristics of yak and sheep dung to various degrees, thereby resulted in significant variation in the nitrogen and phosphorus migration, transformation, and active nitrogen and phosphorus nutrient concentrations. The conclusions of this study can provide theoretical references for optimizing the management of livestock dung in grassland during the seasonal freeze-thaw period and promoting the healthy development of grassland ecosystems.

Per- and polyfluoroalkyl substances (PFASs) are a diverse group of emerging persistent organic pollutants (POPs) known for their versatile applications, complicated properties, and associated ecological and health risks through environmental pollution. While previous published reviews have summarized the sources and distribution of PFASs in soil and water ecosystems, this paper aims to fill the crucial gap by a systematic overview of their sources, spatial and temporal distribution, and human health risk assessment in the atmospheric environment. Sources of PFASs in atmosphere include the industrial production and application of fluoropolymers, product consumption, waste treatment, volatilization and sublimation from soil and water environments. The PFASs accumulate in atmospheric particulate matters, showing significant concentration variations across regions and seasons, influenced by the industrial activities, population density, and meteorological parameters. Typically, PFASs have a broader spatial distribution with low concentrations during warm seasons, while the pollution levels are higher and concentrated near emission sources in winter. Over the past decade, the concentration of atmospheric PFASs in China has decreased, but their types have significantly increased, mainly due to the impact of policy measures shifting towards the production of PFASs substitutes. Atmospheric PFASs can enter the human body and induce health risks through the exposure pathways of inhalation, skin uptake, and oral ingestion. Currently, inhalation exposure assessment models are mainly used to assess their health risks. Pollution prevention and control measures in developed regions, such as the United States and Europe, have achieved some reduction in PFAS emissions to environment, but they mostly targeted at single substance, and production is gradually moving towards substitutes with unclear risks. Looking ahead, future research on atmospheric PFASs should delve into the transport and transformation mechanisms, synergistic effects and toxicity risks with other pollutants (e.g., particulate matters), establishing long-term monitoring networks and quantitative source apportionment methods, revealing their health effect mechanisms in depth, and developing systematic and comprehensive human health risk assessment models.

The investigation of the spatio-temporal evolution of PM_2.5 and its associated risk of population exposure holds paramount significance for environmental risk assessment, habitat enhancement, and the development of precise air pollution prevention and control policies by governmental environmental protection agencies. The Weihe River Basin serves as a crucial industrial base of the country and represents an important part of a national urban agglomeration, as well as the Guanzhong-Tianshui national economic zone. Mitigating the risk of population exposure to PM_2.5 in this region is an inevitable step towards high-quality development. Based on remote sensing inversion data of PM_2.5 and population grid distribution data in the Weihe River Basin from 2000 to 2020, the population exposure risk index was calculated. The temporal evolution characteristics of PM_2.5 quality concentration values and population exposure risk indices were identified using the Theil-Sen Median and Mann Kendall tests, respectively. Additionally, the spatial variation characteristics of these variables were analyzed through the utilization of GIS spatial exploration tools. The results showed that (1) the annual average quality concentration of PM_2.5 in the Weihe River Basin was 47.2 μg·m^-3 from 2000 to 2020. The highest value of 57.6 μg·m^-3 was recorded in 2013, while the lowest value of 31.8 μg·m^-3 was observed in 2020. This indicated a trend of initial increase followed by a decrease. Significance testing revealed a decreasing trend in PM_2.5 pollution levels in the Weihe River Basin. (2) The spatial distribution of annual average PM_2.5 quality concentrations exhibited distinct characteristics, with higher values in the eastern region and lower values in the western region. High values were mainly distributed in the lower reaches of the river basin, such as Xi’an, Xianyang and Weinan. Low values were mainly distributed in the middle and upper reaches of the river basin, such as Tianshui City, Dingxi City, Pingliang City, etc. (3) Overall, the risk level of PM_2.5 population exposure in the Weihe River Basin showed a downward trend from 2000 to 2020. However, the average proportion of the population exposed to more than 35 μg·m^-3 over the years was as high as 96.2%. Between 2000 and 2003, as well as from 2005 to 2014, the entire population in the Weihe River Basin experienced exposure to concentrations of 35 μg·m^-3 or higher. Nevertheless, the extent of high-risk areas decreased from 20.6% in 2000 to 17.1% in 2020. (4) The risk level of PM_2.5 population exposure demonstrated a spatial pattern with higher levels in the east and lower levels in the west, displaying significant spatial variation in the Weihe River Basin from 2000 to 2020. Urban built-up areas such as Weicheng, Qindu, and Weiyang predominantly exhibited a “hot spot” type with higher concentrations. Conversely, the “cold spot” type was mainly concentrated in higher elevation areas in the western part of the basin, including Dingxi, Tianshui, and Pingliang. The findings of this study provide a scientific foundation for formulating a collaborative prevention and control policy in managing PM_2.5 pollution within the Weihe River Basin.

Organic fertilizer and biochar play an important role in improving soil quality and soil fertility in medium and low yield fields. Five treatments (CK: no fertilization, NPK: chemical fertilizer only, NPK+M: chemical fertilizer+sheep manure, NPK+B: chemical fertilizer+corn straw biochar, and NPK+M+B: combined application of sheep manure and corn straw biochar) were applied to a corn field once at the first crop growing season in a 5-year field experiment. High-throughput sequencing was used for exploring the impact of adding sheep manure and corn straw biochar on soil microorganism community diversity and function in saline-alkali sandy soil of Xinjiang. The results showed that sheep manure and corn straw biochar could improve the physical and chemical properties of saline-alkali sandy soil, reduce soil pH, and increase the cation exchange capacity and nutrient content. NPK+M+B treatment had stronger effects on the organic matter, available phosphorus and available potassium, which were significantly increased by 87.80%, 125.15% and 59.52%, respectively. Fertilization increased soil EC, but NPK+B treatment and NPK+M+B treatment could alleviate the increase. The analysis of microorganism α diversity showed that fertilization increased Shannon diversity index and Chao and Ace abundance index of the bacterial community in saline-alkali sandy soil. NPK+M+B treatment had the best effect, which led to increases by 6.31%, 57.98% and 57.25%, respectively. The application of chemical fertilizer increased the soil fungal diversity, but sheep manure and corn straw biochar decreased the diversity. NPK+M+B treatment could increase the abundance of Actinomycetes which tolerated saline-alkali, drought, antibacterial and oligotrophic, and reduce the community composition and abundance of potential pathogenic fungi significantly. So, NPK+M+B treatment alleviated the risk of soil-borne fungal diseases and improved the microenvironment of saline-alkali sandy soil. A redundancy analysis identified AK, OM, TP, TK and TN, TK, CEC, AN as the major factors that affected the bacterial and fungal community structure and functional groups. PICRUSt functional analysis showed that fertilization could improve the bacterial metabolic function related to stress resistance, such as salt alkali and drought, etc. FUNGuild function prediction showed that NPK+M+B treatment significantly reduced the proportion of pathotroph fungi. Overall, sheep manure and corn straw biochar changes soil physiochemical properties, optimizes the niches of beneficial soil microbiome and suppresses the number of harmful fungi, and thus helps create a stable and healthy soil microecosystem.

Forest ecosystems are an important resource for China to address climate change and implement its intended nationally determined contributions. It is of great significance to scientifically evaluate the impact of the Natural Forest Protection Project on the characteristics of forest carbon sink/carbon source in the implementation area for consolidating and improving the function of forest carbon sequestration and carbon sink enhancement at the regional scale and coordinating regional eco-economy-society coordinated development. Based on the multi-period and multi-type resource survey and statistics data, using the volume-biomass method, the impacts of Natural Forest Protection Project measures (such as artificial afforestation, forest care, wood reduction, forest patrol, etc.) were included in the estimation process to comprehensively evaluate the impacts of Natural Forest Protection Project on the forest carbon pool in the key state-owned forest region of Daxing’anling in Heilongjiang Province, China during 1998-2018. The results showed that (1) through the implementation of the Natural Forest Protection Project, the cumulative net carbon sequestration in the key state-owned forest region of Daxing’anling in Heilongjiang Province had been 1.32×10⁸ Mg in the past 20 years, which was equivalent to offsetting nearly 12% of the cumulative carbon dioxide emissions of Heilongjiang Province in the same period, and compared with industrial measures such as biomass energy and carbon capture and storage, it had obvious cost advantages. (2) Among the various measures, forest carbon sequestration generated by forest management measures was the largest contribution to the net carbon sequestration in the study area, accounting for 80.0%. (3) Due to the uneven spatial distribution of the artificial afforestation area and wood reduction task, the net carbon sequestration in the study area had a certain degree of spatial heterogeneity. (4) The carbon emission and carbon leakage caused by the implementation of the Natural Forest Protection Project had offset part of the forest carbon sequestration benefit, but the offset proportion was only 0.29%, and the overall benefit of forest carbon sequestration and sink enhancement was not affected. For the post-Natural Forest Conservation Project to continuously and steadily play the role of forest carbon pool in the study area, we suggest strengthening the effectiveness of natural forest protection and restoration, avoiding or reducing the disorderly loss of forest carbon pool, innovating the realization path of natural forest carbon sink value, reducing the uncertain impact of measurement and monitoring, and finally realizing the continuous improvement of forest ecosystem carbon sequestration and sink benefits.

Phosphorus is a key biogenic element in lakes, and the transformation is driven by a variety of biochemistry reaction. At the late stage of eutrophication, the acetate produced via alga decaying under anaerobic condition can be used as an organic electron donor in the denitrification process, and iron can be used as an electron donor and energy source in the denitrification process. They can pose direct/indirect effect on the phosphorus transformation by affecting the nitrogen transformation. In this study, a sediment-overlying water system using samples from Lake Moshui of Wuhan was set up, where the driving effect of iron and nitrogen on the phosphorus transformation in the presence of organic electron donors (acetate) was investigated via inputting nitrate, iron and acetate into the overlying water. In the presence of different concentrations of acetate, the changes of nitrogen, phosphorus and iron content in the overlying water and interstitial water with time were firstly investigated, then the denitrification enzyme activity and the abundance of nitrate-dependent Fe(II) oxidation bacteria (NDFOB) in the sediment were determined. Furthermore, the form of phosphorus in sediments was explored to clarify the existence form of iron-bound phosphorus. The results showed: (1) The presence of acetate increased the NDFOB abundance and denitrification enzyme activity in the sediments, increasing the NO₃^--N removal efficiency by 22.6%. (2) There was a significant positive correlation between total phosphorus (TP) concentration and total iron concentration (P=0.001). Easily reducible oxides (Fe_ox1) and reducible oxides (Fe_ox2) were the iron forms with the strongest phosphorus adsorption capacity, accounting for 43.8%-54.1% of the total iron content in sediments. (3) The presence of acetate promoted the reduction of Fe(III) in the sediments. Due to the reduction of Fe_ox1 and Fe_ox2 in the sediments, a relatively high content of Fe(II) was produced, accompanied by a drastic decrease of iron-bound phosphorus content. (4) The content of easily reducible iron-bound phosphorus (P-Fe_ox1) in the final sediments was 0.250 mg·g^-1 lower than that in the NO₃^- treated group. Because the presence of acetate inhibited the formation of Fe_ox2 in the sediments, the content of reducible iron-bound phosphorus (P-Fe_ox2) was 0.010 mg·g^-1 lower than that in the NO₃^- treated group, while the total phosphorus concentrations in overlying water and pore water were significantly higher than those in the NO₃^- treated group (P=0.000). These findings contribute to deepen the understanding of the endogenous pollution theory in lakes by elucidating the transformation of phosphorus-iron binding forms in sediments under different mediation.

The zoning of ecological risks in combination with ecologically important areas for ecological functions is an important means of alleviating the contradiction between human activities and ecological protection. With the help of GIS spatial technology, this paper assessed the ecological risk of Qinghai Lake Basin based on the pressure point-exposure framework and the importance and sensitivity evaluation of ecosystem services, using the pressure-state-response model. In addition, the study carried out the ecological function zoning and put forward the management and control recommendations. The results show that (1) the spatial distribution pattern of ecological risk in the basin is obviously polarised, with a high-risk area of 7.77×10³ km², accounting for 26.4% of the basin area, concentrated in the Qinghai Lake ring area and the county town of Gangcha, and a low-risk zone covering 12.7×10³ km², accounting for 43.1% of the basin area, mainly the water bodies and grassland coverage areas in the basin; (2) the spatial pattern of the importance of the basin ecosystem services is heterogeneous. The spatial pattern of the importance of ecosystem services in the watershed is heterogeneous, with the high-value zone covering an area of 7.77×10³ km², accounting for 26.4% of the watershed area, mainly including water bodies, lakes, mountain forests and ecological areas with high alpine grass coverage; the low-value zone is mainly the lagoon, high-altitude areas and areas with obvious urban expansion; (3) the functional zoning of national parks should not only consider ecological protection, but also take into account the production and living needs of residents and the needs of community development, and adopt the optimisation of functional zoning in order to fully reflect the priority of ecological protection and high-quality development. The highly important and high-risk zones are integrated into the ecological red line zone to maintain the originality and integrity of the ecosystems in the region to the greatest extent as possible; the low/medium-risk zones and the mild/moderately important zones are prioritised as development zones, and the superimposed high-risk zones and the more important zones are developed into ecological development zones, which are the development zones for eco-livestock husbandry and eco-tourism for the future operation of the national park; and the remaining areas are planned to be the transition zones for protection and development and the buffer spaces for the future. The zoning scheme aims to alleviate the contradiction between ecological protection and development in order to help promote the construction of the Qinghai Lake National Park, provide new ideas for the ecological functional zone planning of the nature reserve, and provide a scientific reference for the sustainable development of the region.

The aboveground biomass of vegetation is an important index reflecting the carbon sequestration capacity of terrestrial ecosystems. Using remote sensing technology to carry out vegetation aboveground biomass estimation and spatial inversion in arid areas can provide an important basis for health assessment and carbon storage estimation in desert oasis ecosystems. Based on field surveys and field sampling data, seven vegetation indices and 13 band variables were extracted from Landsat 8 OLI multispectral images to form four variable combinations for modeling. Support Vector Machine (SVM), Back Propagation Neural Network (BPNN), eXtreme Gradient Boost (XGBoost), and Random Forest (RF), which are four machine learning algorithms, could estimate aboveground biomass by remote sensing and spatial inversion in the delta oasis of Weigan-Kuqa rivers in Xinjiang. The results showed that (1) the vegetation aboveground biomass inversion models constructed by band variables and random frog jump algorithm preferred variables had significantly better estimation accuracy than the total variables and index variables. The prediction abilities were more stable. Compared with SVM and BPNN, the models constructed by XGBoost and RF algorithms had a better estimation effect and could more accurately estimate the aboveground biomass of vegetation in the study area. (2) Among the constructed estimation models, the band variable combined with the Random Forest algorithm had the highest accuracy and the strongest stability. The coefficients of determination for the modeling set and validation set were 0.898 and 0.742, respectively, and the average absolute error was 82.1 g·m^-2 and 79.2 g·m^-2, respectively. The root-mean-square errors were 110.8 g·m^-2 and 132.1 g·m^-2, and the relative analysis errors were both greater than 1.8, so the model had the best fitting effect. (3) The spatial differentiation of aboveground biomass of vegetation in the study area was obvious, showing higher biomass in the oasis area and lower biomass in the desert area and a gradual decreasing trend from the inner oasis to the outer oasis. Compared with the other three machine learning algorithms, the estimation model constructed by the Random Forest algorithm had a better estimation ability and stability and could accurately estimate the aboveground biomass of the arid oasis. In general, the machine learning algorithm model based on optimal variable combinations provides a scientific basis for aboveground biomass inversion.

With the rapid growth of the printing industry, toner production has increased, resulting in a significant amount of toner waste in the environment. At present, toner waste disposal primarily involves landfills, leading to accumulation and exposure risks to the environment. Various emerging contaminants such as micro- or nanoplastics, nano oxides, and nano carbon pose potential ecological and human health risks. To control the environmental health risk associated with emerging contaminants in toner waste, it is critical to scientifically dispose of and utilize toner waste. This review explores the single and compound ecological effects of various typical emerging particulate contaminants and their interactions with soil, water and other media in the environment. It also proposes toxic risks associated with toner waste. Toner waste may expose humans to toxicity through respiration, skin contact and food chain transmission. It may cause toxicity to the respiratory system, kidney, liver, intestinal metabolism, neurodevelopment, cardio metabolism, blood vessels, and reproduction. The toxicity depends on the size, dose, and exposure time of particulate contaminants. In addition, potential recycling and resource utilization technologies for toner wastes have been proposed based on their composition and properties. The review recommends strengthening research on biogeochemical processes, environmental health risks, and resource utilization of waste toner in the future. Specific areas of study include: 1) develop advanced pre-processing methods for the qualitative and quantitative analysis of toner waste in the environment, clarifying its environmental exposure flux and occurrence; 2) investigate the ecological, human health effects and risk assessment of toner wastes with environmental relevant concentrations based on laboratory batch experiments, mesocosmic systems, and machine learning; 3) strengthen the innovation of recycling and resource utilization technologies for toner waste and develop a whole life toner risk assessment and cycle system. Moreover, the establishment of relevant environmental management policies is crucial to ensure the scientific control of toner waste. This review provides a theoretical basis for effectively controlling the environmental health risks associated with emerging contaminants in toner waste. It also lays a technical foundation for promoting the efficient utilization of toner waste resources and the green development of the printing industry.

Under the background of global warming, the uncertainty in the characteristics of regional dry and wet changes increases. Studying the spatio-temporal evolution trend of meteorological drought under different time scales and identifying the hot spots of drought events are of great significance for agricultural production and drought prevention. Based on the long-term series and multi-time-scale standardized precipitation evapotranspiration index (SPEI) raster data with resolution of 5.5 km generated for Southwest China from 1983 to 2020, this paper constructed four indicators, the maximum lasted drought months (Max_mon), the mean annual drought months (Mean_mon), the count of drought events (C_DE), and the mean lasted months of drought event (MM_DE) (drought events are defined as at least 3 consecutive months with SPEI-1≤-1). And the spatio-temporal evolution of meteorological drought trends and drought events in Southwest China were studied in three time-scales (38, 18 and 10 years) and for four periods (1983-2020, 1983-2000, 2001-2010, and 2011-2020). The results show that (1) the Southwest China is prone to monthly and seasonal droughts. From 1983 to 2020, the Southwest China had experienced periodic dry-wet fluctuations. From 1983 to 2000, southern Sichuan became significantly drier, and so was southern Yunnan from 2001 to 2010, and from 2011 to 2020, the Southwest China was mainly getting wet. (2) The constructed drought intensity indicators Max_mon and Mean_mon can effectively reflect the susceptibility and spatial distribution of meteorological drought in Southwest China. The Max_mon indicator showed that more than 50% of Yunnan and Sichuan were prone to long-term drought for at least 5 months, and the Mean_mon indicator showed that the mean drought intensity in Yunnan increased continuously during the three periods, while Sichuan, Chongqing and Guizhou showed a trend of first increasing and then weakening. (3) The constructed drought event indicators C_DE and MM_DE can effectively identify the hot spots of drought events in different periods. The results show that the hotspots of drought events were in northern Sichuan from 1983 to 2000, in central Yunnan from 2001 to 2010, and in central and northern Yunnan and southern Sichuan from 2011 to 2020. The drought event in Yunnan was the most serious from 2001 to 2010, with an average MM_DE of 4.70 months per time. The SPEI high-resolution products produced in this paper can provide refined meteorological drought distribution information. The constructed drought intensity and drought event indicators based on long-term SPEI can effectively identify the areas with frequent meteorological drought occurrence and the hot spots of drought events in Southwest China. This study has great practical significance for dealing with meteorological and agricultural droughts.

Understanding vegetation dynamics and their response to climate change is essential to improve the carbon sequestration capacity of terrestrial ecosystems in the context of global change. As an important ecological barrier in north China, Inner Mongolia is one of the provinces with the most diverse climate and ecosystem. While net ecosystem productivity (NEP) is strongly associated with climate change, it is unclear whether and how such responses exist in ecologically fragile areas, such as Inner Mongolia, which contains multiple ecological transition zones and vegetation types. In this study, the NEP of vegetation in Inner Mongolia from 2001 to 2020 was estimated by using the net primary productivity and soil respiration models based on remote sensing vegetation index data, land cover data, and meteorological observation data. The temporal and spatial changes of NEP for different vegetation types and their responses to three typical climatic factors including precipitation, temperature, and solar radiation were studied. The results showed that (1) the vegetation NEP in Inner Mongolia gradually decreased from northeast to southwest, and the average NEP was C 61.2 g·m^-2. The average annual NEP of the forest, grassland, and cultivated land was C 270 g·m^-2, 54.7 g·m^-2, and 140 g·m^-2, respectively. (2) From 2001 to 2020, the terrestrial ecosystem carbon sink in Inner Mongolia showed an upward trend, but there were some fluctuations, among which the NEP of forest and grassland showed an upward trend, while the NEP of cropland showed a downward trend. Forest had the largest mean NEP, followed by cropland and grassland. (3) There were significant differences in the response of NEP to climatic factors for different vegetation types, with the NEP of cropland was mainly affected by solar radiation, the NEP of grassland was controlled by precipitation and solar radiation, and the NEP of forest was under the influence of all three climatic factors. This study is of great importance for evaluating the carbon balance of the terrestrial ecosystem in Inner Mongolia, and also for evaluating the carbon sequestration capacity of the ecosystem and studying its carbon cycle mechanism.

The contamination problem of per- and poly-fluorinated compounds (PFASs) in edible plants was of growing concern. Nineteen maize samples were collected from agricultural soil near a fluorine chemical park in Fuxin city, Liaoning province, to evaluate the contamination of PFASs around typical fluorine industry parks. The concentration of seventeen individual-PFASs was identified in the root, shoot, leaf and kernel of maize. The spatial distribution and accumulation patterns of PFASs were analyzed using correlation relationships and ArcGis software. The results showed that (1) the total concentration of PFASs (ΣPFASs) ranged from 15.88 to 62.75 ng·g^-1. The main compounds were the short-chain PFASs (C≤6), PFOA (perfluorooctanoic acid), and PFOS (perfluorooctane sulfonate). (2) PFASs were mainly accumulated in the leaf. ∑PFASs in the leaf were higher than those in the root, shoot and kernel. In addition, the difference between carbon length and the functional group also influenced the concentration and composition of PFASs in maize. (3) PFOA and PFOS tend to accumulate in the root, whereas short-chain PFASs are easily migrated in the interior of maize. The Spearman correlation analysis implied that ∑PFASs in root had a significant positive relationship with those in the shoot (r=0.772, P=0.001) or leaf (r=0.400, P=0.046). ∑PFASs in maize decreased with the increasing distance from the fluorine chemical park. Compared with the PFAS concentration in maize within 1-2 km of the fluorine chemical park, the PFASs concentration in maize decreased by 71.56% when the distance between maize and the fluorine chemical park was more than 4 km, indicating that the fluorine chemical production may be a potential point contamination source. Soils near fluorine chemical park were contaminated by industrial wastewater and sludge, and PFASs from contaminated soils were easy to be absorbed by roots, leading to accumulation in maize; atmospheric and dust uptake was considered to be another source of high PFAS concentrations in maize leaf. Our study analyzed the concentrations and profiles of PFASs in maize around the fluorine industry park, and can be used for pollution control and government of PFASs in plants around typical point pollution sources.

The intensified climate change and human activities have increased the uncertainty of carbon circulation research in regional ecosystems. Net ecosystem productivity (NEP) could quantitatively describe the carbon exchange between terrestrial ecosystems and atmosphere. Exploring the spatiotemporal changes and impact factors of regional NEP would help clarify the carbon budget of ecosystem and effectively respond to climate change. Based on TEC and ecosystem respiration model, we evaluated the spatiotemporal pattern of forest NEP in Fujian Province from 2000 to 2020. And the main driving factors of spatiotemporal variation of NEP in Fujian Province were explored by geographic detector and contribution rate method. The results showed that (1) the annual average NEP of forest in Fujian Province was 528 g·m^-2, and NEP showed a significant increasing trend from 2000 to 2020. NEP showed a distribution of “higher in southern inland while lower in southern coast and the middle north region.” The areas with significant increases accounted for 48.3%, mainly distributed in the southwestern part of the central part of Fujian Province, while the areas with significant decreases accounted for only 1.00%. (2) For the regional distribution, NEP in Fujian Province was mainly affected by vegetation, topography and meteorological factors. Normalized vegetation index was the main driving factor affecting the spatial differentiation of forest NEP in Fujian Province, followed by terrain and solar radiation. The optimal interval of elevation was 891-1491 m, and the optimal interval of radiation was 128-130 W·m^-2. Compared with the single factor, the interaction between the two factors enhanced the impact on NEP distribution. Among them, the interaction between NDVI and solar radiation had the strongest explanatory power for NEP. (3) Climate and vegetation factors accounted for 46.7% of the interannual variation of forest NEP in Fujian Province. The increase of normalized vegetation index was the leading factor for the annual variation of NEP, while the change of meteorological factors inhibited the upward trend of NEP. This indicated that it is necessary to effectively improve the adaptability of vegetation to climate change to fulfill the “two-carbon” goals.

With the development of economy and society, human and trade activities constantly increasing in Qinling Mountains, an important ecological security barrier. Alien plants have invaded and rapidly spread around this region, seriously affecting the conservation of biodiversity. However, there is a lack of comprehensive and detailed research on the present situation, harm and risks of these alien plants. It is urgent to conduct a systematic study on the invasion status of alien plants in the Qinling Mountains and assess the risk of these plants. We analyzed the distribution, habitat, diffusion and other basic information of alien plants on the north and south slopes of the middle Qinling Mountains based on the field investigation. In this paper, we constructed a risk assessment system of alien invasive plants in this area using the analytic hierarchy process (AHP) to evaluate the invasive risk of the alien plants. The results showed that 1) there were 131 alien species in the Qinling Mountains, belonging to 33 families and 87 genera, mainly concentrated in Asteraceae, Amaranthaceae, Poaceae and Fabaceae. Asteraceae had the largest number of alien plants (35 species), accounting for 26.52%; 2) the introduction period of alien plants was mainly concentrated between 50 and 150 years (54.20%). Most of them were intentionally or unintentionally introduced into China (75.57%); 3) the risk assessment system of alien invasive plants included invasive characteristics, invasive status, diffusion characteristics, and harm and impact, with a total of 13 indicators. Among the 131 alien plants, 4, 18, 29 and 80 species were extremely high-risk, high-risk, medium-risk, and low-risk plants, respectively. These results indicated that alien plants in the Qinling Mountains are diverse and have wide distribution range, with varying invasion risks. It is urgent to implement prevention and control measures on alien plants with different invasion risk levels to ensure the integrity of biodiversity and the ecological environment to the maximum extent. Enhanced control and long-term intensive monitoring are recommended for high-risk plants, while attention to potential hazards is recommended for medium-risk and low-risk plants.

Phosphorus is a critical, limiting nutrient in sub-tropical soils, which plays an important role in maintaining the stability of ecosystem functions. The Danxia landform, a typical ecological degradation area in this region, highlights how land utilization impacts soil phosphorus fractions. This has significant implications for the rational utilization and fertility enhancement of the Danxia landform. This study examined four types of land use, i.e., arbor forest (AF), shrubland (SL), abandoned grassland (AG), and cropland (CL), in the typical Danxia landform of Renhua, Shaoguan. Using the Tiessen’s phosphorus grading method, the study aimed to investigate the factors affecting the characteristics and availability of soil phosphorus fractions. The study revealed that land use had significant impacts on soil phosphorus fractions and their availability in Danxia landform. Compared to CL, forest soils (AF and SL) had significantly higher organic and inorganic phosphorus levels, with increases ranging from 71.0% to 319.9% and 70.5% to 346.6%, respectively. However, there were no notable differences between CL and AG. The content of soluble phosphorus, labile phosphorus, and moderately labile phosphorus in AF soil had significantly increased in comparison to that of SL, AG, and CL, resulting in a considerable enhancement in soil phosphorus availability. Moreover, AF soil exhibited the highest concentration of occluded phosphorus, but its proportion to total phosphorus had declined significantly, indicating that shifting land use towards AF enhanced utilization of occluded phosphorus. Soil microbial biomass phosphorus and phosphatase activity (i.e., acid phosphatase and alkaline phosphatase) were significantly influenced by land use. Notably, the AF soil exhibited significantly higher levels of both microbial biomass phosphorus and alkaline phosphatase, as compared to the SL, AG, and CL soils. Moreover, the acid phosphatase activity in the AF soil displayed a substantial increase of 46.8% and 54.8%, respectively, compared to that in the AG and CL soils. Soil microbial biomass phosphorus and phosphatase activity were significantly associated with pH, bulk density, and organic carbon content, while exhibiting an insignificant correlation with iron oxide content. Redundancy analysis indicated that amorphous iron and mineral nitrogen were crucial factors leading to the changes in soil phosphorus fractions in Danxia landform. Specifically, the explanatory power of amorphous iron was 86.3%. Although the conversion of farmland to forest could effectively elevate soil phosphorus levels and improve its biological activity, the iron cycling system played a critical role in maintaining high phosphorus activity in Danxia landform soils.

Carbon absorption of ecological land provides an important way to achieve the goal of “double carbon” from the perspective of increasing carbon absorption, and comprehensive zoning optimization has important guiding significance for promoting the integration of ecological protection and high-quality economic development. Based on the calculation of total carbon absorption and carbon absorption per unit area of various ecological land in 31 provinces (cities, districts) of China, the spatial agglomeration characteristics and temporal and spatial evolution trend of ecological land carbon absorption from 2000 to 2020 were explored by using exploratory spatial data analysis and nuclear density estimation. Based on the decoupling relationship and coordination between carbon absorption and Green GDP, comprehensive zoning was constructed, and optimal governance was carried out in combination with the distribution of important ecological functional areas. The results show that 1) the total carbon absorption of ecological land fluctuated and increased during the study period, with an average annual growth rate of 0.077%; there was a significant agglomeration effect in space. Hunan, Guizhou and Guangxi belonged to high-high agglomeration areas, forming high-value radiation centers, while Shandong belonged to low-low type and is a low-value subsidence area. 2) The total amount of carbon absorption in ecological land was obviously different in space, and the carbon absorption capacity in the high carbon absorption area was stronger than that in other areas. The estimation of nuclear density showed that the carbon absorption in the high carbon absorption area and the low carbon absorption area was increasing, and that in the middle carbon absorption area remained relatively stable, and all three showed the characteristics of regional agglomeration. 3) The carbon absorption of ecological land per unit land area and the carbon absorption of ecological land per unit land area largely belonged to the high-high and low-low agglomeration types, showing strong spatial agglomeration characteristics; in particular, the provinces (cities, districts) in the southern region had the advantage and potential of ecological land carbon absorption per unit area. 4) The carbon absorption of ecological land and Green GDP were mainly decoupled and multi-coordinated. The carbon absorption of ecological land per unit area in most provinces (cities, districts) were in multi-coordinated areas, and the carbon absorption of important ecological functional areas showed positive effects. The research results provide a useful reference for improving the carbon absorption capacity and potential of ecological land and promoting the realization of “double carbon” in the ecological field.