With the acceleration of urbanization and industrialization, the dominant function of land use in the Yangtze River Economic Belt has changed dramatically, and the transformation of production, living, and ecological spaces (i.e., the three types of spaces) strengthens its influence on the eco-environmental quality. It is of great significance to study the eco-environmental quality in the Yangtze River Economic Belt from the perspective of the three types of spaces, which can promote the high-quality development of the Yangtze River Economic Belt. Based on the land use remote sensing monitoring data of 2000, 2010 and 2020, we quantitatively analyzed the spatial heterogeneity and its influential factors of 130 cities in Yangtze River Economic Belt by applying statistical methods including the index of eco-environmental quality and Geodetector. The empirical results showed that (1) during 2000-2020, the eco-environmental quality of the Yangtze River Economic Belt was above the average level. More specifically, the eco-environmental quality remained unchanged during 2000-2010 and mainly consisted of two types: medium and relatively high quality; from 2010 to 2020, the level of eco-environmental quality changed, with a decrease in the areas of medium and high quality and an increase in the areas of high quality. (2) There are significant differences in the spatial distribution of eco-environmental quality. The overall eco-environmental quality of the Yangtze River Economic Belt showed the trend of low in the northeast and high in the west, central and southeast. The spatial distribution of eco-environmental quality was consistent from 2000 to 2010. From 2010 to 2020, the eco-environmental quality level in most regions increased, with the medium quality transforming into higher quality and comparatively higher quality transforming into high quality. (3) There were significant differences among the driving factors that influenced the spatial heterogeneity of eco-environmental quality. The dominant driving factors included land use, population density, and slope, and the value of q were 0.776, 0.409 and 0.406, respectively, while the influence of other factors were relatively weak. (4) The mutual effects between any two factors were greater than the impact of a single factor on the spatial differentiation of eco-environmental quality, and the combination of land use degree and other factors was the most important factor affecting the spatial differentiation of eco-environmental quality in the Yangtze River Economic Belt.

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.

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 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.

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.

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.

Diethylhexyl phthalate (DEHP) is widely distributed in various environmental media and easily accumulated in soil environment. DEHP can be transported into the ecosystem through multiple pathways, which may be harmful for human health along the food chain. The DEHP ecological benchmark based on agricultural land security has not been announced in China. Therefore, it is necessary to research on ecological risks and safety of DEHP in agricultural soil. The most sensitive endpoint toxicity data of terrestrial organisms were obtained by selecting 15 representative species from domestic and foreign databases and relevant literature, including soil enzyme reaction activity, plants, invertebrates, and vertebrates. Species sensitivity distributions (SSD) method was applied to construct the SSD curve of DEHP on terrestrial organisms. The 5% of hazardous concentration (HC₅) for DEHP on different terrestrial species was calculated, and the differences in toxicity sensitivity and characteristics of DEHP to different terrestrial organisms was analyzed and compared. The ecological risks of DEHP in soil environments of regions of China for different biological categories were evaluated by using Risk Quotient (RQ). The results showed that the pollution level of DEHP in agricultural soil was greatly diverse in different regions of China, with an average concentration ranged from 0 to 18.3 mg∙kg⁻¹. The higher regions in descending order were: Qingdao (18.3 mg∙kg⁻¹)>Guizhou (14.3 mg∙kg⁻¹)>Guangzhou (8.87 mg∙kg⁻¹)>Dalian (2.84 mg∙kg⁻¹)>Hangzhou (mg∙kg⁻¹)>Nanjing (1.37 mg∙kg⁻¹)>Chongqing (1.04 mg∙kg⁻¹). Predicted no effect concentration (PNEC) derived on the basis of chronic toxicity data was 1.24 mg∙kg⁻¹. The RQ of RQ based on chronic toxicity data was between 0 and 14.7. The soil ecological risk quotient of agricultural land in survey areas such as Qingdao and Guizhou were relatively high, with values of 14.7 and 11.5, respectively, indicating that a higher ecological risk of DEHP in Qingdao and Guizhou, while agricultural soil in most areas were lower. This study was deduced an ecological environment benchmark for DEHP by using SSD method, which provided some technical supporting for agricultural soil ecological risk assessment and management.

Climate change affects plant growth by altering its growing environment. Understanding the intrinsic relationship between plants and climate and long-term monitoring and assessments of vegetation cover are essential, as well as facilitate a deep understanding of ecological restoration mechanism. The Weihe River basin has a special geographical location and a fragile ecological environment. It plays an important role in the ecological environmental protection of its surroundings and the downstream of the Yellow River. To reveal the spatiotemporal change pattern of vegetation and its response to climate change, this paper takes the Weihe River basin as the research object and uses the difference, linear regression slope and correlation coefficient methods to analyze the NDVI distribution characteristics and the correlation and lag time between NDVI and precipitation and temperature in the Weihe River basin under different climate zones from 2000 to 2019. The results showed that (1) from 2000 to 2019, NDVI in the Weihe River basin showed a fluctuating upward trend. The NDVI growth rate of each zone showed the following order: semi-arid zone (0.0538/10 a)>semi-humid zone (0.0443/10 a)>arid zone (0.0366/10 a); (2) NDVI showed improvement from 2000 to 2009 and from 2009 to 2019. However, the improvement slowed down from 2009 to 2019, and the slope decreased from 0.0727/10 a to 0.0351/10 a. The area of improvement calculated by the difference method was reduced from 98.20% to 86.12%, and the area of improvement calculated by the linear regression slope method was reduced from 87.69% to 61.86%; (3) on the seasonal or monthly scale, temperature had a more significant effect on vegetation growth in the Weihe River basin compared to precipitation; (4) the bi-directional lagged effects between NDVI and climatic factors in the Weihe River basin and its zones existed both in the short term (1-3 months) and in the long term (3-6 months) (except for the lagged effect of temperature on NDVI in the arid zone in the short term). The bi-directional lagged effects of NDVI and precipitation under different climate zones were positive for 1-3 months and negative for 3-6 months. The lagged effect of NDVI on temperature showed positive for 1-3 months and negative for 4-6 months. The lagged effect of temperature on NDVI was positive for 1-2 months and negative for 3-4 months.

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.

Conducting long-term research on the evolution of ecosystem services in mountainous karst areas from both horizontal and vertical perspectives can enhance the understanding of the evolution laws of ecosystem development in mountainous karst areas, provide scientific references for the development of ecological protection policies and rocky desertification prevention measures in mountainous karst areas, and have important significance for regional sustainable development. Based on the InVEST model, this study conducted a quantitative evaluation of the terrestrial ecosystem service water production, soil conservation, and habitat quality functions in the study area from 2000 to 2020. It also reveals the changes in ecosystem service functions in the horizontal and vertical spaces of the study area, and provides a multi-dimensional understanding of the changes in ecosystem service functions in mountainous karst areas. The research results indicated that (1) from 2000 to 2020, the largest change in land use types in the study area was in construction land, while the smallest change was in forest land. (2) From a horizontal perspective, there were significant differences in water yield, soil conservation, and habitat quality functions among different land use types. From 2000 to 2020, the bare land in the research area had the highest water yield per unit area, while the forest land had the lowest water yield per unit area. On the contrary, the soil conservation function showed that the forest land had the highest soil conservation per unit area, while the bare land had the lowest soil conservation per unit area. The habitat quality of both construction land and bare land was relatively low. (3) From the perspective of vertical space, the functions of water yield, soil conservation and habitat quality had significant spatial heterogeneity at different altitudes. From 2000 to 2020, the water production and soil conservation function in the study area fluctuated and decreased with the increase of altitude; the habitat quality showed a tendency to decrease first and then increase (shallow U-shaped) as the altitude increased. (4) According to the research results, ecological protection and rocky desertification prevention policies and measures in the research area should focus on bare land, construction land, and forest land. At the same time, attention should also be paid to the characteristics of changes in various ecosystem service functions at different altitude levels. If necessary, different ecological protection measures can be implemented for high and low altitude areas. These findings can provide more practical and feasible measures for the ecological sustainability of mountainous karst areas, and provide references for other similar areas.

Straw return can change the content of soil microbial biomass carbon (SMBC) in farmland, and analyzing changes in SMBC content and its related influencing factors under the conditions of straw returning is pivotal for understanding the mechanism of soil nutrient turnover and carbon cycling driven by straw returning. In this study, a database of 839 groups containing SMBC contents under straw-returned and straw-not-returned conditions was established based on 68 publicly available papers published in China Knowledge and Web of Science databases from 2001 to 2022. The data was grouped by climate type, cultivation method, tillage method, type of straw, amount of nitrogen applied, and amount of returned straw. A meta-analysis was then conducted to comprehensively analyze the variation characteristics of SMBC content under the conditions of straw returning with experimental results under the conditions of no straw returning set as controls. Results showed that 1) straw return significantly increased SMBC content by 51.4% with a confidence interval from 0.373−0.654. The improvement effect on the SMBC content in different soil layers was different, and the SMBC content in shallow and deep layers increased by 47.9% and 42.7%, respectively. 2) The content of SMBC in the temperate monsoon climate zone and subtropical monsoon climate zone increased by 71.0% and 35.8%, respectively, under straw returning, but it showed a significant negative effect on SMBC content in the temperate continental climate zone, with a decrease of 35.6%. 3) The effect of rotary tillage (99.2%) on the increase of SMBC content under different tillage methods was the most obvious, which was about 2.4 times and 4 times that of conventional tillage and no-tillage. 4) The increase of SMBC content in upland was significantly higher than that in paddy field. The response of maize straw to SMBC content was the highest, with an increase of 99.5%, followed by rice straw, with an increase of 30.8%. Wheat straw was the lowest, with a decrease of 5.8%. 5) The effect of nitrogen application rate on SMBC content increased by −34.5% to 183.9%. Under nitrogen application rates of 0−100 kg•hm⁻² and 101−225 kg•hm⁻², straw returning could significantly increase SMBC content, while under the nitrogen application rate of 226−325 kg•hm⁻² and 326−425 kg•hm⁻², straw returning showed a significant negative effect on SMBC content. 6) For the amount of straw returning, when the amount of straw returning was 9000 kg•hm⁻², the increase was 44.2%, but the increase of SMBC content showed a decreasing trend with the increase of straw returning. In conclusion, straw return has a significant influence on SMBC content in Chinese farmland, and the impact extent varies under different climatic types, planting methods, tillage methods, straw types, nitrogen application rates, and straw returning amounts.

To achieve the successful process regulation and steady operation, gradually increasing the $\mathrm{NO}_2^{-}$ concentration with a proportion of ladder accumulation in the continuous flow reactor is of significance. In this study, we investigated the long-term effects and reaction mechanisms of $\mathrm{NO}_2^{-}$ on the interactions between Anammox bacteria (AnAOB) and sulfur-oxidizing bacteria (SOB) in an autotrophic denitrification (AuDen)-Anammox system, as well as the nitrogen removal performance and microbial community response on the coupled system. An anaerobic biological fluidized bed (AFBR) with an effective volume of 2.5 L was operated for 140 days and the statistical results indicated that, compared with the control group ($\mathrm{NO}_2^{-}$=0), the nitrogen removal efficiency (NRE) and the contribution of Anammox to total nitrogen (TN) removal both significantly improved with the increase in $\mathrm{NO}_2^{-}$ concentrations, while the ratio of actual/theoretical of $\mathrm{SO}_4^{2-}$ markedly decreased. It can be concluded that $\mathrm{NO}_2^{-}$ enhanced the synergy between AnAOB and SOB, thus improving the TN removal capacity of the coupled system. Under a constant TN content, the NRE improved from 80.3%±3.2% to 88.1%±3.4% and the contribution of Anammox to TN improved from 81.7%±2.4% to 92.5%±2.3% in the environment with accumulated $\mathrm{NO}_2^{-}$. The high throughput gene sequencing results of the above process showed that the relative abundance of major functional microorganisms, including Thiobacillus, Candidatus kuenenia and Desulfurivibrio, remained steady or increased with the increase in $\mathrm{NO}_2^{-}$ concentrations. Furthermore, the relative abundance of hydrolytic bacteria, such as SM1A02, 1013-28-CG33, and SC-I-84, increased while the relative abundance of other functional microorganisms decreased. These indicated that the environment with accumulated $\mathrm{NO}_2^{-}$ could optimize the structure and function of the coupled community. Canonical correlation analysis (CCA) showed that the $\mathrm{NO}_2^{-}$ concentration was negatively correlated with the abundance of Ca. kuenenia (P=0.539) while positively correlated with the abundance of Thiobacillus (P=0.00533). Moreover, the accumulated $\mathrm{NO}_2^{-}$ was positively correlated with the TN removal (P=0.00767) in Anammox and AuDen process. Overall, the concentration-induction-adaption mechanism of $\mathrm{NO}_2^{-}$ in the Anammox and AuDen coupled system demonstrated that the environment determines the structure and function of the microbial community; in turn, the microbial populations adapt to and influence the environment through structural adjustment.

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.

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.

Arsenic pollution in paddy fields is a serious problem in China. Pentavalent arsenic is reduced by microorganisms to highly active trivalent arsenic under flooded anaerobic conditions, becoming easy to be absorbed and accumulated by rice, thus threatening human health. On the other hand, rice production requires a large amount of nitrogen fertilizer, and the redox activity of nitrogen in paddy soil is high, which has an important impact on arsenic speciation transformation in paddy field. Based on the summary of the main processes of nitrogen cycling in paddy soils and the characteristics of functional microorganisms, arsenic speciation transformation and related functional microorganisms in paddy soils, the effects of nitrogen cycling processes in paddy soils (nitrification, denitrification, anammox, Feammox and dissimilatory nitrate reduction to ammonium, etc.) on arsenic migration and transformation in paddy soil and the key environmental factors were analyzed in depth. It was concluded that nitrification and denitrification are beneficial to arsenic adsorption and fixation, while anammox, Feammox and dissimilatory nitrate reduction to ammonium can promote the reduction and release of arsenic. In addition, denitrification can be coupled with arsenic demethylation, thus enhancing arsenic toxicity. Among them, the redox process of iron in paddy soil plays an important role, which can be used as a bridge between nitrogen cycle and arsenic migration and transformation. For example, the inhibition of iron reduction by nitrate is beneficial to arsenic adsorption; iron minerals formed by nitrate reduction coupled with iron oxidation promote arsenic adsorption and fixation; Feammox promotes iron reduction, which is beneficial to the reduction and release of adsorbed arsenic. Based on the above summary, it is suggested that the nitrogen cycle process in soil under different redox conditions and its coupling mechanism with arsenic speciation transformation, the main functional microorganisms of Feammox reaction in paddy soil and their contribution to arsenic migration and transformation, and how to directionally regulate the coupling process of nitrogen cycling and arsenic transformation are important scientific issues and main development trends in this field in the future. The solution of the above scientific problems can provide important theoretical support for the research and development of arsenic pollution control technology in paddy fields, and provide a scientific basis for rational nitrogen application in paddy fields to reduce arsenic risk in rice.

Invasive alien species greatly change the forest composition and coverage, and reduce the species richness and diversity therein, which have profoundly altered the terrestrial carbon cycling processes and subsequently influenced the accuracy of carbon calculation that is theoretically based on the terrestrial forest coverage. In recent decades, many scientists have put efforts on the carbon cycle changes in invaded ecosystems and showed that the invasion stages, environmental factors and species compositions in communities influence the processes of carbon cycling. However, whether plant invasions serve as a carbon sink or source function is still obscure, and the main uncertainty comes from the underground ecosystem. In the present paper, we reviewed the recent studies on the effects of exotic plant invasions upon ecosystem carbon cycling. With an emphasis on the underground carbon cycling processes, we analyzed the influences of environment parameters, plant physiological characters, and the relationships between plants and surrounding soil biota. Generally, climate parameters may affect the speed and direction of forest coverage substitution, but are insufficient for explaining the inconsistences resulted from different invasion species at a local scale or even from the same species in the same study. Invasive plants are able to assimilate and install more carbon into ecosystems because of the photosynthesis priority, while the carbon output, usually in the form of root exudates and debris, would depend on the substance composition and degradation rate, as well as soil properties. Soil biota, as an important component of underground carbon, modulates both carbon input and output in ecosystems, and the net flux determines the carbon sink or source function, offering an important rational explanation for the uncertainty. In the end, we raised several research prospects regarding to the key processes of terrestrial carbon cycling, by considering the disciplinary development in the context of global change and the requirement to control invasive alien species.

Forest fires have long-lasting effects on soil nitrogen (N) cycling by affecting both biotic and abiotic soil fractions. Given the prevalence of global forest fires, this study aims to explore the long-term relationship between fire and soil nitrogen cycle. The heavy fire sites of Larix gmelinii were selected as the research object, 1 year, 6 years and 11 years after the fire, to analyze the abundance of soil nitrogen fractions and functional nitrogen cycle genes. The analysis involved measuring soil nitrogen fraction, nitrogen cycle functional genes, and basic physical and chemical properties of the soil, and determining the main influencing factors. The results showed that 1) soil total nitrogen, ammonium nitrogen and microbial nitrogen (MBN) contents showed a decreasing and then increasing trend with the number of years of restoration, with MBN recovering more slowly. The soil nitrate nitrogen content significantly increased (P<0.05) 1 year after fire disturbance and remained lower than that of the control samples 6 and 11 years after fire. 2) Nitrogen-fixing nifH functional genes recovered to pre-fire levels 11 years after fire, while denitrification nirS, nirK and nosZ functional genes were significantly higher than those in control samples 6 years after fire. Fire disturbances significantly increased nitrification amoA-AOA and amoA-AOB functional gene abundance. 3) Correlation analysis showed significant positive correlations between nitrogen-fixing nifH functional genes and soil total nitrogen, ammonium nitrogen and MBN (P<0.05); nitrification amoA-AOA functional genes showed highly significant positive correlations with nitrate nitrogen (P<0.01); and denitrification nirS and nirK functional genes showed significant negative correlations with nitrate nitrogen (P<0.05). 4) The results of redundancy analysis showed that soil organic matter, water content, and quick-acting potassium were the main factors affecting the functional genes of soil nitrogen cycling in post-fire soils, explaining of 63.8%, 18.4%, and 85.8% of the variance, respectively. In summary, the study demonstrates that forest fires have long-term effects on soil nitrogen fractions of Larix gmelinii and functional genes of nitrogen cycling in the soil. Changes in the physical and chemical environment of the soil after fire indirectly affect the recovery of soil nitrogen cycling. The findings provide data support for understanding the mechanism of the influence of forest fires on soil nitrogen cycling in the northern region.

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.

Camptotheca acuminata, one of 120 species of wild plant species with extremely small populations, is endemic to China. It was found that there were wild distribution points of C. acuminata population in Jiaoxi region of Mingxi, Fujian Province, during the second national key conversation wild plant resources survey. In order to investigate the survival status of C. acuminata population in this region, a static life table and four survival analysis function curves were worked out based on quadrat survey data with diameter class instead of age class, for analyzing the quantitative characteristics of the population. Moreover, population dynamics and future development trend were analyzed and predicted by using population dynamics index and time sequence model. The results showed that: (1) The age structure of the C. acuminata population appeared roughly inverted J-shape. Individuals were distributed in each age classes, among which the number of small trees was the highest, and the number of seedlings and young trees was insufficient. The dynamic index of population fluctuates between adjacent age classes, and the values of V_pi and V_pi′ were greater than zero, indicating that the population tended to a stable growth type at present, but the population was sensitive to external disturbances and had poor anti-interference ability. (2) The static life table showed that the survival number and individual life expectancy of the C. acuminata population decreased with the increase of age class. The survival curve tended to the Deevey-Ⅱ type, and the mortality rate decreased rapidly in the early period, while it decreased gradually in the later period. The change trends of mortality and vanishing rate curves were nearly similar, both reaching the peak values at the second and eighth age classes. (3) The four survival functional curves showed that the C. acuminata population was characterized by decline in the early stage, small fluctuation in the middle stage, and gradual decline in the later stage. (4) The time series prediction analysis indicated that the number of individuals at the second and fifth age classes decreased at different ranges after the next 2 age classes while the number of individuals in all age classes increased after the next 4, 6, and 8 age classes. Human disturbance, natural disturbance and low seed seedling rate were the primary factors affecting the growth of the population in the future. We suggested that, in the future conversation effects, it should be introduced to take measures such as in situ protection, near situ conservation and strengthening publicity to protect and improve the habitat and promote the regeneration and development of C. acuminata population.

Rapid urbanization is the main cause of increased risk to the thermal environment. Analyzing the spatial structure characteristics of the thermal environment from a network perspective is of great significance for improving the thermal environment, enhancing urban sustainability, and adapting to climate change. First, taking the urban agglomeration in the Yangtze River's middle reaches as an example, this study analyzed the spatiotemporal characteristics of the land surface temperature (LST) and heat island area of urban agglomerations using LST data and built-up area data in 2000, 2010, and 2020. Second, we adopt the morphological spatial pattern analysis (MSPA) model to extract heat island patches and classify their types, including core, islet, perforation, edge, loop, bridge, and branch. On this basis, this study set up thermal environment sources and corridors and used the circuit theory to identify the thermal environment network of urban agglomerations. Third, this study further evaluated the overall connectivity (α-index, β-index, and γ-index) and spatial connectivity (eigenvector centrality and current density) of the thermal environment network based on multiple indicators. The results show that (1) during 2000-2020, the proportion of high-temperature and sub-high-temperature areas in summer in urban agglomerations of the middle reaches of the Yangtze River showed an overall increasing trend, while the proportion of normal-temperature, low-temperature, and sub-low-temperature areas showed an overall decreasing trend. The median LST was highest in core-type heat island patches and lowest in branch-type heat island patches. (2) During 2000-2020, the total area of heat islands in urban agglomerations of the middle reaches of the Yangtze River increased from 2.80×10³ km² to 12.8×10³ km². The proportion of core-type heat island patches increased from 31.1% to 45.9%, gradually clustering in Wuhan, Changsha, and Nanchang. (3) During 2000-2020, the number of thermal environment sources increased from 56 to 215, the number of thermal environment corridors increased from 89 to 378, and the proportion of cities containing thermal environment corridors increased from 77.4% to 100%, which means that a global thermal environment network of urban agglomerations of the middle reaches of the Yangtze River has been initially constructed. (4) During 2000-2020, the overall connectivity of the thermal environment network in urban agglomerations of the middle reaches of the Yangtze River gradually increased. Regarding the distribution of spatial connectivity, it evolved from a spatially heterogeneous pattern of "high in the south and low in the north" to a spatially stable pattern of “high global connectivity”. This study aims to provide insights into the development strategies for climate adaptation at a regional scale.