Urban biodiversity provides diverse ecosystem services for modern cities, and serves a fundamental role in maintaining sustainable urban development. However, potential threats to urban biodiversity have been increasing along with intensified human perturbations and the consequent transformation from natural landscape to artificial landscape. Naturalness assessment has been widely applied to identify the natural attributes or hemeroby, and to inform urban biodiversity conservation and ecosystem management. In this study, three naturalness assessment methods were summarized based on the concept of naturalness and its assessment. The three methods are indicator biology method, natural distance method, and multi-index comprehensive assessment method. The research progress of naturalness assessment applied in urban biodiversity conservation has been broadly reviewed from the aspects of urban habitat quality assessment, urban landscape dynamic monitoring, and urban ecological space planning. It is proposed that the naturalness assessment of urban ecosystems should be evaluated in a more comprehensive perspective by taking biodiversity status and changes, ecosystem integrity, human disturbance and management decision-making into consideration, and naturalness assessment should be further incorporated into the studies of land use, socio-economic and ecological effects, as well as to reveal the relationship between human activities and biodiversity in urban area.

Biochar is a kind of highly aromatized insoluble solid matter produced by pyrolysis of biomass materials under partially or completely anaerobic conditions. Biochar application can change soil physical and chemical properties, strongly affect the habitat of soil microorganisms, influence the community structure and activity of microbes for soil nitrogen fixation, nitrification and denitrification, and thus affect the main processes of soil nitrogen cycle (nitrogen fixation, nitrification, denitrification, etc.). This paper reviews the published literaturerelated to the effects of biochar application on the main processes of soil nitrogen cycle and their microbial functional genes. The analysis results indicate that biochar application improves soil permeability, raises soil pH value and the effectiveness of soil carbon and nutrients, and significantly increases soil N fixation by 15%-227%, soil nitrification rate by 28%-200% respectively. But it reduces 20%-73% of the total soil ammonia volatilization accumulation and 11%-78% of the soil N₂O emission accumulation. In addition, biochar application increased the gene abundance of nifH and amoA and then promotes nitrogen fixation and nitrification in the soil, The biochar application also increases the gene abundance such as nosZ and the activity of N₂O reductase fittable for the denitrification of soil (final conversion of N₂O to N₂) and suppressed N₂O emissions. And this effect will become stronger with the increase of biochar application rate. Furthermore, impact of biochar application on the soil nitrogen cycling and its functional microorganisms depend on the types of biochar raw materials and production conditions. Different kind of regulatory genes have different contributions to the soil nitrogen cycling. Under the action of biochar, the soil pH value and nutrient availability increases, and AOB may contribute more to soil nitrification than AOA. Compared with other regulatory genes (narG, nirS, nirK), the gene nosZ seems to be more important for the soil denitrification. Therefore, t is necessary to further explore the effects of the biochar application on microbial functional genes for soil nitrogen cycling, especially the specific contribution of different kinds of functional genes to the nitrogen cycling process and factors influencing them in order to deepen the identification of them.

To analyze the current research status and hotspots of nitrogen flow at home and abroad from January 2000 to April 2021, the keywords of "nitrogen balance", or "nitrogen flow", or "nitrogen cascade", or "nitrogen cycle" were searched on the Web of Science and CNKI, respectively, and a total of 6 998 publications were found. Using CiteSpace to visualize the cooperative network and keywords, the results show that: (1) The researches on reactive nitrogen flow abroad were mainly focused on denitrification, agriculture, nitrogen cycle, nitrogen pollution, nitrogen balance, and ecological analysis; whereas the domestic researches were mainly focused on nitrogen cycle, nitrogen balance, crop growth performance, crop yield, nitrogen metabolism, nitrogen deposition, microbial influence on nitrogen transformation, carbon and nitrogen cycle. (2) From 2000 to 2021, the nitrogen cycle can be divided into four stages, which showed an obvious succession trend of macro-micro-macro & micro coupling. (3) The United States and China are the top two countries with most publications. Combined with centrality analysis, it was found that the number of articles published was not completely correlated with the academic influence. (4) The meta-analysis of literature indicate that more attention should be paid to the role of model in quantitative assessment of reactive nitrogen in the future, which could provide an important basis for optimizing nitrogen management and improving ecological and environmental health.

Microplastics can come from a wide range of sources. The physical and chemical properties of microplastics change significantly after aging and exhibit distinct behavior characteristics from that of the original microplastics, which causes potential risks to ecology. This study summarizes sources and characteristics of aged microplastics, and reviews the research progress on the effect of aging of microplastics on its adsorption and photosensitive behaviors. The change of surface morphology, functional groups and crystallinity of microplastics after aging can affect specific surface area, internal arrangement of polymer chain, wettability, surface charge and electrostatic interaction with pollutants. Furthermore, the change has influenced on the behavior of microplastics on the adsorption of organic compounds and metal ions in the environment. In addition, the environmental persistent free radicals and reactive oxygen species generated by the photoaging of microplastics not only affect self-oxidation process of microplastics, but also impact the photosensitive behavior of organic compounds. Finally, focusing on research gaps of previous researches, the future research focus and direction are prospected, so as to provide references and suggestions for the future researches on aged microplastics.

An evaluation index system suitable for the evaluation of agricultural water resources vulnerability and food security in China's main grain producing areas was constructed, and the subjective and objective weights were synthesized to determine integrated weights by using D-S evidence theory, and the agricultural water resources vulnerability and food security in the main grain producing areas from 2010 to 2019 were then evaluated. Coupling coordination degree model and relative development degree model were used to analyze the coupling coordination level and the type of coupling coordination development. The results show that, during the study period, both the agricultural water resources vulnerability and food security in the main grain producing areas showed a trend of continuous improvement and optimization, and their scores increased by 6.22% and 17.22%, respectively. The degree of coupling coordination between agricultural water resources vulnerability and food security increased by 5.11%, from barely coordination to primary coordination, and presented a spatial distribution characteristic of "high in the south and low in the north". The types of coupling coordination development of main grain producing areas were mainly low running-backward agricultural water resources and high running-synchronous development. The backward development of agricultural water resources system has become the main obstacles to food security. Therefore, proposals are put forward for the reducing of the vulnerability of agricultural water resources and improving of the coupling development of these two systems.

The Qinling-Daba Mountains Range is an important geographical transition zone between northern and southern China. This paper aims to fully understand the ecological changes and the influencing factors in this area in the past 20 years. To achieve this, MODIS-EVI data were applied, combined with temperature, precipitation, and DEM data, and the maximum synthesis method, trend analysis method, and partial correlation analysis were used on the basis of altitude. Besides, temporal and spatial changes in the enhanced vegetation index (EVI) for different vegetation types at various altitudes and their correlation with temperature and precipitation from 2000 to 2020 were analyzed. The main conclusions are: (1) From 2000 to 2020, the average annual EVI of vegetation in the Qinling-Daba Mountains area presented a fluctuating upward trend. Overall, 80.67% of the area showed a significant improvement on EVI and 13.29% of the area showed a slight improvemont on EVI. The EVI was relatively stable at an altitude of 1 600-1 800 m, which is more suitable for vegetation growth. (2) Cultivated vegetation and broad-leaved forests are the main types of vegetation in the Qinling-Daba Mountains region. The EVI values of the various vegetation types range in the order of broad-leaved forest > shrub > coniferous forest > grassland > cultivated vegetation > others. The inter-vegetation area accounts for the majority of vegetation in the altitude range of 1 000-2 000 m, while the altitude range of 1 600-1 800 m is the most suitable for natural vegetation growth. (3) From 2000 to 2020, the climate in the Qinling-Daba Mountains area became warmer and more humid. The correlation between EVI and temperature was relatively uniform across the region, and the impact of precipitation on EVI was greater than that of temperature. However, at higher altitudes, the correlation between EVI and temperature is generally greater than precipitation.

The Huang-Huai-Hai region is an important cropping and pig breeding base in China. It is of great significance to study the carrying capacity of pigs for guiding pig breeding planning and returning of pig manure to field. In this paper, the pollutants yield of pig breeding and the load of cultivated land in Huang-Huai-Hai region was estimated. Based on the concept of "The amount of breeding is determined by the amount of cultivation and demand", the whole Huang-Huai-Hai region was taken as the research scope and the most common 6 crops in the area were taken as the research objects to study the carrying capacity of different crops for pig breeding. The results show that, the total output was 180.712 5 million of pigs in 2017 in the region and the annual yield of pig manure, wastewater, TN, TP, Cu and Zn were 38 868 400, 287 694 300, 964 400, 136 200, 5 799 and 8 805 tons, respectively, and the carrying capacity of cultivated land for pig breeding was 6.22-11.33 pigs equivalent·hm^-2. For the six crops studied, their carrying capacity of pigs in the region was 1.58-20.96 pigs equivalent·hm^-2 and crop species and area were the important influencing factors. Overall, the carrying capacity of different crop land for pig breeding in the region was in the order of wheat > rice > cotton ≈ corn > rape > soybean. The land carrying capacity of rice, wheat, rape, corn, soybean and cotton farmlands in the region for pig breeding were 10.32, 11.47, 4.72, 5.39, 3.77 and 5.53 pigs equivalent·hm^-2, respectively. In summary, factors such as crop species, crop yield, soil fertility and replacement ratio of manure in the field should be taken into consideration when evaluating the amount of manure returned from pig breeding and the farmland support of pig farms.

The changes of the boundary between subtropical and warm temperate zones and the spatiotemporal evolution of the actively accumulated temperature of ≥10 ℃ (AAT10) in the Qinling Mountains from 1960 to 2019 was analyzed by using the sliding mean temperature over five days, the Mann-Kendall test, and the Anusplin method based on the daily average temperature data from 74 meteorological stations in and around the Qinling Mountains (QMs). The results show that (1) at the temporal scale, the AAT10 had increased at a rate of 71.72 ℃·(10 a)^-1 in the QMs since 1960. The areas of 1 0004 000 ℃ and 3 0004 000 ℃ and 2 000

The study of the response of grassland vegetation phenology to climate change is the key to understand the history of regional land ecosystem productivity and the mechanism of future change. Based on MODIS NDVI data, grassland type data and ground measurement data, combined with en trend analysis and partial correlation analysis, the temporal and spatial characteristics, trends, stability of changes and their variation characteristics with climate factors of grassland vegetation phenology 2001-2020 were studied. The results show that: (1) with the increase of altitude, the start of growing season (SOS), end of growing season (EOS)and length of growing season (LOS) changed irregularly. (2) SOS was concentrated in mid April to late May (110-150 d), and 79.32% of the area showed a significant advance trend, with a rate of 0-1.5 d·y^-1, the SOS of mountain meadow < temperate grassland, shrub grass and desert < alpine < alpine grassland. EOS concentrated in mid September to mid October (260-290 d), show a delayed trend. The LOA lasted for 130-180 d, show a prolonged trend. (3) The decrease of annual precipitation, the increase of spring temperature, the increase of extreme climate index of temperature and the decrease of maximum 5 d rainfall will lead to the advance of grassland SOS. The increase of annual average temperature, maximum 1 d rainfall, summer and winter temperature, and the decrease of autumn temperature made trend of grassland SOS. (4) The increase of annual precipitation, daily maximum temperature and autumn temperature delay the grassland EOS, while the increase of annual average temperature lead to the advance of grassland EOS. The above results can provide a new understanding of the influencing factors of grassland phenology in Qinghai Province, and also provide a reference for grassland to adapt to future climate change and grassland breeding.

Poyang Lake is the largest freshwater lake in China. Four crane species annually overwinter in this lake, including Siberian crane (Grus leucogeranus), hooded crane (Grus monacha), white-naped crane (Grus vipio) and common crane (Grus grus). The population size and spatial distribution of the four wintering crane species between 2001 and 2019 were monitored. The results show that: (1) Over the 18-year period, the average yearly population of the four wintering crane species in the Poyang lakes were (3 058±797) for the Siberian crane, (322±192) for the hooded crane, (1 291±1 016) for the white-naped crane, and (3 594±3 721) for the common crane. Over the 18-year period, the population size of the Siberian crane was relatively stable, the population size of the hooded crane and white-naped crane decreased and the common crane population increased with extreme annual fluctuations; (2) The hotspots within the Poyang Lake for the distribution of the four wintering crane species clustered in the lakes of Banghu, Dachahu, Dahuchi, Nanhu, Hanchihu, Dalianzihu, Zhuhu, and Qihu; (3) After commencing the operation of the Three Gorges Reservoir, the population densities of the Siberian crane, hooded crane and white-naped crane decreased and concentrated into the Poyang Lake National Nature Reserve. Conversely, the common crane population increased. Our recent surveys indicate that Poyang Lake occupies an important position in crane resources and should remain protected for future crane populations.

The ecological ditches are the key links of agricultural non-point source pollution control. In the present study, ecological ryegrass mats were developed independently and applied in ecological ditches. The removal effect for nitrogen in the simulated farmland drainage by floating ryegrass mat was discussed, and also the growth state of the plants. Results showed that, the growth state of ryegrass were best cultivating in compact mat plus 5 kg·m^-2 sieved fine soil. In the low influent nitrogen concentration stage of the flowing experiment (TN: 8.16 mg·L^-1), the removal rates of NH₄⁺-N were 56.8% and 40.5% in the treatment of high flow velocity (D1) and low flow velocity (D2), respectively, which were higher than Control-without plants in (25.6%). This is the result of denitrification and plant absorption. However, in the high influent nitrogen concentration stage (TN: 20.53 mg·L^-1), the removal rates of NH₄⁺-N dropped to 44.6% and 32.1% in the treatment of D1 and D2, respectively. In the whole stage of the flowing experiment, the average removal rates of TN were not high (13.1%-22.3%), and were not different significantly among top, middle, and bottom layers. Under the conditions of TN influent concentration of about 8.16 mg·L^-1 and influent flow of 1.5-2.5 L ·min^-1, the ryegrass grew better and the removal rates of NH₄⁺-N were higher. Therefore, the dense straw curtain covered with a certain amount of soil was chosen for seedling raising, it can be used for interception and purification of water polluted by low nitrogen load. In the future, the nitrogen removal efficiency can be further enhanced and the application potential can be improved by mixing other grass species or increasing the coverage of grass curtain floating bed.

In order to investigate the phytoremediation potentials of Vetiveria zizanioides to sulfonamides polluted water, the trials with the pretreatment method of MCX solid-phase extraction column and high performance liquid chromatography-tandem mass spectrometry (HPLC-MS) detection method were implemented under the condition of greenhouse hydroponics. Sulfonamides (SAs) were added to the nutrient solution with the initial concentration of 100 μg·L^-1. The results show that the removal rates of Vetiveria zizanioides to sulfonamides (SAs) increased by 27.88% for sulfapyridine (SPY), 32.81% for sulfamethoxazole (SMZ), 29.9% for sulfadimethoxine (SDM) and 20.03% for sulfaquinoline (SQX), in comparison of no Vetiveria zizanioides treatment for the 15th day. The absorption peaks of SAs by Vetiveria zizanioides were on the 6th and 12th day, and the decrease rates of SAs in Vetiveria zizanioides nutrient solution were higher in the the first 6 days. There was a significant negative correlation between the treatment time and the residual concentration of SA_S in nutrient solution (P<0.01), and a significant positive correlation between the treatment time and the increasing proportion of the removal rates in water (P<0.01). The transfer coefficients were significantly positive correlated with the concentration of SA_S in the stems, leaves and roots of Vetiveria zizanioides (P<0.01). Root systems of Vetiveria zizanioides were the main organ tissues in accumulating SAs. In conclusion, Vetiveria zizanioides are of efficient absorbing capability to SDM, strong root enrichment ability to SMZ and SQX, and efficient transferring ability to SPY. Vetiver zizanioides can significantly remove SAs in polluted water.

To investigate both the potential ecological risks of heavy metals in sludge biochar and effects of sludge biochar on plant growth as well as microbial diversity in soil, sludge biochar was prepared by pyrolysis of municipal sludge. The potential ecological risks of sludge and its biochar were evaluated by the risk assessment code (RAC), Muller geo-accumulation index (I_geo) and potential ecological risk index (RI). The effects of sludge biochar application on the growth of ryegrass were then discussed through pot experiments. The changes of microbial diversity in ryegrass root-soil were analyzed by 16S rRNA sequencing technology and bioinformatics. The results indicate that the RAC and RI indexes in the sludge decreased significantly after pyrolysis, and the bioavailability of heavy metals decreased, but the I_geo of each heavy metal increased, and the geological cumulative risk increased. According to the pot experiment, when adding 5% sludge biochar, the germination rate, average leaf weight per plant and average leaf length of ryegrass were promoted to reach 94%, 0.179 8 g and 13.74 cm, increased by 16.0%, 62.12% and 29.15%, respectively in contrast with pots without adding biochar. There was no significant influence in the abundance of bacterial community of ryegrass root soil by adding biochar, but the bacterial community diversity of the soil slightly decreased. The results of this study show that sludge-based biochar has a significant stabilizing effect on heavy metals, and its heavy metal content is lower than the standard of farmland risk screening value in China (GB 15618-2018), and the level of potential ecological risk is relatively low. At the same time, by the application of carbon, the growth of ryegrass could be promoted at a certain ratio.

In aluminum sludge treatment, solid powder adsorbent is easily to be lost and difficult to be separated from the liquid wastewater. In this study, nitrogen and phosphorus removal efficiency from wastewater were investigated with simulated aluminum sludge, immobilized bacteria, immobilized algae/aluminum sludge, and immobilized bacteria algae/aluminum sludge. The results show that the combination of algae powder and aluminum sludge increased the specific surface area of the adsorbent and provided more adsorption sites for nitrogen and phosphorus. The maximum adsorption capacities for phosphorus by the algae/aluminum sludge in the ratios of 1∶10, 1∶5, and 1∶2 were 8.45, 10.06, and 6.68 mg·g^-1, respectively; these values were 2.41, 2.87, and 1.91 times higher, respectively, than those of aluminum sludge alone. The purifying effect of the immobilized bacteria algae/aluminum sludge (1∶5) on wastewater was better than that of aluminum sludge, immobilized bacteria, and immobilized algae/aluminum sludge (1∶5). The removal rates of chemical oxygen demand, total phosphorus, ammonia nitrogen, and total nitrogen by immobilized bacteria algae/aluminum sludge were 80.35%, 91.88%, 90.92%, and 92.51%, respectively. The removal of phosphorus by immobilized bacteria algae/aluminum sludge (1∶5) adsorbent mainly depends on the ion exchange and electrostatic interaction between the aluminum sludge and phosphate. The mass transfer of the immobilized rubber ball adsorbent provides excellent conditions for simultaneous nitrification and denitrification.