To analyze the effects of in situ vegetable residue return on soil properties and microorganisms, this study conducted a continuous three-season in situ residue return experiment with four treatments: no return (CK), residue return (HTJ), residue return + compound microbial inoculant (HTJS), and residue return + ammonia water (HTJN). This study compared the treatment effects on soil quality. The results showed that, after the third tillage, the HTJS treatment increased soil organic carbon, total nitrogen, and mineralizable organic carbon content, and significantly enhanced the activity of soil β-glucosidase and soil peroxidase, which are related to carbon cycling enzymes compared to other treatments. There were no significant differences in bacterial or fungal α-diversity among treatments. Differences in fungal community soil β-diversity among treatments were significant. The HTJS treatment enriched organic matter-degrading bacteria Flavisolibacter and Devosia. Although HTJS increased the relative abundance of Fusarium, the field disease incidence index did not increase. The soil quality index (SQI), based on the minimum dataset (MDS), showed that HTJS had the highest SQI after the third tillage. Further path model analysis revealed that soil carbon components index and soil physicochemical index were the main controlling factors influencing the SQI. In conclusion, in situ residue return with a compound microbial inoculant (HTJS) is an effective strategy to simultaneously enhance soil fertility and biological activity by regulating the microbial community structure and associated enzyme activities.

Straw returning is essential for soil conservation and mitigating wind erosion in semiarid regions bearing black soil areas. Quantitative studies on crop development and soil water-nitrogen dynamics processes under complete straw returning are fundamental for establishing a rational farmland management system. To model crop yields and soil profile water-nitrogen distribution under various fertilization treatments, we used the soil water heat carbon nitrogen simulator (WHCNS), namely CK (no fertilization), T1 (compound fertilizer), T2 (compound fertilizer + straw returning), and T3 (humic acid fertilizer + straw returning). We calibrated and evaluated the performance of the WHCNS model by using soil water content, nitrate nitrogen content, aboveground dry matter mass, and yield data collected from the Meilisi Daur District experimental farm in Qiqihar, Heilongjiang Province, in 2022. We also simulated the effects of different fertilization methods on spring maize field evapotranspiration, crop yield, and water-nitrogen use efficiency. The results indicate that the hydraulic parameters Qs and n significantly impacted the soil water content in the parameter sensitivity analysis. In contrast, SLAmax had the largest impact on soil nitrate nitrogen content among crop parameters, and Ts was the most influential factor on crop yield. The relative root mean square errors of simulated and observed soil water storage, nitrate nitrogen content, and aboveground dry matter mass were all lower than 32%. Consistency indices for the 0-60 cm and 60-100 cm soil layers were greater than or equal to 0.68 and 0.30, respectively. Finally, the Nash coefficients were within reasonable ranges. The evapotranspiration rate under the straw returning treatment (T2) was 6.33% lower than without straw returning (T1). T2 exhibited the highest water-nitrogen use efficiency among all treatments, and compared with T1 and T3, water-nitrogen use efficiency increased by 10.27%, 7.78%, 26.71%, and 48.15%, respectively. These findings suggest that straw returning can effectively reduce evapotranspiration and improve resource utilization efficiency. Overall, the calibrated WHCNS model can reliably simulate the dynamics of soil water- nitrogen movement and crop growth under straw returning in the semiarid regions of northeastern China.

In response to China’s drive to bring newly cultivated land into production, this study evaluated how combined organic fertilizer and microbial inoculants affect soil quality, bacterial community structure, and maize yield. Four treatments were evaluated: FC (chemical fertilizer only), T50 (50% organic fertilizer + 50% chemical fertilizer), T50M (T50 plus microbial inoculant), and CK (no fertilizer). T50M significantly increased yield compared to FC and CK (p < 0.05), achieving the highest yield of 6995.73 kg ha−1. This was 20.09% greater than FC. Community composition analyses showed that soil in newly cultivated land was dominated by Blastocatellia, Vicinamibacteria, and Alphaproteobacteria, together accounting for over 35.7% of total bacterial abundance. Redundancy analysis at the class level explained 55.7% of variance; soil organic matter (SOM) and available potassium positively correlated with Alphaproteobacteria and Bacteroidia, while available phosphorus and nitrate nitrogen aligned with Actinobacteria and Bacilli. Path analysis indicated that SOM and total nitrogen were the strongest positive drivers of yield. Actinobacteria and Acidobacteriae also showed direct positive effects, whereas Verrucomicrobiae had a negative effect. These results demonstrate that integrated organic–microbial amendments can enhance soil fertility and alter microbial diversity toward taxa that can improve maize productivity.

Soil erosion results in dissolved organic matter (DOM) loss and is one of the main paths of soil carbon loss. Bacteria affect the generation and transformation of DOM. However, the effect of bacteria on the composition and slope distribution of DOM has rarely been investigated under field conditions. Based on a long-term experiment of three gradients (3°, 5°, 8°) in a black soil erosion area of Northeast China, the content, composition, and source of DOM were studied. The results showed that the DOM of the 3° and 5° slope was enriched midslope, and the DOM of the 8° slope was enriched downslope. Parallel factor (PARAFAC) analysis indicated that the main substances in DOM were fulvic-like acid, humic-like acid, tryptophan-like protein, and soluble microbial metabolites. The upslope and downslope soils of 3° and 5° slopes showed high DOM bioavailability, while the downslope soil of the 8° slope showed high DOM bioavailability. The content of new DOM in downslope soil increased with the gradient. Bacteria played an important role in the synthesis and transformation of DOM and affected its composition and slope distribution. Verrucomicrobiota, Firmicutes, Planctomycetota, and Gemmatimonadota were the main factors affecting soil DOM. The results could be helpful in understanding the loss mechanism of DOM in eroded black soil and provide support for soil carbon sequestration.

Rainfall intensity and slope gradient are the main drivers of slope surface runoff and nitrogen loss. To explore the distribution of rainfall runoff and nitrogen loss on the Miyun Reservoir slopes, we used artificial indoor simulated rainfall experiments to determine the distribution characteristics and nitrogen migration paths of surface and subsurface runoff under different rainfall intensities and slope gradients. The initial runoff generation time of subsurface runoff lagged that of surface runoff, and the lag time under different rainfall intensity and slope conditions ranges from 3.97 to 12.62 min. Surface runoff rate increased with increasing rainfall intensity and slope gradient; compared with a rainfall intensity of 40 mm/h, at a slope of 15°, average surface runoff rate at 60 and 80 mm/h increased by 2.38 and 3.60 times, respectively. Meanwhile, the subsurface runoff rate trended upwards with increasing rainfall intensity, in the order 5 > 15 > 10°. It initially increased and then decreased with increasing slope gradient, in the order 5 > 10 > 15°. Total nitrogen (TN) loss concentration of surface runoff shows a decrease followed by a stabilization trend; the concentration of TN loss decreases with decreasing rainfall intensity, and the stabilization time becomes earlier and is most obvious in 5° slope conditions. TN loss concentration in subsurface runoff decreased with increasing rainfall intensity, i.e., 40 > 60 > 80 mm/h. The surface runoff rainfall coefficient was mainly affected by rainfall intensity, a correlation between αs and slope gradients S was not obvious, and the fitting effect was poor. The subsurface runoff rainfall coefficient was mainly affected by slope gradient, the R2 of all rainfall intensities was <0.60, and the fitting effect was poor. The main runoff loss pathway from the Miyun Reservoir slopes was surface runoff, which was more than 62.57%. At the same time, nitrogen loss was subsurface runoff, more than 51.14%. The proportion of surface runoff to total runoff increases with the increase of rainfall intensity and slope, with a minimum of 62.57%, and the proportion of nitrogen loss from subsurface runoff also decreases with increasing rainfall intensity but does not change with slope gradient. The order of different runoff modulus types was mixed runoff (surface and subsurface runoff occur simultaneously) > surface runoff > subsurface runoff. The surface and mixed runoff modulus increased significantly with increasing rain intensity under different rain intensities and slope gradients. Overall, rainfall intensity significantly affected slope surface runoff, and slope gradient significantly affected nitrogen loss.

Human disturbance impacts mixed-species bird flocks ( "flocks "). Unfortunately, the impact on flocks by one large-scale disturbance, plantation forestry, has remained little explored. We examined how plantation forestry of a widespread yet understudied timber species, Alder-leaf Birch ( Betula alnoides , "birch "), affects the composition and interactions of flocks in the Indo-Burma biodiversity hotspot in southwestern China. We conducted transect surveys to sample flocks in birch plantations and natural forests of two age classes (mature and young). While flock size and species richness per flock were similar across land-use types, rarefied species richness accounting for unequal sampling effort was noticeably higher in mature forests. Furthermore, flock composition differed across land-use types, with differences related to species ' morphological characteristics, dietary preferences, and foraging substrates. Specifically, mature forests supported flock participants with large bodies, poor dispersal ability, and a fruit-eating diet. Birch plantations offered equal support to invertivores as both natural forests, and additional support to bark foragers. Lastly, interactions among flocking species quantified by social network metrics were similar across land-use types, suggesting that birch plantations perserved the flocking behavior itself. Our study reveals the conservation potential of birch plantations in supporting invertivorous birds and preserving interactions in flocks. More importantly, it highlights the irreplaceability of mature forests because of their unique species composition. We recommend promoting birch planting without compromising local economies and protecting remnant mature forests through education programs and continued research.

Surface flow (SF) and subsurface flow (SSF) are important hydrological processes occurring on slopes, and are driven by two main factors: rainfall intensity and slope gradient. To explore nitrogen (N) migration and loss from sloping farmland in the Miyun Reservoir, the characteristics of total nitrogen (TN) migration and loss via SF and SSF under different rainfall intensities (30, 40, 50, 60, 70, and 80 mm/h) and slope gradients (5°, 10°, and 15°) were studied using indoor stimulated rainfall tests and mathematical models. Nitrogen loss via SF and SSF was found to increase exponentially and linearly with time, respectively, with SSF showing 14–78 times higher loss than SF. Under different rainfall intensities, SSF generally had larger TN loss loading than SF, thereby indicating that SSF was the main route for TN loss. However, the TN loss loading proportion via SF increasing from 14.03% to 35.82% with increasing rainfall intensity is noteworthy. Furthermore, compared with the measurement data, the precision evaluation index Nash-Suttcliffe efficient (NSE) and the determination coefficient (R2) of the effective mixing depth model in the numerical simulation of TN loss through SF in the sloping farmland in the Miyun Reservoir were 0.74 and 0.831, respectively, whereas those of the convection-dispersion equation for SSF were 0.81 and 0.811, respectively, thus indicating good simulation results. Therefore, this paper provides a reference for studying the mechanism of N migration and loss in sloping farmland in the Miyun Reservoir.

Environmental loss is primarily caused by soil, water, and nutrient loss, and runoff is associated with nutrient transport and sediment loss. Most existing studies have focused on one influencing factor, namely slope gradient or rainfall intensity, for slope erosion and nutrient loss, but the joint effects of the two factors have rarely been researched. In this context, the impact of slope gradients (0°, 5°, 10°, and 15°) and rainfall intensities (30, 40, 50, 60, 70, and 80 mm/h) on soil erosion and nutrient loss on the sloping fields of Miyun Reservoir were explored using the indoor artificial rainfall simulation testing system. Based on the results of the study, the variation of runoff coefficient with slope gradient was not noticeable for rainfall intensities <40 mm/h; however, for rainfall intensities >40 mm/h, the increased range of runoff coefficient doubled, and the increase was the fastest under 0° among the four slope gradients. The slope surface runoff depth and runoff rate showed positive correlations with the rainfall intensity (r = 0.875, p < 0.01) and a negative correlation with the slope gradient. In addition, the cumulative sediment yield was positively related to the slope gradient and rainfall intensity (r > 0.464, p < 0.05). Moreover, the slope surface runoff-associated and sediment-associated loss rates of total nitrogen (TN) rose as the rainfall intensity or slope gradient increased, and significant linear positive correlations were found between the runoff-associated TN loss rate (NLr) and the runoff intensity and between the sediment-associated NLr and the erosion intensity. In addition, there were positive linear correlations between slope runoff-associated or sediment-associated TN loss volumes and rainfall intensity, surface runoff, and sediment loss volumes, which were highly remarkable. The slope gradient had a significant positive correlation with the slope surface runoff-associated TN loss at 0.05 (r = 0.452) and a significant positive correlation with the sediment-associated TN loss at the level of 0.01 (r = 0.591). The rainfall intensity exhibited extremely positive correlations with the slope surface runoff-associated and sediment-associated TN loss at 0.01 (r = 0.717 and 0.629) Slope gradients have less effect on nitrogen loss on sloped fields than rainfall intensity, mainly because rainfall intensity affects runoff depth. Based on the findings of this study, Miyun Reservoir may be able to improve nitrogen loss prevention and control.

Excessive and deficit foliar fertilization adversely affects pear fruit yield and its qualitative characteristics. In the present study, we investigated the impact of higher to a lower foliar spray of amino acid selenium fertilizer concentrations on the Huangtukan pear variety. Foliar fertilizer treatments were 50.0 mg plant-1, 60.0 mg plant-1, 75.0 mg plant-1, 100 mg plant-1, 150.0 mg plant-1and 0.0 mg plant-1(Control check, CK), which were sprayed on the interval of every 15 days since the full-bloom period (8 times in total) and stopped before the maturity stage. The results demonstrated that the pear's yield, quality, and absorption of nutrient elements first increased and then decreased with the increase of the selenium fertilizer concentration. In contrast, the absorption of the selenium was constantly increasing. When the mass concentration of the selenium fertilizer was 75 mg plant-1, the pear yield, the soluble solids, and the vitamin-C content increased by 19.07%, 21.69%, and 85.2%, respectively, and titratable acid content decreased by 52.45%; content of major elements such as phosphorus and potassium increased by 42.48% and 89.18% respectively; sodium, magnesium, and sulfur increased by 191.53%, 78.68%, and 157.84% respectively; trace elements including selenium, boron, manganese, zinc, iron, and copper increased by 52.39%, 179.02%, 72.11%, 26.8%, 100.33%, and 55.94% respectively. Thus, based on the comprehensive analysis of different yield and quality attributes, it is concluded that the optimum foliar spraying mass concentration of the selenium fertilizer for the Huangtukan pear is 75 mg plant-1.

为了探究光周期和占空比组合补光光源对生菜生长、光合及叶绿素荧光参数的影响,以玻璃生菜为研究材料,通过调节光周期和占空比共得到 T1(P16D25)、T2(P16D50)、T3(P16D75)、T4(P8D100)、T5(P12D100)、T6(P16D100)、T7(P20D100)和T8(P24D100)(P为光周期,D为占空比)8个不同的光照处理,测定各处理下生菜形态指标、生物量、色素含量、光合特性及叶绿素荧光参数指标.结果表明:T8处理下的生菜形态指标优于其他光周期和各占空比处理;叶绿素荧光参数中T4、T5、T6、T7和T8处理PSⅡ实际光化学量子效率(Y(Ⅱ))均显著高于其他非100％占空比处理;T1和T2表观光合电子传递速率显著高于其他各处理;T2与T7处理的生物量、色素含量、净光合速率、胞间二氧化碳浓度和气孔导度方面均表现较好且无显著差异.综上,从生产和节能效果综合考虑,T2处理更适宜作为生菜补光光源.

In order to analyze the influence of coupling environmental factors on melon seedlings and realize the precise management of greenhouse melon environment.In the study, the daytime air temperature, carbon dioxide concentration and nutrient solution concentration were used as the regulatory factors, and the universal rotating combination design with three factors and five levels was adopted. The factor analysis method was introduced to extract the common factors of six growth indicators（total fresh weight, total dry weight, net photosynthetic rate, seedling index, leaf area and chlorophyll content）, and the obtained common factors were used as the comprehensive evaluation index of seedlings. According to the evaluation value, the response model of integrated growth of melon seedlings to environmental factors was fitted, and the synergistic regulation of environmental factors was analyzed. The results showed that the coefficient of determination（R~2） of the model was 0.944, and the root mean square error（RMSE） was 0.07, which was a good fit. In the experimental range, the effect of daytime air temperature on melon seedlings was greater than that of CO 2 concentration and nutrient solution concentration. The comprehensive evaluation value of melon seedlings increased first and then decreased with the increases of CO 2 concentration and nutrient solution concentration, and increased with the increase of temperature. The optimal combination of environmental factors for the comprehensive growth of melon seedlings was daytime air temperature 33 ℃-35 ℃, CO 2 concentration 1 043-1 408 μmol/mol and nutrient solution concentration 2.0-2.9 mS/cm. This study can provide decision support for the optimization of environmental regulation of melon seedlings.

Excessive, long-term chemical fertilizer application adversely affects soil quality and maize yield. The combined application of biochar with chemical fertilizer can increase maize yield and improve soil fertility. A four-year field experiment was conducted to determine soil physio-biochemical properties and maize yield under a soybean–maize rotation in the black soils of Northeast China. There were five treatments, including no fertilization (CK), fertilizer (NPK), fertilizer + biochar (15.75 t·hm−2, BC1), fertilizer + biochar (31.50 t·hm−2, BC2), and fertilizer + biochar (47.25 t·hm−2, BC3). Compared with CK, the number of macroaggregates and the average weight diameter of soil aggregates in BC2 treatment increased significantly by 10.3% and 24.5%, respectively. The soil pH in the study area was 7.03, and it increased in all treatments except for BC1. The highest pH of 7.17 was recorded in NPK and BC2 treatments, which was around the optimal soil pH. In contrast to the CK and NPK treatments, the biochar application increased soil organic carbon (SOC) and total nitrogen (TN) content. The BC2 treatment improved soil C/N and increased the copy number of soil bacteria by 25.6% compared to CK. The combined application of chemical fertilizer and biochar was better than NPK treatment alone, and improved soil mechanical composition and fine soil particle contents (powder and clay). Mixed biochar with chemical fertilizer application also significantly increased maize yield and the weight of 100 grains increased from 9.5% to 10.9% compared to CK. The maize yield of the three fertilizer and biochar treatments was higher than treatments with applied chemical fertilizer alone, in the order of BC2 > BC3 > BC1 > NPK > CK (BC2 treatment increased by 34.8%). Additionally, the maize yield was significantly and positively correlated with soil aggregates, organic carbon and total nitrogen (p < 0.05) as well as the 100-grain weight (p < 0.01). The application of 31.50 t·hm−2 (BC2 treatment) of biochar can enhance soil physicochemical properties and improve maize yield.

Significant climate variations have decreased the stability of water resource systems, leading to multiple uncertainties in streamflow response, reservoir operation optimization, decision-making, and adaptive adjustments for water resource scheduling. Understanding the impact of climate change on reginal streamflow is necessary and crucial to identifying reservoir operation strategies and decision-making responses. In this study, we created an integrated systematic “uncertain streamflow responses”– “reservoir operation”– “optimization”– “decision-making risk analysis” chain. Three bias-corrected and downscaled general circulation models (GCMs) were used to analyze the inter-model uncertainties under three representative concentration pathways (RCPs). The streamflow responses and uncertainty in the future were determined using a distributed hydrological model and the fuzzy extension principle under predefined scenarios and uncertainty levels. Then, a stochastic simulation model and modified stochastic multi-criteria decision-making model were applied to identify the effects of climate change projections and streamflow responses on reservoir multi-objective operation and decision-making. Moreover, risk quantification indices were used to determine the uncertainty propagation and potential risks accumulated in the chain. We applied this framework to cascade reservoirs in the Qing River Basin. The results indicate that the mean annual streamflow projected using selected GCMs will increase, enhancing the hydropower response and weakening the ecological benefit response. The Pareto non-dominated solutions optimized based on the streamflow projections obtained using the GCMs (under the same RCP) and hydrological model are more distinct than those based on different RCPs and the same GCM. Moreover, a high emission scenario may increase the uncertainty of the streamflow projections and reservoir operation responses, which is consistent with the finding that the decision-making process becomes more variable and sensitive with increasing streamflow uncertainty. Finally, we identified the preferred solutions for reservoir operation under different uncertainties, the respective expected values, and the 95% confidence interval bands to enhance the adaptability of future reservoir operation.

Heilongjiang Province is the main grain producing region in China and an important part of Northeast China Plain, which is one of the three black soil belts in the world. The cultivated region of black soil accounts for 50.6% of the black soil region in Northeast China. Due to the obvious rise of temperature and uneven distribution of precipitation in the 20th century, it has been considered to be one of the important reasons for agricultural drought and aridity. Under the background of climate change, understanding the multiyear changes and occurrence characteristics of cultivated land drought in different agricultural regions in Heilongjiang Province is of great significance for the establishment of agricultural drought prediction and early warning system in the future, guiding agricultural high-standard farmland irrigation in different regions, promoting black soil protection, and then improving grain yield. This paper calculates the temperature vegetation drought index (TVDI) based on the normalized difference vegetation index (NDVI) and surface temperature (TS) product data of MODIS from 2000 to 2021. Taking TVDI as the drought evaluation index, this paper studies the temporal and spatial variation distribution characteristics and occurrence frequency of drought in the whole region and four agricultural regions of Heilongjiang Province: Daxing an Mountain and Xiaoxing an Mountain (region I), Sanjiang Plain (region II), Zhangguangcai Mountains (region III), and Songnen Plain (region IV). The results show that medium drought generally occurred in Heilongjiang Province from 2000 to 2021, accounting for about 70% of the total cultivated land. The drought was severe from 2000 to 2009 and weakened from 2010 to 2021. In the 110 months of the crop growing season from 2000 to 2021, about 63.84% of the region suffered more than 60 droughts. It is found that the frequency of drought varies from region to region. More than 80 droughts occurred in the west of region IV and the middle of region II. The characteristics of region IV are large sandstorm, less precipitation, and lack of water conservancy facilities, resulting in frequent and strong drought. It is also found that the occurrence frequency, degree grade and regional distribution of drought are closely related to seasonal changes. In spring, the occurrence grade and frequency of drought in region IV are the strongest and the drought phenomenon is serious. In autumn, drought is frequent and distributed in all regions, but the grade is not strong (mainly medium drought), and the drought phenomenon is medium. It is humid in summer. Crops in Heilongjiang Province are one crop per annual. Spring drought seriously restricts the water content of crops. Long-term drought will lead to poor crop development and reduce yield. Therefore, only by clarifying the characteristics of regional time drought, monitoring accurate drought events and accurately predicting the occurrence of drought, can we guide high-standard farmland precision irrigation, improve crop yield and ensure national food security. At the same time, severe drought will affect the terrestrial ecosystem, resulting in the distribution of crops and microorganisms, and the transformation between carbon sink and carbon source.

Drought is a complex climatic hazard with major impacts on both human and natural system. It is very likely leading to agricultural loss, forest mortality and drinking water scarcity. In recent years, the occurrence frequency and intensity of droughts has been increasing within a warming climate. This poses serious threats to future food security, ecosystem (e.g., changing the forest structure and carbon content) and fresh water stress for small islands. Precipitation, temperature and other atmospheric factors have an influence on the drought conditions. Furthermore, the impact of land cover change on climate mostly on precipitation and temperature has been established in previous studies. To our best knowledge, the effect of change in land cover, especially in large forest cover, on droughts is largely unexplored. This, however, is important to understand the impact of land cover on climate variability and the sensitivity of the droughts to changes in the climate. This study aims at quantifying the effect of forest cover change and changing meteorological factors on long-term and short-term droughts across four different climate regions (i.e. equatorial, arid, temperate and snow region). We analyse the influence of forest cover changes to droughts. Meteorological data (precipitation and temperature), land cover dataset, and drought indices (the Palmer Drought Severity Index and the Standardized Precipitation Evapotranspiration Index) for almost 30 years are used to study the influence of forest cover fraction variability on droughts for different time scales and across different climate zones. Linear model and analysis of variance (ANOVA) have been used in the analysis to explore how forest cover changes impact on the drought occurrence frequency and intensity. Our findings can be used in making policy decision involved in forest management and water resource planning.

In agroecosystems, different cropping patterns cause changes in soil physicochemical properties and thus in microbial communities, which in turn affect crop yields. In this study, the yields of soybean continuous cropping for 5 years (C5), 10 years (C10), and 20 years (C20) and of soybean-corn rotational cropping (R) treatments were determined, and samples of the tillage layer soil were collected. High-throughput sequencing technology was used to analyze the diversity and composition of the soil bacterial and fungal communities. The factors influencing microbial communities, along with the effects of these communities and those of soil chemical indexes on yield, were further evaluated. The results showed that the community richness index of bacteria was higher in C20 than in R and that of fungi was highest in C5. The differences in the bacterial and fungal communities diversity indexes were not significant among the different continuous cropping treatments, respectively. The soil microbial community composition of all continuous cropping treatments differed significantly from R. The dominant bacterial phylum was Actinobacteriota and the dominant fungal phylum was Ascomycota. The relative abundance of Fusarium did not differ significantly among the continuous cropping treatments, while that of the plant pathogen fungi Lectera sp., Plectosphaerella sp., and Volutella sp. increased with continuous cropping years. Soil pH, SOM, N, and TP had significant effects on both bacterial and fungal communities, and TK and C/N had highly significant effects on fungal communities. The yield of C5 was significantly lower than that of R, and the differences in yield between C10, C20, and R were not significant. TN, TP, and pH had significant effects on yield, and fungal community abundance had a greater negative effect on yield than bacterial community abundance.

Dissolved organic matter (DOM) plays an important role in transforming organic matter into inorganic matter in the natural ecosystem. DOM can provide nutrition and energy for microorganisms and has an important role in indicating the transfer and transformation of humus. Cow dung can improve the humification efficiency of corn straw, which makes better use of agricultural waste. In order to study the characteristics of DOM in the fermentation process of corn straw-cow dung, which were treated with 2 : 8 (11), 4 : 6 (T2), 6 : 4 (T3) and 8 : 2 (T4), we adopted three dimensional fluorescence spectrum - parallel factor analysis method to analyze the fluorescence components of DOM in the fermentation substrate. Fluorescence index (FI) and biological index (BIX) were used to analyze the source of DOM; humification index (HIX) was used to characterize the humification degree of fermentation, and the correlation among the maximum fluorescence intensity of DOM components was analyzed. The results showed that the sources of DOM were influenced by both autochthonous and allochthonous sources (FI>1. 4, 0. 8<BIX<1. 0), and the T3 had strong autochthonous characteristics. On the 40th day, the humification degree of thefour treatments was still weak (HIX<1. 5), and the humification degree of T3 was relatively high. During the fermentation, DOM contained three fluorescence components: fulvic-like acid [UV fulvic-like acid (230 similar to 275 nm/415 similar to 455 nm) and visible fulvic-like acid (300 similar to 360/415, 455 nm)] humic-like acid (250 similar to 275, 340 similar to 370/455 nm) and protein-like [tryptophan-like (225, 275/330 345 nm) and tyrosine-like (220/303 nm)]. The fluorescence intensity and relative percentage of the three fluorescence components of DOM in the four treatments showed the same trend: fulvic-like acid and humic-like acid increased, and protein-like decreased; the total fluorescence intensity increased first and then decreased with the fermentation time, and finally tended to be stable; the maximum total fluorescence intensity appeared at the 15th day of the fermentation process, and the T3 humic-like acid has the highest fluorescence intensity and relative percentage among them. With the increase of straw proportion, the relative percentage of fluorescence components was protein-like>fulvic-like acid>humic-like acid. There was a significant positive correlation between fulvic-like acid and humic-like acid. Based on these, according to the DOM fluorescence spectroscopy characteristics, to improve the utilization rate of straw in the fermentation process, the ratio of straw and cow dung is 6 : 4, which can be used as the reference value of actual composting.

•Potential evapotranspiration is different from reference crop evapotranspiration•The development histories of these two kinds of evapotranspirations are described•The equations for calculating these two kinds of evapotranspirations are listed•The difference between these two kinds of evapotranspirations are compared

Remote sensing freely provides many processed image products such as moderate resolution imaging spectroradiometer (MODIS), and long-term data record (LTDR), for the investigation of drought evolution. Our objectives are to investigate drought evolution and spatiotemporal variations from 1982 to 2017 based on two remote-sensing indices, namely, the normalized difference vegetation index (NDVI) and the vegetation condition index (VCI), and a popular meteorological index—standardized precipitation index (SPI)—under four different land cover types, cropland, forestland, grassland, and desertland in China. The modified Mann–Kendall test was used to detect the significance of a trend. The Pearson correlation method was used to find the relationship between NDVI anomaly, VCI, precipitation, and SPI. The results revealed that (a) both mean monthly and yearly precipitation had a general land cover type rank of forestland > grassland ≈ cropland > desertland. (b) A positive correlation was found between drought indices (NDVI anomaly, VCI, SPI) and precipitation for different land cover types. The NDVI anomaly and VCI were well correlated with 3-month SPI for cropland and were well correlated with 6-month SPI for forestland. VCI performed better than NDVI anomaly when correlating with SPI. (c) The coefficient of determination (R2) was obtained for precipitation and VCI in the driest (2011) and wettest (2016) years. The R2 values for desert and grassland ranged from 0.70 to 0.90 and for cropland and forestland were lower (0.54–0.69). (d) Only precipitation, SPI, and VCI of cropland had significant increasing trends. The spatial distribution patterns of precipitation, NDVI, and VCI increased with the decreased elevation. The study revealed that desert and grassland had been regularly exposed to moderate or extreme droughts conditions and confirmed that desert and grassland are more sensitive to short-term drought.

Due to the small number of train samples, the classifier with ideal generalization ability for small sample size is not easy to obtain. However, the problem of constructing small sample classifier exists widely in the real world, especially in the field of biological medicine. Therefore, building a classifier based on small number of samples has become a research hotspot. In this study, we proposed a machine learning classifier based on statistical methods to solve this problem. In this method, Bootstrap, chi-square test and other statistical methods were firstly combined to solve the performance evaluation of multiple machine learning classifiers under small sample sizes dataset. Then, the application of Youden index in machine learning classifiers was optimized to meet the requirements of clinical application. The simulation experiment on the UCI breast cancer data set shows that this method is more stable and accurate for the performance evaluation, and at the same time，optimized Youden index in machine learning classifier is able to flexibly meet the application requirements of small number of samples in the medical research field.