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Coal combustion is the primary source of air pollution in China, especially the heavy metals (HMs) concentrated in the submicron particles. This paper discusses the enhancement of HMs absorption efficiencies during coal combustion experiments. By adding the modified Ca-based sorbents, the orthogonal design was used in this experiment. Combining with the analysis of variance and capturing rate of HMs, the optimal combination was arrived at. BP neural network model was established and trained using orthogonal capturing tests data to reach the best compositions. Confirmatory trial was conducted, thus the BP neural network model can be used to solve complex nonlinear optimization problems. [ABSTRACT FROM AUTHOR]

Purpose: Erosion processes spatially redistribute soil particles and the associated carbon across landscapes. Their spatial redistribution pattern is governed by the transport distances of individual displaced soil particles, which is not only dependent on their settling velocity, but also affected by slope topography. However, the potential impacts of fine-scale variation of slope topography on the erosion-induced lateral and carbon fluxes are often over-generalized by coarse digital elevation models. Material and methods: In this study, two topo-sequences, convex and concave, over a long gentle slope in the northeast China were investigated. Surface soils were sampled at predetermined space intervals from upslope to downslope along the two toposequences, and then fractionated by the settling velocity of individual fractions into four classes: > 250, 63 – 250, 20 – 63 and < 20 μm. The soil organic carbon (SOC) and δ13 C of the unfractionated soils and all the settling classes were measured, and their CO2 emission rates were also determined at six temperature gradients: 5°C, 10°C, 15°C, 20°C, 25°C and 30°C. Results and disucssion: Our results show that: 1) The soil fractions along the upper lying convex segment showed a coarsening effect toward the knee point and then a fining trend at the slope toe, whilst the soil compositions along the lower lying concave segment stayed fairly comparable as the slope descended. 2) The net loss of surface soil along the eroding convex segment resulted in depleted SOC and more positive δ13 C signatures than that along the depositional concave segment. 3) The CO2 emission rates of almost all the settling fractions were enhanced compared with that of the unfractionated soil, and the settling class-specific CO2 emission rates and their temperature sensitivity (Q10) also differed along the two topo-sequences. Conclusions: This demonstrates that fine scale topographic variations had a strong control over the lateral and vertical carbon fluxes, which has been often disguised by coarse grid size in digital elevation models or average sediment delivery ratios. Topography-dependency must be properly accounted for when calculating slope-scale carbon balances. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen (N) and precipitation are the main limiting factors in food production under rain-fed cropping systems in arid and semiarid regions. A long-term field experiment was conducted from 1984 to 2009 in the Changwu State Key Agro-Ecological Experimental Station of the Loess Plateau, China, to study interactions between precipitation and N fertilization. Winter wheat (Triticum aestivum L.) was grown with N fertilization at 0, 45, 90, 135, and 180kgNha−1. With 25-year N fertilization, soil organic carbon and total N were increased by 18% and 26%, respectively. Mean yields and precipitation use efficiency (PUE) levels with N fertilization were increased by onefold to twofold compared with unfertilized soils. Generally, during the period of 1984–2009, grain yields with 45–`180kgN ha−1 increased at the rate of 38–49kgha−1 year−1 (p <0.05), whereas PUE increased at the rate of 0.071–0.088kgmm−1 year−1. These increases over time are largely attributable to improvements in soil organic carbon and total N. Variations in yield were proportionally reduced by N fertilization, but heavily depended on the fluctuation of precipitation. Grain yields with 45–180kgN ha−1 decreased by approximately 10%–45% (p <0.05) in the dry years (drought index<−0.35) compared with the normal years, whereas significant increases were not detected in the wet years (drought index>0.35). Grain yields with 90–180kgN ha−1 were positively correlated (p <0.05) with fallow season precipitation, but insignificantly correlated with growing season precipitation. The optimum N fertilization rates in the dry, normal and wet years increased following an increasing sequence of 45, 135 and 180kgNha−1. These results have significant implications for optimizing N fertilization and maximizing yield and PUE in rain-fed cropping systems in arid and semiarid regions. [Copyright &y& Elsevier]

Aims: Concerns over food security and global climate change require an improved understanding of how to achieve optimal crop yields whilst minimizing net greenhouse gas emissions from agriculture. In the semi-arid Loess Plateau region of China, as elsewhere, fertilizer nitrogen (N) inputs are necessary to increase yields and improve local food security. Methods: In a dryland annual cropping system, we evaluated the effects of N fertilizers on crop yield, its long-term impact on soil organic carbon (SOC) concentrations and stock sizes, and the distribution of carbon (C) within various aggregate-size fractions. A current version (RothC) of the Rothamsted model for the turnover of organic C in soil was used to simulate changes in SOC. Five N application rates [0 (N0), 45 (N45), 90 (N90), 135 (N135), and 180 (N180) kg N ha] were applied to plots for 25 years (1984-2009) on a loam soil (Cumulic Haplustoll) at the Changwu State Key Agro-Ecological Experimental Station, Shaanxi, China. Results: Crop yield varied with year, but increased over time in the fertilized plots. Average annual grain yields were 1.15, 2.46, 3.11, 3.49, and 3.55 Mg ha with the increasing N application rates, respectively. Long-term N fertilizer application increased significantly ( P = 0.041) SOC concentrations and stocks in the 0-20 cm horizon. Each kilogram of fertilizer N applied increased SOC by 0.51 kg in the top soil from 1984 to 2009. Using RothC, the calculated annual inputs of plant C (in roots, stubble, root exudates, etc.) to the soil were 0.61, 0.74, 0.78, 0.86, and 0.97 Mg C ha year in N0, N45, N90, N135 and N180 treatments, respectively. The modeled turnover time of SOC (excluding inert organic C) in the continuous wheat cropping system was 26 years. The SOC accumulation rate was calculated to be 40.0, 48.0, 68.0, and 100.0 kg C ha year for the N45, N90, N135 and N180 treatments over 25 years, respectively. As aboveground biomass was removed, the increases in SOC stocks with higher N application are attributed to increased inputs of root biomass and root exudates. Increasing N application rates significantly improved C concentrations in the macroaggregate fractions (>1 mm). Conclusions: Applying N fertilizer is a sustainable practice, especially in carbon sequestration and crop productivity, for the semiarid Loess Plateau region. [ABSTRACT FROM AUTHOR]

Aerbuba was a Tibetan who defected to the Qing regime and was given an official Qing noble title. He played an active role in Qing\Tibetian relations during the reign of the Kangxi and Yongzheng Emperors. In 1728, Aerbuba was captured by the Tibetan leader Poluoding, taken to the the Lhasa Bamari Mountains, and put to death by dismemberment. Much research has been conducted on the family ties shared between Aerbuba and Suonuomudaerzha, the father of the 7th Dalai Lama Kelsang Gyatso. Using mutiple sources, this article sets out to prove that Suonumuderzha was Aerbuba’s aunt’s husband, contrary to the common belief that Suonumuderzha was Aerbuba’s biological uncle. [ABSTRACT FROM AUTHOR]

• Soil and nutrient redistribution caused localized land degradation. • The SOC and TN were halved on the sloped cropland compared to the nearby tree rows. • Atomic ratios of C:N:P differed as the slope curvatures diverted. • Minor geomorphic features govern localized biochemical cycling of major nutrients. • Topography-specific conservation practices must be integrated to local land use policy. Erosion-induced land degradation in the northeastern China, the Chinese breadbasket, has become one of the biggest risks to national food security. Apart from depleting topsoil, incising gullies, and waterlogging depositional sites, slope-scale erosion also spatially redistributes soil nutrients and introduces localized soil degradation. This requires to systematically understanding topography-specific spatial distribution patterns of eroded soil compositions and the relative abundance of each nutrient at different topographic settings. In this study, topsoil at predetermined space intervals were collected from two adjacent but differently curved segments (convex vs. concave) on a sloped cropland in northeastern China. The spatial distributions of topsoil soil organic carbon (SOC), total nitrogen (TN), total phosphorous (TP), and the variations of their atomic ratios were compared. Our results show that: (1) Compared with the nearby undisturbed tree rows, the SOC and TN was halved on the investigated slope, demonstrating great degradation since the land use conversion. (2) The spatial distribution of topsoil nutrients were evidently topography specific, with the SOC being comparable at slope summit, but declining from 27.57 to 4.72 g kg−1 (depletion ratio of 0.17) at the convex segment meanwhile accumulating up to 34.71 g kg−1 (enrichment ratio of 1.26) at the concave segment. Similar but more deviated spatial patterns were also observed on the TN and TP. (3) The atomic ratios of C:N:P also differed as the slope curvatures diverted, by being more variable from 51:3:1 to 105:6:1 along the convex segment but rather stable between 74:5:1 and 89:5:1 along the concave segment. (4) The lower content of SOC and the heavier δ 13C along the convex segment suggest more advanced mineralization of C and thus greater susceptibility of C-limitation. Meanwhile, the slightly lower C:N ratios and the greater δ 15N along the concave segment indicate greater stability of C, more advanced mineralization of N and thus likely a N-limited process. Overall, our findings demonstrate the controlling influences of minor geomorphic features to on-site soil dislocation and localized degradation at slope scale. Apart from general soil conservation measures, topography-specific practices must also be integrated to local land use policy to effectively target localized land degradation. [ABSTRACT FROM AUTHOR]

Abstract Soil erosion influences both lateral soil organic carbon (SOC) re-distribution and vertical soil CO 2 emissions. While potential SOC mineralization during transport and the burial effects of SOC at depositional sites have been addressed in previous reports, erosion induced on-site CO 2 emissions are still under-studied. In this study, two soils (Loess soil and Black soil) with similar texture but contrasting aggregate structure and SOC content were subject to a set of 60-min long simulated rainfall events. There were two different rainfall intensities (30 and 90 mm h−1) at three slope gradients (5°, 15° and 25°). Runoff and sediment from erosion plot were collected at 10-min intervals over 60 min. Soil CO 2 emissions from eroding slopes, SOC and particle size distribution of the eroding soil were measured after the erosion events. The results show that the runoff rates from the two soils were comparable, but the sediment rates from the Loess soil roughly three times that from the Black soil. In general, the SOC erosion from the Loess soil was 1.8 times that from the Black soil, even though the SOC concentration in the original Black soil was 56% higher than the Loess soil. The cumulative soil CO 2 emissions from the eroding slopes of the Loess soil ranged from 15.4 to 19.7 g C m−2, which was doubled on the Black soil (from 28.1 to 59.6 g C m−2). When the rainfall intensity raised from 30 mm h−1 to 90 mm h−1, the cumulative soil CO 2 emissions from the Black soil decreased by 38.2%, but only declined by 10.0% on the Loess soil. When the slope gradient increased from 5° to 25°, the cumulative soil CO 2 emissions decreased by 23.8% on the Black soil but by 12.6% on the Loess soil. Therefore, our observations suggest that the soil CO 2 emissions on the Black soil was much more sensitive to the variations of rainfall intensity and slope gradients than the Loess soil. Greater SOC erosion should not be directly translated to less on-site soil CO 2 emissions. The selective depletion/enrichment of SOC and the lability of individual components must be fully understood when accounting for slope-scale carbon balances. Highlights • Loess soil has lower SOC content but greater SOC erosion than Black soil. • On-site soil CO 2 emissions on Black soil decreased with erosion intensity. • On-site soil CO 2 emissions on Loess soil barely changed with erosion intensity. • Greater SOC erosion does not mean less on-site soil CO 2 emissions. • On-site CO 2 emissions from Black soil may not be regulated by erosional removal but by inherent SOC. [ABSTRACT FROM AUTHOR]

The influence of vegetation coverage and topography on soil organic carbon (SOC) stocks has been intensively studies. However, very few of the studies have recognized the potential combining effects of vegetation types and topographic positions onto SOC distribution, especially on the Chinese Loess Plateau where vegetation recovery has generated complex combination of fragmented topography and vegetation coverage. This study systematically sampled soil cores (259) from four vegetation types (woodland, grassland, cropland, and orchard) at three topographic positions (tableland, slope and valley bottom). Each soil core was divided into three layers: surface soil (0–20 cm), subsoil (20–60 cm) and deep soil (60–200 cm). Our results show that: (1) the SOC concentration declined over soil depths, regardless topographic positions or vegetation types. The absence of ancient cultivation layers at the valley bottoms further made the SOC stocks deep to 200 cm there much less than the tableland with thick loess soil layers (8.3 kg km –2 vs. 13.4 kg km –2 ). (2) The SOC concentration of cropland varied evidently with topographic positions, with the greatest on the tableland (8.0 g kg –1 ), and the least along the slope (5.3 g kg –1 ). However, grassland was rather stable across the three topographic positions. (3) In addition, the SOC concentrations of the three vegetation types were comparable on the tableland (6.1 g kg –1 ), while differed noticeably at the valley bottoms (5.0 g kg –1 ). Overall, our findings in this study call for the account for each combination of topographic position and vegetation type, so as to properly assess regional SOC stocks for sustainable land use. [ABSTRACT FROM AUTHOR]

Microbial community composition differs between soil aggregate sizes, which markedly affects phosphorus cycling in agroecosystems. The genes phoD and pqqC regulate phosphorus mobilization and act as molecular markers of phosphate-mobilizing bacteria, but differences in phoD - and pqqC -harbouring bacterial communities between different-sized aggregates remain unclear. The abundance and community composition of phoD - and pqqC -harbouring bacteria were determined in three aggregate size classes (> 250, 63–250, and < 63 µm) in calcareous soil from northwest China in a 38-year experiment. The > 250 and < 63 µm aggregates showed the lowest and highest cumulative relative abundance, respectively, of operational taxonomic units in phoD - and pqqC -harbouring bacterial communities. Simpler co-occurrence networks (fewer nodes, links, and shorter network diameter) were found in > 250 and < 63 µm aggregates, compared to 63–250 µm aggregates. For phoD and pqqC gene networks, > 250 and < 63 µm aggregates (phoD : α-Proteobacteria and Actinomycetia; pqqC : Actinomycetia) contained keystone taxa distinct from 63 to 250 µm aggregates (phoD : Rubrobacteria and γ-Proteobacteria; pqqC : β-Proteobacteria). Total nitrogen (TN) and Olsen-P significantly affected the abundance and community richness of phoD - and pqqC -harbouring bacteria. phoD and pqqC gene abundance was determined by TN in > 250 µm aggregates, whereas they were indirectly determined by Olsen-P in < 63 µm aggregates. Our results emphasized the distinct distribution characteristics of phosphate-mobilizing bacterial communities in different-sized aggregates and identified the main factors regulating phoD and pqqC gene abundance. • phoD and pqqC bacterial communities differed among soil aggregate sizes. • Different keystone taxa of phoD and pqqC were found between soil aggregate sizes. • TN regulate the gene abundances of phoD and pqqC in >250 µm aggregates. • Olsen-P regulate the gene abundances of phoD and pqqC in < 63 µm aggregates. [ABSTRACT FROM AUTHOR]

As the essential driving force of soil redistribution, runoff and sediment are not often considered when quantifying and integrating the effects of soil erosion and deposition on soil CO 2 emissions. Therefore, in this study, variations in soil CO 2 emissions from erosion-deposition plots were regularly monitored in China's Loess Plateau (2015–2019). The cumulative soil CO 2 emissions from the depositional zones with slope gradients of 5°, 10°, and 20° were increased by 0.4–16.7%, 20.1–32.6%, and 31.9–51.5%, respectively, than those of their respective eroding slopes. Relative to the 5° eroding slopes, the cumulative soil CO 2 emissions decreased by 2.8–13.5% and 11.3–15.6% on the steeper 10° and 20° eroding slopes, respectively. Conversely, cumulative soil CO 2 emissions increased by 1.0–7.9% and 6.9–13.3% in the depositional zones of 10° and 20°, respectively, as compared with that in the 5° depositional zones. Considering both the eroding slopes and depositional zones, the total amount of CO 2 emissions from the 10° and 20° erosion-deposition plots were 114 g CO 2 -C y−1 and 177 g CO 2 -C y−1 lower than those from the 5° erosion-deposition plots, respectively. This can be attributed to the combined effects of the amounts of runoff and sediment displacement on soil CO 2 emissions from eroding slopes and depositional zones. Our results indicate that, soil erosion and deposition together have great potential to mitigate soil organic carbon mineralization and preserve soil carbon pools in slope lands. Furthermore, soil organic carbon mineralization at the slope scale is sensitive to displaced runoff and sediment. Therefore, possible variations in soil-atmospheric carbon exchanges induced by erosion-displaced runoff and sediment should be properly accounted for when attributing carbon fluxes in regions dominated by sloping landscapes. • Soil CO 2 emissions on eroding slopes were lower than that in the depositional zones. • Increasing slope gradients exacerbated the reduction of soil CO 2 emissions on eroding slopes. • Soil CO 2 emissions in the depositional zones enhanced by increasing slopes gradients. • Total soil CO 2 emissions from the whole erosion-deposition plots decreased as slopes steepened. [ABSTRACT FROM AUTHOR]

• Enzyme activity decreased by erosion leading to an increase in the depositional plot. • Slope enhanced the difference in enzyme activity between the erosional and depositional plot. • Enzyme activity mitigated total soil CO 2 emission in the erosion-deposition plots. Soil C-acquiring enzymes are good indicators for the biological mechanism of soil nutrients and organic matter cycles. However, they have been used less frequently to assess the ecological stability and soil C cycle in eroding landscapes due to a lack of knowledge of the responses of C-acquiring enzyme activities to soil erosion and deposition. In the present study, a 3-year field simulation experiment was conducted to examine the variations in the activities of C-acquiring enzymes (β-1,4-xylosidase (βX), β-1,4-glucosidase (βG) and β-D-cellobiohydrolase (CBH)) from erosion-deposition plots with different slope gradients (5°, 10° and 20°) on the Loess Plateau in China (2016–2018). The activities of βX, βG and CBH were higher in the depositional plots than in the erosional plots, and those differences were enlarged with increasing slope gradients. Compared to the 5°-erosional plot, the activities of βX, βG and CBH respectively declined by 3.2–4.5%, 14.3–37.5% and 12.7–29.1% in the 10°-and 20°-erosional plots. The βX, βG and CBH activities were 2.2–18.1%, 17.3–32.1% and 14.8–86.2% higher in the 10°- and 20°-depositional plots than in the 5°-depositional plot. Moreover, the total soil CO 2 emissions from the whole erosion-deposition plots decreased as slopes steepened. The displaced runoff and sediment depleted soil moisture, SOC, clay and microbial biomass in the erosional plots but enhanced these resources in the depositional plots, which can account for the changes in C-acquiring enzyme activities. The spatial distribution of enzyme activities affected soil CO 2 emissions in a positive linear function. The sensitive responses of the C-acquiring enzyme activities and the controlling effects of C-acquiring enzyme activities on soil CO 2 emissions during erosion and deposition processes, should be properly considered in assessing the biological mechanism for nutrition cycling in regions predominated with fragmented eroding landscapes. [ABSTRACT FROM AUTHOR]

• Topsoil removal decreased C sequestration in soil-plant ecosystems. • Topsoil addition increased C sequestration in soil-plant ecosystems. • Soil redistribution reduced integrated C sequestration in soil-plant ecosystems. Soil redistribution is an important movement process of surface material that drastically affects the dynamic cycling of essential elements and soil productivity in the terrestrial ecosystem. Although a number of studies have focused on the soil organic carbon (SOC) pool under soil redistribution, few studies have comprehensively assessed the effects of soil redistribution on the ecosystem carbon pool. A five-year experiment of simulated topsoil redistribution (removal and addition, R-A) was conducted to explore the effects of soil redistribution on soil CO 2 emissions, the SOC pool and the plant C pool in the semi-arid Loess Plateau of China. The soil properties, soil CO 2 emissions, and crop parameters were measured after the topsoil removal (R 20) treatment and topsoil addition (A 20) treatment and in the undisturbed control (CK). Our results showed that 1) compared with the undisturbed control, the mean soil CO 2 emissions of the R-A treatment decreased by 8% while the mean SOC pool increased by 3.0%; 2) the plant C pool was significantly reduced by 53.8% in 2015 and 5.8% in 2019 compared with the undisturbed control; 3) the ecosystem C pool (the sum of the SOC pool and plant C pool) of the R-A treatment was reduced by 10.3%, 3.7% and 1.1% compared with the ecosystem C pool of the undisturbed CK for 2015, 2016 and 2017, respectively, but increased by 0.6% and 1.9% from 2018 to 2019. During the first three experimental years, the decrease in the ecosystem C pool of the R-A treatment was caused by the reduced plant C pool in R 20 exceeding the elevated plant C pool in A 20. Over time, the soil bulk density (BD) decreased in R 20 and the SOC, microbial biomass carbon (SMBC) and total nitrogen (TN) increased, which jointly improved the plant C pool in R 20 and the ecosystem C pool by 2019. The gradual recovering pattern of the ecosystem C pool in the later years highlights the key role of plants in restoring soil properties and stabilizing ecosystem C cycling. Overall, our findings highlight that any attempt to assess the net impacts of soil redistribution, whether as a sink or source for atmospheric CO 2 , should comprehensively consider the changes in the SOC pool and plant C pool. [ABSTRACT FROM AUTHOR]

• Bacterial alpha diversity was increased by deposition but not changed by erosion. • Erosion altered bacterial community structure but deposition did not. • Bacterial co-occurrence network was more complex at depositional than eroding site. Soil erosion and deposition occur widely from regional to global scales and have profound impacts on ecological services and sustainability. Despite their crucial roles in biogeochemical cycles, the responses of soil bacterial communities to soil erosion and deposition remain largely unclear. In this study, a field simulation experiment was conducted to examine variation in soil bacterial communities across eroding slopes and depositional zones with three slope gradients (5°, 10° and 20°) on the Loess Plateau of China (2015–2017). The results showed that soil physicochemical properties were altered by redistribution of runoff and sediment across eroding slopes and depositional zones. Soil bacterial alpha diversity was higher in the depositional zones of both 10° and 20° slopes compared with the 5° reference slopes but no markedly difference was found between eroding slopes and reference slopes. By contrast, bacterial community structure differed between eroding slopes and reference slopes but not between depositional zones and reference slopes. Differentiation of bacterial communities between eroding slopes and depositional zones increased with increasing slope gradients. The bacterial network was greater and more complex within depositional zone than eroding slope, indicating more extensive bacterial interactions and greater community stability potential. Erosion- and deposition-induced redistribution of soil moisture, soil organic matter, available P, and available K were the key determinants of variation in bacterial community structure. Our findings demonstrate the contrasting effects of soil erosion and deposition on soil bacterial communities, which should be given further attention across eroding landscapes. [ABSTRACT FROM AUTHOR]