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A less invasive and more convenient workflow is needed for dynamic navigation-guided implant surgery for the edentulous arch. The purpose of this in vitro study was to evaluate the accuracy of a novel dynamic navigation device developed for the completely edentulous mandible. Two temporary 1-piece mini-implants were placed in the anterior region of a completely edentulous mandibular model for fixation of the navigation device. A total of 40 implants were inserted in 10 completely edentulous mandibular models with the aid of the dynamic navigation device. The accuracy of placement was determined by overlapping the preoperative plan with the postoperative cone beam computed tomography (CBCT) scans. The difference in the accuracy at different implant positions was compared by MANOVA and Bonferroni-corrected ANOVAs. The difference in accuracy between implants #1-20 and #21-40 was assessed for learning progression. The deviation of the implants (mean ±standard deviation) was 1.14 ±0.50 mm at the entry point and 1.29 ±0.48 mm at the apex. The mean ±standard deviation angular deviation was 3.02 ±1.32 degrees. No significant difference was seen between the planned and the placed deviation among the 4 implant positions. After repeated placement with this dynamic approach, implant accuracy at the entry (P =.001) and apex (P =.017) improved significantly. The navigation device achieved acceptable implant placement accuracy in the edentulous mandible. Deviations between the planned and placed locations were not affected by different implant positions. After repeated operations with this dynamic approach, accuracy at the entry and apex improved significantly. [ABSTRACT FROM AUTHOR]

Implant placement in the pterygoid region is a reliable treatment for posterior maxillary tooth loss. However, the surgery is not widely applied because the implant placement region is hard to access and the direct visual access is limited. This clinical report describes the use of a dynamic navigation system to improve the pterygoid implant placement surgery. Real-time imaging of the surgery area and full-time guidance are provided by the system to alleviate the problem of lack of visibility and to reduce the complexity of placement. [ABSTRACT FROM AUTHOR]

Highlights • Converting grassland to shrubland increased soil N availability and mineralization. • The positive effect on soil mineral N was higher in lower slope than upper slope. • The positive effect on soil mineral N was similar across soil textures. • The effect on net N mineralization varied with slope position and soil texture. Abstract Grassland afforestation, which is a major form of land-use change, has expanded considerably in the last few decades. However, the effect of conversion from grassland to shrubland on soil nitrogen (N) cycling and availability with regard to soil textures and slope positions is unclear. This lack of clarity has hindered our understanding of how grassland afforestation influences soil N availability and transformation on a larger spatial scale. In this study, we compared the net N mineralization rates and mineral N concentrations in soils from native grassland and under legume shrub (Caragana korshinskii Kom.) with contrasting soil textures (sandy-loam vs. loamy-sand) and slope positions (upper vs. lower) in the northern region of China's Loess Plateau. The objective of this study is to understand how soil texture and slope position regulate the response of soil N cycling to grassland afforestation. The results showed that the concentrations of soil nitrate and total mineral N and the rates of net nitrification and mineralization were higher in soils under shrub (0.64 ± 0.10 g N m−2, 1.01 ± 0.11 g N m−2, 23.19 ± 5.22 mg N m−2 d-1 and 22.07 ± 5.44 mg N m−2 d-1) than in grassland (0.22 ± 0.03 g N m−2, 0.56 ± 0.04 g N m−2, 1.48 ± 1.51 mg N m−2 d-1 and 1.36 ± 1.96 mg N m−2 d-1). However, soil ammonium concentration and net ammonification rate were not affected by grassland afforestation. The effect of afforestation on nitrate and total mineral N concentrations was greater in the lower slope than in the upper slope but was similar between the sandy-loam and loamy-sand soils. The effect of this land-use change on net nitrification and mineralization rates varied with soil texture and slope position, with greater effects in the upper slope than in the lower slope in more clayey soils, but with the opposite influencing pattern in more sandy soils. These results suggested that planting C. korshinskii in grassland ecosystems increased soil N mineralization and availability. More importantly, soil texture and slope position should be considered when assessing the effects of grassland afforestation in complex landscape conditions. [ABSTRACT FROM AUTHOR]

Abstract The creation of "fertile islands" beneath shrubs in dryland ecosystems has been widely reported worldwide and is the major factor influencing ecosystem structure and function. However, studies investigating whether and how shrubs affect soil biogeochemical cycles in deep soil layers are relatively limited. In this study, we examined the vertical distribution of the soil nutrient contents and enzymatic activities at the 0–100 cm soil profiles beneath three common xerophytic shrubs (Artemisia ordosica , Caragana korshinskii and Salix psammophila) and in interspace bare soils in a transition zone from desert to loess in the north of China. The soil metrics included the contents of organic carbon, total nitrogen, total phosphorus, nitrate and ammonium nitrogen, available phosphorus and potassium, and the activities of saccharase, urease, alkaline phosphatase and amylase. We found that the contents of organic carbon, total nitrogen and available potassium, and the activities of saccharase, urease and alkaline phosphatase were higher in the soils beneath shrubs than in the interspace bare areas, but these differences only occurred in the 0–10 cm soil profile but not in the soils below the depth of 10 cm. The soil quality index was consistently improved among the three shrub species in the topsoil. In addition, the soil nutrients were positively correlated with enzymatic activities, and the organic carbon content explained approximately 50% of the variations in the enzymatic activities. Collectively, our results demonstrated that the establishment of xerophytic shrubs improved the soil chemical and biological conditions in the desert-loess transition region, and the effect was restricted to the 0–10 cm soil layer. Highlights • Xerophytic shrubs significantly increased soil nutrient contents and enzymatic activities. • Effects of shrubs on soil nutrients and enzyme activities occurred at 0–10 cm depth. • Soil quality index was similar among A. ordosica , C. korshinskii and S. psammophila. • Soil nutrient contents were positively correlated with enzymatic activities. • Organic carbon explained ~50% of the variations in enzymatic activities. [ABSTRACT FROM AUTHOR]

Abstract Shrubs play a vital role in ecosystem restoration in the desert transition zone, which suffers intensive desertification, land degradation, and nitrogen (N) limitation. To evaluate the effects of different shrub species on soil N availability, transformation, and their seasonal dynamics, we determined mineral N contents and mineralization rates in soils under three common shrub species (Artemisia ordosica Krasch., Caragana korshinskii Kom., and Salix psammophila C.) and in bare land during the growing season in the desert-loess transition zone in northwestern China. The average contents of soil nitrate N and mineral N were 153% and 55% greater, respectively, and cumulative net N nitrification and mineralization were 101.2 and 121.0 mg N m−2 higher, respectively, in soils beneath C. korshinskii than in bare land (P < 0.05) at the 0–10 cm depth over the growing season. The net N mineralization rate in 0–10 cm depth was significantly higher in soils under C. korshinskii than that in bare land during 21 Jun-23 Jul and 23 Aug-15 Oct of the growing season. However, C. korshinskii did not influence soil N metrics at the 10–20 cm depth. The incorporation of A. ordosica and S. psammophila into bare land did not influence soil N availability or transformation rates. Our results demonstrated that C. korshinskii was more preferable than A. ordosica and S. psammophila in ameliorating soil N cycling in the desert-loess transition zone. Highlights • Xeric shrub species: Artemisia ordosica , Caragana korshinskii , Salix psammophila • The fragile transition zone between the desert and the Loess Plateau of China • C. korshinskii increased mineral N content and net N mineralization rate • Effects of C. korshinskii were greater in dry and cold period and the 0–10 cm soil. • A. ordosica and S. psammophila did not influence soil N mineralization. [ABSTRACT FROM AUTHOR]

Abstract The presence of vegetation has significant effects on soil nitrogen (N) turnover. However, whether these effects vary with slope aspect, vegetation type and time of season were not understood in previous studies, precluding our ability to understand how vegetation affects soil N cycling in sloping land. In this study, we investigated the effects of vegetation presence (plots with vs. without vegetation), vegetation type (grassland vs. woodland) and slope aspect (east vs. west slope) on soil N turnover during the growing season in sloping lands of the Loess Plateau, China. Soil metrics measured included concentrations of ammonium (NH 4 +), nitrate (NO 3 −) and total mineral N (Min-N) in soil solution and rates of ammonification (R a), nitrification (R n) and net N mineralization (R m). We hypothesized that the presence of vegetation would deplete the soil Min-N pool and decrease R m and that these effects would be greater in east slopes and woodlands than in west slopes and grasslands. In partial support of these hypotheses, vegetation presence decreased soil Min-N concentration but did not affect R m. NH 4 + and NO 3 − contributed similarly to Min-N, while R n dominated R m. The effects of vegetation presence on soil mineral N and N mineralization varied with the time of the season but were not related to the vegetation type and slope aspect. The soil Min-N and R m were significantly higher in woodlands, east slopes and 0–10 cm depth than grasslands, west slopes and 10–20 cm depth, respectively. The R a and NH 4 + increased, while the R n , R m , NO 3 − and Min-N decreased with increasing soil moisture. These results indicated that soil Min-N and R m in the sloping lands of the Loess Plateau consistently respond to vegetation presence across slope aspect and vegetation type, and were regulated by soil moisture. Highlights • Vegetation decreased soil inorganic N pool because of plant uptake. • Effects of vegetation presence (plots with vs. without vegetation) on soil mineral N and N mineralization varied with season. • Effects of vegetation presence on N turnover were irrespective to vegetation type and slope aspect. • Soil mineral N pool and mineralization rate were higher in woodland and east than grassland and west slope. [ABSTRACT FROM AUTHOR]

Soil erosion can dramatically alter soil nitrogen (N) cycling, but it has rarely been examined under in-situ conditions due to the complicated interaction between erosion and vegetation. Comparing the effects of vegetation presence at eroding and depositional sites would provide a direct understanding of such effects. Herein, we investigated how soil N dynamics (mineral N pools and net N mineralization rates) responded to vegetation presence (plot with vs. without vegetation), landscape position (eroding vs. depositional sites) and vegetation type (grassland vs. woodland) during a two-year manipulation experiment using an in-situ incubation method in the hilly-gully region of China's Loess Plateau. The results showed that soils on eroding site had higher concentrations of nitrate (3.820 ± 0.302 vs. 2.642 ± 0.280 mg kg-1) and mineral N (5.853 ± 0.320 vs. 4.308 ± 0.287 mg kg-1) but similar rates of net nitrification (0.057 ± 0.013 vs. 0.051 ± 0.011 mg kg-1 d-1) and mineralization (0.056 ± 0.014 vs. 0.056 ± 0.013 mg kg-1 d-1) in comparison to depositional site in all grassland plots. The concentrations of soil nitrate and mineral N and rates of net nitrification and mineralization in legume woodland were 26%, 19%, 88% and 64% higher than that in grassland in all slope plots, respectively. Although vegetation presence significantly decreased soil nitrate (−57%) and total mineral N (−27%) concentrations, it did not affect the rates of net nitrification and mineralization. The effects of vegetation presence on soil net N mineralization occurred irrespective of landscape position and vegetation type(P > 0.05), but varied with season or year, with greater effects in 2017 growing season than in the non-growing season and 2018 growing season. Redundancy analysis and hierarchical partitioning indicated that the above- and blow-ground biomass accounted for most of the variation in soil N mineralization. These results suggested that the variations in soil mineral N and net N mineralization in relation to vegetation presence in this eroding watershed were consistent across different landscape positions and vegetation types, but showed intra- and inter-annual variability. • Vegetation presence decreased soil mineral N pools because of plant uptake. • Soil mineral N concentrations in eroding site were higher than deposition site for the grassland. • Soil mineral N and mineralization rates were higher in woodland than grassland for the eroding sites. • Effects of vegetation presence on soil mineral N and mineralization rates were irrespective to landscape position and vegetation type, but varied with season or year. [ABSTRACT FROM AUTHOR]

Re-vegetation of cropland is an important measure for carbon (C) sequestration, while the combined effects of land-use change, re-vegetation type and time on soil organic C (OC) turnover and temperature sensitivity have been less studied. Here, we investigated soil cumulative OC mineralization (C min), specific OC mineralization (C min /C 0 , normalized by initial OC) and temperature sensitivity (Q 10) with an 84-d incubation experiment after the conversion of cropland to artificial grassland (6, 10, 15 and 20 yr), to natural grassland (6, 10 and 20 yr) and to pea shrub woodland (10, 20 and 40 yr) in the agro-pastoral ecotone of northern China. Results showed that re-vegetation significantly increased C min (from 38.21 to 57.79 mg kg−1 soil, +51%) at the 0–10 cm depth but not the 10–20 cm depth, with greater increases after the conversion of cropland to artificial grassland (+77%) than the other two patterns but similar among different conversion years for each pattern. Variations in C min among different re-vegetation patterns and times were mostly explained by changes in total nitrogen concentration (TN) in the macro-aggregate fraction. Across all treatments, 6.20–20.29 g kg−1 OC was mineralized during the incubation and Q 10 was 1.16–2.40. The C min /C 0 and Q 10 changed not significantly during the post-agricultural re-vegetation chronosequences for each pattern, which were mostly due to the unchanged TN concentration in silt and clay fraction. Re-vegetation also changed the dependence of C min , C min /C 0 on N availability, with significant relationships in re-vegetated artificial grassland and pea shrub woodland which may due to the influence of legumes on microbes. In conclusion, OC mineralization increased with conversion, varying by re-vegetation type, while OC decomposability and temperature sensitivity were stable regardless of re-vegetation type and time, indicating the similar biodegradability and stability in face of warming. • OC mineralization and Q 10 were tested in varied re-vegetation types and times. • Cropland re-vegetation increased C min especially for artificial grassland. • •N in macro-aggregate explained about 50% of cumulative OC mineralization. • •OC biodegradability and Q 10 were similar during the post agricultural restoration. [ABSTRACT FROM AUTHOR]

• We investigated soil physical and hydraulic properties across a cultivation chronosequence. • A greater decrease in aggregate stability was found in cropland after long-term cultivation. • Long-term cultivation partially improved deep soil bulk density, porosity, field capacity and K s. • The parameters of soil water retention curve were unaffected by the cultivation time. Black soils (Mollisols) are inherently productive and fertile but are deteriorating due to long-term intensive cultivation. Understanding the changes in soil physical and hydraulic properties in topsoils and deep soils after converting forest to cropland would reveal the mechanism related to the black soil degradation. Herein, we investigated the variations in the soil water-stable aggregates, soil water content, bulk density, field capacity, total porosity, saturated hydraulic conductivity, and parameters of soil water retention curve at the 0–100 cm depth in four sampling fields. These fields included a forest as control and three croplands that were converted from forest 41, 50 and 65 years ago in the black soil region of Northeast China. We showed that converting forest to cropland decreased >2 mm aggregates and aggregate stability especially at 0–15 and 70–100 cm depths, with a greater decrease in cropland after relatively longer time of cultivation. Conversion of forest to cropland significantly decreased the soil water content at the 0–15 cm depth but increased it at the 15–100 cm depth, and the increase in the 50–100 cm soil layer was strengthened with cultivation time. The decreases in field capacity, total porosity and saturated hydraulic conductivity and increase in bulk density at the 0–50 cm depth following the conversion of forest to cropland were higher after 41 and 50 years of cultivation than those after 65 years of cultivation. However, changes in these metrics at the 50–100 cm depth increased with cultivation time. The parameters (i.e., θ r , θ s , α and n) of the soil water retention curve were not affected by the cultivation time after converting forest to cropland. These results highlighted that long-term cultivation after the conversion of forest to cropland resulted in the changes in soil physical and hydraulic properties in the 0–100 cm soil profiles, and thus, the response of deep soils should not be ignored in this black soil region. [ABSTRACT FROM AUTHOR]

Deforestation can lead to severe losses of soil nutrients. However, the impacts of the slope morphology and position on the spatial distributions of soil nutrients after deforestation and their relationships are unclear, thereby limiting our understanding of the mechanism of soil degradation. In this study, we aimed to identify the relationships between the changes in soil nutrients and the slope morphology (i.e., slopes with different widths or lengths) after deforestation. Soil samples were collected from forestland slopes with different morphologies after deforestation for 28 years in the hilly area of the Loess Plateau, China. We analyzed the effects of the length, width, and position of the slope on the pH, soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), nitrate-N (NO 3 −), ammonium-N (NH 4 +), available phosphorus (AP), and available potassium (AK) distributions after deforestation. The spatial autocorrelation analysis indicated that the Moran's I index value for soil nutrients was larger on deforested slope than that of forest land, thereby suggesting that deforestation increased the spatial heterogeneity of the soil nutrients. After deforestation, the spatial autocorrelation distances increased for the soil pH and TP, whereas they decreased for SOC, TN, NH 4 +, NO 3 −, and AK. The TN, NH 4 +, and NO 3 − contents were significantly higher on the narrow slope than the wide slope. Among the three slope lengths, the soil nutrient losses were greater on the longer slope because of the more severe erosion of the slope after deforestation. The slope position significantly affected the distributions of the soil nutrients. In the vertical direction, the soil nutrient contents decreased continuously in the 0–10, 10–20, and 20–40 cm soil layers, but then increased in the 40–60 cm soil layers, mainly due to the eluviation of nutrients to deep soil layers. These results demonstrate that the slope morphology and position should not be overlooked when predicting the responses of soil nutrients to deforestation in the hilly loess region of China. • Deforestation changed the spatial distributions of the soil nutrients on the slope. • The nutrient contents were higher on the narrow slope than the wide and medium slopes. • Among the three slope lengths, the soil nutrient losses were greater on the longer slope. • Slope morphology and position should not be overlooked when predicting the responses of soil nutrients to reclamation. [ABSTRACT FROM AUTHOR]

Soil nitrogen (N) mineralization is an important ecological process influencing N availability and ecosystem functionality, and is sensitive to vegetation presence and soil erosion. However, how vegetation presence affects N mineralization and its response to erosion has not been directly examined, hindering our ability to predict N cycling in eroding environments. Herein, we compared the effect of vegetation presence on N mineralization and mineral N dynamics in two growing seasons between erosion vs. deposition sites in three sub-watersheds in the transition zone between water erosion and wind erosion of North China. We aim to examine how soil N cycling responds to erosion and vegetation presence at temporal and spatial scales. The mineral N concentration in the soil solution and mineralization rates between May 2017 and October 2018 in plots with and without vegetation were measured to assess the effects of vegetation presence. We showed that N mineralization rates did not significantly vary among the three sub-watersheds or between erosion and deposition sites. The concentrations of mineral N in the soil solution were higher in relatively larger sub-watersheds for the erosion sites and in smaller sub-watersheds for the deposition sites. Vegetation decreased soil NO 3 --N and total mineral N and increased NH 4 +-N concentrations in the early and middle periods of the growing season. The effects of vegetation presence on net N mineralization rates varied with size of sub-watersheds, with increased rates of net nitrification and mineralization at both deposition and erosion sites in relatively larger sub-watershed, but reduced rates of net nitrification and mineralization in smaller sub-watersheds. Moreover, the presence of vegetation shifted the seasonal pattern of N mineralization. Therefore, vegetation presence had important ecological regulation on soil N cycling at spatial and temporal scales in the transition zone between water erosion and wind erosion. • Soil mineral N varied with sub-watershed scales and landscape positions. • Vegetation decreased nitrate and total mineral N but increased ammonium. • The effects of vegetation on N mineralization varied with sub-watershed scales. • Vegetation presence shifted the seasonal pattern of N mineralization. [ABSTRACT FROM AUTHOR]

Cultivation after the converting natural ecosystems to agricultural land is often accompanied by accelerated soil erosion. To better understand how land-use conversion and agricultural erosion separately affect aggregate-associated nitrogen (N) and organic carbon (OC), we examined the responses of aggregate-associated N and OC to both the converting forest to agricultural land and erosion in the agricultural region of Northeast China. Non-erosion sites in forest and agricultural land converted from forestland 60 years ago were selected to address the effects of land-use change. The sites with various erosion intensities in an eroding area of sloping cropland (i.e., non-erosion, light erosion, moderate erosion and heavy erosion) were selected to compare the effects of the erosion intensity. The measured soil metrics included the soil bulk density, water-stable aggregates, and aggregate-associated OC and N along 0–70 cm soil profiles. Converting forest to agricultural land did not significantly influence the OC and N concentrations in each aggregate, while the land-use change significantly reduced the OC and N stocks in macroaggregates but increased them in microaggregates and silt+clay fraction. However, erosion significantly decreased the OC and N concentrations and stocks in each aggregate. The changes in the OC and N stocks in aggregates were mainly due to the depletion of soil aggregates in responding to the conversion of forest to agricultural land but due to decreases in OC and N concentrations in aggregates in responding to soil erosion. Our results indicated that the effects of erosion on aggregate-associated OC and N were greater compared with the effects of converting forest to agricultural land in this Mollisol region. • Land-use change didn't significantly affect OC and N concentrations in aggregates. • Erosion decreased OC and N concentrations in aggregates. • OC and N stocks in aggregates were determined by their concentrations during erosion. • OC and N stocks in aggregates were dominated by aggregates mass following land-use change. [ABSTRACT FROM AUTHOR]

• Afforestation increased significantly soil OC and N mineralization. • The increase of OC and N mineralization were larger in sites with high clay content. • The temperature sensitivity decreased in sites with relative high clay content. • Soil texture regulated OC and N mineralization and their temperature sensitivity. Afforestation on abandoned cropland has great potential to increase soil organic carbon (OC) and nitrogen (N). Identifying the effect of afforestation on mineralization of OC and N as well as their temperature sensitivity at large spatial and temporal scales is essential to understand soil OC and N dynamics. In this study, we measured mineralization of soil OC and N at standard temperatures (15 and 25 °C) by laboratory incubation, and calculated their temperature sensitivity (Q 10). Soil samples were collected from cropland (0 years, selected as a control) and adjacent woodlands with different afforestation age (10, 20 and 30 years) at five sites from north to south on China's Loess Plateau. The objectives were to understand how long-term afforestation affects OC and N mineralization and their Q 10 and whether such effects depend on afforestation age and soil texture. The results showed that afforestation increased OC and N mineralization, but this effect was not affected by afforestation age (10–30 years). The Q 10 of OC and N mineralization increased in the first 10 years of afforestation but decreased in the late stage. Furthermore, the increases of OC and N mineralization by afforestation were higher at sites with fine-textured soils than those at sites with coarse-textured soils. However, the Q 10 increased at sites with a relatively high sand content but decreased or remained unchanged at sites with a relatively high clay content. The changes in OC and N mineralization and their Q 10 were related to soil OC and N contents, pH and clay content. Overall, we concluded that long-term afforestation would contribute to the stability of soil OC and N in afforested ecosystems. Soil texture is an important factor controlling OC and N mineralization and their Q 10 , and should be considered when predicting soil OC and N dynamics in response to temperature change in different landscapes. [ABSTRACT FROM AUTHOR]

• Simulated erosion decreased mineralization of OC and N in soils • Decrease in OC and N mineralization was mainly occurred in small aggregate sizes • Changes in OC and N availability determined decrease in OC and N mineralization • The OC and N mineralization increased with OC and N contents but texture independent Soil erosion has important influence on soil processes and particularly soil nutrient dynamics, which in turn affects the terrestrial C and N cycling and greenhouse gases emission. However, the responses of carbon (C) and nitrogen (N) cycling in soils and soil fractions to erosion remain largely unclear, hindering the precise prediction of the fate of C and N in the terrestrial ecosystem. Herein, we compared the mineralization of organic carbon (OC) and N at two different temperatures (15 and 25 °C) in bulk soils and aggregate fractions of 19 soils before and after a simulated rainstorm. The temperature sensitivity (Q 10) of OC and N mineralization was calculated. Soil samples were collected from 9 sites across China, with soil types of Alfisols, Inceptisols, Mollisols, Ultisols, and land uses of croplands, grasslands, and woodlands. The soil aggregate fractions were >2, 2-1, 1-0.25 and <0.25 mm, respectively. We hypothesized that erosion will decrease OC and N mineralization due to the loss of labile organic matter from soils and that the effects of erosion would decrease with clay content and vary with different aggregate fractions. In support of these hypotheses, the cumulative mineralized OC and N (C m and N m) in the soils and aggregate fractions were decreased of 78-85% and 37-52% after erosion, and the temperature sensitivities of OC and N mineralization were decreased of 80-84% and 4-43%, respectively. The effects of erosion varied with site where the soil was collected. The decreases in C m and N m mainly occurred in small aggregate sizes (1-0.25 and <0.25 mm fractions). The C m and N m in bulk soils and aggregates increased significantly with the contents of OC, N, labile OC and mineral N but were texture independent. These results highlighted significantly reduction of OC and N mineralization at eroding sites, which should be carefully considered when assessing emissions of greenhouse gases in eroding environments. [ABSTRACT FROM AUTHOR]