Surface Soil Layer Research Articles

ANN-Based Assessment of Soft Surface Soil Layers’ Impact on Fault Rupture Propagation and Kinematic Distress of Gas Pipelines

Large-scale lifelines in seismic-prone regions very frequently cross areas that are characterized by active tectonic faulting, as complete avoidance might be techno-economically unfeasible. The resulting Permanent Ground Displacements (PGDs) constitute a major threat to such critical infrastructure. The current study numerically investigates the crucial impact of soil deposits, which usually cover the ruptured bedrock, on the ground displacement profile and the kinematic distress of natural gas pipelines. For this purpose, a decoupled numerical methodology, based on Finite Element Method (FEM), is adopted and a detailed parametric investigation is performed for various fault and soil properties. Moreover, the advanced capabilities of Artificial Neural Networks (ANNs) are utilized, aiming to facilitate the fast and reliable assessment of soil response and pipeline strains due to seismic faulting, replacing time-consuming FEM computations. An extensive sensitivity analysis is performed to select the optimal architecture and training algorithm of the employed ANNs for both the geotechnical and structural parts of the decoupled approach, with suitable input and target values related to bedrock offset, fault and soil properties, surface PGDs, and pipeline strains. The proposed ANN-based approach can be efficiently applied by practice engineers in seismic design and route optimization of natural gas pipelines.

Estimation of Soil Losses in Çapakcur Watershed (Bingol, Turkey) Using RUSLE Method and Comparison of Predicted Soil Losses with Sediment Yield

The present study aimed to determine the total and net erosion in the Capakcur watershed, which has a high erosion risk. Accordingly, annual soil loss in the Capakcur watershed was estimated using RUSLE method. Net erosion was determined directly by measuring the monthly flow rate and sediment concentrations of the Capakcur stream, which originated from the Capakcur watershed and flowed into the Murat River throughout 2019. Estimated soil loss in the Capakcur watershed was 96916.20 ton yr-1, and the amount of soil transported from the Capakcur stream was 68656.09 ton yr-1. Sediment delivery ratio (SDR) was calculated as 0.78. This ratio was well above the average SDR of Turkey (0.23). Topographic factors such as slope length and degree, rainfall, and low vegetation cover ratio in the watershed are the main causes of the high SDR. Due to the high SDR, the fertile surface soil layers of lands in the basin are carried to the streams. This causes both decrease in fertility in soils and pollution of the limited freshwater resources. In order to improve vegetation and management practices in the watershed, soil protection practices such as afforestation and terraces, wire cages and stone walls in gullies should be increased.

Adaptive evaluation of green manure rotation for a low fertility farmland system: Impacts on crop yield, soil nutrients, and soil microbial community

Green manure-based rotations have been shown to be an effective sustainable farming practice and were considered a dual solution to resource conservation and crop productivity maintenance. However, our understanding of the adaptations of green manure rotation to the regional agricultural environments lags significantly behind other farming practices. Here, a 6-year field experiment with four green manure cropping treatments and one conventional treatment has been conducted in a typical low fertility farmland in the arid land. Maize yield was significantly increased after green manure was planted, and on a 6-year average, maize grain yield in the green manure intercropping system was 11.7% higher than that in the conventional cropping system. Green manure rotation or intercropping with maize can significantly increase SOM (soil organic matter), TN (total nitrogen), and TP (total phosphorus) in the surface soil layer. Perennial alfalfa planting significantly increased SOM and TN, but significantly decreased TP. Continuous maize planting had no significant effect on TN and TP, but significantly decrease SOM. Green manure planting promoted shifts in soil bacteria composition, with increased the relative abundance of Actinobacteria but decreased the relative abundance of Chloroflexi and Acidobacteria. For fungal abundance, green manure intercropping with maize increased the relative abundance of Ascomycota, but green manure rotation decreased the relative abundance of Mortierellomycota. In summary, our study elucidated that green manure planting especially intercropping with maize can be adopted as the most effective cropping system in the future to decrease environmental stress and enhance agricultural production conditions through improving the crop productivity, increasing soil fertility and nutrients, and regulating soil microbial communities in the low fertility farmland.

Eucalyptus clones respond differentially for heavy-metals phytoextraction and carbon sequestration in tree biomass and soil with distillery effluents irrigation in north-western India

Forest ecology has significant potential for carbon (C) and heavy-metals’ accumulation, and is considered important for mitigating environmental impacts within the ecosystem. Heavy-metals enter the soil–plant system via different anthropogenic activities per se industrialization, which has huge contribution through the discharge of heavy-metals enriched effluents. Although, irrigation with effluents to large biomass producing forestry plantation e.g. Eucalyptus sp. with high net primary production (NPP) are considered ecologically and environmentally safe, yet the information on differential response of diverse clones towards applied effluents is scares. We therefore, performed field evaluation of nine Eucalyptus clones originated from diverse agro-ecological environments irrigated with distillery effluents to investigate their growth attributes, heavy-metals (e.g. As, Cr, Cd and Ni) and micro-nutrients (e.g. Cu, Zn, Fe and Mn) uptake potential, and C storage in above-and below-ground biomass and sequestration in soil C pool. The diameter at breast height (DBH), tree volume, fresh and dry biomass of stems, leaves, branches and roots of C-316 clone was significantly (p < 0.05) higher, lowest for PE-6, whilst the C-411, C-2045, PE-5, PE-7, PE-8, PE-11 and C-413 were in-between. The Cr uptake was significantly higher for PE-8 and C-413, Ni uptake in PE-6 and C-413 and Pb uptake in clone C-2045. Among micro-nutrients, Zn, Mn and Fe uptake was significantly higher for C-316, compared with other clones. However, the metal content in surface (0–15 cm) soil layer was well below the threshold level. The partitioning of NPP among different above-and below-ground biomass components revealed that dry stem biomass comprised ~ 54.8–56.7%, branches ~ 15.8–17.1%, while leaves ~ 5.6–7.5% of total dry tree biomass. Root biomass comprised ~ 21.3% of total tree biomass. Carbon stocks in dry above-ground biomass (stems + branches + leaves) varied between 33.9 and 59.5 kg C tree−1, and were significantly higher for C-316, and lowest for PE-6 clones. The total C sequestration in tree biomass varied between 229.7 and 450.9 Mg C ha−1 in different clones; with significantly higher in C-316 and lowest in PE-6. Carbon sequestration rate varied between 57.4 and 112.7 Mg C ha−1 year−1 for different Eucalyptus clones. Total organic C (TOC) stocks in surface soil layer under C-413, C-411 and C-316 clones were significantly (p < 0.05) higher than others. The discriminant function analysis (DFA) showed that two significant canonical discriminant functions (DFs) viz. DF-1 and DF-2 involving total tree biomass, total uptake of As, Pb, Zn, Mn and Fe in above-ground biomass of Eucalyptus clones distinguished different cones, appropriately grouping 97.5% of the tested clones. These results underpin overwhelming significance of C-316 plantation for increased heavy-metals’ uptake with co-benefits of C sequestration in tree biomass as well as in soils. Therefore, a stringent policy framework for large scale C-316 clone plantation in regions with availability of distillery effluents is required for restoring the forest ecosystem on sustainability basis.

Prediction of deep soil water content (0–5 m) with in-situ and remote sensing data

Accurate and timely evaluation of soil water content (SWC) in water-limited arid and semiarid regions will provide an essential reference for scientifically based water management strategies and vegetation restoration practices. Theoretical and empirical models based on remote sensing data have been successfully applied to predict large-scale SWC. However, most existing models are limited to the surface soil layer, while the prediction of SWC in the deep soil layer (1–5 m) has been overlooked because of the shortage of long-term and large-scale filed-observed data. In this study, a south-north transect (ca. 860 km) was selected across the Chinese Loess Plateau (CLP). Based on both long-term remote sensing and in-situ data (2013–2016), pedo-transfer functions (PTFs) for the SWC in the 0–5 m profile were developed using multiple regression, random forest, and artificial neural network. The results showed that evapotranspiration, potential evapotranspiration, soil surface temperature, total shortwave broadband albedo, and normalized difference vegetation index were important remote sensing parameters, whereas soil texture and bulk density were important in-situ parameters for SWC PTFs development. Among the three PTF development methods, machine learning (i.e. random forest and artificial neural network) obtained a higher accuracy than multiple regression. For different combinations of input parameters, the introduction of in-situ factors significantly improved the accuracy of PTFs compared with PTFs based on remote sensing data only. The artificial neural network developed a PTF with only five input variables that predicted SWC with reasonable accuracy (root mean square error = 0.039, R2 = 0.697, mean absolute percentage = 24.8) and is thus useful for many applications on the Loess Plateau of China. In the future, more attention should be given to the role of in-situ parameters when developing PTFs for deep SWC prediction.

Spatial Differentiation of the Coupling Characteristics of Soil Carbon and Nitrogen on Mulberry Plantations in China

Soil is the most important carbon pool of the mulberry plantation ecosystem, so understanding the characteristics of the soil carbon pool in mulberry plantations provides an important basis for the research of carbon sinks in economic forest ecosystems and farmland ecosystems. In order to explore the spatial differentiation pattern of the relationship between carbon and nitrogen in mulberry plantation soil, this study analyzed the organic carbon content and total nitrogen content of the surface soil layer (0–20 cm) and the subsurface soil layer (20–40 cm) of 475 mulberry plantations in five major regions of China, Southwest China (SWC), Central South China (CSC), East China (EC), North China (NC), and Northwest China (NWC). The research showed seven key aspects of this system. (1) The soil organic carbon of mulberry plantations was significantly different at the two soil depths. The average content of organic carbon in the surface layer of mulberry plantation soil was 10.71±7.01g kg–1, which was 37.13% higher than that of the subsurface layer. (2) The soil organic carbon of mulberry plantations had significant differences in spatial differentiation, which was manifested as SWC>CSC>EC>NC>NWC. (3) The total nitrogen content in mulberry plantation soil had significant responses to the region, the soil layer depth, and the interaction between the region and soil layer depth. Among the regions, NWC had no significant difference between the surface layer and subsurface layer of the soil. EC had the maximum difference in total nitrogen content, with the total nitrogen content in the surface soil layer being 56.68% higher than that of the subsurface soil layer. The total nitrogen contents of the surface soil layers in the SWC and NC were 34.27% and 20.79% higher than those of the respective subsurface soil layers. (4) The mulberry plantation soil C/N ratios had a significant response to regional differences, as NWC>SWC> EC>CSC>NC, but this ratio had no significant response to soil depth. (5) Soil pH had significant spatial differentiation in relation to soil organic carbon and total nitrogen content in mulberry plantations. NWC had no significant correlation between pH and organic carbon or total nitrogen content, while CSC had a significant positive correlation between pH and both soil organic carbon and total nitrogen content. Other regions showed significant negative correlations between pH and both organic carbon and total nitrogen content. (6) There was a significant negative correlation between the C/N ratio of the surface soil layer and pH in mulberry plantations, which was mainly contributed by SWC, while the other regions' surface soil layers had no significant correlations between C/N ratio and pH. (7) There was no significant correlation between the C/N ratio and pH in the subsurface soil layer in mulberry plantations. These results reveal that in either the research on mulberry plantation carbon pools or the innovation of green and low-carbon planting technology in mulberry plantations, the spatial differentiation characteristics of soil must be considered. Furthermore, the spatial differentiation of soil organic carbon can be used as the basic foundation for the planning and design of mulberry afforestation or ecological restoration projects.

Effects of magnetized municipal effluent on some physical properties of soil in furrow irrigation

Due to the water crisis, effluent reuse is an effective method in order to supply crop water requirements. In order to study the impact of treated and magnetic effluent on the soil properties, this research was conducted in randomized complete block design with three irrigation treatments; including "effluent", "magnetic effluent" and "normal water" in four replications. Soil samples were taken from two surface and subsurface soil layers and at the upper and the downstream of each furrow. Evaluating the apparent specific gravity of soil in different water quality treatments showed that this soil property was increased effectively at the upstream part of the furrow. Similar results were also observed in the field capacity but more fluctuations were observed. Simultaneously, effluent treatment showed decreasing effects on soil water holding capacity during the time, which can be attributed to the increasing of soil organic matters. It seems that the high fluctuations between different design blocks are related to the gravelly nature of soil. However, intensification or weakening effect of these changes was not even found by magnetic.

Experimental study on the shear characteristics of different pile-soil interfaces and the influencing factors

In seasonally frozen region, landslides and slope failures start during the thawing season due to the enrichment of water for the surface soil layer. Piles and anchored system are common remediation techniques in slope reinforcement projects. A cost-effective and reliable design relies on a comprehensive understanding of the interfacial shear characteristics of the pile-soil interface under different in-situ conditions. Series of laboratory direct shear tests are performed to evaluate the shear characteristics of wood-soil, concrete-soil, and steel-soil interfaces. The effects of soil density, water content and freezing-thawing cycles on the interfacial shear behavior are investigated and a multi-linear regression formula is proposed to predict the interfacial shear strength parameters. Test results show that the cohesion and friction angle at the pile-soil interface are influenced by surface roughness of the pile, soil density, water content, freezing-thawing cycles, and stress levels, but with different degrees of sensitivity. Moreover, the proposed regression formula is able to predict the interfacial cohesion and friction angle of the wood-soil, concrete-soil, and steel-soil interfaces under different in-situ conditions.

THE SIGNIF ICANCE OF HARVEST RESIDUES IN THE SUSTAINABLE MANAGEMENT OF ARABLE LAND. II. HARVEST RESIDUES MANAGEMENT

&amp;lt;p&amp;gt;Harvest residues (HR) are one of the important aspects of sustainable management in agriculture, representing a significant portion of organic matter (OM) that can be retained or removed from agroecosystems. There are several ways to manage plant residues: (i) burning, (ii) incorporation in soil, (iii) leaving plant residues after harvest on the soil surface in form of mulch, (iv) undersowing crops in HR and (v) baling and removing HR from the plot. Burning is the most unreasonable action in agricultural production, which is prohibited by legal regulations in force. The burning means a complete loss of OM &amp;amp;ndash; N and S are irretrievably lost in the air, mineral substances remain in ash, and microorganisms in the soil surface layer are destroyed. Incorporation of HR may be complete or partial, depending on the soil cultivation method applied. This HR management method has a number of soil benefits: increases content of nutrients, OM and humus; increases microbiological activity; improves soil water, air and physical properties; improves soil structure, ultimately contributing to the increase in soil fertility and plant growth. Two practical approaches that were once common, have been neglected. Namely, undersowing and mixed cultivation where various species are simultaneously grown with or between plantings of a main crop. Removal of HR indirectly leads to a decrease of the organic matter in the soil. In essence, there is a need to determine the size of acceptors and the return rates of organic residues of different quality, and to increase the efficiency of nutrient cycling from residues through various land acceptors and crops, with minimal losses from the system.&amp;lt;/p&amp;gt;

Constructing the active surface soil layer with ZVI-biochar amendment for simultaneous immobilization of As and Zn in both contaminated soil and groundwater: Continuous versus intermittent infiltration mode

In this study, the zero valent iron-biochar composite (ZVI-BC) was applied to construct an active surface soil layer for the simultaneous remediation of As-Zn contaminated soil and groundwater, focusing on the influence of the infiltration mode of pumped-up groundwater into soil. The active surface soil treated more contaminated groundwater for As (4.45-5.46 L kg-1 soil) than that for Zn (2.52-3.13 L kg-1 soil) under both continuous and intermittent infiltration modes, with about 98% As and 95% Zn removed from groundwater and retained in the soil. As(V) precipitated with Fe(III) due to ZVI oxidation, which was responsible for the As immobilization. The soil under the intermittent infiltration mode was enriched by the Sphingomonas with arsenate reductase gene, which promoted more reduction of As(V) into As(III) and facilitated coprecipitation of As(III) with Fe(III). The Mn oxide determined the sorption of Zn in the active soil layer, where the Hyphomicrobium, one type of manganese oxidizing bacteria, was much higher under the continuous infiltration mode, which accounted for the more Zn immobilization. After the remediation, both As and Zn immobilized in the active surface soil showed high stability, with the average downward migration rate of only 0.207-0.368 cm year-1 within 20-year rainfall exposure. Our findings indicate that this active surface soil layer is applicable for simultaneous immobilization of As and Zn in both contaminated soil and groundwater, and the groundwater intermittent infiltration could be a better option considering the remediation effectiveness, the immobilization mechanism, the long-term stability, and the energetic efficiency.

Distribution Pattern and Structure of Vascular Plant Communities in Riparian Areas and Their Response to Soil Factors: A Case Study of Baoan Lake, Hubei Province, China

The vascular plant community in a riparian area is the main substrate and vehicle of many ecological functions for the lakeshores of grass-type shallow lakes. However, there is still a lack of knowledge regarding the responses of vascular plants to soil factors of the habitat in riparian areas, which restricts the ecological adaptation management for riparian vegetation. In this work, a typical grass-type shallow lake (Baoan Lake) in the Yangtze Basin in Central China was taken as the study area. We describe the plant species distribution and community structure in riparian areas under two habitat types (lake and tributary) and their responses to soil factors. The results showed that (1) the soil chemical factors have a significant effect on the distribution and community structure of vascular plants, even though there was a significant interaction among three group factors of soil habitats; (2) compared with other factors, the total nitrogen (TN) and available phosphorus (AP) have the most significant correlations with the distribution of vascular plants; (3) the rate of soil nutrient sorption determines the distribution of vascular species, closely related to the biological characteristics of plants and the microbial enzymatic activity in soil; and (4) vascular plant diversity and the proportion of perennial plants were generally higher in the lakeshore areas than in the tributaries and showed a low-high-low “hump-shaped” species richness and diversity distribution. The Shannon-Wiener index value increased with the increasing soil-available phosphorus in the surface soil layer. Therefore, this study advanced our knowledge of the species distribution and diversity patterns of lakeshores and tributaries, providing scientific and theoretical guidance for the biodiversity conservation and sustainable ecosystem management of grass-type shallow lakes.

Stochastic and deterministic processes shape bioenergy crop microbiomes along a vertical soil niche.

Sustainable biofuel cropping systems aim to address climate change while meeting energy needs. Understanding how soil and plant-associated microbes respond to these different cropping systems is key to promoting agriculture sustainability and evaluating changes in ecosystem functions. Here, we leverage a long-term biofuel cropping system field experiment to dissect soil and root microbiome changes across a soil-depth gradient in poplar, restored prairie and switchgrass to understand their effects on the microbial communities. High throughput amplicon sequencing of the fungal internal transcribed spacer (ITS) and prokaryotic 16S DNA regions showed a common trend of root and soil microbial community richness decreasing and evenness increasing with depth. Ecological niche (root vs. soil) had the strongest effect on community structure, followed by depth, then crop. Stochastic processes dominated the structuring of fungal communities in deeper soil layers while operational taxonomic units (OTUs) in surface soil layers were more likely to co-occur and to be enriched by plant hosts. Prokaryotic communities were dispersal limited at deeper depths. Microbial networks showed a higher density, connectedness, average degree and module size in deeper soils. We observed a decrease in fungal-fungal links and an increase of bacteria-bacteria links with increasing depth in all crops, particularly in the root microbiome.

Analysis on the temporal and spatial characteristics of the shallow soil temperature of the Qinghai-Tibet Plateau

Shallow soil refers to the soil layer within the 50 cm depth. Shallow soil temperature (ST) directly or indirectly affects many processes in the soil, such as seed germination, plant growth, and water evaporation. Therefore, the study of shallow ST is of great significance in understanding the surface energy, water cycle, ecology and climate change. This work collected observational data from 141 meteorological stations on the Qinghai-Tibet Plateau from 1981 to 2020 and ERA5 reanalysis data, used the “Moving Surface Spline Interpolation Algorithm Based on Green’s Function” and “Fuzzy C-means algorithm”, and analyzed the temporal and spatial change characteristics of ST at different levels. The results showed that 1) the temperature increase of 0–20 cm (the surface layer of the shallow soil) was roughly the same. The average annual ST was 9.15–9.57°, and the interdecadal variabilities were 0.49–0.53 K/10a. The average annual ST of 40 cm (the bottom layer) was 8.69°, and the interdecadal variability reached 0.98 K/10a. 2) Considering the 7 regions, the warming trend was obvious, and there were certain regional differences. The average annual ST in different regions ranged from 5.2 (northeastern Plateau) to 17.1 °C (western Sichuan Plateau), with a difference of nearly 12 K. The standard deviation ranged from 0.40 (western Sichuan Plateau) to 0.61 K (Qiangtang Plateau), with a difference of 0.21 K. 3) The errors of the obtained grid data were basically less than 3%, which were much smaller than the errors obtained from the ERA5 reanalysis data. This work is significant for understanding the characteristics of ST evolution and land‒atmosphere interactions on the Qinghai-Tibet Plateau and provides important data support for improving the underlying surface boundary conditions of models.

Effects of Warming on Microbial Community Characteristics in the Soil Surface Layer of Niaodao Wetland in the Qinghai Lake Basin

Lakeshore wetlands are important terrestrial ecosystems worldwide, and the lakeshore wetlands of the Tibetan Plateau are sensitive to climate change. Therefore, in the context of global warming, studying the effects of temperature rise on surface soil microbial communities is essential for wetland biodiversity conservation. In this study, we used metagenomic sequencing to examine changes in the structure of surface soil microbial communities and their metabolic pathways in the Niaodao lakeshore wetland (NLW) in Qinghai Lake at 1.2 °C warming. Under natural control and warming conditions, Proteobacteria and Actinobacteria were the most dominant bacterial phyla, and Ascomycota and Basidiomycota were the predominant fungal phyla. Soil pH, electrical conductivity, and temperature affected the relative abundances of the dominant soil microbes. Effect size estimation in a linear discriminant analysis revealed 11 differential pathways between warming and natural conditions. Warming considerably enhanced the peptidoglycan biosynthetic pathways but inhibited the ATP-binding cassette transporter pathway. Warming treatment affected α-diversity indices, with an increase in the Shannon, Chao1, and richness indices and a decrease in the Simpson index compared with the index changes for the natural control conditions. Analysis of similarities showed significant differences between warming and control samples. Overall, temperature rise altered surface soil microbial community structure and increased surface soil microbial diversity and abundance in NLW.

Soil morphological, physical and chemical properties affecting Eucalyptus spp. productivity on Entisols and Ultisols

Soil fertility in forestry systems has usually been constrained to soil nutrients, with little attention to soil morphological attributes and physical properties. Our hypothesis was that soil physical properties and morphological attributes are more closely related with commercial forest growth than soil chemical fertility. The objective of the study was to analyze the influence of soil properties, in different soil types, on dendrometric variables and productivity of clonal E. saligna and seminal E. dunnii, both widely employed in commercial plantations managed for pulp and lumber production in southern Brazil. On inventory plots with two Eucalyptus species, namely Eucalyptus saligna (clone 32864) and seminal E. dunnii, we evaluated morphological attributes and physical and chemical properties of 17 soils (Ultisols and Entisols), and the dendrometric variables tree height, tree dominant height (h100) and diameter at breast height (DBH), all measured in 7-years old plantations. Eucalyptus growth was variable and influenced by profile attributes and soil properties, but correlations between h100 and soil properties were weak (r < 0.7) and usually not significant. Tree height and DBH were not affected by Eucalyptus species, soil type and their interaction. Overall, DBH ranged from 77.98 to 304.30 mm, with an average value of 183.23 mm. By contrast, tree h100 was affected by Eucalyptus species and soil type, but not by their interaction. Trees of E. saligna (23.4 m) were taller than E. dunnii (22.1 m), while among soil types Ultisols had the tallest (23.4 m) and Entisols the shortest trees (22 m). Chemical properties were more variable in surface soil layers, whereas physical properties mainly differentiated subsurface soil layers. The lowest dominant height resulted from the interaction between the lowest field capacity and plant available water capacity and the smaller depth of Entisols' soil profile. Contrary to our hypothesis, most soil properties/attributes were not significantly correlated with dominant tree height. Neither soil physical, morphological properties nor soil chemical fertility are determinants to forest growth when these parameters are not at critical limits for forest growth, particularly with absence of extreme edaphoclimatic conditions such as low rainfall or high temperatures. Associations among soil morphological attributes, physical properties and edaphoclimatic variables should be validated in future studies to better understand their effect of forest productivity in subtropical environments.

Intensity and persistence of water repellency at different soil moisture contents and depths after a forest wildfire

Abstract The Mediterranean mixed coniferous and broad-leaved forest of Moarda (Palermo) was affected by a large wildfire in summer 2020. In spring 2021, burned and unburned loam soil sites were sampled and the water drop penetration time (WDPT) and ethanol percentage (EP) tests applied to assess the influence of wetting-drying processes and soil water content on post-fire soil water repellency (SWR) as well as its vertical distribution. According to the WDPT test, the surface layer of the natural unburned soils was severely hydrophobic at intermediate soil water contents roughly corresponding to wilting point and SWR reduced either for very dry conditions (air- or oven-dried conditions) or wetter conditions close to field capacity. For these soils, EP test yielded results in agreement with WDPT. An influence of the wetting/drying cycle was detected as, for a given soil water content, WDPT was generally higher for the drying than the wetting process. The surface of burned soils was always wettable independently of the soil water content. The vertical distribution of SWR was modified by wildfire and the maximum hydrophobicity layer, that was located at the surface of the unburned soils, moved to a depth of 2–4 cm in the soils of burned sites. The results confirmed that wildfire can induce destruction of soil water repellency (SWR) naturally occurring at the surface of forest soils and create a shallow hydrophobic layer that may increase overland flow and erosion risk.

A 40 % paddy surface soil organic carbon increase after 5-year no-tillage is linked with shifts in soil bacterial composition and functions

Soil organic carbon (SOC) is related to soil fertility, crop yield, and climate change mitigation. Paddy soil is a significant carbon (C) sink, but its C sequestration potential has not been realized as the various driving factors are still not fully understood. We performed a 5-year paddy field experiment in southern China to estimate tillage effects on SOC accumulation and its relation with soil bacteria. The C input from rice residue, SOC content, CO2 flux, soil bacterial community composition, and predicted functions were analyzed. No-tillage (NT) increased (p < 0.05) rice residue C inputs (by 12.6 %–15.9 %), SOC (by 40 % at the surface soil layer compared with conventional tillage, CT), and CO2 fluxes compared with reduced tillage (RT) and CT. Also, NT significantly altered the soil bacterial community. The random forest model showed that the predicted bacterial functions of “Degradation/Utilization/Assimilation Other”, “C1 Compound Assimilation”, and “Amin and Polyamine Degradation” were the most important functions associated with SOC accumulation. Analysis of metabolic pathway differences indicated that NT significantly decreased the BENZCOA-PWY (anaerobic aromatic compound degradation) and the AST-PWY (L-arginine degradation II). Therefore, the rapid paddy SOC increase is associated with both residue C input (from higher rice yields) and the degradation functions regulated by soil bacteria.

Soil carbon storage is related to tree functional composition in naturally regenerating tropical forests.

Regenerating tropical forests are increasingly important for their role in the global carbon cycle. Carbon stocks in above-ground biomass can recover to old-growth forest levels within 60-100 years. However, more than half of all carbon in tropical forests is stored below-ground, and our understanding of carbon storage in soils during tropical forest recovery is limited.Importantly, soil carbon accumulation does not necessarily reflect patterns in above-ground biomass carbon accrual during secondary forest succession, and factors related to past land use, species composition and soil characteristics may influence soil carbon storage during forest regrowth.Using tree census data and a measure of tree community shade tolerance (species-specific light response values), we assessed the relationship between soil organic carbon stocks and tree functional groups during secondary succession along a chronosequence of 40- to 120-year-old naturally regenerating secondary forest and old-growth tropical forest stands in Panama.While previous studies found no evidence for increasing soil C storage with secondary forest age, we found a strong relationship between tree functional composition and soil carbon stocks at 0-10cm depth, whereby carbon stocks increased with the relative influence of light-demanding tree species. Light demanding trees had higher leaf nitrogen but lower leaf density than shade-tolerant trees, suggesting that rapid decomposition of nutrient-rich plant material in forests with a higher proportion of light-demanding species results in greater accumulation of carbon in the surface layer of soils. Synthesis. We propose that soil carbon storage in secondary tropical forests is more strongly linked to tree functional composition than forest age, and that the persistence of long-lived pioneer trees could enhance soil carbon storage as forests age. Considering shifts in tree functional groups could improve estimates of carbon sequestration potential for climate change mitigation by tropical forest regrowth. Read the free Plain Language Summary for this article on the Journal blog.

Effects of artificial restoration on vertical distribution of soil carbon storage following revegetation in a semiarid grassland of North China

AbstractArtificial restoration is an important strategy to restore plant communities and soil nutrients in degraded grassland ecosystems. Despite that research has been extensive on the impacts of vegetation restoration on soil carbon storage, little work has been tried to examine the impacts of artificial restoration on the vertical distribution of soil organic carbon (SOC) storage following revegetation in grassland ecosystems. In this paper, the responses of plant species diversity, litter biomass (LB), aboveground biomass (AGB), the relative biomass of three dominant plant species, and the belowground biomass (BGB) were quantified under five different restoration regimes (natural recovery, harrowing, harrowing plus fertilization, harrowing plus irrigation, harrowing plus fertilization and irrigation), to explore the direct and indirect effects of artificial restoration, mediated by changes in the plant properties following revegetation, on SOC storage in Leymus chinensis steppe, North China. We found that artificial restoration greatly facilitated the recovery of Leymus chinensis but lowered the plant diversity. Irrigation treatment, particularly harrowing plus irrigation, was associated with both higher BGB and LB, which had positive effects on SOC storage at the 30–60 cm soil layer when compared with natural restoration. In addition, artificial restoration had positive but not significant effects on SOC storage in the surface soil layer (0–10 cm) mediated directly by changes in BGB, while it exerted negative indirect effects on SOC storage at the 10–30 cm soil layer through low level of plant species diversity. The loss of two dominant species (Stipa krylovii and Cleistogenes squarrosa) could greatly impact SOC storage not only due to lowered species diversity but also the reduced quality of litter input into soil. It is therefore proposed that maintaining high levels of plant species diversity could help sustain higher soil carbon storage through producing high‐quality root and litter. Our findings from the 9‐year restoration experiment suggested that natural restoration is a sustainable grassland restoration regime to conserve both plant diversity and soil nutrients over short timescales in semi‐arid grasslands in North China. In the long term, SOC storage can be substantially enhanced by artificial restoration, especially under treatments that include irrigation.

Effects of Herbaceous Plant Roots on the Soil Shear Strength of the Collapsing Walls of Benggang in Southeast China

Failure of collapsing walls is an important process affecting the development of Benggang and is closely related to the soil shear strength. Plant roots can increase the soil shear strength. However, the effects and mechanisms of root reinforcement on the soil shear strength of collapsing walls remain unclear. To explore the shear strength characteristics of collapsing walls and their influencing factors under different vegetation conditions, Pennisetum sinese, Dicranopteris dichotoma, Odontosoria chinensis, and Neyraudia reynaudiana were adopted as experimental objects in the Benggang district of Anxi County, Southeast China. We measured the root characteristics and in situ shear strength of root–soil complexes by dividing soil with the four vegetation conditions into five soil layers: 0–5 cm, 5–10 cm, 10–15 cm, 15–20 cm, and 20–25 cm. The average shear strength of the root–soil complexes of the various plants ranked as follows: Pennisetum sinese (30.95 kPa) &gt; Odontosoria chinensis (28.08 kPa) &gt; Dicranopteris dichotoma (21.24 kPa) &gt; Neyraudia reynaudiana (14.99 kPa) &gt; bare soil (11.93 kPa). The enhancement effect of the root system on the soil shear strength was mainly manifested in the 0–5 cm soil surface layer. The soil shear strength attained an extremely significant positive correlation with the root length density, root surface area density, root volume density, root biomass density, for root diameters (L) less than or equal to 0.5 mm and between 0.5 and 1 mm, the soil shear strength could be simulated by using root volume density. The shear strength of undisturbed root–soil complexes measured with a 14.10 pocket vane tester was higher than the value obtained with the Wu–Waldron model (WWM). The correction coefficient k′ varied between 0.20 and 20.25, mostly exceeding 1, and the average correction coefficient k′ value was 4.94. The average correction coefficient determined in this test can be considered to modify the WWM model when conducting experiments under similar conditions.