Surface Soil Layer Research Articles

IMPACT OF CREEPING VEGETABLE COVER CROPS ON MINERAL N AND MICROBIAL GROUP POPULATION OF A SANDY LOAM ULTISOL UNDER IMMATURE RUBBER PLANTATION IN SOUTHERN NIGERIA

The use of forage legume species as cover crops in the management of immature rubber plantation soils is not attractive to smallholder rubber farmers (owners of about 75% of the global acreage under rubber production). We sampled immature rubber plantation soils under the following respective creeping vegetable cover crops: Vegetable cowpea (Vigna unguiculata L., Walp. Ssp. Sessquipedallis.), Egusi melon (Cucumeropsis manni Naaudi) and Broadleaf pumpkin (Cucurbita pepo) and a forage legume species (Centrosema pubescens) for four consecutive years at the Rubber Research Institute of Nigeria, Benin. The samples were analyzed for mineral N (NO3- and NH4+) content, and microbial group populations at the onset and end of rains, as well as selected physical and chemical properties. Generally, the result showed that the creeping vegetable cover crop species had a comparative positive effect on the soil properties assessed relative to the forage legume species. The two sampled period mean values of NO3- and NH4+ (10.62 and 8.18 mgkg-1, respectively) obtained from the plantation that had vegetable cowpea were significantly (P≤ 0.05) higher than those of the Egusi melon and Broadleaf pumpkin, but slightly (not significant) lower than that of the Centrosema pubescens. The soil microbial groups (Fungi, Bacteria and Actinomycetes) populations were significantly affected by the cover crop species. At the onset and end of rains, plantations that had vegetable cowpea and Centrosema pubescense cover crops had the maximum number of bacteria (29.58 and 29.50 C.fug-1drywt.soil ×10-6, in that order), while the maximum number of fungi was found in the broadleaf pumpkin (23.66 C.fug-1drywt.soil ×10-6) and Egusi melon (22.92 C.fug-1drywt.soil ×10-6) cover crop plantations. The broadleaf pumpkin and Egusi melon had significant positive effect on the soil surface layer (0-15cm) pH, Org. C, base cations, bulk density and percentage water filled pore space. These findings suggest that the creeping vegetable cover crops could be considered as alternative to the forage legumes in the management of immature rubber plantation soils.

Особенности формирования субфоссильных спорово-пыльцевых спектров острова Кетой (Центральные Курилы)

The composition and ratios of main components of pollen assemblages from the surface layer of peatlands, soils, lake sediments, and alluvial silts in different parts of the Ketoi Island were analyzed. The island, despite its small size, is distinguished by a complex organization of the landscapes. The pollen spectra represent well the local vegetation at the sampling sites, regardless of the genesis of sediments. Pollen brought from adjacent territories does not have a significant effect on the composition of pollen spectra. The spectra from soil deposits in the southeastern part of the island are represented by heather pollen; in the southwestern part, by tree pollen, mostly Siberian dwarf pine, alder, and birch pollen. Among nonarborescent pollen, Asteraceae and Ericaceae are dominant. The pollen spectra obtained from pioneer soil in the western part of the island consist of club moss spores (Lycopodium clavatum), which represent communities on overgrown rockfall deposits. The assemblages of the surface layer of peatlands contain large amounts of sedge and grass pollen. The pollen spectra from alluvial silts represent the vegetation of small valleys, where alder, dwarf pine, and Erman’s birch along the sides are common. The pollen spectra from the sediments of small lakes represent local biotic communities very well. Allochthonous pollen of dark coniferous and broad-leaved trees is present in the spectra in small quantities, except for two samples. This pollen was brought from the southern islands, including those of Japan. The data obtained can be used for paleogeographic reconstructions in the analysis of the formation of pollen spectra on small oceanic islands.

The content of heavy metals in the habitat of birds, Zeya-Bureya plain

From 2019 to 2021, the content of heavy metals in the components of the aquatic ecosystem, which is the habitat of birds on the territory of the Zeya-Bureya plain, was studied (water, sediments, macrophytes, bird feathers). High levels of iron and manganese were found in the water of small rivers. Due to heavy rains and floods, heavy metals were washed out of the surface layers of soil in agricultural fields into rivers. High concentrations of copper and lead were found in the bottom sediments of small rivers. Agricultural pollution of aquatic ecosystems affected the accumulation of lead and manganese in macrophytes. Bird feathers contained the highest amounts of iron, zinc, copper, and manganese, and the lowest amounts of cobalt and cadmium. The feathers of protected bird species such as Swan Goose, Red-crowned Crane, Hooded Crane and Daurian white-naped Crane contained lead 13.5 -38.2 mg/kg, cadmium 0.17 - 0.51 mg/kg. The elements in the feathers of birds were of exogenous origin. Birds are bioindicators of anthropogenic pollution. Researches in this direction are necessary for an estimation of ecological risk of environment and acceptance of measures on its protection.

Оценка состояния подземных инженерных сооружений мелиоративной системы с помощью карт влажности, полученных на основе данных дистанционного зондирования земли беспилотным летательным аппаратом DJI Phantom 4 Multispectra

Reclamation system is a complex of engineering structures and devices that ensure the creation of the required water, air, thermal and nutrient regimes of soils. The composition of reclamation systems includes underground pipelines, drains, hydraulic structures that may fail and require repair, but it is impossible to detect a problem area without monitoring the area of the system by antediluvian methods or conducting survey work. The purpose of the work: to justify the use of soil moisture maps obtained by the DJI PHANTOM 4 MULTISPECTRA UAV to identify problem areas of the reclamation network or vice versa absence. Aerial photography was carried out in May 2021 on the treated section of the drainage and humidification network of the Yakhrom floodplain of the Moscow region. As a result of the survey, a digital relief model, an operational humidity map based on the calculated NDWI water index were obtained. The flight altitude of the quadcopter was 180 m above the earth’s surface, the pixel size of the image of the earth’s surface to be 7.9 cm. According to the results of aerial photography on the selected site, the absolute marks of the earth’s surface vary from 134.67 to 135.23. On average, the slope of the earth’s surface of the selected site is 0.002 in the direction from northwest to southeast. There are no pronounced microforms of relief moisture in the surface layer of the soil obtained in the field corresponds to the variety of color areas of the NDWI water indices highlighted on the operational humidity map. In the soil conditions of the studied area, the moisture content of the surface soil layer is logarithmic with the normalized difference water index NDWI. The correlation coefficient is 0.9 ± 0.06, which indicates a very high relationship between the studied indicators. Such a map can be used to identify problem areas of the reclamation network.

Effect of forwarder multipassing on forest soil parameters changes

In the lowland part of Croatia, heavy machinery such as forwarders is mainly used for the purpose of extracting wood from even-aged forest stands. According to the forest management plan, forwarders are used intensively in the winter period when the soil is mostly saturated with water and when their activity can cause significant damage to the soil. The aim of this study was to determine changes in soil characteristics as a consequence of the repeated passage of a loaded 8-wheel forwarder on silty clay loam type of soil. The research was conducted in an area where the forwarder usually works and in a way that did not significantly disrupt his normal workflow. The results indicate that during the study period the soil had a good bearing capacity and that the observed changes in soil characteristics (bulk density, total soil porosity, soil moisture, particle density, soil water retention capacity etc.) occurred as a result of breaking structural soil aggregates after soil compaction by multiple passes. Characteristic points (T) of equalized penetration curves indicate the compaction of the soil surface layer. Cone penetration index (CI) values did not show a proportional increase as the number of forwarder passes increased, although significant differences in their values with respect to the number of passes were found. Shear strength (τ) did not significantly increase with increasing the number of passes, but a statistically significant difference in the measured values was detected at the soil surface, which was not observed at a depth of 15 cm. Exceeding the rut depth limit of 10 cm occurred only after the 20th pass. Our results indicate that the soil at the harvesting site had a good bearing capacity during the study period.

Changing climatic indicators and mapping of soil temperature using Landsat data in the Yangan-Tau UNESCO global geopark

Changes in key climate index affect ecosystems and biodiversity. In this regard, the assessment of the climatic conditions is of particular relevance. This study presents the results of an analysis of climate change and digital mapping of soil temperature in the Yangan-Tau UNESCO Global Geopark (Russia). The steady increase in air temperature was revealed, which causes an increase in the sum of active temperatures and the duration of the warm period of the year. Annual total precipitation during 1966-2020 changed the sign of the trend: positive trend (increase in precipitation) in 1966-1990, while in 1991-2020 is negative. The hydrothermal indicators determined the increase in aridity during the warm period. Based on the analysis of changes in the climatic conditions of the geopark, a comparison was made of the temperature regimes of air and soil, and the relationship between these indicators in the snow-free period was revealed (R2 = 0.62). An approach is presented for digital mapping of the temperature regime of the surface layer of soils based on ground-based research data and the results of interpretation of the Landsat thermal bands. A significant relationship between soil temperature and Earth surface temperature for the snow-free period was revealed (R2 = 0.83). Based on the obtained regression model and Landsat 8-9 data for the snow-free period of 2013-2022 the map of the distribution of average temperatures of the surface layer of soil from May to October was produced, which clearly demonstrated the relationship between soil temperature and biomes. Keywords: soil temperature; surface land temperature; remote methods; climate change; Yangan-Tau UNESCO global geopark; Bashkortostan.

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.