Soil Environmental Properties Research Articles

Earthworms impact the availability of Si to plants in northern Vietnamese paddy fields

Silicon (Si) is an essential element for the growth and development of rice plants, playing a crucial role in their overall health and productivity. This study aimed to measure earthworm's impact on Si dynamics in northern Vietnam's paddy fields. The properties of earthworm casts from 23 different sites were compared to the surrounding topsoil. The results showed that the casts were enriched in biogenic silica (herein phytoliths) and plant-available Si (measured through acid acetic extraction, SiAC) compared to the reference topsoil. Also, casts had a higher sand content, while their carbon content was similar to the reference soils. This suggests a possible preference for sand particles by earthworms (e.g., for grinding plant material within their gizzards) and/or the consumption of soil from another layer enriched in sand content. The influence of earthworms on Si dynamics was found to be dependent on the soil's environmental properties. In soils with low fertility (characterized by a higher proportion of sand and lower concentrations of C and oxides), earthworms increased the concentration of SiAC. However, beyond a certain level, the effect of earthworms on Si availability became neutral. While this study highlights the critical role of earthworms in paddy fields, further research is needed to understand how earthworms enhance the concentration in SiAC in the topsoil, and the consequences to rice growth and resistance to environmental hazards.

Alterations in litter chemical traits and soil environmental properties limit the litter decomposition of near-mature Robinia pseudoacacia plantations

Increases in stand age can significantly change litter and soil microenvironmental properties of plantations. However, how these factors change and by which pathways they act together to affect litter decomposition are not well understood. In this study, litters were collected from four Robinia pseudoacacia (Rp) plantations from a 10 ∼ 43-year sequence in the Loess Plateau (China) and used to conduct a 592-day in-situ decomposition experiment using litterbag method. The changes in litter chemical traits, soil physiochemical environment, and the litter and soil microbial community were detected. Then, the pathways of these changes affecting litter decomposition were analyzed based on partial least squares structural equation modeling. The results indicated that with increasing stand age, the increased litter substrate quality stimulated litter lignocellulase activity by affecting the fungal community structure in early and late stages of decomposition and the bacterial community structure in early decomposition, which tended to accelerate litter decomposition. However, the decrease in litter chemical diversity weakened the synergistic effects of mixed litter decomposition, and thus directly hindered the overall decomposition. On the other hand, increasing stand age caused excessive soil temperature and low soil moisture in early decomposition stage, which indirectly affected the litter microbial communities through changes in the soil fungal community, leading to decreases in litter lignocellulase activity and litter decomposition. Overall, changes in litter chemical traits with increasing stand age tended to cause dual effects, while those in the soil microenvironment tended to cause increasing negative effects. Together these changes finally affected litter decomposition by litter microbes and their enzymatic activities, leading to depressed litter decomposition and a risk of weakening material cycling in near-mature (33-year) Rp plantations.

Stochastic processes in the structure and functioning of soil biodiversity

Ecologists are increasingly recognizing the importance of stochastic processes in generating spatial and temporal variation in biological communities. This variation is very high in soil, which hosts not <¼ of all biodiversity on Earth and is central to how terrestrial ecosystems respond to perturbations. Measurement errors, demographic stochasticity (individual variability in traits such as birth and death rates), and environmental stochasticity (fluctuations in environmental properties) are the three main sources of stochasticity in ecology. Here, we synthesize how these three sources of stochasticity are quantified and incorporated in the study of soil biodiversity, highlighting current limits, possible solutions, and future research needs. We stress the relevance of all these factors to our future understanding of terrestrial ecosystems via plant-soil and soil-climate interactions and feedbacks. In soil, measurement errors are due to the small size, high abundance, and broad distributions of soil organisms, which limit sampling in space and especially over time. We argue that positive autocorrelation is a main characteristic of soil environmental properties, which may have important consequences on the response of soil biota to perturbations. At a local scale, large populations of soil organisms also imply a minor role of demographic stochasticity. Despite demographic stochasticity being a less significant source of variability than environmental stochasticity, we show that demographic stochasticity can be sizeable, but that within soil systems, stochasticity of environmental conditions must be accounted for. Explicit consideration of stochastic processes in soil biodiversity research is essential to our future understanding of the processes that control soil biodiversity. In classical ecology, stochasticity implies probabilistic predictions in terms of population growth, extinction, species coexistence, and community diversity. In soil, stochasticity implies very variable responses to climate change and the soil-climate feedback. Future studies will have to identify the major sources of environmental stochasticity with a particular focus on the interaction between multiple global change factors.

Aggregate sizes regulate the microbial community patterns in sandy soil profile

Soil microorganisms play a key role in the function of soil ecosystem, yet our knowledge about how microbial communities respond to the typically sandy soil environmental properties along the soil profile is still insufficient. We investigated the soil microbial community patterns from top (0–20 cm) to clay-layer (>80 cm) of the typical sandy soils in three regions in China with different levels of precipitation, including Lishu County in Jilin Province (LS), Langfang City in Hebei Province (LF) and Zhengzhou City in Henan Province (ZZ). Our findings showed that small-size aggregates (<0.5 mm) rather than large ones (⩾ 0.5 mm) dominated the soil profile. The relative abundances of Actinobacteria, Crenarchaeota and Firmicutes were highly related to aggregate proportions of the deep clay-layer soil. The network analysis revealed the distinct community patterns among modules, evidencing niche differentiation along the soil profile. The keystone species OTU_11292 was observed having migrated clearly into the other module of the clay-layer soil. Different roles of the OTU_30 (belonging to Gemmatimonadetes) in soil processes might partly explain the different microbial distribution between top- and clay-layer soils. These findings provided new insights into the candidate mechanisms of microbial diversity maintenance and community patterning of sandy soils, which were necessary for better understanding of ecological rules guiding long-term agricultural practice.

Long-term nitrogen input alters plant and soil bacterial, but not fungal beta diversity in a semiarid grassland.

Anthropogenic nitrogen (N) input is known to alter plant and microbial α-diversity, but how N enrichment influences β-diversity of plant and microbial communities remains poorly understood. Using a long-term multilevel N addition experiment in a temperate steppe, we show that plant, soil bacterial and fungal communities exhibited different responses in their β-diversity to N input. Plant β-diversity decreased linearly as N addition increased, as a result of increased directional environmental filtering, where soil environmental properties largely explained variation in plant β-diversity. Soil bacterial β-diversity first increased then decreased with increasing N input, which was best explained by corresponding changes in soil environmental heterogeneity. Soil fungal β-diversity, however, remained largely unchanged across the N gradient, with plant β-diversity, soil environmental properties, and heterogeneity together explaining an insignificant fraction of variation in fungal β-diversity, reflecting the importance of stochastic community assembly. Our study demonstrates the divergent effect of N enrichment on the assembly of plant, soil bacterial and fungal communities, emphasizing the need to examine closely associated fundamental components (i.e., plants and microorganisms) of ecosystems to gain a more complete understanding of ecological consequences of anthropogenic N enrichment.

Abiotic factors influencing soil microbial activity in the northern Antarctic Peninsula region

Microorganisms play a key role in the carbon (C) cycle through soil organic matter (SOM). The rate of SOM mineralization, the influence of abiotic factors on this rate and the potential behaviour of SOM are of particular interest in the northern Antarctic Peninsula and offshore islands. This is one of the most rapidly warming regions on Earth with numerous ice-free areas, some with abundant wildlife and with the greatest known soil organic carbon (SOC) storage in Antarctica. The latter implies extended Antarctic summer conditions promote increased terrestrial plant growth and soil microbial activity (SMA). SMA, determined by respirometry, is a measure of ecosystem function, and depends on microclimatic conditions and soil environmental properties. SMA and the effect of abiotic variables have been analysed in locations with different soil types, on Cierva Point (Antarctic Peninsula), Deception Island and Fildes Peninsula (King George Island). Soil microbial biomass carbon (SMBC) ranged from 5.66 to 196.6 mg SMBC kg−1and basal respiration (BR) from 2.86 to 160.67 mg CO2 kg−1 d−1. SMBC and BR values were higher in Cierva Point, followed by Fildes Peninsula and Deception Island, showing the same trend of SOM abundance. Except for Cierva Point, low nitrogen, phosphorus and C concentrations were observed. SMBC/total organic carbon (TOC) levels indicated that SOC was recalcitrant and SOM content was closely related to the extent of vegetation cover observed in situ. High metabolic quotient values obtained at Cierva Point and Deception Island (median values 7.27 and 6.53 mg C-CO2 g SMBC−1 h−1) and low SMBC/TOC in Cierva Point suggest a poor efficiency of the microbial populations in the consumption of the SOC. High SMBC/TOC values obtained in Deception Island indicates that SMBC may influence SOM stabilization. Mineralization rates were very low (negligible values to 1.44%) and sites with the lowest values had the highest SOM.

Soil properties and heavy metal concentrations affect the composition and diversity of the diazotrophs communities associated with different land use types in a mining area

Biological nitrogen fixed by diazotrophs is important because it is the largest natural source of nitrogen to support primary productivity and maintain ecosystem sustainability when anthropogenic nitrogen inputs are lacking, especially in mining areas. The present study selected six different land use types (a corn field, a vegetable field, an area of shrubs, a mine tailing, a forest and a citrus orchard) as variables related to the mining activities around the Siding mining area, Liuzhou, Guangxi Province, China. A 0–10 cm soil layer was sampled, and the heavy metal concentrations and soil physicochemical properties were measured. Illumina MiSeq sequencing technology was used to analyze the abundance and structural diversity of the diazotroph community. The distribution of diazotroph assemblages among the different land use types and the main soil environmental properties that drive diazotroph community compositions were determined. The results indicated that the phylum Cyanobacteria (85.89%) was the most dominant taxon in the diazotrophic community in the citrus orchard. However, in the soils of the five other land use types, Proteobacteria was the most dominant taxon in the diazotrophic community, with a high abundance that ranged from 60.08% to 99.96%. Spearman's correlation analysis and redundancy analysis results indicated that the soil organic matter (OM) content in the citrus orchard was significantly higher than that in other areas, and the difference in soil OM content might be the main reason for the difference in the diazotrophic communities. The diazotrophic communities and their associated diversity under different land use types were driven by soil heavy metal and soil N (including NH4+-N, NO3−-N and total N (TN)) contents. Specifically, TN was highly correlated with the NMDS1 score of the soil diazotrophic community, which indicated that the soil TN content was the main reason for the high similarity among the diazotrophic communities in the corn field, vegetable field and shrub soils. Overall, our study offers a detailed description of the characteristics of the diazotroph community structure under different land use types around a mining area.

Environmental evaluation of remediated lands quality of manganese quarry lands (Zaporizhsky and Olexandrovsky opencast workings) on humus content and salinity

Environmental protection, rational use of natural resources and ensuring the ecological safety of human life are integral conditions of sustainable economic and social development of European Union. Mining industry is one of the powerful factors that leads to degradation of various native landscapes. Withdrawal of agricultural land from intended use results from the minerals extraction. Instead them man-made landscapes (dumps and quarries) are formed, as well as destructive territories characterized by subsidence, contamination with toxic compounds, decrease of species richness and biological diversity. Disturbed territories formed during mining process are usually partially restored with remediation. Remediation process consist of two stages: technical and biological. In the result of technical stage implementation, substrates with different potential fertility having different environmental properties and quality are formed. However, in quality assessment of remediated soils insufficient attention is paid to restoration of the soil environmental properties, namely their suitability for existence of soil biota, which ensures the soil sustainability and vitality. Purpose of the presented work was to assess quality of remediated lands in condition of Ordzhonikidzevsky manganese quarry (Olexandrovskiy and Zaporizhkiy careers) on the possibility of their use and suitability for soil biota existence, as well as providing recommendations for further rational economic use of them. Data on chemical properties of reclaimed soil were collected on the sites of performed recultivation. Humus content was determined according to DSTU 4289: 2004, analysis of water extraction was carried out according to GOST 26425-85, GOST 26426-85, GOST 26427-85, GOST 26428-85. The study is novel in that it is proposed to take into account environmental conditions for existence of soil invertebrates which play a crucial role in formation of agro-system stability mechanisms. The main indicators determining the productivity of remediated lands and the degree of their suitability for soil biota existence are values of actual acidity and salinity degree. An assessment of the reclaimed lands quality on the Ordzhonikidzevsky ore mining and processing enterprise was carried out on the example of Zaporizhsky and Olexandrovsky open-cast workings on the possibility of their economic use and suitability for the soil biota existence, as well as recommendations for further rational use. It was found that studied areas by the main characteristics are suitable for the further settlement and successful existence of soil biota. It is concluded that as a result of the technical stage of reclamation, an artificial reclaimed soil was obtained, which, according to the main characteristics, is similar to native zonal soils located in this area prior to mining; the recultivated soil has somewhat less fertility and greater salinity of lower horizons, but it is able to perform ecological functions and can not only be used for economic purposes, but also perform ecological role, serving as an environment for existence of soil invertebrates.

Analysis of Environmental Properties of Paddy Soils with Regard to Seasonal Variation and Farming Methods

The aim of this study is to investigate the environmental properties of paddy soils depending on farming methods and seasonal variation. The paddy soils in 11 plots of conventional paddy and 24 plots of organic paddy were sampled and analyzed in four season of March, May, August, and October. The obtained data of soil properties were used for statistical analysis. A nalysis of variance showed that only NH4-N and P2O5 were significantly different depending on farming methods. However, the differences of all soil properties depending on seasonal variation were strongly significant. Principal component analysis also presented t hat nitrogen and phosphorus concentration in soils were more significantly influenced by seasonal variation than farming method. Electric conductivity in soil was decreased from March to October. Amounts of soil organic matter in August and October were higher than that in March and May. T-N was decreased from March to October. NH4-N and NO3-N in the soil of both conventional and organic paddy were higher in May than other seasons. T-P concentration was found to be highest in August, but P2O5 concentration was lowest in August. It can be concluded that seasonal variation should be considered for analysis and comparison o f soil environmental properties. Key words: Paddy Soil, Soil Chemical Properties, Farming Method, Seasonal Variation, Analysis of Variance, Principal Component Analysis

Soil Properties and Spatial Processes Influence Bacterial Metacommunities within a Grassland Restoration Experiment

AbstractMetacommunity theory proposes that a collection of local communities are linked by dispersal and the resulting compositions are a product of both niche‐based (species sorting) and spatial processes. Determining which of these factors is most important in different habitats can provide insight into the regulation of community assembly. To date, the metacommunity organization of heterotrophic soil bacteria is largely unknown. Spatial variation of soil bacterial communities could arise from (1) the resource heterogeneity produced by plant communities through root exudation and/or litter inputs; (2) the heterogeneity of soil environmental properties; and (3) pure spatial processes, including dispersal limitation and stochastic assembly. Understanding the relative importance of these factors for soil bacterial community structure and function could increase our ability to restore soil communities. We utilized an ongoing tallgrass prairie restoration experiment in northeastern Kansas to assess if restoring native plant communities produced changes in bacterial communities 6 years after restoration. We further examined the relative importance of the spatial heterogeneity of plant communities, soil properties, and pure spatial effects for bacterial community structure in the old‐field restoration site. We found that soil bacterial communities were not influenced by plant restoration, but rather, by the local heterogeneity of soil environmental properties (16.9% of bacterial community variation) and pure spatial effects (11.1%). This work also stresses the idea that restoring bacterial communities can take many years to accomplish due to the inherent changes that occur to the soil after cultivation and the time it takes for the re‐establishment of soil quality.

Soil bacterial communities shaped by geochemical factors and land use in a less-explored area, Tibetan Plateau

BackgroundAs the largest low-latitude permafrost region, the Tibetan Plateau (TP) is an important part of the earth’s terrestrial ecosystem and one of the most vulnerable areas to climate change and human activities. However, to the best of our knowledge, the bacterial communities in TP soils and their roles in biogeochemical cycles remain limited.ResultsIn this study, we report the bacterial community structure and function as well as their correlation with environmental factors in TP major ecosystems (farmland, alpine meadow and oligosaline lake) by using metagenomic approaches. Compared with other soil samples in various environments, TP soils share a core set of microorganisms with a distinct abundance and composition. Among TP soil samples, the taxonomic and functional composition of bacterial communities among the upper (3-5 cm) and lower (18-20 cm) soils of farmland sites were highly similar, whereas the dissimilarities within alpine meadow samples were significantly greater than among farmland samples. A similar pattern was observed in elements cycles and pathways associated with adaption to environment and land use types. Canonical correlation analysis revealed that the bacterial communities in most of farmland and alpine meadow soil samples were also significantly correlated with geogenic variables. Specifically, the root-nodule bacteria are negatively correlated with the soil moisture and pH, while Thiobacillus associated with sulfur cycles show potential responses to low temperature and intense UV radiation.ConclusionsThese findings indicate that the bacterial community structure and functions in TP soils were influenced by both human activities and soil environmental properties, and that the bacterial communities appeared to be more homogenized in the farmland soils compared with pristine alpine meadows.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-14-820) contains supplementary material, which is available to authorized users.

The relative impact of land use and soil properties on sizes and turnover rates of soil organic carbon pools in Subtropical China

AbstractThe dynamics of soil organic carbon (SOC) pools determine potential carbon sequestration and soil nutrient improvement. This study investigated the characteristics of SOC pools in five types of cultivated topsoils (0–15 cm) in subtropical China using laboratory incubation experiments under aerobic conditions. The sizes and turnover rates of the active, slow and resistant C pools were simulated using a first‐order kinetic model. The relative influence of soil environmental properties on the dynamics of different SOC pools was evaluated by applying principal component analysis (PCA) and aggregated boosted trees (ABTs) analysis. The results show that there were significantly greater sizes of different SOC pools and lower turnover rates of slow C pool in two types of paddy soils than in upland soils. Land use exerted the most significant influence on the sizes of all SOC pools, followed by clay content and soil pH. The soil C/N ratio and pH were the major determinants for turnover rates of the active and slow C pools, followed by clay content which had more impact on the turnover rates of the active C pool than the slow C pool. It is concluded that soil type exerts a significant impact on the dynamics of SOC.

Long-term effects of different tillage and field operation regimes on soil structure

Only little is known about the rate and extent of structural evolution under the combined influence of tillage and wheeling. Whereas some quantitative information on the regeneration of compacted soils is available, the course and potential of structure formation and recovery under the absence of wheel traffic – as made possible by Controlled Traffic Farming (CTF) systems using permanent traffic lanes – are not well investigated and understood. Therefore the effects of tillage practices and field traffic organization on soil structure were studied in a crop sequence under practical soil management conditions on a loamy orthic luvisol at Tänikon, Switzerland (1187 mm mean annual precipitation, 8.0 °C mean annual temperature). From 2000 to 2008 the effect of no-till on soil structure evolution was studied on a formerly ploughed field and compared to continuously ploughed plots. Since 2008 the previous random field traffic organization was maintained in the ploughed and no-till plots, but changed to controlled traffic in plots formerly under shallow tillage and consecutively managed by no-till. Soil structure evolution was described by repeated samplings of undisturbed soil cores in the top- (10-15 cm) and subsoil (35-40 cm) and subsequent analysis of porosity, permeability and strength characteristics in the lab. In situ measurements of parameters characterizing soil water regime (volumetric water content, matric potential) and the soil environment (O2- and CO2-concentrations in soil air, oxygen diffusion rate, redox potential) under field conditions were done quasi continuously at several soil depths. Results show a slow evolution of structural properties in the subsoil and a limited structure formation in the absence of tillage measures in the topsoil. Soil structure evolution can be followed up in short-term cycles covering individual vegetation periods as well as in medium-term cycles covering crop rotation periods. In situ measurements of water retention characteristics and properties of soil environment revealed consistent but minor effects of field traffic organisation on processes depending on soil structure as well as on weather conditions.

Effect of site conditions and tree species composition on physico-chemical properties of soil environment in the Western Carpathians area

The objective of pedological research conducted in the Kněhyně–Čertův mlýn National Nature Reserve was to verify to what extent the properties of the soil environment are influenced by: a) chemistry of soil-forming substrate, b) site conditions, c) species composition of forest stand. The results of this study document that the soil taxonomic units in the area of interest are of podzol character and that the altitudinal soil zonality has not developed there. The total content of basic macrobioelements in soil-forming substrates is not in correlation with their accessible fraction in top genetic horizons of the profile depth. The results of this study also show that lead content reaches a significantly hazardous boundary level at sites of ridge stands in the exposure of northern quadrants. The soil environment under forest stands with prevailing Norway spruce (Picea abies/L./ Karst.) is enriched with C-compounds and active humus in the entire profile more than the soil under stand types with prevailing European beech (Fagus sylvatica). In top horizons of soil Norway spruce influences significantly negatively humus quality (C:N) and also the content of accessible potassium which decreases in humification horizons below the limit of 200 mg∙kg-1.

Characteristics of Soil Environmental Properties at Vegetation Transition Zone in Forests

Characteristics of Soil Environmental Properties at Vegetation Transition Zone in Forests