Seasonal Patterns of Microbial Community Structure and Enzyme Activities in Coastal Saline Soils of Perennial Halophytes

Perennial halophytes are known to be one of the most influential parameters in coastal ecosystem affecting ecosystem processes. The aim of this study was to investigate the changes in soil microbial community structure and enzyme activities in different halophyte‐covered soils (Arthrocnemum indicum , Aeluropus lagopoides , Heleochloa setulosa and Suaeda nudiflora ) with control soil (un‐vegetated) that were collected in three seasons (rainy, winter and summer) from intertidal coastal soils of Gujarat, India. Soil microbial community structure was assessed using phospholipid fatty acid (PLFA) profiling. Halophytes influenced significantly soil micro‐environment by exerting effects on the soil chemical characteristics, enzyme activities and microbial community structure. The activities of β‐glucosidase, urease and alkaline phosphatase were significantly higher in halophyte‐covered soils than in control soil. Among four halophyte‐covered soils, the highest amounts of total, bacterial, actinomycetes and fungal PLFAs were observed in Arthrocnemum soil. The concentrations of total, bacterial, actinomycetes and fungal PLFAs were also significantly higher in summer and winter seasons than in rainy season, whereas enzyme activities also vary with seasons. The non‐metric multidimensional scaling analysis PLFA profiling revealed that the structure of microbial community significantly differed in all seasons as well as between control and halophyte‐covered soils. These shifts in microbial community were due to the higher abundance of Gram‐positive, total bacterial and actinomycetes PLFAs in summer and winter seasons than in rainy season, whereas abundance of fungal biomarker was significantly higher in rainy season than in other seasons. Among halophytes, significantly higher abundance of Gram‐positive, Gram‐negative and total bacteria was observed in Arthrocnemum , Heleochloa and Suaeda whereas the lowest in control soil. Halophytes exhibited improved soil microbial activities, which is important for healthy ecosystem. Copyright © 2017 John Wiley & Sons, Ltd.     

Variations in pore distribution of reconstructed soils induced by opencast mining and land rehabilitation based on computed tomography images

Opencast coal mining is an anthropogenic activity that changes the antecedent soil profile, and it was important to understand the distribution characteristics of soil pore and then select suitable land rehabilitation measures. To better quantify the pore distribution characterization of reconstructed soils in opencast coalmine dumps, high-resolution and non-destructive computed tomography (CT) method was used to study the effect of opencast coal-mining and land rehabilitation on the soil pore distribution by scanning soils from the Antaibao Opencast Coal-mine in China. The soils were taken from the dump platforms with different rehabilitation time and an unmined site. ImangeJ 2 was used to process the scanned images and the soil pore densities and porosities of different pore sizes were used to analyze the distribution characteristics of soil pore. Opencast mining activities decreased soil pore density and soil porosity, especially in macropores. Compared to unmined soils, the total porosity of the non-rehabilitated soils reduced by 25.0%, 20.5%, 17.7% at the depths of 0–25, 25–50, 50–75 cm, respectively. Vegetation rehabilitation should be used to develop soil pore structure and improve the proportion of different pore sizes.     

滕州表层土壤硒异常特征及来源分析

为确定影响滕州地区表层土壤硒含量变化的因素,对研究区土壤的地球化学指标进行统计分析,结果显示,研究区土壤硒背景值为0.08mg/kg,异常下限值为0.17 mg/kg,表层土壤硒平均含量为0.23 mg/kg,标准差为0.144 mg/kg,变异系数为62.6%。综合相关性分析、主成分分析以及富集因子分析结果,表明表层土壤硒异常主要受人为因素的影响。不同区域表层土壤硒含量由高到低依次为煤矿区交通繁忙区农田区。在土壤垂直方向上,煤矿周边土壤中硒含量自下而上增加的趋势要明显快于不受煤矿直接影响的区域,同时前者的变化速率和转折端的出现均快于后者。因此,滕州地区表层土壤硒异常主要受煤矿开发的影响。     

Microbiology of soils at opencast coal sites. II. Population transformations occurring following land restoration and the influence of ryegrass/fertilizer amendments

Data from field work and pot experiments gave insight into transformations occurring in soil microbial populations at opencast coal sites during the first year of land restoration. Total bacterial biomass increased markedly immediately following restoration, while pot experiments revealed that this flush was confined to soil stored below 1 m depth in stockpiles, where anaerobic conditions develop. Fungal and actinomycete propagules declined at the outset of restoration, but rallied during the first year, while the bacterial flush subsided. Fungal hyphae, which accounted for 50% of microbial biomass in surface mound and freshly restored soils, accounted for > 99% one year after restoration. Experiments involving fertilizer and ryegrass amendments showed the biomass of restored soil to be limited by carbon, rather than nitrogen or phosphorus.     

Accumulation and composition of total organic carbon in reclaimed coal mine lands

Reclaimed coal mine lands have the potential to sequester atmospheric carbon (C); however, limited information exists for the western USA coalfields. This study was carried out on two chronosequences (BA‐C₃ grasses and DJ‐shrubs) of reclaimed sites at two surface coal mines to determine the effects of vegetation, soil texture, and lignin content on soil total organic carbon (TOC) accumulations. In the BA chronosequence, TOC increased over 26 years at an average rate of 0·52 Mg C ha⁻¹ yr⁻¹ in the 0–30 cm depth and was significantly correlated with clay content. Comparison between < 1 and 16‐year‐old stockpile soils indicated TOC content did not differ significantly. In the DJ chronosequence, TOC content in the 0–30 cm depth declined from 31·3 Mg ha⁻¹ in 5‐year‐old soils to 23·4 Mg ha⁻¹ in 16‐year‐old soils. The C:N ratios suggested that some (up to 2·0 per cent) of the TOC was potentially derived from coal particles in these reclaimed soils. Soil total N (TN) contents followed a similar trend as TOC with TOC and TN concentrations strongly correlated. Lignin contents in TOC of all reclaimed soils and topsoil stockpiles (TSs) were higher than that of nearby undisturbed soils, indicating the recalcitrant nature of TOC in reclaimed soils and/or possibly the slow recovery of lignin degrading organism. Results indicated that TOC accumulations in DJ were largely controlled by its composition, particular lignin content. In BA sites TOC accumulation was strongly influenced by both clay and lignin contents. Copyright © 2008 John Wiley & Sons, Ltd.     

Phyllostachys edulis (moso bamboo) rhizosphere increasing soil microbial activity rather than biomass

Purpose

Rhizosphere and fertilization might affect soil microbial activities, biomass, and community. This study aimed to evaluate the impacts of Phyllostachys edulis (moso bamboo) rhizospheres on soil nutrient contents and microbial properties in a moso bamboo forest with different fertilizer applications and to link soil microbial activities with abiotic and biotic factors.

Materials and methods

The experiment included three treatments: (1) application of 45% slag fertilizer (45%-SF); (2) application of special compound fertilizer for bamboos (SCF); and (3) the control without any fertilizer application (CK). Simultaneously, bulk soils and 0.5, 2.5, 4.5, and 6.5-year-old (y) bamboo rhizosphere soils were selected. Soil nutrient contents were analyzed. Microbial activities were evaluated based on the activities of soil enzymes including β-glucosidase, urease, protease, phosphatase, and catalase. The total microbial biomass and community were assessed with the phospholipid fatty acids (PLFAs) method.

Results and discussion

In the CK and SCF treatments, organic matter contents of rhizosphere soils were significantly higher than those of bulk soils. Soil β-glucosidase, urease, protease, phosphatase, and catalase activities in rhizosphere soils were higher than those of bulk soils, with the sole exception of β-glucosidase of 0.5 y rhizosphere soil in the 45%-SF treatment. Compared with the CK treatment, fertilizer applications tended to increase soil total PLFAs contents and changed soil microbial community. Moso bamboo rhizospheres did not significantly increase the total microbial biomass. In the SCF treatment, the Shannon index of bulk soil was significantly lower than those of rhizosphere soils.

Conclusions

Our results suggested that both rhizospheres and fertilizer applications could change the soil microbial community structures and that moso bamboo rhizosphere could increase microbial activity rather than biomass in the forest soils with different fertilizer applications.

     

Soil enzyme activities in dependence on tree litter and season of a social forest,Burdwan, India

The study was done to evaluate enzyme activities (amylase, cellulase and invertase) from the soils of different vegetation sites, with seasonal variation, of social forest, Burdwan, India. Study results showed significant lower enzymatic activities in the subsoil compared to those of the topsoil. The seasonal variations indicated that amylase, cellulase and invertase enzyme activities had reached peaks during the rainy seasons in different soil depths. Amylase activity was highest in Tectona litter containing soil in all seasons in both the soil layers. All the three enzyme activities have shown significant positive correlation with available nitrogen (p < 0.05) and available phosphorous (p < 0.05) during rainy season in both the soil depths. Correlation study revealed that soil organic carbon was positively correlated with cellulase and invertase activities except in the Anacardium vegetation site in the topsoil during rainy season. Irrespective of the seasons and the depths of soil, control site without vegetation showed much lower levels of organic carbon and enzyme activity compared to those of the experimental sites. Therefore, it is concluded that carbon transformation will be higher during rainy season in the vegetation sites of forest soil under such agroclimatic conditions.     

Effective alleviation of Cd stress to microbial communities in mining reclamation soils by thiourea-modified biochar amendment

Reclaimed soils in mining area usually display low fertility and present Cd stress. The amendment of modified biochar effectively fixes Cd in soils, enhances soil fertility, and reduces Cd stress in soil microorganisms. However, the effect of thiourea-modified biochar (TBC) on microbial adaptability to Cd stress in mining reclamation soils is still unclear. The present work studied the Cd immobilization and microbial community changes in a mining reclamation soil displaying extreme Cd contamination under TBC amendment. The results indicated that the amendment of TBC significantly enhanced (P < 0.05) soil pH, the content of available phosphorus (AP), and the activities of urease and polyphenol oxidase by 1.3%, 463.4%, 54.4%, and 84.0%, respectively, compared to the control without amendment. The amount of toxicity characteristic leaching procedure-extracable Cd decreased (P < 0.05) by 68.0% in the TBC-amended soil compared with the unamended soil. The structure of soil microbiota was reorganized and the alpha diversity index was increased in the TBC treatment. The TBC amendment increased the relative abundances of Proteobacteria, Bacteroidota, and Zoopagomycota, which were strongly associated (P < 0.01) with higher soil pH and AP. Structural equation model results demonstrated that Cd immobilization was directly influenced by soil pH, AP, and urease, and indirectly affected by bacterial structure in the TBC treatment. The TBC amendment can effectively improve the structural composition of soil bacteria under Cd stress and enhance the pathways of decreasing soil Cd availability as well. The results might facilitate the development of in-situ remediation programs in Cd-contaminated soils in the future.     

Shrub-interspace dynamics alter relationships between microbial community composition and belowground ecosystem characteristics

In desert ecosystems, belowground characteristics are influenced chiefly by the formation and persistence of “shrub-islands of fertility” in contrast to barren plant interspaces. If soil microbial communities are exclusively compared between these two biogeochemically distinct soil types, the impact of characteristics altered by shrub species, especially soil C and N, are likely to be overemphasized and overshadow the role of other characteristics in structuring microbial composition. To determine how belowground characteristics influence microbial community composition, and if the relative importance of these characteristics shifts across the landscape (i.e., between and within shrub and interspace soils), changes in microbial communities across a 3000-year cold desert chronosequence were related to 27 belowground characteristics in surface and subsurface soils. When shrub and interspace communities in surface and subsurface soils were combined across the entire chronosequence, communities differed and were primarily influenced by soil C, NO₃⁻ concentrations, bulk density, pH, and root presence. Within shrub soils, microbial communities were shrub species-specific, especially in surface soils, highlighting differences in soil characteristics created by specific shrub species and/or similarity in stresses structuring shrub species and microbial communities alike. Microbial communities in shrub soils were not influenced by soil C, but by NO₃⁻ and NH₄⁺ concentrations, pH, and silt in surface soils; and Cl, P, soil N, and NO₃⁻ concentrations in subsurface soils. Interspace soil communities were distinct across the chronosequence at both depths and were strongly influenced by dune development. Interspace communities were primarily associated with soil stresses (i.e., high B and Cl concentrations), which decreased with dune development. The distribution of Gram-positive bacteria, Actinobacteria, and fungi highlighted community differences between and within shrub and interspace soils, while Gram-negative bacteria were common in all soils across the chronosequence. Of the 27 belowground characteristics investigated, 13 separated shrub from interspace communities, and of those, only five emerged as factors influencing community composition within shrub and interspace soils. As dunes develop across this cold desert chronosequence, microbial community composition was not regulated primarily by soil C, but by N and P availability and soil stresses in shrub soils, and exclusively by soil stresses in interspace soils.     

Functional and structural responses of bacterial and fungal communities from paddy fields following long-term rice cultivation

Purpose

Rice paddy soils undergo pedogenesis driven by periodic flooding and drainage cycles that lead to accumulation of organic matter and the stratification of nutrients and oxygen in the soil profile. Here, we examined the effects of continuous rice cultivation on microbial community structures, enzyme activities, and chemical properties for paddy soils along a chronosequence representing 0–700 years of rice cropping in China.

Materials and methods

Changes in the abundance and composition of bacterial and fungal communities were characterized at three depths (0–5, 5–10, and 10–20 cm) in relation to organic carbon, total nitrogen, dissolved organic carbon, microbial biomass carbon/nitrogen, and activities of acid phosphatase, invertase, and urease.

Results and discussion

Both soil organic carbon and total nitrogen increased over time at all three depths, while pH generally decreased. Microbial abundance (bacteria and fungi) and invertase and urease activity significantly increased with the duration of rice cultivation, especially in the surface layer. Fungal abundance and acid phosphatase activity declined with depth, whereas bacterial abundance was highest at the 5–10-cm soil depth. Profiles of the microbial community based on PCR-DGGE of 16S rRNA indicated that the composition of fungal communities was strongly influenced by soil depth, whereas soil bacterial community structures were similar throughout the profile.

Conclusions

Soil bioactivity (microbial abundance and soil enzymes) gradually increased with organic carbon and total nitrogen accumulation under prolonged rice cultivation. Microbial activity decreased with depth, and soil microbial communities were stratified with soil depth. The fungal community was more sensitive than the bacterial community to cultivation age and soil depth. However, the mechanism of fungal community succession with rice cultivation needs further research.

     

Post-reclamation Age Effects on Soil Physical Properties and Microbial Activity Under Forest and Pasture Ecosystems

During surface mining and subsequent reclamation efforts, physical, chemical, and biological properties of soils are disturbed. A study was conducted to evaluate the effects of age chronosequence on soil physical property and microbial activity in chronosequence reclaimed sites covering successional ages in the ranges 1, 4, 8, 11, and 13 years under forest and pasture ecosystems. The adjacent normal and unmined pasture and forest were used as a control for comparison purposes. The study site was located at the Red Hill Mine in east central Mississippi (approximately 33.3 N latitude and 89 W longitude), which is used by the North America Mining Company, LLC. Soil samples were collected from the reclaimed and unmined sites at 0–15- and 15–30-cm depth and analyzed for selected soil quality indicators. Results indicated that water stable aggregate and infiltration were increased, but soil bulk density and compaction decreased with increasing reclamation age. Soil penetration resistance was greater in the pasture than forest ecosystem. All reclaimed soils had less microbial enzyme activity than an unmined forest ecosystem; however, bacteria population level after 11 years since reclamation was similar to that of unmined forest soils. Soil organic carbon increased with increasing reclamation age strongly correlated with soil physical indicators and appears to be the main driving force during the development of soil physical and biological properties in the humid southeast.     

Enzyme activity and carbon dioxide evolution from upland and wetland rice soils under three agricultural practices in hilly regions

Summary Dehydrogenase activity (a measure of microbial biomass), urease activity and CO₂ evolution were measured in soils planted to rice (Oryza sativa L.) under three different agricultural practices prevalent in hill regions. The effects of hill slope, terrace and valley agriculture were investigated for two cropping seasons. The valleys and terraces were kept flooded during each cropping season while the hill slopes were cultivated with dryland practices. The type of agricultural practice and the date of observation had a significant influence on enzyme activity and CO₂ evolution. A positive correlation was observed between dehydrogenase and urease activity and soil moisture content. Dehydrogenase and urease activity and soil respiration were positively correlated among themselves. The activity of both enzymes and CO₂ evolution were highest in valley soils followed by terrace and hill-slope sites.     

Long-term and legacy effects of manure application on soil microbial community composition

We analyzed soil prokaryotic and fungal community composition in soils with varying histories of cattle manure application. The manure treatments were (i) annual application for 43 years (MF), (ii) annual application for 14 years followed by 29 years without application (MF14), and (iii) annual application for 30 years followed by 13 years without application (MF30). An annual application of chemical nitrogen (N) fertilizer (CNF) and a non-amended control (Con) were also included. Soil prokaryotic evenness and diversity significantly decreased in MF relative to other treatments in fall, but were similar to the other fertilizer treatments in spring and summer. Distinct prokaryotic and fungal community composition was observed in MF compared to other treatments across fall, spring, and summer seasons. The MF treatment significantly increased the relative abundance of Firmicutes, Gammaproteobacteria, and Gemmatimonadetes, but significantly decreased the relative abundance of Acidobacteria. In fall, the soil prokaryotic and fungal community composition with MF30 was significantly different than the other fertilization treatments. Overall, the study showed that annual manure application (MF) led to a different microbial community composition than the other fertilizer treatments. Soil without manure application for 13 years (MF30) had a significantly different microbial community composition from other fertilizer treatments in fall, while the soil without manure application for 29 years (MF14) resembled a microbial community that had never received manure.     

Changes in the composition and diversity of topsoil bacterial,archaeal and fungal communities after 22 years conventional and no-tillage managements in Northern China

A comprehensive comparison about microbial community (bacterial, archaeal and fungal) response to different tillage managements in Northern China remain little studied, in this study we compared no-tillage (NT) versus conventional tillage (CT) management on topsoil microbial community diversity and composition in field experiment. We found that NT practice significantly increased the soil moisture content (SMC), bulk density, stocks of soil organic carbon (SOC), total nitrogen (TN), and microbial biomass carbon and nitrogen (P < 0.05). Moreover, higher levels of bacterial and archaeal alpha diversity were observed in NT relative to CT while unexpectedly, there was no significant difference found in fungal diversity between two treatments. The most pronounced shifts in the composition of the different microbial groups were found for the archaeal community, which followed by bacterial and fungal. NT practice markedly enhanced abundances of Proteobacteria (belongs to bacteria) phyla, Thaumarchaeota phyla (belongs to archaea) and Glomeromycota phyla (belongs to fungi). Redundancy analysis revealed that the factor that most closely correlated with bacterial, archaeal and fungal composition were SMC, TN and SOC, respectively. Considering NT enhanced both microbial composition and C storage in topsoil, we suggest that NT offers significant promise to improve topsoil health in this region.     

Effects of addition of maize litter and earthworms on C mineralization and aggregate formation in single and mixed soils differing in soil organic carbon and clay content

C mineralization and aggregate stability directly depend upon organic matter and clay content, and both processes are influenced by the activity of microorganisms and soil fauna. However, quantitative data are scarce. To achieve a gradient in C and clay content, a topsoil was mixed with a subsoil. Single soils and the soil mixture were amended with 1.0 mg maize litter C g soil⁻¹ with and without endogeic earthworms (Aporrectodea caliginosa). The differently treated soils were incubated for 49 days at 15 °C and 40% water holding capacity. Cumulative C mineralization, microbial biomass, ergosterol content and aggregate fractions were investigated and litter derived C in bulk soil and aggregates were determined using isotope analyses. Results from the soil mixture were compared with the calculated mean values of the two single soils. Mixing of soil horizons differing in carbon and clay content stimulated C mineralization of added maize residues as well as of soil organic matter. Mixing also increased contents of macro-aggregate C and decreased contents of micro-aggregate C. Although A. caliginosa had a stimulating effect on C mineralization in all soils, decomposition of added litter by A. caliginosa was higher in the subsoil, whereas A. caliginosa decreased litter decomposition in the soil mixture and the topsoil. Litter derived C in macro-aggregates was higher with A. caliginosa than with litter only. In the C poor subsoil amended with litter, A. caliginosa stimulated the microbial community as indicated by the increase in microbial biomass. Furthermore, the decrease of ergosterol in the earthworm treated soils showed the influence of A. caliginosa on the microbial community, by reducing saprotrophic fungi. Overall, our data suggest both a decrease of saprotrophic fungi by selective grazing, burrowing and casting activity as well as a stimulation of the microbial community by A. caliginosa.     

Impacts of continuous excessive fertilization on soil potential nitrification activity and nitrifying microbial community dynamics in greenhouse system

Purpose

Sampling and analysis of greenhouse soils were conducted in Shouguang, China, to study continuous excessive fertilization effect on nitrifying microbial community dynamics in greenhouse environment.

Materials and methods

Potential nitrification activity (PNA), abundance, and structure of nitrifying microbial communities as well as the correlations with soil properties were investigated.

Results and discussion

Short-term excessive fertilization increased soil nutrient contents and the diversity of nitrifying microbial communities under greenhouse cultivation. However, the abundance and diversity of nitrifying communities decreased greatly due to the increase of soil acidity and salinity after 14 years of high fertilization in greenhouse. There was a significant positive correlation between soil PNA and the abundance of ammonia-oxidizing bacteria (AOB) but not that of ammonia-oxidizing archaea (AOA) in topsoil (0–20 cm) when pH ≥7. Soil PNA and AOB were strongly influenced by soil pH. The groups of Nitrososphaeraceae, Nitrosomonadaceae, and Nitrospiraceae were predominant in the AOA, AOB, and nitrite-oxidizing bacteria (NOB) communities, respectively. Nitrifying community structure was significantly correlated with soil electrical salinity (EC), organic carbon (OC), and nitrate nitrogen (NO₃ ^?–N) content by redundancy analysis (RDA).

Conclusions

Nitrification was predominated by AOB in greenhouse topsoil with high fertilizer loads. Soil salinity, OC, NO₃ ^?–N content, and pH affected by continuous excessive fertilization were the major edaphic factors in shaping nitrifying community structure in greenhouse soils.

     

Assessment of Seasonal and Site-Specific Variations in Soil Physical, Chemical and Biological Properties Around Opencast Coal Mines

Coal mining adversely affects soil quality around opencast mines. Therefore, a study was conducted in 2010 and 2011 to assess seasonal and site-specific variations in physical, chemical, and biological properties of soil collected at different distances from mining areas in the Jharia coalfield, India. Throughout the year, the soil in sites near coal mines had a significantly higher bulk density, temperature, electrical conductivity, and sulfate and heavy metal contents and a significantly lower water-holding capacity, porosity, moisture content, pH, and total nitrogen and available phosphorus contents, compared with the soil collected far from the mines. However, biological properties were site-specific and seasonal. Soil microbial biomass carbon (MBC) and nitrogen (MBN), MBC/MBN, and soil respiration were the highest during the rainy season and the lowest in summer, with the minimum values in the soil near coal mines. A soil quality index revealed a significant effect of heavy metal content on soil biological properties in the coal mining areas.     

Influence of nitrogen fertilization on soil ammonia oxidizer and denitrifier abundance,microbial biomass,and enzyme activities in an alpine meadow

Terrestrial ecosystems are predicted to experience an increasing level of atmospheric nitrogen (N) deposition, which may cause significant shifts in plant community composition and concomitantly stimulate soil acidification. However, little is known concerning the effects of N deposition on belowground microbial communities in alpine grassland ecosystems such as on the Tibetan Plateau. This study examined the responses of soil N-transforming microbes (measured after DNA extraction and quantitative PCR), soil microbial biomass C (SMBC) and N (SMBN), and soil enzyme activities to different forms (NH₄ ⁺-N, NO₃ ^?-N, and NH₄NO₃-N) and rates (1.5 and 7.5 g N m^?2 year^?1, denoted as low and high N, respectively) of N fertilization (addition) in two successive plant growing seasons. The N rate, not N form, influenced the abundance of ammonia-oxidizing archaea (AOA). High N addition significantly increased ammonia-oxidizing bacteria (AOB) abundance which differed across different N form treatments. Nitrogen addition had no significant impact on the abundance of soil denitrifiers. The SMBC and SMBN were significantly decreased by high N additions, but no difference was found among different N forms. Despite higher urease activities being detected in the late plant growing season, the activities of invertase and alkaline phosphomonoesterase stayed unchanged irrespective of the different N amendments and plant growing season. Significant positive correlations were found between potential nitrification rates and AOB abundances. These results highlight that AOB seemed to respond more sensitively to different N fertilization and might have prominent roles in soil N cycling processes in this Tibetan Plateau alpine meadow than AOA.     

煤矸石组分与表土质地对充填重构土壤导气率的影响

研究煤矸石组分及表土质地对煤矸石重构土壤导气率的影响,探讨重构土壤这种差异显著的非均质土壤导气内在机理,为进一步研究复杂的非均质土壤导气特性提供理论基础。通过在煤矸石中掺杂不同粒径碎石来改变其组分,并利用3种不同质地的土壤在土柱内进行土壤剖面重构,采用一维瞬态法测量其导气率。结果表明:(1)不同碎石粒径和质量分数对混合基质饱和含水量影响不同,掺杂2~5mm粒径碎石,随着质量分数的增加,饱和含水量逐渐增加,从7.29%增加到12.9%;掺杂5~10mm粒径碎石,饱和含水量随着质量分数的增加先增加后减少,分别为7.28%,8.5%,6.9%。(2)煤矸石的导气率远大于土壤,并且煤矸石的导气率对水分的敏感度随质量含水量的增加而增加,而土壤的导气率对水分变化的敏感度均随质量含水量的增加而降低。(3)碎石的存在为大孔隙的产生创造条件的同时也会减少了土壤通气断面,阻隔空气传输的通道。(4)重构土壤导气率受表土质地和底部填充介质的共同影响,覆土土壤导气率决定了重构土壤的导气率大小,而充填基质导气率决定了充填介质对重构土壤导气率影响的系数(Ska)。Ska与充填介质导气率呈显著相关,可以通过指数函数进行拟合(R2=0.93)。通过充填介质及覆土土壤的导气率可以对重构土壤导气率进行估算,简化了重构土壤导气率的测定过程。     

Effects of harvester ant (<Emphasis Type="Italic">Messor</Emphasis> spp.) activity on soil properties and microbial communities in a Negev Desert ecosystem

Harvester ants (Messor spp.) function as an essential link between aboveground resources and below-ground biota such as the microbial community. We examined changes in soil microbial biomass and functional diversity resulting from harvester ant (Messor spp.) activity in the Negev Desert, Israel. Abiotic and biotic soil parameters were recorded during two seasons—wet and dry—also representing food availability periods for the ants (low and high seed availability, respectively). Soil samples were collected monthly from the 0- to 10- and 10- to 20-cm soil layers: (1) near the nest entrance, (2) under chaff piles, and (3) at a 2-m radius from the nest entrance (control). Harvester ant activity increased the percentage of organic matter, total soluble nitrogen, and microbial activity in nest-modified soils in comparison to the control soils. Higher CO₂ evolution was recorded in the low-seed season in ant nest soils than in the control soils. During the high-seed season, higher carbon dioxide evolution was recorded only at the nest entrance locations. There were no differences in microbial biomass between the low- and high-seed seasons, but highest microbial biomass was found under chaff in low-seed season and in nest soils in high-seed season. Microbial functional diversity was higher in nest-modified soils than in the control soils. This study suggests that the effect of harvester ant nests on soil fertility is due to increased microbial biomass and microbial activity in ant nest-modified soils.