Nitrogen availability decreases prokaryotic diversity in sandy soils

In this study, the interrelation between nitrogen availability and prokaryotic diversity are studied using a well-characterised system from a long-term field experiment on a loamy sandy soil. The prokaryotic potential functional diversity and community composition were assessed using community-level physiological profiling (CLPP), and their phylogenetic diversity was analysed using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) in combination with sequencing analysis. Highest prokaryotic potential functional diversity was measured in the control soil receiving no N fertilisation, indicating an efficient as well as versatile utilisation of the substrates in this soil. Both substrate utilisation richness and substrate utilisation evenness, the two constituents of the functional diversity, were decreased with increasing N supply. Furthermore, distinct prokaryotic community compositions were generated in N-enriched soils compared to unfertilised control soils. These differences suggest a dominance of populations adapted to utilising readily available substrates. We demonstrated that the shift in prokaryotic functional diversity was connected to a shift in the phylogenetic structure of the bacterial and archaeal communities. Taken together, our data clearly show that, for the sandy soil system, prokaryotic diversity and N availability were interrelated.     

不同秸秆还田方式对和田风沙土土壤微生物 多样性的影响

秸秆还田是有效利用秸秆资源的重要途径,能够提高土壤养分含量、调节土壤微生物的群落结构和多样性,但目前还缺乏不同秸秆还田方式对新疆沙化土壤肥力和微生物多样性影响的系统报道。为探索新疆沙化土壤肥力可持续提升模式,于2010—2012年在和田风沙土土壤上设置秸秆直接还田(NPKS)、过腹还田(NPKM,15.0 t×hm~(-2))和炭化还田(NPKB1,2.5 t×hm~(-2);NPKB2,15.0 t×hm~(-2))定位试验,研究不同秸秆还田处理对和田风沙土土壤养分、微生物数量、土壤酶活性和Biolog碳源利用的影响。结果表明:1)与单施化肥(NPK)相比,不同秸秆还田方式均能显著提高风沙土土壤养分含量,其中NPKM处理效果最好,其次是NPKB2处理,NPKS和NPKB1处理分别为第3和第4。2)不同秸秆还田方式对土壤微生物数量影响差异显著,均增加了土壤中细菌、放线菌和生理菌群的数量,与NPK处理相比,细菌数量NPKB2处理最高,放线菌数量NPKM处理最高,分别显著提高了413.16%和574.19%。但NPKB1和NPKB2处理对生理菌群数量的提升效果好于NPKS处理和NPKM处理。土壤酶活性,不同秸秆还田方式总体好于NPK处理,NPKM处理的提升效果最好。3)Biolog碳源利用分析表明不同秸秆还田方式均能提高风沙土土壤微生物活性和丰富度指数。主成分分析表明,不同秸秆还田方式土壤微生物群落明显不同,起分异作用的碳源主要为羧酸类和糖类。聚类分析显示NPKB2和NPKM处理之间、NPKB1和NPKS处理之间土壤微生物功能相似。由此可以看出,不同秸秆还田方式均能显著提高和田沙化土壤微生物活性和功能多样性,但不同方式的增效不同。从3年定位试验结果看,秸秆过腹还田和炭化还田的效果较好,秸秆直接粉碎还田有增加土传病害的风险。该结果将为南疆沙化土壤肥力可持续提升提供一定的理论指导。     

Spatial variability of glyphosate mineralization and soil microbial characteristics in two Norwegian sandy loam soils as affected by surface topographical features

The aim of this study was to investigate the possible influence of surface topographical features on the spatial variability of glyphosate degradation and some microbial characteristics in sandy loam soil. Soil samples were taken from the ploughed layer across an agricultural field after seedbed preparation for grain (Grue site), and down to 1 m depth under a ridge tilled field (Målselv site), both sites having similar soil textural characteristics (sandy loam soil). Laboratory experiments were performed looking at glyphosate mineralization and soil microbial activity at the Grue site, as well as microbial biomass, activity and substrate utilization patterns at the Målselv site. Microbial biomass and activity decreased, and substrate utilization patterns changed with increasing soil depth, reflecting naturally occurring changes in quantity and quality of soil organic carbon. Further, our results show that considerable spatial heterogeneity in the degradation rate of glyphosate and general carbon utilization exists even across small areas within a single agricultural field. This horizontal variability was observed over several spatial scales, and could not be clearly explained. It evidently arose from differences in environmental factors affecting microbial activity and growth, and topographical features controlling redistribution of water and matter flow patterns were correlated to the investigated soil microbial variables.     

Soil microbial community response to surfactants and herbicides in two soils

The environmental impacts of herbicides on desirable plants and the soil biota are of public concern. The surfactants that are often used with herbicides are also under scrutiny as potentially harmful to soil biological systems. To address these concerns, we used two soils, a silt loam and a silty, clay loam from south central Missouri, to investigate the impacts of herbicides and surfactants on soil microbial communities using phospholipid fatty acid (PLFA) analysis. The surfactants used in this study were alkylphenol ethoxylate plus alcohol ethoxylate (Activator 90), polyethoxylate (Agri-Dex), and a blend of ammonium sulfate, drift reduction/deposition polymers and anti-foam agent (Thrust). The herbicides were glyphosate, atrazine and bentazon. Surfactants and herbicides were applied to soils at label rate, either alone or combined, to 4000 g soil per pot. The two soils differed in history, texture, some chemical characteristics and several microbial community characteristics. A few of the chemicals altered some of the components of the microbial community after only one application of the chemical at field-rate. The Cole County, MO silt loam showed larger changes in the microbial community with application of treatments. For the Boone County, MO silty clay loam, Activator 90, Agri-Dex and bentazon treatments increased microbial biomass determined by PLFA; Thrust decreased PLFA markers, bacteria to fungi ratio; and Agri-Dex at both rates decreased monounsaturated fatty acids. Changes in the microbial community due to herbicides or surfactants were minimal in this study of a single application of these chemicals, but could be indicators of potential long-term effects. Long-term studies are needed to determine the changes in the microbial community after several years of annual applications of herbicides and surfactants on a wide array of soil types and management practices.     

生物复混肥对土壤微生物群落功能多样性和微生物量的影响

在温室盆栽条件下,采用Biolog微平板法和氯仿熏蒸浸提法,研究了玉米施用等养分量的无机肥、有机无机复混肥和生物复混肥后土壤微生物群落功能多样性及土壤微生物量的变化。结果表明:生物复混肥处理的土壤微生物平均颜色变化率(AWCD)、微生物群落Shannon指数(H)和微生物群落丰富度指数(S)均最高;施用生物复混肥可明显提高土壤微生物对碳源的利用率,尤其是多酚化合物类和糖类;不同处理土壤微生物碳源利用特征有一定差异,生物复混肥在第1主成分上的得分值为正值,其他各处理在第1主成分上的得分值基本上为负值,起分异作用的主要碳源是糖类和羧酸类。在玉米生长期间各处理土壤微生物量大致呈先升高后逐渐平稳的趋势,且土壤微生物量碳、氮、磷的含量均以生物复混肥处理最高,最高值分别为333.21mg.kg 1、53.02 mg.kg 1和22.20 mg.kg 1。研究表明,生物复混肥的施用比等养分量的有机无机复混肥处理能显著提高土壤微生物群落碳源利用率、微生物群落丰富度和功能多样性,显著增加土壤微生物量碳、氮、磷的含量,有利于维持良好的土壤微生态环境。     

Predominant bacterial and fungal assemblages in agricultural soils during a record drought/heat wave and linkages to enzyme activities of biogeochemical cycling

Identification of microbial assemblages predominant under natural extreme climatic events will aid in our understanding of the resilience and resistance of microbial communities to climate change. From November 2010 to August 2011, the Southern High Plains (SHP) of Texas, USA, received only 39.6 mm of precipitation (vs. the historical average of 373 mm) and experienced the three hottest months (June–August 2011) since record keeping began in 1911. The objective of this study was to characterize soil bacterial (16 S rRNA gene) and fungal (internal transcribed spacer 1–4, ITS1-ITS4) species distribution and diversity via pyrosequencing during the peak of the drought/heat wave in July 2011 and when the Drought Index and temperatures were lower in March 2012. Samples were collected from two different soil types (loam and sandy loam) under two different dryland cropping histories (monoculture vs. rotation). Fungal Diversity Indexes were significantly higher after the drought/heat wave while Bacterial Indexes were similar. Bacterial phyla distribution in July 2011 was characterized by lower relative abundance of Acidobacteriaand Verrucomicrobia, and greater relative abundance of Proteobacteria, Chloroflexi, Actinobacteria and Nitrospirae than March 2012 samples. Further grouping of pyrosequencing data revealed approximately equal relative proportions of Gram positive (G+) and Gram negative (G−) bacteria in July 2011, while G− bacteria predominated in March 2012. Fungal class Dothideomycetes was approximately two times greater in July 2011 than in March 2012, while the class Sordariomycetes and a group of unidentified OTUs from Ascomycota increased from July 2011 to March 2012. Microbial community composition was less influenced by management history than by the difference in climatic conditions between the sampling times. Correspondence analysis identified assemblages of fungal and bacterial taxa associated with greater enzyme activities (EAs) of C, N, or P cycling found during the drought/heat wave. Microbial assemblages associated with arylsulfatase activity (key to S cycling), which increased after the drought/heat wave, were identified (Streptomyces parvisporogenes, Terrimonas ferruginea and Syntrophobacter sp.) regardless of the soil and management history. The distinct microbial composition found in July 2011 may represent assemblages essential to maintaining ecosystem function during extreme drought and intense heat waves in semiarid agroecosystems.     

Plant biomass, soil water content and soil N:P ratio regulating soil microbial functional diversity in a temperate steppe: A regional scale study

Soil microorganisms are influenced by various abiotic and biotic factors at the field plot scale. Little is known, however, about the factors that determine soil microbial community functional diversity at a larger spatial scale. Here we conducted a regional scale study to assess the driving forces governing soil microbial community functional diversity in a temperate steppe of Hulunbeir, Inner Mongolia, northern China. Redundancy analysis and regression analysis were used to examine the relationships between soil microbial community properties and environmental variables. The results showed that the functional diversity of soil microbial communities was correlated with aboveground plant biomass, root biomass, soil water content and soil N: P ratio, suggesting that plant biomass, soil water availability and soil N availability were major determinants of soil microbial community functional diversity. Since plant biomass can indicate resource availability, which is mainly constrained by soil water availability and N availability in temperate steppes, we consider that soil microbial community functional diversity was mainly controlled by resource availability in temperate steppes at a regional scale.     

Comparative study of the microbial diversity of bulk paddy soil of two rice fields subjected to organic and conventional farming

Two adjacent paddies of an experimental rice field, subjected to organic and conventional farming, were characterized aiming the comparative assessment of microbiological variations occurring in the bulk paddy soil over the rice cycle. This study comprehended the simultaneous characterization of general physicochemical soil properties [total carbon and nitrogen, pH (H₂O and KCl), C:N ratio and water content], biochemical properties [enzymatic activities and Community Level Physiological Profiles (CLPP)], the estimation of cultivable organisms (enumeration of fast growing heterotrophic bacteria, actinomycetes and fungi) and the assessment of bacterial diversity using a culture-independent method (PCR-DGGE fingerprinting). The linkage of the parameters measured was analysed by canonical correspondence analysis (CCA).CCA ordination plots of the CLPP showed a similar pattern of microbial functional activity in both agronomic management systems, except in June. Enzymatic activity, water content and fungi counts were the main factors affecting the observed CLPP time variation. Such a variation was not expressed by the Shannon and evenness indices, which did not evidence significant differences in the bacterial and functional diversity between or within farming type over the analysed period. The cluster and CCA analyses of the DGGE profiles allowed the distinction of the bacterial communities of both paddies, with temporal variations being observed in the organically managed field but not in the conventional paddy. Enzymatic activity, pH and molinate content were the factors which most contributed to the observed variations. Altogether these results underline the functional redundancy of the rice paddy soil and evidence the temporal variations on the metabolic activity of soil, irrespective of farming type.     

Combined effects of compost containing Sulfamethazine and zinc on pakchoi (Brassica chinensis L.) growth,soil sulfonamide resistance genes,and microbial communities

To understand the ecotoxicity of antibiotics and heavy metals in soil, 5% (w/w) composts containing different concentrations of sulfamethazine (SMZ) and/or zinc (Zn) were applied to soil to investigate their effects on pakchoi (Brassica chinensis L.) growth, soil sulfonamide resistance genes (SRGs: sul1, sul2, and dfrA7), and soil microbial communities. Composts containing less than 1.0 mg SMZ kg^–1 or less than 2.8 g Zn kg^–1 promoted pakchoi growth and the metabolic activity of soil microbial communities. Compared with the control, the absolute abundances (AAs) of soil SRGs significantly increased by 0.85–4.54 times with 50.6 μg kg^–1 SMZ treatment (P < 0.05), the AA of sul2 increased by 166% with 248.8 mg Zn kg^–1 treatment. The combination treatments with 19.8 μg SMZ kg^–1 and 179.9 mg Zn kg^–1 in soil had synergistic stimulatory effects on pakchoi growth, soil SRGs and microbial metabolism, whereas 53.5 μg SMZ kg^–1 and 262.1 mg Zn kg^–1 had an opposite effect. Pearson’s correlation analysis showed that carbon metabolism by soil microorganisms had significant positive correlations with shoot height of pakchoi (r = 0.84, P < 0.05) and AAs of SRGs (r > 0.80, P < 0.05).     

Taxonomic and functional diversity of the soil microbiome recruited from alternative crops in a rotation system

Intensive cropping is considered to contribute to negative effects both on soil physiochemical properties and on long-term grain yield, which can be alleviated by appropriate crop rotations. The soil microbial community can vary with different crop rotations, which in turn affect soil quality and grain yield. Therefore, it is of great significance to elucidate the response of the soil microbial community to crop rotation. In this study, the structural and functional changes of microbial community in different crop rotations were analyzed using high-throughput sequencing and metagenomics analysis in a field experiment. The continuous winter wheat-summer maize cropping system was the control, and three crop rotations were established in October 2016 as follows: (1) spring peanut→winter wheat-summer maize, (2) winter wheat-summer peanut→winter wheat-summer maize and (3) spring sweet potato→winter wheat-summer maize. Soil samples were collected in September 2021 for soil microbial assessment. The results showed that the relative abundance of Actinobacteriota in the soil of spring sweet potato→winter wheat-summer maize was significantly higher (15.2%) than that in the control. The relative abundance of Ascomycota was significantly higher (19.8%–23.2%) in the soil following crop rotation compared with the control. Compared with the control, spring peanut→winter wheat-summer maize enriched energy metabolism genes, and spring sweet potato→winter wheat-summer maize reduced the genes related to plant–pathogen interaction. Compared with the control, crop rotation significantly decreased the relative abundance of the inorganic phosphorus solubilization gene (gcd) and the phosphorus transport gene (upgE) and increased the abundance of organic phosphorus mineralization genes (phoA and phyA). Based on these results, we concluded that the composition of the soil microbial community and functional genes can be altered by crop rotation, and spring peanut→winter wheat-summer maize and spring sweet potato→winter wheat-summer maize had more significant effects. This study provided a reference for the selection of crop rotations in the North China Plain based on the soil microbial community and its function.     

Microarray analysis of bacterial diversity and distribution in aggregates from a desert agricultural soil

Previous research has shown that soil structure can influence the distribution of bacteria in aggregates and, thereby, influence microbiological processes and diversity at small spatial scales. Here, we studied the microbial community structure of inner and outer fractions of microaggregates of a desert agricultural soil from the Imperial Valley of Southern California. To study the distribution of soil bacteria, 1,536 clones were identified using phylogenetic taxon probes to classify arrays of 16S rRNA genes. Among the predominant taxonomic groups were the α-Proteobacteria, Planctomycetes, and Acidobacteria. When compared across all phyla, the taxonomic compositions and distributions of bacterial taxa associated with the inner and outer fractions were nearly identical. Our results suggest that the ephemeral nature of soil aggregates in desert agricultural soils may reduce differences in the spatial distribution of bacterial populations as compared to that which occur in soils with more stable aggregates.     

Genetic diversity of Rhizobium present in nodules of Phaseolus vulgaris L. cultivated in two soils of the central region in Chile

Although Phaseolus vulgaris L. is native from the Americas and is currently cultured in diverse areas, very little is known about the diversity of symbiotic nitrogen fixing Rhizobium (mycrosymbiont) in many of those cultures. Therefore, the aim of this study was to assess the genetic diversity of Rhizobium present in nodules of P. vulgaris in the central region of Chile. A method to extract DNA from surface-sterilized nodules was applied to two populations of the same seed variety grown in different fields. The 16S rRNA and nifH genes were amplified directly from the DNA extracted. DGGE analysis and clone libraries showed a restricted genetic diversity of the microsymbiotic populations that nodulate P. vulgaris. Both molecular markers revealed the presence of a microsymbiont closely related to Rhizobium etli in all the plants from the soils studied, indicating that the populations of Rhizobium sp. nodulating P. vulgaris in the central region of Chile displayed an extremely low genetic diversity. The level of genetic diversity in microsymbiont populations in plants grown in soils with different origin suggested that other factors rather than the indigenous soil rhizobial populations play a major role in the selection of the symbiotic partner in P. vulgaris.     

不同作物间作对黄瓜病害及土壤微生物群落多样性的影响

分别采用RAPD和T-RFLP技术,研究了小麦、毛苕子和三叶草分别与黄瓜间作对黄瓜病害、黄瓜根际土壤微生物群落多样性和黄瓜产量的影响。结果表明,小麦、毛苕子与黄瓜间作均能提高黄瓜根际土壤微生物群落多样性,其中,小麦-黄瓜间作对黄瓜根际土壤微生物群落多样性的影响最为突出;3种作物分别与黄瓜间作均显著提高了黄瓜产量(p<0.01),其中小麦-黄瓜间作的产量优势最强;同时,3种作物分别与黄瓜间作均降低了黄瓜角斑病、白粉病、霜霉病和枯萎病的病情指数和尖孢镰刀菌的数量。间作有利于提高土壤微生物群落的多样性、减轻病害、提高黄瓜产量。     

Plot-scale manipulations of organic matter inputs to soils correlate with shifts in microbial community composition in a lowland tropical rain forest

Little is known about the organisms responsible for decomposition in terrestrial ecosystems, or how variations in their relative abundance may influence soil carbon (C) cycling. Here, we altered organic matter in situ by manipulating both litter and throughfall inputs to tropical rain forest soils, and then used qPCR and error-corrected bar-coded pyrosequencing to investigate how the resulting changes in soil chemical properties affected microbial community structure. The plot-scale manipulations drove significant changes in microbial community composition: Acidobacteria were present in greater relative abundance in litter removal plots than in double-litter plots, while Alphaproteobacteria were found in higher relative abundance in double-litter and throughfall reduction plots than in control or litter removal plots. In addition, the bacterial:archaeal ratio was higher in double-litter than no-litter plots. The relative abundances of Actinobacteria, Alphaproteobacteria and Gammaproteobacteria were positively correlated with microbial biomass C and nitrogen (N), and soil N and C pools, while acidobacterial relative abundance was negatively correlated with these same factors. Bacterial:archaeal ratios were positively correlated with soil moisture, total soil C and N, extractable ammonium pools, and soil C:N ratios. Additionally, bacterial:archaeal ratios were positively related to the relative abundance of Actinobacteria, Gammaproteobacteria, and Actinobacteria, and negatively correlated to the relative abundance of Nitrospira and Acidobacteria. Together, our results support the copiotrophic/oligotrophic model of soil heterotrophic microbes suggested by Fierer et al. (2007).     

Experimental warming effects on the microbial community of a temperate mountain forest soil

Soil microbial communities mediate the decomposition of soil organic matter (SOM). The amount of carbon (C) that is respired leaves the soil as CO₂ (soil respiration) and causes one of the greatest fluxes in the global carbon cycle. How soil microbial communities will respond to global warming, however, is not well understood. To elucidate the effect of warming on the microbial community we analyzed soil from the soil warming experiment Achenkirch, Austria. Soil of a mature spruce forest was warmed by 4 °C during snow-free seasons since 2004. Repeated soil sampling from control and warmed plots took place from 2008 until 2010. We monitored microbial biomass C and nitrogen (N). Microbial community composition was assessed by phospholipid fatty acid analysis (PLFA) and by quantitative real time polymerase chain reaction (qPCR) of ribosomal RNA genes. Microbial metabolic activity was estimated by soil respiration to biomass ratios and RNA to DNA ratios. Soil warming did not affect microbial biomass, nor did warming affect the abundances of most microbial groups. Warming significantly enhanced microbial metabolic activity in terms of soil respiration per amount of microbial biomass C. Microbial stress biomarkers were elevated in warmed plots. In summary, the 4 °C increase in soil temperature during the snow-free season had no influence on microbial community composition and biomass but strongly increased microbial metabolic activity and hence reduced carbon use efficiency.     

Community structure of bacteria on different types of mineral particles in a sandy soil

Various types of mineral particles in a soil probably provide different microenvironments for microorganisms. The purpose of this study is to investigate whether different types of mineral in a soil harbor different bacterial populations. DNA was extracted from five types (quartz, feldspar, pyroxene, magnetite, iron-coated reddish brown particles) of sand-size mineral particles separated from a sandy soil, and was amplified for partial 16 S rRNA gene by polymerase chain reaction (PCR). Twenty-nine to 69 amplicons per each type of mineral were cloned and sequenced, followed by phylogenetic affiliation of the sequences. As a result, some types of bacteria were detected on all of the types of mineral including the orders Rhizobiales, Bacillales, and Acidobacteriales. In the case of Acidobacteriales, higher percentages were found on magnetite and quartz. Some taxa were restricted to specific types of mineral; the class Actinobacteria was found on pyroxene but not on quartz, and rarely on magnetite and feldspar. Bacterial diversity at the order level estimated by Chao1 value was higher in feldspar and pyroxene than the other three types of mineral. The UniFrac Significance test indicated that the differences in bacterial communitiy structures among the particles were suggestive except that between feldspar and pyroxene. These results support the idea that different communities of bacteria were associated with each of the mineral types.     

Microbial community structure and functionality under peanut-based cropping systems in a sandy soil

Little information is available on soil microbial and biochemical properties, important for understanding nutrient cycling and organic matter dynamics, as affected by different peanut cropping systems and how they relate to soil functioning. Thus, we studied a Tifton loamy sand (fine-loamy, kaolinitic, thermic Plinthic Kandiudults) in Georgia, which is first in peanut production in USA, after 5 and 8 years under continuous cotton (Gossypium hirsutum, L) (CtCtCt), cotton–cotton–peanut (CtCtPt), corn (Zea mays L.)–peanut–cotton (CrPtCt), peanut–peanut–cotton (PtPtCt), and continuous peanut (PtPtPt). Soil organic carbon (OC) at 0–20 cm was already higher under PtPtPt (average, 8.7 g C kg⁻¹ soil), PtPtCt (average, 7.7 g C kg⁻¹ soil), and CrPtCt (average, 7.8 g C kg⁻¹ soil) compared with CtCtPt (average, 4.7 g C kg⁻¹ soil) and CtCtCt (average, 3.3 g C kg⁻¹ soil). Similarly, alkaline phosphatase, acid phosphatase, and phosphodiesterase as a group showed higher activities under PtPtPt, PtPtCt, and CrPtCt than under CtCtPt and CtCtCt. The activities of glycosidases (α-galactosidase, β-glucosidase, and β-glucosaminidase) as a group were more sensitive to the cropping systems than phosphastases and showed a distinctive cropping system separation as follows: PtPtPt = CrPtCt > PtPtCt > CtCtPt > CtCtCt. Similar to OC and microbial biomass C trends, distinctive differences were found in the microbial community structure of this sandy soil after 8 years between peanut-based cropping systems (CrPtCt, PtPtCt, and PtPtPt) and cotton-based cropping systems (CtCtCt and CtCtPt) as indicated by the fatty acid methyl esters profiles. Trade names and company names are included for the benefit of the reader and do not infer any endorsement or preferential treatment of the product by USDA-ARS.     

Interaction between earthworms and arbuscular mycorrhizal fungi on the degradation of oxytetracycline in soils

The interactive impact of earthworms (Eisenia fetida) and arbuscular mycorrhizal fungi (Rhizophagus intraradices, AM fungi) on the degradation of oxytetracycline (OTC) in soils was studied under greenhouse conditions. Treatments included maize plants inoculated vs. not inoculated with AM fungi and treated with or without earthworms at low (1 mg kg⁻¹ soil DM) or high (100 mg kg⁻¹ soil DM) OTC rates. The root colonization rate, the hyphal density of mycorrhizae, the residual OTC concentration in soils, catalase, dehydrogenase, urease, soil microbial biomass C, Shannon–Wiener index (H) for microbial communities from T-RFLP profiles were measured at harvest. The results indicated that earthworms and AM fungi would individually or interactively enhance OTC decomposition and significantly decreased the residual OTC concentration at both high and low OTC rates. Both earthworms and AM fungi could promote the degradation of OTC by increasing soil microbial biomass C at both high and low OTC rates. The effect of soil enzyme activity and soil microbial diversity on OTC decomposition was different between high and low OTC rates. Hyphomicrobium and Bacillus cereus were dominant bacteria, and Thielavia and Chaetomium were dominant phyla of fungi at all occasions. Earthworm activity stimulated the growth of Hyphomicrobium and Thielavia, while AM fungi may stimulate B. cereus, Thielavia and Chaetomium, resulting in greater OTC decomposition. The interaction between earthworms and AM fungi in affecting the degradation of OTC may be attributed to different mechanisms, depending on soil microbial biomass, function (enzyme activity) and communities (the abundance of Hyphomicrobium, B. cereus, Thielavia and Chaetomium) in the soil.     

A comparison of the texture of grassland and eroded sandy soils from Shropshire, UK

In previous studies, periodic sampling of topsoils on runoff plots on sandy soils at the Hilton experimental site, Shropshire, UK, suggested erosion decreased the topsoil clay content and increased the coarse fraction. However, a comparison of soil and sediment properties suggested erosion selectively removed sand. Therefore, to cross-check the effects of erosion on soil properties, topsoil samples were collected from bare, eroded runoff plots and compared with samples from adjacent non-eroded grassland. Bare, eroded soil was stonier and particularly deficient in sand compared with grassed soil. Textural differences were very marked in the medium and coarse sands, especially the 0.5–1.0 mm fraction. On the basis of mean properties, the grassed soil was a very slightly stony loamy sand and the bare soil a slightly stony sandy loam. Soil organic matter was significantly less in the bare soils than the grassed soils and thus may have contributed to the higher erodibility of sands in bare soils.