Shifting microbial community structure across a marine terrace grassland chronosequence, Santa Cruz, California

Changes in the biomass and structure of soil microbial communities have the potential to impact ecosystems via interactions with plants and weathering minerals. Previous studies of forested long-term (1000s - 100,000s of years) chronosequences suggest that surface microbial communities change with soil age. However, significant gaps remain in our understanding of long-term soil microbial community dynamics, especially for non-forested ecosystems and in subsurface soil horizons. We investigated soil chemistry, aboveground plant productivity, and soil microbial communities across a grassland chronosequence (65,000-226,000 yrs old) located near Santa Cruz, CA. Aboveground net primary productivity (ANPP) initially increased to a maximum and then decreased for the older soils. We used polar lipid fatty acids (PLFA) to investigate microbial communities including both surface (<0.1 m) and subsurface (≥0.2 m) soil horizons. PLFAs characteristic of Gram-positive bacteria and actinobacteria increased as a fraction of the microbial community with depth while the fungal fraction decreased relative to the surface. Differences among microbial communities from each chronosequence soil were found primarily in the subsurface where older subsurface soils had smaller microbial community biomass, a higher proportion of fungi, and a different community structure than the younger subsurface soil. Subsurface microbial community shifts in biomass and community structure correlated with, and were likely driven by, decreasing soil P availability and Ca concentrations, respectively. Trends in soil chemistry as a function of soil age led to the separation of the biological (≤1 m depth) and geochemical (>1 m) cycles in the old, slowly eroding landscape we investigated, indicating that this separation, commonly observed in tropical and subtropical ecosystems, can also occur in temperate climates. This study is the first to investigate subsurface microbial communities in a long-term chronosequence. Our results highlight connections between soil chemistry and both the aboveground and belowground parts of an ecosystem.     

Water-stable aggregates, glomalin-related soil protein, and carbohydrates in a chronosequence of sandy hydromorphic soils

The conversion of pasture to cropland leads to a decline of aggregation in topsoils and to a decrease of aggregate-binding agents such as carbohydrates and glomalin-related soil protein (GRSP). Till now, studies on soil aggregation focused either on carbohydrates or on GRSP as a binding agent in aggregates. In this study we analyse the development of the relationship between carbohydrates, GRSP, TOC and aggregate-stability following land-use change. Furthermore, we discuss the contents of carbohydrates, GRSP and TOC in each of the aggregate fractions. For these purposes, a chronosequence of sites, which were converted from pasture to cropland at different periods in history, was established. To get further insight into the impact of different types of land-use, also soils under forest, either afforested or permanent, were studied. The mean-weight diameter (MWD) of water-stable aggregates, the carbohydrate, and the GRSP content were determined in 49 soils. It was found that the MWD of the water-stable aggregates decreased monoexponentially (R² = 0.66) by 66% during the first 46 years after conversion of the soils from pasture to cropland. During the same period, the carbohydrate content decreased very rapidly after the land use change by 64% and the GRSP content decreased more slowly by 57%. The MWD of the forest soils were in the same range as those of the permanent pasture soils although they exhibit significantly higher TOC contents, which indicate that other stabilization mechanisms are dominant in forest soils, less important in the chronosequence soils. TOC, carbohydrates and the GRSP contents were sigmoidally correlated with the MWD. Among the four water-stable aggregate fractions TOC and carbohydrates exhibited high contents in the macroaggregates and were less present in the microaggregates. GRSP, in contrast, was more equally distributed among the four water-stable aggregate fractions.     

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.     

Physiological, biochemical and molecular responses of the soil microbial community after afforestation of pastures with Pinus radiata

Afforestation and deforestation are key land-use changes across the world, and are considered to be dominant factors controlling ecosystem functioning and biodiversity. However, the responses of soil microbial communities to these land-use changes are not well understood. Because changes in soil microbial abundance and community structure have consequences for nutrient cycling, C-sequestration and long-term sustainability, we investigated impacts of land-use change, age of stand and soil physico-chemical properties on fungal and bacterial communities and their metabolic activities. This study was carried out at four sites in two geographical locations that were afforested on long-established pastures with Pinus radiata D. Don (pine). Two of the sites were on volcanic soils and two on non-volcanic soils and stand age ranged from 5 to 20 y. Microbial communities were analysed by biochemical (phospho-lipid fatty acids; PLFA) and molecular (multiplex-terminal restriction fragment length polymorphism; M-TRFLP) approaches. Both site and stand age influenced microbial properties, with changes being least detectable in the 5-y-old stand. Land use was a key factor influencing soil metabolic activities as measured by physiological profiling using MicroResp. Pasture soils had higher microbial biomass (P < 0.001), and metabolic activities (P < 0.001), and basal respiration rates were up to 2.8-times higher than in the pine soils. Microbial abundance analysis by PLFA showed that the fungal to bacterial ratio was higher in the pine soils (P < 0.01). Community analysis suggested that soil bacterial communities were more responsive to site (principal component 1; P < 0.001) than to land use (principal component 5; P < 0.001). In contrast, the fungal community was more affected by land-use change (principal component 1; P < 0.001) than by site, although site still had some influence on fungal community structure (principal component 2; P < 0.001). Redundancy analysis also suggested that bacterial and fungal communities responded differently to various soil abiotic properties, land-use change and location of sites. Overall, our results indicate that the change in land use from pasture to P. radiata stands had a direct impact on soil fungal communities but an indirect effect, through its effects on soil abiotic properties, on bacterial communities. Most of the changes in bacterial communities could be explained by altered soil physico-chemical properties associated with afforestation of pastures.     

Soil bacterial growth and nutrient limitation along a chronosequence from a glacier forefield

Resource availability and limiting factors for bacterial growth during early stages of soil development (8-138 years) were studied along a chronosequence from the glacial forefield of the Damma glacier in the Swiss Alps. We determined bacterial growth (leucine incorporation) and we investigated which resource (C, N or P) limited bacterial growth in soils formed by the retreating glacier. The latter was determined by adding labile sources of C (glucose), N and P to soil samples and then measuring the bacterial growth response after a 40 h incubation period. Bacterial growth increased with increasing soil age in parallel with the build up of organic matter. However, lower bacterial growth, when standardized to the amount of organic C, was found with time since the glacier retreat, indicating decreasing availability of soil organic matter with soil age. Bacterial growth in older soils was limited by the lack of C. The bacteria were never found to be limited by only N, only P, or N + P. In the youngest soils, however, neither the addition of C, N nor P singly increased bacterial growth, while a combination of C and N did. Bacterial growth was relatively more limited by lack of N than P when the C limitation was alleviated, suggesting that N was the secondary limiting resource. The availability of N for bacterial growth increased with time, as seen by an increased bacterial growth response after adding only C in older soils. This study demonstrated that bacterial growth measurements can be used not only to indicate direct growth effects, but also as a rapid method to indicate changes in bacterial availability of nutrients during soil development.     

Relationships between biological and physico-chemical soil characteristics in a mediterranean agricultural area

Fourteen agricultural soils from various areas of Tuscany were characterized by a range of measurements indicative of soil biological activity. The objective of our research was to identify soil parameters suitable as indicators for evaluating their quality. In general, enzyme activities were found to vary widely, with the highest activity for each enzyme being distributed among only five of the 14 soils studied. The narrowest range (14-fold) in enzyme activities for the various soils was observed for catalase and the widest range (577-fold) for g -glucosidase. Biomass C and, among the measured enzyme activities, amylase, were well correlated with total organic carbon, total N, cation and anion exchange capacity. Positive correlations were found between the maximum water holding capacity and dehydrogenase, amylase, biomass C, FDA hydrolytic activity, the biological index of fertility and the enzyme activity number, so showing that soil moisture may play an important role in affecting soil biological characteristics. No significant correlations were observed among the soil enzymes themselves. The FDA hydrolytic activity appeared to be the index most related with the other biological characteristics tested in this study and, for this reason, can be considered the most effective index for putting in evidence relationships existing between the different biological characteristics in the soils investigated.     

滨海沉积物发育的水稻土时间序列母质均一性判定与特性演变

时间序列方法是研究土壤发生特性演变的重要途径,而比较土壤变化的重要前提之一是序列中的土壤具有相同的起源,即具有母质的相对均一性。本研究根据史料记载中浙江慈溪海塘修筑年代估计出水稻土的耕作年龄,选择了植稻年龄约为50、300、500、700、1000a以及一个未垦滩涂剖面组成的一个时间序列作为研究对象。利用各种土壤属性参数对该时间序列的母质不连续性(或母质均一性)以及水稻土相对年龄进行了判定和验证。结果表明,时间序列的6个剖面虽然具有微小的差异,但其剖面内与剖面间母质来源相同。在水稻土母质不连续性判定中,去除黏粒的粉粒与粉粒中稳定元素Ti/Zr比值具有较好的指示作用。相对易变的土壤属性参数如碳酸钙、磁化率以及游离铁的剖面分异程度在水稻土相对年龄的判定中具有较好的指示作用。综合这些参数在时间序列中的演化趋势,发现500a剖面与整个序列的变化趋势不相符合,可能是利用历史的差异所致,在相关的性质演变研究中应该从序列中剔除。     

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.     

不同利用方式旱地红壤水稳性团聚体及其碳、氮、磷分布特征

针对江西红壤地区不同利用方式引起的土壤质量和肥力的相应变化,研究了不同肥力水平、不同利用方式下红壤旱地水稳性团聚体含量及其养分分布规律。研究表明,荒地土壤中>5 mm水稳性团聚体含量显著高于其他利用方式,花生地和果园土壤则以0.25～0.053 mm的水稳性团聚体为主。各肥力水平下,菜地土壤中除>5 mm水稳性团聚体外,各粒级团聚体中有机碳、全氮和全磷含量均显著高于花生地、果园和荒地土壤。说明菜地土壤长期大量施肥,导致土壤碳、氮、磷养分含量均相对丰富。不同利用方式旱地红壤中,有机碳、全氮主要分布在>5 mm、5～2 mm和2～1 mm的较大粒径水稳性团聚体中。说明随着团聚体粒径增大,其有机碳含量增加,土壤全氮的消长趋势和有机碳一致。土壤全磷较均匀地分布在水稳性团聚体中,如高肥力菜地和荒地土壤各粒级团聚体中全磷含量间均无显著性差异。各利用方式旱地红壤中2～1 mm和1～0.5 mm的水稳性团聚体含量与土壤有机碳、全氮和全磷含量间均达到了极显著正相关。     

中亚热带四种森林土壤团聚体及其有机碳分布特征

选择中亚热带地区4种典型森林类型:杉木林、湿地松林、毛竹林和次生林4种森林土壤为研究对象,研究了森林类型对土壤不同发生层水稳性团聚体及其有机碳分布特征的影响。结果表明:不同森林类型对>5 mm和2~5 mm土壤团聚体含量影响显著(p<0.05),表现为次生林>杉木林>毛竹林>湿地松林,而在其他粒径无显著差异。0~30 cm土层内团聚体R0.25和MWD次生林显著高于其他人工林,杉木林次之,湿地松林和毛竹林最低,其他土层无显著差异。各森林类型同土层不同粒径团聚体中有机碳含量随粒径大小变化,团聚体粒径越小,有机碳含量越高。0~10 cm土层同粒径土壤团聚体有机碳含量从大到小依次是次生林、杉木林、湿地松林和毛竹林,而在其他土层各森林类型之间差异不显著。     

Changes in plant community structure and soil biota along soil nitrate gradients in two deciduous forests

Anthropogenic nitrogen (N) deposition is a serious threat to biodiversity and the functioning of many ecosystems, particularly so in N-limited systems, such as many forests. Here we evaluate the associations between soil nitrate and changes in plant community structure and soil biota along nitrate gradients from croplands into closed forests. Specifically, we studied the composition of the understory plant and earthworm communities as well as soil microbial properties in two deciduous forests (Echinger Lohe (EL) and Wippenhauser Forst (WF)) near Munich, Germany, which directly border on fertilized agricultural fields. Environmental variables, like photosynthetically active radiation, distance to the edge and soil pH were also determined and used as co-variates. In both forests we found a decrease in understory plant coverage with increasing soil nitrate concentrations. Moreover, earthworm biomass increased with soil nitrate concentration, but this increase was more pronounced in EL than in WF. Soil microbial growth after addition of a nitrogen source increased significantly with soil nitrate concentrations in WF, indicating changes in the composition of the soil microbial community, although there was no significant effect in EL. In addition, we found changes in earthworm community composition along the soil nitrate gradient in WF. Taken together, the composition and functioning of forest soil communities and understory plant cover changed significantly along soil nitrate gradients leading away from fertilized agricultural fields. Inconsistent patterns between the two forests however suggest that predicting the consequences of N deposition may be complicated due to context-dependent responses of soil organisms.     

Stability of desiccated rhizosphere soil aggregates of mycorrhizal Juniperus oxycedrus grown in a desertified soil amended with a composted organic residue

Adequate soil structural stability favours the establishment and viability of a stable plant cover, protecting the soil against water erosion in desertified Mediterranean environments. We studied the effect of soil drying-rewetting, inoculation with a mixture of three exotic arbuscular mycorrhizal (AM) fungi (Glomus intraradices Schenck & Smith, Glomus deserticola (Trappe, Bloss. & Menge) and Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe) and addition of a composted organic residue on aggregate stabilisation of the rhizosphere soil of Juniperus oxycedrus. The AM fungi and composted residue produced similar increases in plant growth, independently of the water conditions. Under well-watered conditions, the highest percentages of stable aggregates were recorded in the amended soil, followed by the soil inoculated with AM fungi. Excepting microbial biomass C, the soil drying increased labile C fractions (water soluble C, water soluble and total carbohydrates), whereas the rewetting decreased significantly such C fractions. Desiccation caused a significant increase in aggregate stability of the rhizosphere soil of all plants, particularly in the amended and inoculated plants. In all treatments, the aggregates formed after soil drying were unstable, since, in the rewetting, they disappear, reaching the initial levels before soil drying. Our results suggest that the aggregation mechanisms developed by rhizosphere microbial community of the amended and inoculated plants under water stress can be particularly relevant in desertified soils exposed to long desiccation periods.     

Microbial residues as indicators of soil restoration in South African secondary pastures

Prolonged intensive arable cropping of semiarid grassland soils in the South African Highveld resulted in a significant loss of C, N and associated living and dead microbial biomass. To regenerate their soils, farmers converted degraded arable sites back into secondary pastures. The objective of this study was to clarify the contribution of microorganisms to the sequestration of C and N in soil during this regeneration phase. Composite samples were taken from the topsoils of former arable land, namely Plinthustalfs, which had been converted to pastures 1-31 years ago. Amino sugars were determined as markers for microbial residues in the bulk soil and in selected particle-size fractions. The results showed that when C and N contents increased during the secondary pasture usage, the amino sugar concentration in the bulk soil (0-5 cm) recovered at similar magnitude and reached a new steady-state level after approximately 90 years, which corresponded only to 90% of the amino sugar level in the primary grassland. The amino sugar concentration in the clay-sized fraction recovered to a higher end level than in the bulk soil, and also at a faster annual rate. This confirms that especially the finer particles contained a high amount of amino sugars and were responsible, thus, for the restoration of microbially derived C and N. The incomplete recovery of amino sugars in bulk soil can only in parts be attributed to a slightly coarser texture of secondary grassland that had lost silt through wind erosion. The soils particularly had also lost the ability to restore microbial residues below 5 cm soil depth. Overall, the ratios of glucosamine to muramic acid also increased with increasing duration of pasture usage, suggesting that fungi dominated the microbial sequestration of C and N whereas the re-accumulation of bacterial cell wall residues was less pronounced. However, the glucosamine-to-muramic acid ratios finally even exceeded those of the primary grassland, indicating that there remained some irreversible changes of the soil microbial community by former intensive crop management.     

Functional resilience of soil microbial communities depends on both soil structure and microbial community composition

The effects of soil structure and microbial community composition on microbial resistance and resilience to stress were found to be interrelated in a series of experiments. The initial ability of Pseudomonas fluorescens to decompose added plant residues immediately after a copper or heat stress (resistance) depended significantly on which of 26 sterile soils it was inoculated into. Subsequent studies showed that both the resistance and subsequent recovery in the ability of P. fluorescens to decompose added plant residues over 28 days after stress (resilience) varied significantly between a sandy and a clay-loam soil. Sterile, sandy and clay-loam soil was then inoculated with a complex microbial community extracted from either of the soils. The resulting microbial community structure depended on soil type rather than the source of inoculum, whilst the resistance and resilience of decomposition was similarly governed by the soil and not the inoculum source. Resilience of the clay-loam soil to heat stress did not depend on the water content of the soil at the time of stress, although the physical condition of the soil when decomposition was measured did affect the outcome. We propose that soil functional resilience is governed by the physico-chemical structure of the soil through its effect on microbial community composition and microbial physiology.     

Seasonal and long-term resource-related variations in soil microbial communities in wheat-based rotations of the Canadian prairie

Like all other living organisms, microorganisms depend on nutrients, carbon and energy. Since microorganisms are central to most soil processes, the sustainable management of agricultural soils may need to consider the impact of soil fertility management on the soil microbial community. We tested the hypothesis that different rates of N and P fertilizers, and cropping frequency (modifying C input to soil) influence the size, structure and physiological condition of soil microbial populations residing in the plough layer (top 7.5 cm). For this study, we used a 37-yr old long-term wheat-based rotation experiment located in the semiarid Brown soil zone of Saskatchewan. The experiment included (1) four input treatments: (i) no N or (ii) no P fertilizer application to wheat (Triticum aestivum L.) grown in fallow-wheat-wheat (F-W-W) rotations, and (iii) recommended rates of both N and P fertilizer applied to fallow-wheat (F-W) and (iv) to F-W-W; (2) two rotation phases: fallow and wheat-after-fallow; and (3) four sampling times: 8 June, 4 July, 5 August and 16 September 2003. Increased partitioning into storage lipids of the arbuscular mycorrhizal fungi (AMF) fatty acid methyl ester (FAME) biomarker 16:1ω5 (P=0.04), suggested the accumulation of storage material under low soil N availability. Discriminant analysis detected modifications in soil microbial community structure due to cropping frequency (P=0.001) and sampling time, the effect of which was different in the fallow (P<0.0001) and wheat-after-fallow (P<0.0001) phases of the rotations. Correlation analysis of soil variables conducted in plots growing wheat revealed a dual effect of plants, which stimulated active soil microbial biomass (SMB), possibly through the release of soluble extractable C (C_sol−ext) in soil and, at the same time, SMB competed with wheat for soil water and N. The 37 y of different nutrient input treatments had no effect upon the active soil microbial biomass according to PLFA measurements, despite changes in soil resource-related variables (soil water potential, soil PO₄-P and NO₃-N fluxes, and C_sol−ext concentrations) (P?0.003). The biomass of each of three microbial populations monitored was lowest on 4 July, when the amounts of the soil resources monitored were average, and greatest on 5 August, when N, P and soil moisture availability was lowest. The temporal effect on the biomass of microbial populations seemed unrelated to variation in nutrient or water availability. We conclude that the soil microbial community is adaptable to a wide range of soil conditions. We propose therefore that the occurrence of sudden and dramatic events, such as a heavy rainfall on a dry soil, is the most important determinant of seasonal variation in active soil microbial biomass.     

Changes in microbial community structure in soil as a result of different amounts of nitrogen fertilization

The changes in size, activity and structure of soil microbial community caused by N fertilization were studied in a laboratory incubation experiment. The rates of N fertiliser applied (KNO₃) were 0 (control), 100 and 2,000 μg N g⁻¹ soil. Despite no extra C sources added, a high percentage of N was immobilized. Whereas no significant increase of microbial C was revealed during incubation period, microbial growth kinetics as determined by the substrate-induced growth-response method demonstrated a significant decrease in the specific growth rate of microbial community in soil treated with 2,000 μg N g⁻¹ soil. Additionally, a shift in microbial community structure resulting in an increase in fungal biomarkers, mainly in the treatment with 2,000 μg N g⁻¹ soil was visible.     

Contributions of soil biota to C sequestration varied with aggregate fractions under different tillage systems

It is increasingly believed that substantial soil organic carbon (SOC) can be sequestered in conservation tillage system by manipulating the functional groups of soil biota. Soil aggregates of different size provide diverse microhabitats for soil biota and consequently influence C sequestration. Our objective was to evaluate the contributions of soil biota induced by tillage systems to C sequestration among different aggregate size fractions. Soil microbial and nematode communities were examined within four aggregate fractions: large macroaggregates (>2 mm), macroaggregates (2–1 mm), small macroaggregates (1–0.25 mm) and microaggregates (<0.25 mm) isolated from three tillage systems: no tillage (NT), ridge tillage (RT) and conventional tillage (CT) in Northeast China. Soil microbial and nematode communities varied across both tillage systems and aggregate fractions. The activity and abundance of microbes and nematodes were generally higher under NT and RT than under CT. Among the four aggregate fractions, soil microbial biomass and diversity were higher in microaggregates, while soil nematode abundance and diversity were higher in large macroaggregates. Structural equation modelling (SEM) revealed that the linkage between microbial and nematode communities and their contributions to soil C accumulation in >1 mm aggregate fractions were different from those in <1 mm aggregate fractions. Higher abundance of arbuscular mycorrhizal fungi (AMF) could enhance C retention within >1 mm aggregates, while more gram-positive bacteria and plant-parasitic nematodes might increase C accumulation within <1 mm aggregates. Our findings suggested that the increase in microbial biomass and nematode abundance and the alteration in their community composition at the micro-niche within aggregates could contribute to the higher C sequestration in conservation tillage systems (NT and RT).     

Effects of regenerating vegetation on soil enzyme activity and microbial structure in reclaimed soils on a surface coal mine site

The aim of this study was to evaluate the influence of reclaimed scenarios on soil enzyme activities and microbial community in a reclaimed surface coal mine on the Northwest Loess Plateau of China. Soil samples were collected from a bare land (CK), and a plantation (PL) and four mixed forests (MF1-4). Soil physicochemical characteristics, four enzyme activities and microbial abundance and T-RFLP (terminal restriction fragment length polymorphism) profiles were measured. Effects of reclaimed scenarios on soil nutrients content, enzyme activities and microbial community were pronounced. Soil organic carbon could be well used to predict the major differences in enzyme activities, and microbial abundance and composition. Soil enzyme activities were more significantly correlated with fungal abundance than bacterial and archaeal ones. The higher soil nutrient content, enzyme activities, and microbial abundance and diversity were from mixed forests and the lowest ones were from CK, which suggested mixed forests would be feasible scenarios in semi-arid Loess Plateau. Soil bacteria, archaea and fungi evolved with reclaimed process, but the influences of reclaimed scenarios on each domain of microbial abundance, diversity and composition were different. These findings suggested that soil bacteria, archaea and fungi play different ecological roles during restoration process.     

Effect of metal contamination on microbial enzymatic activity in soil

Anthropogenic metal contamination is a pervasive problem in many urban or industrial areas. The interaction of metals with native soil communities is an important area of research as scientists strive to understand effects of long-term metal contamination on soil properties. Measurements of free soil enzyme activities can serve as useful indicators of microbial metabolic potential. The goals of this study are to determine extracellular soil enzymatic activities with respect to corresponding metal concentrations within a site of long-term contamination. These data are examined to understand relationships between extracellular soil enzyme activities and persistent metal loads in situ. Here we present such results from a rare research opportunity at an un-remediated, urban brownfield in Jersey City, NJ, USA. The soils of the site developed over the last 150 years through the dumping of urban fill from New York City as well as industrial rail use. The site was abandoned and fenced in the late 1960s, and within it, there is a mapped gradient of metal concentration in the soils, including As, Pb, Cr, Cu, Zn, and V. We measured soil enzymatic potential (alkaline phosphatase, cellobiohydrolase, and l-leucine-amino-peptidase) across four plots within the site and at an uncontaminated reference site that is of the same successional age and geographic influence. We found the highest enzymatic activities for all three activities measured at the site with the greatest soil metal loads and a particularly strong relationship among enzyme activity and the metals V and Cr. Our results differ from many experimental studies that show decreased soil enzyme activity in soils experimentally treated with metals. The results may indicate the effects of long-term adaptation of soil communities within these metal contaminated soils.     

Rapid and sensitive determination of microbial activity in soils and in soil aggregates by dimethylsulfoxide reduction

Summary Based on the reduction of dimethylusulfoxide (DMSO) to dimethylsulfide (DMS) by microorganisms, a simple, rapid, sensitive and inexpensive method for the determination of microbial activity in soil samples was developed. When DMSO was added to samples, DMS appeared immediately in the gas phase, which was quantitatively analyzed by gas chromatography. The DMS liberation rate was constant for several hours. The reaction immediately starts and its linearity indicate that neither the physiological state nor the number of organisms were changed by the assay. DMSO reduction is widespread among microorganisms; out of 144 strains tested (both fungi and bacteria) only 5 were unable to carry out this reaction. The reaction in soil samples was strongly inhibited by toluene, cyanide, azide, or by fumigation, but was considerably stimulated by glucose. These findings demonstrate that the reaction was due to the activity of microorganisms. The DMSO reduction in different soil samples was significantly correlated with arginine ammonification and heat output (r>0.9). A good correlation was observed with the organic-matter content (r = 0.74), but not with microbial numbers, clay content, or the pH of the soil. Standard deviations of less than 10% were routinely found. Furthermore, the method is sufficiently sensitive to allow measurements of activity in very small samples (< 0.1 g). For example, a microbial activity profile can be established for a single soil aggregate, revealing marked differences in activity on the outside and in the interior.