Humus macro-morphology and soil microbial community changes along a 130-yr-old Fagus sylvatica chronosequence

We aimed to characterize humus macro-morphology and the associated soil microbial community within the unmodified litter (OL), the fragmented and humified layers (FH) and the organo-mineral (A) layer along a beech (Fagus sylvatica L.) forest chronosequence with four stand age-classes (15-, 65-, 95-, 130-yr-old) in Normandy, France. Humus macro-morphology was described with 36 quantitative and semi-quantitative variables. We measured microbial biomass N (N_mic), microbial N quotient (N_mic-to-N_t), fungal ergosterol, bacterial and fungal DNA using 16S and 18S rDNA real-time qPCR and evaluated the potential metabolic profile of heterotrophic bacteria within each soil layer and stand age-class. The log-transform ergosterol/fungal DNA ratio (EFR index) was used as an indicator related to active fungal biomass and the fungal/bacterial (F/B) ratio was calculated from qPCR results. There was a shift from mull (mainly dysmull) to moder humus forms along the chronosequence. While the N_mic did not change significantly, the N_mic-to-N_t decreased along the chronosequence in the OL layer. Ergosterol content increased in FH and A layers and the F/B ratio increased in the FH layer with increasing beech forest age. The EFR index was significantly higher in the OL and A layers of the oldest stands, whereas the highest EFR index in the FH layer occurred in the 15-yr-old stands. The functional diversity of heterotrophic bacteria was greater within OL and FH layers of 130-yr-old stands, but highest in the A layer of 15-yr-old stands while the Average Well Color Development remained stable for all soil layers. We found significant correlations between macro-morphology and microbial variables, especially between FH-based morphology and fungal biomass. Our main results are that beech forest maturation is accompanied by (1) an increase in fungal biomass in the FH layers and, (2) an increase in heterotrophic bacteria functional diversity in the organic layers. We have identified key macro-morphology variables that are good predictors of the structural and functional profile of the soil microbial community during beech forest development.     

Soil organic matter dynamics along a rice chronosequence in north-eastern Argentina: Evidence from natural C abundance and particle size fractionation

We studied the consequences of rice cultivation and its subsequent abandonment for soil organic matter (SOM) dynamics in north-eastern Argentina. Two chronosequences, which included a pristine grassland with C4 vegetation as a control, and several stages of rice (C3) fields abandoned for 1, 2, 4, 6 and 15 years were selected, and soil samples from the first 10 cm were gathered from each plot. Natural ¹³C abundance coupled with particle-size fractionation were employed to characterize SOM changes through time discriminated by SOM origin. Soil samples up to 50 cm were also collected throughout one chronosequence. Most changes in SOM occurred on the first 20 cm layer and, bulk density, carbon and nitrogen content, as well as δ¹³C remained similar at greater depths. After the rice cropping, the bulk density was slightly greater than in the natural grassland, and remained stable after the abandonment. Carbon and nitrogen contents remained almost stable in the surface layer during the cultivation. δ¹³C varied accordingly with the changes in vegetation cover with a C4 signature in the natural grassland and mainly a C3 signature in the rice fields. The abandonment of the rice cropping induced a decrease of the soil organic matter content, mainly of natural grassland origin, during the first 4 years. When the abandonment extended, the SOM content (from C4 origin) increased slowly and after 15 years, was almost the same as that of the natural grassland. The carbon turnover was greater in the coarser fractions than in the finer ones, confirming that soil organic carbon in the sand fraction was relatively labile. However, all the fractions were affected by inputs and outputs of C derived from rice and natural grassland. This fact could indicate that the former protected carbon could become less stable due to cultivation.     

Biochar soil amendment increased bacterial but decreased fungal gene abundance with shifts in community structure in a slightly acid rice paddy from Southwest China

Biochar’s role on greenhouse gas emission and plant growth has been well addressed. However, there have been few studies on changes in soil microbial community and activities with biochar soil amendment (BSA) in croplands. In a field experiment, biochar was amended at rates of 0, 20 and 40 t ha⁻¹ (C0, C1 and C2, respectively) in May 2010 before rice transplantation in a rice paddy from Sichuan, China. Topsoil (0–15 cm) was collected from the rice paddy while rice harvest in late October 2011. Soil physico-chemical properties and microbial biomass carbon (MBC) and nitrogen (MBN) as well as selected soil enzyme activities were determined. Based on 16S rRNA and 18S rRNA gene, bacterial and fungal community structure and abundance were characterized using terminal-restriction fragment length polymorphism (T-RFLP) combined with clone library analysis, denaturing gradient gel electrophoresis (DGGE) and quantitative real-time PCR assay (qPCR). Contents of SOC and total N and soil pH were increased but bulk density decreased significantly. While no changes in MBC and MBN, gene copy numbers of bacterial 16S rRNA was shown significantly increased by 28% and 64% and that of fungal 18S rRNA significantly decreased by 35% and 46% under BSA at 20 and 40 t ha⁻¹ respectively over control. Moreover, there was a significant decrease by 70% in abundance of Methylophilaceae and of Hydrogenophilaceae with an increase by 45% in Anaerolineae abundance under BSA at 40 t ha⁻¹ over control. Whereas, using sequencing DGGE bands of fungal 18S rRNA gene, some bands affiliated with Ascomycota and Glomeromycota were shown inhibited by BSA at rate of 40 t ha⁻¹. Significant increases in activities of dehydrogenase, alkaline phosphatases while decreased β-glucosidase were also observed under BSA. The results here indicated a shift toward a bacterial dominated microbial community in the rice paddy with BSA.     

Using lipid analysis and hyphal length to quantify AM and saprotrophic fungal abundance along a soil chronosequence

We evaluate the use of signature fatty acids and direct hyphal counts as tools to detect and quantify arbuscular mycorrhizal (AM) and saprotrophic fungal (SF) biomass in three Hawaiian soils along a natural soil fertility gradient. Phospholipids16:1ω5c and 18:2ω6,9c were used as an index of AM and saprotrophic fungal biomass, respectively. Both phospholipid analysis and hyphal length indicated that the biomass of AMF was greatest at the highest fertility site, and lowest where phosphorus limits plant growth. Saprotrophic fungal biomass did not vary. Hyphal length counts appeared to under-estimate SF abundance, while the phospholipid AMF:SF ratio was in line with expectations. This study indicates that phospholipids may be a valuable and reliable tool for studying the abundance, distribution, and interactions between AM and saprotrophic fungi in soil.     

Clay mineral evolution along a soil chronosequence in an Alpine proglacial area

As a consequence of global warming, additional areas will become ice-free and subject to weathering and soil formation. The most evident soil changes in the Alps will occur in proglacial areas where young soils will continuously develop due to glacier retreat. Little is known about the initial stages of weathering and soil formation, i.e. during the first decades of soil genesis. In this study, we investigated clay minerals formation during a time span 0-150 years in the proglacial area of Morteratsch (Swiss Alps). The soils developed on granitic till and were Lithic Leptosols.Mineralogical measurements of the clay (< 2 μm) and fine silt fraction (2-32 μm) were carried out using XRD (X-ray Diffraction) and DRIFT (Diffuse Reflectance Infrared Fourier Transform). Fast formation and transformation mechanisms were measured in the clay fraction. The decreasing proportion of trioctahedral phases with time confirmed active chemical weathering. Since the start of soil formation, smectite was actively formed. Some smectite (low charge) and vermiculite (high charge) was however already present in the parent material. Main source of smectite formation was biotite, hornblende and probably plagioclase. Furthermore, irregularly and regularly interstratified clay minerals (mica-HIV or mica-vermiculite) were formed immediately after the start of moraine exposure to weathering. In addition, hydroxy-interlayered smectite (HIS) as a transitory weathering product from mica to smectite was detected. Furthermore, since the start of soil evolution, kaolinite was progressively formed. In the silt fraction, only little changes could be detected; i.e. some formation of an interstratified mica-HIV or mica-vermiculite phase.The detected clay mineral formation and transformation mechanisms within this short time span confirmed the high reactivity of freshly exposed sediments, even in a cryic environment.     

Earthworm distribution and abundance along a mineral-peat soil transect

The earthworm fauna along a gradient from undisturbed mineral soil to an artificial acid peat soil up to 25 cm deep and ca. 30 yr old was studied in the Phoenix Park, Dublin. The peat held only 15% of the total numbers of worms in the mineral soil and 9% of the biomass, but 9 out of the 12 species recorded were present in the peat. Aporrectodea caliginosa, A. tuberculata and Allolobophora chlorotica were the most numerous species in the mineral soil but were scarce in the peat where the surfaced-welling, pigmented species L. rubellus, L. castaneus and Satchellius mammalis were most abundant. Low pH and shortage of suitable food were considered to be the main factors limiting earthworm populations in the peat.     

Changes in the community structure and diversity of soil invertebrates across the Franz Josef Glacier chronosequence

Following the creation of new land surfaces, there is an initial build-up phase of ecosystem development, but after a prolonged absence of major disturbance a retrogressive (decline) phase often follows due to reduced nutrient availability over time. Although many studies have considered how the soil community changes during the build-up phase, the response of this community to the retrogressive phase is poorly known. We measured litter and soil communities of microfauna and macrofauna along the Franz Josef Glacier chronosequence in New Zealand that spans ca. 120,000 years, and includes well-established build-up and retrogressive stages. We aimed to assess whether the abundances, community structure and diversity of these groups show the same pattern across the sequence as that for vegetation. With regard to microfaunal abundances, litter-dwelling microbe-feeding nematodes were most abundant in the first stage of the chronosequence, but several other groups of microfauna in both the soil and litter increased sharply during the first few stages and declined sharply during the last (retrogressive) stages. The ratios of bacterial- to fungal-feeding nematodes in both soil and litter were lowest for the final stages of the chronosequence, and (in the case of soil) for some of the early stages, pointing to domination by the fungal-based energy channel at those stages for which soil organic matter content or quality were lowest. This is consistent with the fungal-based energy channel being better adapted than the bacterial-based channel for resource-poor conditions. The main groups of macroinvertebrates typically had their lowest abundances at the very early and late stages of the chronosequence, although the relative abundances of different taxa differed during the intermediate stages. Taxonomic diversity of nematodes and macroinvertebrates in both litter and soil varied strongly with chronosequence stage but differed among taxa; diversity of only one group (macroinvertebrates in litter) declined significantly during retrogression. Diversity of nematodes and macroinvertebrates along the sequence did not closely match tree diversity or soil chemical properties, but community composition of these groups was often related to tree community composition and ratios of soil C to N, C to P and N to P. Different groups of soil invertebrates show contrasting responses to chronosequence stage, probably because they differ in their relative response to bottom-up and top-down controls. However, the abundance of most groups increased during the build-up phase and declined during retrogression. As such, the build-up and decline phases observed for plant communities and ecosystem processes across long-term chronosequences also apply to soil communities, pointing to the importance of resource availability as a major driver of soil biota during long-term ecosystem change.     

Factors affecting phosphate sorption along a Mediterranean, dolomitic soil and vegetation chronosequence

Phosphate sorption by calcareous soils has been studied mainly on heavily fertilized agricultural soils and soils with calcite as the main carbonate mineral. We examined factors affecting phosphate adsorption in the soils of a semi-arid, mediterranean, dolomitic, soil and vegetation chrono-sequence in southeastern Spain. The youngest soils are highly eroded, Sandy Regosols (Typic Xerorthents) under gorse-scrubland vegetation. These have small P sorption capacities, large Mg-Ca carbonate contents but small amounts of Fe and Al oxides. Small total P (HNO₃/HClO₄ digestion) concentrations (30–130 μg P g^?1), of which up to 90% is Ca-bound (HCl-extractable), are typical of these young soils. P sorption markedly increased when Ca²⁺ was added to the solution. The fractionation of previously sorbed P indicates that the fate of most of this extra-sorbed P is the labile-P fraction sorbed on to (carbonate) surfaces and the apatite-like fraction (NaHCO₃-extractable and HCl-extractable fractions). At the other extreme, older more-intensively weathered, sandy-clay-loam rendzinas (Entic Haploxerolls), supporting dense mature garrigue, have a much greater P adsorption capacity and larger clay and Fe and Al oxide concentrations. They have more total P (ca 400 μg P g^?1), much of it in occluded form (residual fraction). These soils show no significant differences in P sorption whether or not CaCl₂ was used as a background electrolyte. Considering the overall variations within the chronosequence, dithionite extractable Fe and Al are the properties best correlated with P sorption. This support the general finding that crystalline Fe-oxides (e.g. goethite and haematite) appear to be the most important P-sorbing component for soils in the Mediterranean region, rather than amorphous Fe-oxides (e.g. ferrihydrite) as is reported for more mesic areas. Stepwise multiple regression and fractionation data, however, suggest that, provided the soil solution is rich in Ca²⁺, carbonate may also be a significant contributing factor to P sorption, especially in the youngest of these dolomitic soils.     

Evaluation of soil microbial indices along a revegetation chronosequence in grassland soils on the Loess Plateau,Northwest China

There is a growing interest in using soil microbial parameters as indicators of soil quality changes after revegetation of disturbed soils. This study investigated the changes in different soil microbial parameters as well as physico-chemical parameters as affected by vegetation rehabilitation of soil in the Loess plateau of China subjected to natural succession after enclosure. The results showed that the soil nutrients tend to be concentrated in the soil surface layer, especially the soil organic C, total N and alkali extractable N with soil organic C being doubled (up to 20 g kg⁻¹) after 50 years of revegetation. Soil enzyme activities and microbial biomass C (Cmic) and N (Nmic) increased with rehabilitation time up to 23 years. After 23 years, soil Cmic and Nmic and enzyme activities remained stable. Enzyme activities increased rapidly during the early stage of revegetation, about 15–20 years after enclosure. Soil Cmic and Nmic also increased about 20% faster up to 23 years since enclosure in the 0–20-cm soil layer. Soil basal respiration (BR) in the 23 years site was higher than in other sites, indicating high microbial activity in this site. These findings demonstrated significant impacts of natural vegetation succession in overgrazed grassland on the properties of the surface soils, including the soil nutrients, organic matter, soil microbial biomass, respiration, and enzyme activities.     

Soil bacterial and fungal communities along a soil chronosequence assessed by fatty acid profiling

Microbial communities are important components of terrestrial ecosystems. The importance of their diversity and functions for natural systems is well recognized. However, a better understanding of successional changes of microbial communities over long time scales is still required. In this work, the size and composition of microbial communities in soils of a deglaciation chronosequence at the Damma glacier forefield were studied by fatty acid profiling. Soil fatty acid concentrations clearly increased with soil age. The abundances of arbuscular mycorrhizal fungi (AMF), bacteria and other soil fungi, however, were more affected by abiotic soil parameters like carbon content and pH than by soil age. Analysis of ratios of the different microbial groups (AMF, fungi, bacteria) along the soil chronosequence indicated that: i) the ratios of AMF to bacteria and AMF to fungi decreased with soil age; and ii) the ratio of fungi to bacteria remained unchanged along the soil chronosequence. These two pieces of evidence suggest that the evolution of this ecosystem proceeds at an uneven pace over time and that the role of AMF is less important in older, more organic and acidified soils than in mineral soils. In contrast to other studies, no successional replacement of bacteria with fungi in more acidified and organic soil was observed.     

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.     

Spatio-temporal variability of microbial abundance and community structure in the puddled layer of a paddy soil cultivated with wetland rice (Oryza sativa L.)

The puddled layer of paddy soils represents a highly dynamic environment regarding the spatio-temporal variability of biogeochemical conditions. To study these effects on the abundance and community structure of microbial populations, a rhizotron experiment was conducted throughout an entire growing season of wetland rice. Soil samples were taken from selected areas of the puddled layer (bulk soil, oxidized layer, rhizosphere) at main plant developmental stages such as (i) the initial stage, (ii) tillering, (iii) panicle initiation, (iv) flowering, and (v) maturity. Cell numbers of archaea, bacteria, and selected phyla were assessed by catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH). The structure and diversity of microbial communities was analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) along with sequencing of selected bands. Following submergence of the paddy soil, shifts of bacterial community structure were observed in the oxidized layer and the rhizosphere. Members of the β-Proteobacteria became predominant in the rhizosphere at tillering stage and were affiliated with aerobic, iron-oxidizing bacteria of the genus Sideroxydans. Seasonal effects were mainly visible in the rhizosphere, as several phylogenetic subgroups including methanotrophic bacteria showed increased cell numbers at flowering stage. Cell numbers of methanogenic archaea were also highest at flowering stage (bulk soil, rhizosphere) and members of the Methanocellales were identified as predominant archaeal populations in areas of oxic and anoxic conditions. In contrast to bacteria, the communities of archaea in the puddled layer of the studied paddy soil were less influenced by spatio-temporal variations of biogeochemical conditions.     

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.     

Land use effects on soil carbon fractions in the southeastern United States. II. changes in soil carbon fractions along a forest to pasture chronosequence

Since land use change can have significant impacts on regional biogeochemistry, we investigated how conversion of forest and cultivation to pasture impact soil C and N cycling. In addition to examining total soil C, we isolated soil physiochemical C fractions in order to understand the mechanisms by which soil C is sequestered or lost. Total soil C did not change significantly over time following conversion from forest, though coarse (250–2,000 m) particulate organic matter C increased by a factor of 6 immediately after conversion. Aggregate mean weight diameter was reduced by about 50% after conversion, but values were like those under forest after 8 years under pasture. Samples collected from a long-term pasture that was converted from annual cultivation more than 50 years ago revealed that some soil physical properties negatively impacted by cultivation were very slow to recover. Finally, our results indicate that soil macroaggregates turn over more rapidly under pasture than under forest and are less efficient at stabilizing soil C, whereas microaggregates from pasture soils stabilize a larger concentration of C than forest microaggregates. Since conversion from forest to pasture has a minimal impact on total soil C content in the Piedmont region of Virginia, United States, a simple C stock accounting system could use the same base soil C stock value for either type of land use. However, since the effects of forest to pasture conversion are a function of grassland management following conversion, assessments of C sequestration rates require activity data on the extent of various grassland management practices.     

Changes in enzyme activities and soil microbial community composition along carbon and nutrient gradients at the Franz Josef chronosequence, New Zealand

During primary succession, the abundance of carbon (C) and nitrogen (N) in soil increases, while phosphorus (P) declines. These changes in nutrient concentrations in organic matter are likely to play an important role in controlling enzyme-mediated nutrient mineralization. We examined how enzyme activity and efficiency changed with successional time in organic and mineral soils taken from the 120 000-year-old Franz Josef soil development sequence, New Zealand, and the relationship between enzyme activity and efficiency and soil nutrient concentrations. We found that the activity of enzymes involved in P mineralization increased with site age across the Franz Josef chronosequence, while the activity of enzymes regulating C and N mineralization declined in organic but not mineral soil. Sulfatase activity peaked at an intermediate-aged site, possibly indicating a transient period of S limitation. The activity of phosphatase enzymes was negatively correlated with the concentration of P in the soil, whereas activity of C-, N- and S-hydrolyzing enzymes was not strongly dependent on nutrient concentrations. When assessed as efficiency (activity per unit microbial biomass), there were strong patterns of increasing efficiency of P-, and decreasing efficiency of C- and N-hydrolyzing enzymes with site age. We suggest that activity patterns for C-, N- and S-hydrolyzing enzymes were obscured by simultaneous and opposing changes in enzyme efficiency and microbial biomass. In mineral soil, efficiency of enzymes was negatively correlated with soil nutrient availability. In contrast, in organic soil, efficiency of C-, N- and S-hydrolyzing enzymes was positively correlated with soil P, while efficiency of P-hydrolyzing enzymes was negatively correlated with soil P. The increase in efficiency of P-hydrolyzing enzymes, and decrease in efficiency of C-, N- and S-hydrolyzing enzymes with site age was accompanied by a shift in microbial community composition towards higher relative abundances of fungi. Changes in enzyme efficiency with site age are likely to be due to both constitutive differences in enzyme production, and down-regulation of enzyme expression.     

长期施肥对氨氧化古菌丰度及群落结构的影响

【目的】氨氧化古菌对土壤氮素转化有着重要的作用。本研究以长期定位施肥黄泥田土壤为研究对象探讨了长期不同施肥模式对土壤氨氧化古菌数量和多样性的影响,为制定合理的施肥制度提供理论基础。【方法】试验在福建省农科院试验站上进行,以30年长期定位施肥的红壤性水稻土为研究对象采用荧光定量PCR和克隆文库技术,研究了长期不同施肥模式对氨氧化古菌(ammonia-oxidizing archaea,AOA)丰度及群落结构的影响。试验设4个处理:1)不施肥(CK);2)单施氮磷钾肥(NPK);3)氮磷钾肥配施牛粪(NPKM);4)氮磷钾肥配施秸秆(NPKS)。小区面积为12 m~2每个处理设3个重复。土样采集时间为2012年10月份(水稻收获后),测定土壤养分和氨氧化古菌的数量及多样性。【结果】1)与CK相比,NPKM和NPKS处理显著增加了土壤有机质含量,NPKM和NPKS处理之间无显著差异。2)与CK相比施肥均能提高土壤全氮含量;NPKM和NPKS处理能够显著提高土壤全磷含量,NPKM处理全磷含量最高;仅NPKS处理能显著增加全钾含量。3)与CK相比,长期施肥均能提高土壤有效氮(AN)、速效磷(AP)和速效钾(AK)的含量,并且NPKM处理AN和AP含量最高,NPKS处理中AK含量最高。4)与CK相比,长期施肥均对土壤pH值无显著影响。5)与CK处理相比,NPKM和NPKS处理的amoA基因拷贝数显著增加增加幅度分别为168.4%和95.7%;单施化肥处理与CK无显著差异。土壤氨氧化古菌数量与土壤有机质含量呈显著正相关,与土壤全磷、有效氮、速效磷和速效钾含量呈极显著正相关。6)长期不同施肥处理影响土壤氨氧化古菌的种群结构,单施化肥增加了土壤AOA的多样性,而化肥配施有机肥则降低了AOA的多样性。7)本试验中得到的土壤氨氧化古菌amoA基因序列均为不可培养的古菌,包括泉古菌(Crenarchaeote)和奇古菌(Thaumarchaeote)。本试验所得氨氧化古菌绝大多数与来自土壤、沉积物的amoA基因克隆非常相似,少数与水体环境相似。【结论】不同培肥模式下,土壤中氨氧化古菌均为不可培养的古菌,包括泉古菌(Crenarchaeota)和奇古菌(Thaumarchaeota),然而水稻土壤养分和氨氧化古菌丰度及群落结构变化显著。单施化肥的作用不明显,有机无机肥配施有利于土壤有机质和养分的积累以及氨氧化古菌的生长增加了氨氧化古菌优势菌群的比例。     

覆盖作物对猕猴桃园土壤氨氧化微生物丰度和群落结构的影响

[目的]果园行间播种覆盖作物有利于改善土壤理化性状,改变氮循环过程中的氨氧化微生物群落结构.因此,我们分析不同覆盖作物下猕猴桃园土壤氨氧化微生物的群落结构和基因丰度,以探究其与土壤硝化作用的关系.[方法]选择湖北十堰的一个5年生猕猴桃果园进行了种植多年生覆盖作物试验,供试覆盖作物有白三叶草(Trifolium repe...     

Soil quality degradation processes along a deforestation chronosequence in the Ziwuling area, China

Accelerated erosion caused by deforestation and soil degradation has become the primary factor limiting sustainable utilization of soil resources on the Loess Plateau of Northwestern China. We studied the physical, chemical, and microbiological processes of soil degradation along a chronosequence of deforestation in the Ziwuling area of northwestern Shaanxi province. The results indicated that soil wet aggregate stability, mean aggregate diameter decreased with years following deforestation. Accelerated erosion resulted in soil nutrient loss, and a decrease in soil enzyme activities including notable losses of total soil N, organic C, alkaline phosphatase activity, and invertase activity. During the early time period, the rates of total soil N, organic C, alkaline phosphatase activity, and invertase activity decreasing were rapid and gradually decreased with deforestation years. Increased use of nitrogen fertilizers made determination of soil quality based on measured NO₃–N and NH₄–N inconclusive. The differences in measured parameters between the topsoil and subsoil horizons decreased with time since deforestation, and we concluded that soil erosion was the primary process responsible for the degradation of measured soil physical, chemical, and microbiological properties.