马铃薯||玉米间作对土壤细菌多样性的影响

为探明连续马铃薯、玉米单作及间作种植对土壤细菌群落组成的影响,利用IonS5~(TM)XL高通量测序平台,分析了单作玉米(M)、单作马铃薯(P)、马铃薯||玉米间作(PM)下,土壤细菌群落组成以及多样性间的差异。结果表明:与单作相比,马铃薯||玉米间作土壤有机质含量显著升高(P0.05),但土壤全氮、碱解氮、全磷、速效钾、土壤pH等没有显著变化。所获得的56 787个土壤细菌可操作分类单元(OTUs)共分为46门、55纲、114目、208科、455属。土壤变形菌门(Proteobacteria)、酸杆菌门(Acidobacteria)和放线菌门(Actinobacteria)细菌占总相对丰度的57.68%～65.11%,为优势菌门;间作对土壤细菌群落多样性(香农指数、辛普森指数)、丰富度(ACE指数和Chao1指数)无显著影响,但改变了基于门、属水平上的细菌群落组成。与单作马铃薯相比,间作显著降低了土壤变形菌门(Proteobacteria)相对丰度(P=0.023),提高了浮霉菌门(Planctomycetes)的相对丰度(P=0.043)。在属水平上,相对丰度较低的芽单胞菌属(Gemmatimonas)、Candidatus Solibacter属更易受到种植方式的影响;间作提高了节杆菌属(Arthrobacter)、芽球菌属(Blastococcus)和芽孢杆菌属(Bacillus)的相对丰度。随细菌群落结构变化,细菌群落功能上出现差异,通过KEGG功能预测共得到7个一级功能层, 35个二级功能层,表现出功能上的丰富性,土壤细菌群落在代谢、遗传信息处理和细胞过程方面功能活跃。7个一级功能层中的代谢功能组在马铃薯||玉米间作与马铃薯单作间有显著差异。利用前向选择,经蒙特卡罗检验表明,连续马铃薯、玉米单作及间作栽培5年后的土壤各理化性状指标与土壤细菌群落组成、多样性间的相关性均不显著。连续马铃薯||玉米间作及单作5年条件下土壤细菌群落组成的变化是由马铃薯||玉米间作作物种间互利和竞争关系而驱动的。     

Impact of plant species grown as monocultures on sporulation and root colonization by native arbuscular mycorrhizal fungi in potato

Rhizosphere soils from 12 different plant species grown as monocultures at a field site of biodiversity and ecological processes in terrestrial herbaceous ecosystems (BIODEPTH) in northern Sweden were used as inoculum on potato to investigate mycorrhizal traits. Potato roots showed significantly higher mycorrhizal colonization when inoculated with soil samples from Festuca ovina and Leucanthemum vulgare compared to soil samples from other plants. The soil samples of F. ovina, L. vulgare, Phalaris arundinacea and Trifolium pratense rhizospheres were chosen for arbuscular mycorrhizal fungi identification based on spore morphology and large subunit (LSU) ribosomal DNA sequences amplified from single spores and roots. Spore morphological identification showed that Glomus mosseae and Glomus intraradices were found in F. ovina and L. vulgare soils at the site as well as in our potato trap experiment. Also, Glomus geosporum spores were present in all four plants’ soils in the potato trap experiment. LSU rDNA sequences were obtained from AM fungal spores from the collection site or potato trap experiment and colonized potato roots inoculated with L. vulgare soil. Sequences showed highest similarity to G. mosseae. Our results suggest that the host F. ovina and L. vulgare could be considered in crop rotation to enhance AM fungal inocula for potatoes.     

Effects of soil moisture on soil solution chemistry,biomass production,and shoot nutrients in two native grasses on a calcareous soil

Abstract

Two native grasses, Festuca ovina of dry and Agrostis stolonifera mainly of moist habitats of calcareous grasslands, were studied in an experiment with the objective of elucidating the effect of soil moisture level on soil solution chemistry, biomass production and shoot mineral nutrients. Eight levels of moisture, corresponding to 30–100% of the water‐holding capacity (WHC) of the soil, were tested. High correlation coefficients with soil moisture were observed for magnesium (Mg), phosphorus (P), and HCO₃ in soil solution. Amounts of calcium (Ca), Mg, and iron (Fe) in soil solution were lowest in the intermediate soil moisture range (60–70%). Shoot production, relative to maximum, was higher at low moisture levels for F. ovina than for A. stolonifera. Differences of P, Fe, and potassium (K) concentrations in shoots and maximum relative shoot production between the two species, are consistent with their field distributions as related to soil moisture. Lower soil moisture on calcareous soil is more favorable for F. ovina than for A. stolonifera. Variation in soil moisture regimes may greatly influence amounts of mineral nutrients in soil solution and uptake by plants and might even be a prerequisite for adequate acquisition of mineral nutrients and growth of plants on limestone soils.     

Rapid effects of plant species diversity and identity on soil microbial communities in experimental grassland ecosystems

Changes in plant community structure, including the loss of plant diversity may affect soil microbial communities. To test this hypothesis, plant diversity and composition were experimentally varied in grassland plots cultivated with monocultures or mixtures of 2, 3 or 4 species. We tested the effects of monocultures versus mixtures and of plant species composition on culturable soil bacterial activity, number of substrates used and catabolic diversity, microbial biomass N, microbial respiration, and root biomass. These properties were all measured 10 months after seeding the experiment. Soil bacterial activity, number of substrates used and catabolic diversity were measured in the different plant communities using BIOLOG GN and GP microplates, which are redox-based tests measuring capacity of soil culturable bacteria to use a variety of organic substrates. Microbial biomass N, microbial respiration, and root biomass were insensitive to plant diversity. Culturable soil microbial activity, substrates used and diversity declined with declining plant diversity. Their activity, number of substrates used and diversity were significantly higher in plots with 3 and 4 plant species than in monocultures and in plots with 2 species. There was also an effect of plant species composition. Culturable soil microbial activity and diversity was higher in the four-species plant community than in any of the plant monocultures suggesting that the effect of plant diversity could not be explained by the presence of a particular plant species. Our results showed that changes in plant diversity and composition in grassland ecosystems lead to a rapid response of bacterial activity and diversity.     

Relationship between vegetation diversity and soil functional diversity in native mixed-oak forests

Most studies on the interactions between aboveground vegetation and belowground soil diversity have been carried out in microcosms or manipulated field plots. In the current study, we investigated the relationship between forest vegetation diversity and soil functional diversity (calculated from the activity of soil enzymes) in naturally developed plant communities of native mixed-oak forests without imposing any disturbances to already existing plant–soil relationships. In order to do so, five different vegetation types, i.e., herbaceous plants, climbing plants, trees, shrubs, and ferns, were considered. Correlations between plant diversity, soil physicochemical properties, and soil enzyme activities were determined. Soil physicochemical parameters appeared strongly correlated with both enzyme activities (e.g., pH was positively correlated with amidase and arylsulphatase, and negatively with acid phosphatase; OM content was positively correlated with β-glucosidase, acid and alkaline phosphatase and urease, and negatively with amidase; total N was positively correlated with β-glucosidase, and acid and alkaline phosphatase, and negatively with amidase) and soil functional diversity. For ferns, strong correlations between enzyme activities and plant diversity indexes were found (i.e., dehydrogenase was positively correlated with species richness and Shannon's diversity; acid and alkaline phosphatase were negatively correlated with Shannon's diversity; acid phosphatase was also negatively correlated with species richness). Most interestingly, herbaceous plants and ferns showed a strong positive correlation between Shannon's plant diversity and soil functional diversity. Furthermore, herbaceous plants showed a strong positive correlation between species richness and soil functional diversity. Although these correlations between plant diversity and soil functional diversity might possibly be due to the fact that higher values of plant richness and diversity result in a greater habitat heterogeneity in the soil, current knowledge on the topic is mixed and very incomplete and, then, one must be extremely cautious when interpreting such correlations.     

Nine years of enriched CO2 changes the function and structural diversity of soil microorganisms in a grassland

To gain insight into microbial function following increased atmospheric CO₂ concentration, we investigated the influence of 9 years of enriched CO₂ (600 μl litre⁻¹) on the function and structural diversity of soil microorganisms in a grassland ecosystem under free air carbon dioxide enrichment (FACE), as affected by plant species (Trifolium repens L. and Lolium perenne L. in monocultures and mixed culture) and nitrogen (N) supply. We measured biomass and activities of enzymes covering cycles of the most important elements (C, N and P). The microbial community was profiled by molecular techniques of phospholipid fatty acid (PLFA) and denaturing gradient gel electrophoresis (DGGE) analysis. The enrichment in CO₂ increased soil microbial biomass (+48.1%) as well as activities of invertase (+36.2%), xylanase (+22.9%), urease (+23.8%), protease (+40.2%) and alkaline phosphomonoesterase (+54.1%) in spring 2002. In autumn, the stimulation of microbial biomass was 25% less and that of enzymes 3–12% less than in spring. Strong correlations between activities of invertase, protease, urease and alkaline phosphomonoesterase and microbial biomass were found. The stimulation of microbial activity in the enriched atmosphere was probably caused by changes in the quantity and kind of root litter and rhizodeposition. The response of soil microorganisms to enriched CO₂ was most pronounced under Trifolium monoculture and under greater N supply. The PLFA analysis revealed that total PLFA contents were greater by 24.7% on average, whereby the proportion of bioindicators representative of Gram‐negative bacteria increased significantly in the enriched CO₂ under less N‐fertilized Lolium culture. Discriminant analysis showed marked differences between the PLFA profiles of the three plant communities. Shannon diversity indices calculated from DGGE patterns were greater (+12.5%) in the enriched CO₂, indicating increased soil bacterial diversity. We conclude that greater microbial biomass and enzyme activity buffer the potential increase in C sequestration occurring from greater C addition in enriched CO₂ due to greater mineralization of soil organic matter.     

Microbial dynamics and natural remediation patterns of Fusarium‐infested watermelon soil under 3‐yr of continuous fallow condition

Long‐term monoculture of watermelon results in inhibited growth and decreased crop yields, possibly because of imbalance in microbial ecology caused by accumulation of the pathogen in soil. This results in serious problems in the economics of watermelon production. We investigated the build‐up of Fusarium in soil under watermelon cultivation and changes over 3 yr of fallow in a microcosm. We focused on changes in the microbial community of Fusarium‐infected soil, including the diversity of the microfloral species composition, and species abundance. Long‐term monoculture of watermelon leads to changes in microbial diversity and community structure. The microbes most readily cultured from infested soil were suppressed by watermelon wilt pathogen Fusarium oxysporum f. sp. niveum (FON). Of 52 isolated and identified culturable microbes, 83.3% of bacteria, 85.7% of actinomycetes, 31.6% of fungi and 20.0% of Fusarium sp. were inhibited by FON on bioassay plates. Prior to fallowing, infested soil was a transformed ‘fungus‐type’ soil. After 3 yr of fallow, the infested soil had remediated naturally, and soil microbial diversity recovered considerably. Abundance of dominant bacterial populations was increased by 118–177%, actinomycetes, fungi and FON were decreased by 23–32, 33–37 and 50%, respectively. The ratio of bacteria: actnomycetes: fungus: Fusarium sp. in infested soil changed from 24 000:100:4:1 prior to fallow to 57 000:100:3.5:1 after fallowing, nearer to the 560 000:400:8:1 ratio of healthy soil not used for watermelon cultivation. This suggests the ‘fungus‐type’ soil was converting to ‘bacteria‐type’ soil and that disrupted microbial communities in infested soil were restored during fallow.     

Does genetic diversity of grass improve yield,digestibility, and resistance to weeds,pests and disease infection?

ABSTRACT

Intraspecies genetic level diversity has the potential to improve ecosystem functions and services, similar to that by species-level diversity. Although yield, pollination, and pest and disease control have been enhanced by crop genetic diversity, mixing multiple cultivars of grass within a species in an agricultural field have not been fully tested by farmers.

We, therefore, tested whether multiple ecosystem functions are increased in a grass mixture of multiple cultivars compared to monoculture and whether this relationship differs with soil fertility. We performed monocultures of four Orchard Grass cultivars and a mixture of these cultivars with and without fertilizer application and examined the aboveground net primary productivity (ANPP), their stability, dry matter digestibility, and resistance to weed, pest, and disease. We found significant differences between cultivars in the second yield and disease lesion area on the leaf, but not between mixed culture and monoculture. Moreover, no significant difference was found in the first and third yields in terms of stability, dry matter digestibility, and leaf damage by insects, although the number of leaves damaged by insects for mixed culture was less than half of that on average for monoculture. Although genetic diversity is not always an important driver of ecological processes due to fluctuation among plots, it may play a role in pest control of agricultural land in the long term.     

Plant carbon partitioning below ground in the presence of different neighboring species

Knowledge about carbon allocation below ground is necessary to understand soil ecosystem functioning and the global C cycle. It is common knowledge that different plant species coexist in natural and agricultural systems. By using a modified ¹³C pulse-chase approach, which enabled us to label individual plants in either mono- or mixed cultures, we investigated the effect of coexistence of different neighboring species on plant carbon partitioning. Maize and faba bean were used as our test plants and isotope pulse labeling was performed twice at 26 and 54 d after emergence. The results showed that a higher proportion of photoassimilates was distributed below ground in maize than in faba bean, resulting in a greater ratio of root to shoot biomass for maize plants during the experiment. The carbon distribution to roots was slightly higher in mixed cultures at 26 d than the counterpart monocultures. The distribution of the plant-assimilated ¹³C to soil dissolved organic carbon was also greater in mixed cultures at 26 d relative to the monocultures. The most significant effect of the mixed culturing was a dramatic increase of ¹³C incorporation into the soil microbial biomass. These results indicated that the plant carbon allocation below ground was altered in the presence of a different neighboring species. The increase of plant diversity probably enhances the soil microbial activity and hence the turnover of the plant-derived carbon in soil.     

盐地碱蓬根际土壤细菌群落结构及其功能

盐地碱蓬作为生物改良盐碱地的理想材料,其根际土壤微生物对土壤改良发挥着重要作用。为了深入探索环渤海滨海盐碱地碱蓬根际土壤细菌群落结构组成及其功能,采用Illumina Misep高通量测序平台对环渤海地区滨海盐碱地盐地碱蓬根际土壤和裸地土壤进行测序。从16个样本中获得有效序列734 792条, 4 285个OTUs,归属于41门、100纲、282目、400科、892属、1 577种。盐地碱蓬根际土壤细菌群落由变形菌门(Proteobacteria)、放线菌门(Actinobacteria)、绿弯曲门(Chloroflexi)、拟杆菌门(Bacteroidetes)、芽单胞菌门(Gemmatimonadetes)、酸杆菌门(Acidobacteria)、厚壁菌门(Firmicutes)、蓝藻细菌门(Cyanobacteria)、髌骨细菌门(Patescibacteria、浮霉菌门(Planctomycetes)组成。Alpha多样性计算结果表明,盐地碱蓬根际土壤细菌群落结构多样性高并与裸地土壤间差异显著;LEfSe(LDAEffectSize)分析发现,盐地碱蓬与裸地差异指示种明显不同。PCoA与相关性Heatmap表明,盐地碱蓬、速效氮、速效钾、速效磷、电导率是影响土壤细菌目类水平群落组成的主要因子。PICRUSt(Phylogenetic InvestigationofCommunitiesbyReconstructionofUnobserved States)分析表明微生物群落在新陈代谢等40个功能方面盐地碱蓬根际土壤比裸地土壤高。本研究表明盐地碱蓬覆盖能够降低土壤盐分,增加土壤养分,对土壤细菌群落多样性及其功能有积极作用。     

Structural differences in the rhizosphere communities of legumes are not equally reflected in community-level physiological profiles

The relationship of structural diversity and differences in the functional potentials of rhizosphere communities of alfalfa, common bean and clover was investigated in microcosms. PCR-SSCP (single strand conformation polymorphism) analysis of 16S rRNA genes revealed significant differences in the composition of the leguminous rhizosphere communities at the shoot stage of plants grown in the same soil. Sequencing of dominant SSCP-bands indicated the presence of plant specific organisms. The partial rRNA gene sequences were related to members of the α- and γ-Proteobacteria, Bacteroidetes and Actinobacteria. Besides the plant species, the soil also affected the structural diversity in rhizospheres. The dominant bacterial populations of alfalfa grown in soils with different agricultural histories were assigned to different taxonomic groups. Addressing the functional potentials, community-level physiological profiles (CLPP) were generated using BIOLOG GN^®. The three leguminous rhizosphere communities could be differentiated by principle component analysis, though the overall analysis indicated that the metabolic potential of all rhizosphere samples was similar. The functional variation examined in rhizospheres of alfalfa was minor in response to the soil origin and was found not to be significant different at different growth stages. The results indicate that similar functional potentials may be provided by structurally different bacterial communities.     

Adaptive attributes of tropical forage species to acid soils II. Differences in shoot and root growth responses to varying phosphorus supply and soil type

Identification of plant attributes that improve the performance of tropical forage ecotypes when grown as monocultures or as grass+legume associations in low fertility acid soils will assist the development of improved forage plants and pasture management technology. The present work compared the shoot and root growth responses of four tropical forages: one grass and three legumes. The forages were grown in monoculture or in grass+legume associations at different levels of soil phosphate. Two infertile acid soils, both Oxisols, were used: one sandy loam and one clay loam. They were amended with soluble phosphate at rates ranging from 0 to 50 kg ha^‐1. The forages, Brachiaria dictyoneura (grass), Arachis pintoi, Stylosanthes capitata and Centrosema acutifolium (legumes), were grown in large plastic containers (40 kg of soil per container) in the glasshouse. After 80 days of growth, shoot and root biomass production, dry matter partitioning, leaf area production, total chlorophyll content in leaves, soluble protein in leaves, root length, and proportion of legume roots in grass+legume associations were determined. The grass, grown either in monoculture or in association responded more to phosphorus supply than did the three legumes in terms of both shoot and root production. At 50 kg ha^‐1 of phosphorus, the grass's yield per plant in association was greatly enhanced, compared with that of grass in monoculture. The increase in size of grass plants in association compared with that in monoculture may have been caused by reduced competition from the legumes. These differences in shoot and root growth responses to phosphorus supply in acid soils between the grass and the three legumes may have important implications for improving legume persistence in grass+legume associations.     

Linking plant identity and interspecific competition to soil nitrogen cycling through ammonia oxidizer communities

Both plants and microbes influence soil nutrient cycling. However, the links between plants, microbes and nutrient cycling are poorly understood. In this study, we investigated how plant identity and interspecific competition influence soil nitrogen cycling and attempted to link plant identity and interspecific competition to community structures of bacterial and archaeal ammonia oxidizers based on terminal restriction fragment length polymorphism analysis (T-RFLP) of bacterial and archaeal ammonia monooxygenase (amoA) genes. Faba bean and maize monocultures and a faba bean/maize mixture were planted with two nitrogen levels (0 and 100 mg N kg⁻¹ soil as urea). Soil mineral nitrogen, ammonia oxidizer function (potential nitrification activity, PNA) and community structures were measured 28 and 54 days after plant emergence. Faba bean and maize substantially differed in their influences on mineral nitrogen concentrations and PNA in rhizosphere soils. Soil mineral nitrogen and PNA in the rhizosphere soils of the faba bean/maize mixture were closer to those of the maize monoculture than to those of the faba bean monoculture. T-RFLP with restriction enzymes BsaJI and Hpy8I distinguished variations in bacterial and archaeal ammonia oxidizers community structure, respectively, and detected both between-cluster and within-cluster variations in bacterial ammonia oxidizers. T-RFLP data showed that nitrogen addition favored part of a Nitrosospira cluster 3b sequence type and suppressed part of a cluster Nitrosospira 3a sequence type of bacterial ammonia oxidizers, while it had no influence on the archaeal ammonia oxidizer community structure. Although multivariate analysis showed that the function and community structure of bacterial ammonia oxidizers were significantly correlated, plant species and interspecific competition did not significantly change the community structure of bacterial and archaeal ammonia oxidizers. These results indicate that plant species and interspecific competition regulate soil nitrogen cycling via a mechanism of other than alteration in the community structure of ammonia oxidizers as investigated by DNA based methods.     

Changes of Bacterial Community Structure in Copper Mine Tailings After Colonization of Reed (Phragmites communis)

Soil samples were collected from both bare and vegetated mine tailings to study the changes in bacterial communities and soil chemical properties of copper mine tailings due to reed (Phragmites communis) colonization. The structures of bacterial communities were investigated using culture-independent 16S rRNA gene sequencing method. The bacterial diversity in the bare mine tailing was lower than that of the vegetated mine tailing. The former was dominated by sulfur metabolizing bacteria, whereas the latter was by nitrogen fixing bacteria. The bare mine tailing was acidic (pH = 3.78), whereas the vegetated mine tailing was near neutral (pH = 7.28). The contents of organic matter, total nitrogen, and ammonium acetate-extractable potassium in vegetated mine tailings were significantly higher than those in the bare mine tailings (P< 0.01), whereas available phosphorus and electrical conductivity were significantly lower than those in the bare mine tailings (P< 0.01). The results demonstrated that 16S rRNA gene sequencing could be successfully used to study the bacterial diversity in mine tailings. The colonization of the mine tailings by reed significantly changed the bacterial community and the chemical properties of tailings. The complex interactions between bacteria and plants deserve further investigation.     

Effects of collembola on nutrient cycling and microbial biomass on intact soil microcosm

(Jpn. J. Soil Sci.Plant Nutr., 77, 299–306, 2006)

The effects of Collembola (Folsomia candida Willem) on nutrient cycling, microbial biomass, and soil respiration were studied using intact soil microcosms. Intact soil microcosms (dia. 10·6 cm and depth 15 cm) were taken from pine forest soil, and were divided into four treatments · the unmanipulated control and three Collembolan manipulations in which microcosms were defaunated by deep-freezing, and then F. candida were introduced at three densities (0, 50, 100 per microcosm). The microcosms were incubated on forest floor with a roof. At 3- to 4-week intervals the microcosms were irrigated with deionized water for analyses of nutrients (Na+, K+, NH4+, Ca2+, Mg2+, Cl?, NO3?, SO42?) in the leachate. Soil respiration was measured using an infrared gas analyser. After 13 and 34 weeks of exposure, microcosms were destructively sampled. Collembola did not significantly affect microbial biomass C, N, and P nor soil respiration. Because the experiment was started in winter, nutrient leaching increased from spring to summer with increasing microbial activity. At the end of the experiment, leached nitrate from microcosms was significantly different between the 0 and 50 Collembolan treatments. Total established Collembolan biomass was under 4% of the soil microbial biomass in the microcosms, while manipulation of Collembola affected soil nitrogen dynamics at high microbial and collembolan activity.     

Degradation and humification of maize straw in soil microcosms inoculated with simple and complex microbial communities

Microbial communities are responsible for soil organic matter cycling and thus for maintaining soil fertility. A typical Orthic Luvisol was freed from organic carbon by thermal destruction at 600°C. Then the degradation and humification of ¹⁴C‐labelled maize straw by defined microbial communities was analysed. To study the role of microbial diversity on the humification of plant material, microcosms containing sterilized soil were inoculated with a natural microbial community or with microbial consortia consisting of bacterial and fungal soil isolates. Within 6 weeks, 41 ± 4% of applied ¹⁴C‐labelled maize straw was mineralized in the soil microcosms containing complex communities derived from a soil suspension, whilst the most efficient communities composed of soil isolates mineralized less than 35%. The humification products were analysed by solution state ¹³C‐NMR‐spectroscopy and gel permeation chromatography (GPC). The analyses of humic acids extracts by solution state ¹³C‐NMR‐spectroscopy revealed no difference in the development of typical chemical functional groups for humic substances during incubation. However, the increase in specific molecular size fractions of the extracted humic acids occurred only after inoculation with complex communities, but not with defined isolates. While it seems to be true that redundancy in soil microbial communities contributes to the resilience of soils, specific soil functions may no longer be performed if a microbial community is harshly affected in its diversity or growth conditions.     

Effect of vegetation manipulation of abandoned arable land on soil microbial properties

 The effect of vegetation composition on various soil microbial properties in abandoned arable land was investigated 2 years after agricultural practice had terminated. Microbial numbers and processes were determined in five replicate plots of each of the following treatments: continued agricultural practice (monoculture of buckwheat in 1997), natural colonization by the pioneer community (arable weeds), and manipulated colonization from low (four species, three functional groups: grasses, forbs and legumes) or high diversity (15 species, three functional groups) seed mixtures from plant species that are characteristic of abandoned fields in later successional stages. The results indicated that differences in above-ground plant biomass, plant species composition and plant species diversity had no significant effect on soil microbial processes (net N mineralization, short-term nitrification, respiration and Arg ammonification), microbial biomass C and N (fumigation-incubation) or colony-forming units of the major microbial groups. Hence, there were no indications that soil microbial processes responded differently within 2 years of colonization of abandoned arable land by later successional plants as compared to that by plants from the natural pioneer weed community. Therefore, it seems that during the first few years after arable field abandonment, plants are more dependent on the prevailing soil microbiological conditions than vice versa. Received: 8 April 1999     

EFFECTS OF CALCIUM AND SALINITY STRESS ON QUALITY OF LETTUCE IN SOILLESS CULTURE

Abstract

Fine fescues (Festuca spp.) are generally considered acid tolerant compared to other cool‐season turfgrasses. However, there is little information on aluminum (Al) tolerance of fine fescues at both the species and cultivar levels. The objectives of this study were to identy cultivars of fine fescues with superior ability to tolerate Al, and compare the Al tolerance of endophyte infected and endophyte‐free cultivars in Al tolerance. A total of 58 cultrvars of fine fescues belonging to five species or subspecies [14 hard fescue (F. longifolia Thuill), 25 Chewings fescue (F. rubra L. ssp. commutata Gaud), 15 strong creeping red fescue (F. rubra L. ssp. rubra), two slender creeping red fescue (F. rubra L. ssp. trichophylla), and two sheep fescue (F. ovina L.)] were selected from the 1993 National Fineleaf Fescue Test and screened under greenhouse conditions using solution culture, sand culture, and acid Tatum soil (Clayey, mixed, thermic, typic, Hapludult). The acid Tatum soil had 69% exchangeable Al and a pH of 4.4. An Al concentration of 640 μM and a pH of 4.0 were used in solution culture and sand culture screening. The grasses were seeded and grown for three weeks before harvesting. Aluminum tolerance was assessed by measuring relative root length, shoot length, root weight, shoot weight, and total dry matter. Differences in Al tolerance were identified at both the species and cultivar level based on relative growth were as follows: i) hard fescue and Chewings fescue were more Al tolerant than strong creeping red fescue; ii) within species or subspecies, significant differences were found among cultvars of Chewings fescue, strong creeping red fescue, slender creeping red fescue, and sheep fescue; whereas no difference was observed among the hard fescue cultivars; and iii) the cultivars containing endophyte exhibited greater Al tolerance compared the eudophyte‐free cultivars. The results indicate that fine fescues vary in Al tolerance and there is potential to improve Al tolerance with breeding and to refine their management recommendations regarding soil pH.     

Soil structural responses to alterations in soil microbiota induced by the dilution method and mycorrhizal fungal inoculation

This investigation examines the effect of manipulating soil microbial community composition and species richness on the development of soil structure over a seven month period in planted (with or without mycorrhizal fungi) and in unplanted macrocosms. The dilution method effectively resulted in soil communities with consistently contrasting levels of species (TRF) richness. In particular, the 10^?6 dilution of field soil resulted in less rich communities in bare unplanted soil than did the 10^?1 soil dilution. However, this was not the case in planted soils where root activity was a powerful influence on species richness. After seven months, principal components analysis (PCA) separated bacterial community composition primarily on planting regime; planted mycorrhizal, planted non-mycorrhizal and bare soil treatments all contained different bacterial community compositions. A consistent finding in planted and unplanted soils was that aggregate stability was positively correlated with small pore sizes. Mycorrhizal colonisation decreased plant biomass and also resulted in reduced soil bacterial species richness, lower percentage organic matter and smaller pore sizes relative to planted but non-mycorrhizal soils. However, soil aggregate stability and water repellency were increased in these (mycorrhizal) soils probably due to AMF hyphal activities including enmeshment and/or glomalin production. In contrast, bacterial TRF richness was positively correlated with aggregate stability in the bare and non-mycorrhizal planted soils. Soil organic carbon was an important factor in all treatments, but in the bare soil where there was no additional input of labile C from roots, the percentage C could be directly related to fungal TRF richness. The less species rich bare soil contained more organic C than the more species rich bare soil. This suggests a degree of redundancy with regard to mineralisation of organic matter when additional, more utilisable C sources are unavailable. Understanding the effects of microbial diversity on functional parameters is important for advancing sustainable soil management techniques, but it is clear that soil is a dynamic ecosystem.     

芒萁侵入红壤退化裸地对土壤理化性质和细菌组成的影响

芒萁是最早侵入红壤退化裸地的先锋植物,其侵入过程对土壤环境的改变在退化裸地生态恢复进程中具有重要意义。以福建省长汀县红壤侵蚀裸地为研究对象,分析测定退化裸地中芒萁侵入区和非侵入区土壤理化性质和细菌组成及多样性。结果表明：芒萁侵入裸地显著提高土壤最大持水量、土壤含水率、全碳、全氮、全钾、有机质和pH,并显著降低土壤容重;芒萁侵入区增加根瘤菌目和慢生根瘤菌属等14种土壤优势细菌,变形菌门和甲型(α)变形杆菌的相对丰度显著提高(p<0.05),而土壤绿弯菌门和AD3菌纲的相对丰度显著降低(p<0.05),这些土壤细菌主要功能为化能异养、好氧化能异养和纤维素分解;芒萁侵入裸地显著提高土壤细菌群落结构多样性(p<0.05);芒萁侵入区和非侵入区土壤细菌群落结构差异显著(p<0.05);土壤细菌群落结构的主要影响因子是土壤含水率、全碳、有机质、土壤容重和pH。这些影响因子与疣微菌门、变形菌门、疣微菌纲和甲型(α)变形杆菌纲正相关。综上所述,芒萁侵入后可显著改善红壤侵蚀退化裸地的土壤理化性质,改善土壤细菌群落组成,增加土壤细菌群落多样性和优势菌群,对土壤细菌群落有积极效应。