Use of Shallow Basins to Restore Cutover Peatlands: Hydrology

Basins 20‐, 10‐, and 4‐m wide were excavated 15 to 20 cm into cutover peat fields near Lac Saint Jean, Québec, Canada to facilitate the establishment of Sphagnum mosses. Sphagnum diaspores (fragments) and straw mulch were spread over the excavated surfaces, a control peat field, and a mulch‐protected site without basins. Mean water tables in the 20‐, 10‐, and 4‐m wide basins and the mulch‐protected site were 27.2, 8.3, 11.4, and 9.7 cm higher, respectively, than in the control peat field in May to August 1996. Similar improvements were observed in 1997 (a drier summer). The higher water table was due to lowering of the peat surface with respect to the local water table, retention of meltwater and stormwater by the peripheral ridges formed during excavation, retention of water during drier periods by the groundwater mound beneath the ridges, and mulch. Soil moisture was always higher in the experimental basins than in the control peat field or in the mulch‐protected site, demonstrating the superior soil wetness characteristic of sites with basins and straw mulch. Water tension data signaled the absence of the capillary fringe (i.e., capillary drainage) near the surface for some finite period, thus possibly limiting water for best Sphagnum growth. At the experimental basins and mulch‐protected site, 100% of these periods lasted four or fewer days. In the control peat field, 20% of the periods when capillary drainage had occurred lasted more than four days, with one period of 17 days. The mulch protection alone provided considerable improvement in hydrological conditions compared with the control peat field, but the additional water retained in the experimental basins protected against Sphagnum desiccation and loss during more extreme dry periods.     

Minor Changes in Soil Bacterial and Fungal Community Composition Occur in Response to Monsoon Precipitation in a Semiarid Grassland

Arizona and New Mexico receive half of their annual precipitation during the summer monsoon season, making this large-scale rain event critical for ecosystem productivity. We used the monsoon rains to explore the responses of soil bacterial and fungal communities to natural moisture pulses in a semiarid grassland. Through 454 pyrosequencing of the 16S rRNA gene and ITS region, we phylogenetically characterized these communities at 22 time points during a summer season. Relative humidity increased before the rains arrived, creating conditions in soil that allowed for the growth of microorganisms. During the course of the study, the relative abundances of most bacterial phyla showed little variation, though some bacterial populations responded immediately to an increase in soil moisture once the monsoon rains arrived. The Firmicutes phylum experienced over a sixfold increase in relative abundance with increasing water availability. Conversely, Actinobacteria, the dominant taxa at our site, were negatively affected by the increase in water availability. No relationship was found between bacterial diversity and soil water potential. Bacterial community structure was unrelated to all environmental variables that we measured, with the exception of a significant relationship with atmospheric relative humidity. Relative abundances of fungal phyla fluctuated more throughout the season than bacterial abundances did. Variation in fungal community structure was unrelated to soil water potential and to most environmental variables. However, ordination analysis showed a distinct fungal community structure late in the season, probably due to plant senescence.     

On the Use of Shallow Basins to Restore Cutover Peatlands: Plant Establishment

Since the early 1990s, restoration techniques have been developed for milled and cutover peatlands in eastern Canada. These techniques are based on the active reintroduction of peatland plant diaspores, blocking drainage, and the use of straw mulch to improve surface conditions. This study examines the effectiveness of using shallow (20 cm deep) basins of various widths to improve the success of current peatland restoration techniques. It comprises three different experiments, each spanning three or four growing seasons and combining both small‐scale manual and large‐scale mechanized plant reintroductions. Cover data recorded in two of the experiments were regressed against a series of environmental factors to determine how Sphagnum establishment success was related to abiotic variables such as moisture, water ponding, surface roughness, and mulch cover. Results of these experiments demonstrate that shallow basins were generally effective at promoting Sphagnum establishment and that this effect extends beyond the positive impact that basins have on hydrological conditions. Basins of various widths were equally successful. Soil‐moisture content (linear positive effect) and duration and severity of flooding events (quadratic effect) were shown to be determinant of plant recovery. Other factors such as the density of straw cover (positive effect) and surface roughness (negative effect) were also instrumental in explaining local variation in Sphagnum cover. Plant cover after three and four growing seasons averaged 20–25% in mechanical reintroductions and 40–60% in manual reintroductions, demonstrating the overall effectiveness of the restoration techniques used.     

Soil Fungal Diversity and Community Composition in Response to Continuous Sweet Potato Cropping Practices

Soil fungi are extremely important for maintaining soil health and plant production in agricultural systems. Currently, the effect of continuous cropping of sweet potato on soil fungal communities and physiochemical parameters has not been well documented. In the present study, four sweet potato fields consecutively monocultured for 1, 2, 3, and 4 years were selected to investigate the effect of monoculture on soil fungal communities through Illumina MiSeq sequencing. Continuous cropping of sweet potatoes dramatically altered the fungal community composition, whereas fungal diversity was almost unchanged. Ascomycota and Basidiomycota were the most abundant phyla in all soil samples, accounting for 32.59% and 21.14% of the average relative abundance, respectively. The abundance of some potential pathogens, such as Ascobolus spp, specifically Ascobolus stercorarius, and some unknown fungi increased significantly as the sweet potato monoculture period increased, and their presence were highly positively correlated with disease incidence. In contrast, Basidiomycota, Bullera, Fusarium and Trichocladium most likely play roles as antagonists of sweet potato disease development, as their relative abundance decreased significantly over time and were negatively correlated with disease incidence. Redundancy and correlation analyses revealed that soil pH and organic carbon content were the most important factors driving these changes. Our findings provided a dynamic overview of the fungal community and presented a clear scope for screening beneficial fungi and pathogens of sweet potato.     

Bacterial Community Succession in Natural River Biofilm Assemblages

Temporal bacterial community changes in river biofilms were studied using 16S rRNA gene-based polymerase chain reaction–denaturing gradient gel electrophoresis (DGGE) followed by sequence analysis. Naturally occurring biofilms were sampled in 2001 during an undisturbed 7-month low-water period in the River Garonne (SW France). During the sampling period epilithic biomass exhibited a particular pattern: two 3-month periods of accumulation that resulted in two peaks in summer and fall, each at about 25 g ash-free dry mass per square meter. Bacterial community DGGE profiles differed between the summer and fall biomass peaks and shared only 30% common operational taxonomic units (OTUs), suggesting the influence of seasonal factors on these communities. During the second biomass accrual phase, bacterial richness and the appearance of new OTUs fitted a conceptual model of bacterial biofilm succession. During succession, five OTUs (corresponding to Dechloromonas sp., Nitrospira sp., and three different Spirosoma spp.) exhibited particular patterns and were present only during clearly defined successional stages, suggesting differences in life-history strategies for epilithic bacteria. Co-inertia analysis of DGGE banding patterns and physical–chemical data showed a significant relationship between community structure and environmental conditions suggesting that bacterial communities were mainly influenced by seasonal changes (temperature, light) and hydrodynamic stability. Within the periods of stability, analysis of environmental variables and community patterns showed the dominant influence of time and maturation on bacterial community structure. Thus, succession in these naturally occurring epilithic biofilm assemblages appears to occur through a combination of allogenic (seasonal) and autogenic changes.     

Fungicide Effects on Fungal Community Composition in the Wheat Phyllosphere

The fungicides used to control diseases in cereal production can have adverse effects on non-target fungi, with possible consequences for plant health and productivity. This study examined fungicide effects on fungal communities on winter wheat leaves in two areas of Sweden. High-throughput 454 sequencing of the fungal ITS2 region yielded 235 operational taxonomic units (OTUs) at the species level from the 18 fields studied. It was found that commonly used fungicides had moderate but significant effect on fungal community composition in the wheat phyllosphere. The relative abundance of several saprotrophs was altered by fungicide use, while the effect on common wheat pathogens was mixed. The fungal community on wheat leaves consisted mainly of basidiomycete yeasts, saprotrophic ascomycetes and plant pathogens. A core set of six fungal OTUs representing saprotrophic species was identified. These were present across all fields, although overall the difference in OTU richness was large between the two areas studied.     

Soil Fungal Community Structure Changes in Response to Different Long-Term Fertilization Treatments in a Greenhouse Tomato Monocropping System

Greenhouse vegetable cultivation (GVC) is an example of intensive agriculture aiming to increase crop yields by extending cultivation seasons and intensifying agricultural input. Compared with cropland, studies on the effects of farming management regimes on soil microorganisms of the GVC system are rare, and our knowledge is limited. In the present study, we assessed the impacts of different long-term fertilization regimes on soil fungal community structure changes in a greenhouse that has been applied in tomato (Solanum lycopersicum L.) cultivation for 11 consecutive years. Results showed that, when taking the non-fertilizer treatment of CK as a benchmark, both treatments of Conventional chemical N (CN) and Organic amendment only (MNS) significantly decreased the fungal richness by 16%–17%, while the Conventional chemical N and straw management (CNS) restored soil biodiversity at the same level. Saprotroph and pathotroph were the major trophic modes, and the abundance of the pathotroph fungi in treatment of CNS was significantly lower than those in CK and CN soils. The CNS treatment has significantly altered the fungal composition of the consecutive cropping soils by reducing the pathogens, e.g., Trichothecium and Lecanicillium, and enriching the plant-beneficial, e.g., Schizothecium. The CNS treatment is of crucial importance for sustainable development of the GVC system.     

Rapid Changes in Polyphosphoinositide Metabolism in Pea in Response to Fungal Signals

Effects of the elicitor and/or suppressor from Mycosphaerellapinodes on polyphosphoinositide metabolism (PI metabolism) inpea were examined both in vivo and in vitro. The elicitor induceda rapid and biphasic increase in levels of phosphatidylinositol-4,5-bisphosphate(PtdInsP₂) and inositol 1,4,5-trisphosphate (IP₃) in epicotyltissues that was apparent within 15 min. A transient increasein levels of PtdInsP₂ and IP₃ was detected immediately in elicitor-treatedplasma membranes. However, the concomitant presence of suppressorwith elicitor resulted in inhibition of these increases bothin vivo and in vitro. These findings suggest that the elicitorrapidly activates phosphatidylinositol kinase, phosphatidylinositol-4-monophosphatekinase and phospholipase C, which are involved in PI metabolism,whereas the suppressor markedly inhibits these enzymes. Neomycin,a known inhibitor of phospholipase C, blocked the elicitor-inducedaccumulation both of IP₃ and pisatin and it also induced localsusceptibility in pea tissues that resembled that of the fungalsuppressor. From these results, it appears that rapid changesin PI metabolism are indispensable in the signal transductionrelated to defense responses of pea plants. (Received January 18, 1993; Accepted May 13, 1993)     

Recruitment and Succession in a Tropical Benthic Community in Response to In-Situ Ocean Acidification

Ocean acidification is a pervasive threat to coral reef ecosystems, and our understanding of the ecological processes driving patterns in tropical benthic community development in conditions of acidification is limited. We deployed limestone recruitment tiles in low aragonite saturation (Ω_arag) waters during an in-situ field experiment at Puerto Morelos, Mexico, and compared them to tiles placed in control zones over a 14-month investigation. The early stages of succession showed relatively little difference in coverage of calcifying organisms between the low Ω_arag and control zones. However, after 14 months of development, tiles from the low Ω_arag zones had up to 70% less cover of calcifying organisms coincident with 42% more fleshy algae than the controls. The percent cover of biofilm and turf algae was also significantly greater in the low Ω_arag zones, while the number of key grazing taxa remained constant. We hypothesize that fleshy algae have a competitive edge over the primary calcified space holders, coralline algae, and that acidification leads to altered competitive dynamics between various taxa. We suggest that as acidification impacts reefs in the future, there will be a shift in community assemblages away from upright and crustose coralline algae toward more fleshy algae and turf, established in the early stages of succession.     

秦岭南坡松栎林群落演替过程中物种组成及多样性动态分析

为揭示秦岭南坡植物群落演替与物种多样性之间的复杂关系,采用空间代替时间的方法在秦岭南坡油松林、松栎混交林和锐齿栎林群落典型分布区域设置45个样地进行了群落学调查,统计分析了油松林→松栎混交林→锐齿栎林这一演替序列过程中草、灌、乔3层的物种组成和α物种多样性动态。结果表明:(1)秦岭南坡油松林、松栎混交林和锐齿栎林3种群落共有维管植物312种,隶属于73科183属,其中草本植物136种,灌木(含木质藤本)98种,乔木78种;油松林群落包含52科117属190种,松栎混交林群落含有60科95属129种,锐齿栎林群落则为50科109属178种。(2)沿油松林→松栎混交林→锐齿栎林群落演替序列,草本层物种均匀度和物种多样性显著降低,物种丰富度呈"V"形变化趋势;灌木层物种丰富度、均匀度以及物种多样性均无显著差异;乔木层物种多样性呈明显的单峰型变化,其中松栎混交林群落物种多样性指数最高。研究表明,秦岭南坡松栎林群落物种多样性随演替进展总体上呈现单峰型变化,与中期物种多样性假说一致;物种多样性可能仅仅是群落稳定的一个基础或前提条件。     

Succession of Acidophilic Bacterial Community During Bio-oxidation of Refractory Gold-Containing Sulfides

To optimize the rate of bio-oxidation to recover gold from sulfide minerals, it is important to understand the dynamic change of acidophilic bacteria involved in this process. In this study, a batch bio-oxidation experiment was set up to bioleach Au from refractory pyrite and arsenopyrite using a mixed acidophilic culture over the duration of eight days. The 16S rRNA gene clone library and denaturing gradient gel electrophoresis approaches (DGGE) were used to monitor the dynamic succession of the acidophilic bacterial population. The results showed that there were five bacteria in the bio-oxidation reactor: Leptospirillum ferriphilum, Acidithiobacillus caldus, Sulfobacillus thermotolerans, Alicyclobacillus sp. and a heterotrophic iron-oxidizing bacterium. The overall succession pattern was that Acidithiobacillus caldus, a sulfur oxidizer, and Sulfobacillus thermotolerans, a sulfur-iron oxidizer, were predominant at the beginning of the bio-oxidation process, but they were replaced by iron oxidizer L. ferriphilum at a later stage. The competitive advantage of At. caldus and Sb. thermotolerans over L. ferriphilum at the early stage was availability of abundant inorganic sulfur compounds, but lower pH, higher redox potential, and ferrous iron favored L. ferriphilum growth at a later stage. These results have important implications for understanding the role of acidophilic bacterial population in bio-oxidation of refractory gold-containing sulfides.     

草原群落退化与恢复演替中的植物个体行为分析

定度植物个体小型化是在草原过度放牧条件下草原植物植株地片变短、变窄,节间缩短,以及根条分布浅层化等笥状的集合。小型化个体的生态学属性介于环境饰变与生态型之间,特称之为响应型。个体小型化逆转变过程表现出集体行为,小型化个体具有维持其形状的保守性,变化的阶段性和突变性;小型化的逆过程即正常化过程号常规替时间有关。个体经是过度放牧下群落生产力衰退的重要表现,是对过度放牧的负反馈机制。在草原群落经演替机理     

Forest Age and Plant Species Composition Determine the Soil Fungal Community Composition in a Chinese Subtropical Forest

Fungal diversity and community composition are mainly related to soil and vegetation factors. However, the relative contribution of the different drivers remains largely unexplored, especially in subtropical forest ecosystems. We studied the fungal diversity and community composition of soils sampled from 12 comparative study plots representing three forest age classes (Young: 10–40 yrs; Medium: 40–80 yrs; Old: ≥80 yrs) in Gutianshan National Nature Reserve in South-eastern China. Soil fungal communities were assessed employing ITS rDNA pyrotag sequencing. Members of Basidiomycota and Ascomycota dominated the fungal community, with 22 putative ectomycorrhizal fungal families, where Russulaceae and Thelephoraceae were the most abundant taxa. Analysis of similarity showed that the fungal community composition significantly differed among the three forest age classes. Forest age class, elevation of the study plots, and soil organic carbon (SOC) were the most important factors shaping the fungal community composition. We found a significant correlation between plant and fungal communities at different taxonomic and functional group levels, including a strong relationship between ectomycorrhizal fungal and non-ectomycorrhizal plant communities. Our results suggest that in subtropical forests, plant species community composition is the main driver of the soil fungal diversity and community composition.     

Specificity of DNA Methylation Changes During Fungal Dimorphism and Its Relationship to Polyamines

We utilized our modification of the amplified fragment length polymorphism technique for the determination of changes occurring in the DNA methylation patterns during the dimorphic transition of the fungi Mucor rouxii, Yarrowia lipolytica, and Ustilago maydis. To determine the specificity of differential methylation in regards to dimorphism, we obtained the yeast-like form of the three fungi under conditions that induced mycelial growth, by addition of 1,4-diaminobutanone (DAB), an inhibitor of ornithine decarboxylase in the case of M. rouxii and Y. lipolytica. In an odc null mutant of U. maydis, repression of the dimorphic transition was brought about by limitation in the amounts of exogenous putrescine. Yeasts from the three fungi thus obtained conserved a significant number of the differential DNA fragments with the methylation pattern displayed by normal yeasts, indicating their true correlation with dimorphism. Our results also confirm a role of polyamines in differential DNA methylation and fungal dimorphic transition.     

Response of Microbial Community Composition and Function to Soil Climate Change

Soil microbial communities mediate critical ecosystem carbon and nutrient cycles. How microbial communities will respond to changes in vegetation and climate, however, are not well understood. We reciprocally transplanted soil cores from under oak canopies and adjacent open grasslands in a California oak–grassland ecosystem to determine how microbial communities respond to changes in the soil environment and the potential consequences for the cycling of carbon. Every 3 months for up to 2 years, we monitored microbial community composition using phospholipid fatty acid analysis (PLFA), microbial biomass, respiration rates, microbial enzyme activities, and the activity of microbial groups by quantifying ¹³C uptake from a universal substrate (pyruvate) into PLFA biomarkers. Soil in the open grassland experienced higher maximum temperatures and lower soil water content than soil under the oak canopies. Soil microbial communities in soil under oak canopies were more sensitive to environmental change than those in adjacent soil from the open grassland. Oak canopy soil communities changed rapidly when cores were transplanted into the open grassland soil environment, but grassland soil communities did not change when transplanted into the oak canopy environment. Similarly, microbial biomass, enzyme activities, and microbial respiration decreased when microbial communities were transplanted from the oak canopy soils to the grassland environment, but not when the grassland communities were transplanted to the oak canopy environment. These data support the hypothesis that microbial community composition and function is altered when microbes are exposed to new extremes in environmental conditions; that is, environmental conditions outside of their “life history” envelopes.     

The Community Dynamics of the Forest Secondary Succession in Heishiding Natural Reserve of Guangdong Province

Studying on the community structure, species composition and species diversities of the secondary succession of lower subtropical forest in Heishiding Natural Reserve, Guangdong Province, the following results were obtained. In 2 ~4 years of restored stage the seedlings of pioneer species, heliophytes and mesophytes occur simultaneously. In 10 years of restored stage pioneer species are superior as heliophytes maintain stable and mesophytes are being decreased. In the stage of mixed forest pioneer species are on the decreasing and heliopytes are on the increasing trend. In the stage of evergreen broad-leaved forest dominated by heliophytes pioneer species are being declined, heliophytes are dominant and mesophytes are being increased. In the stage of evergTeen broad-leaved forest dominated by mesophytes heliophytes are being declined and mesophytes are superior. The vertical structure, horizontal structure, the structure of species composition determine stability of communities in secondary succession process. The vertical structure of community is building up in the stage of restoration. The community is composed of the stands under the third class. The forest canopy is not stratified. The individual density is stable. From restored stage to mixed forest the vertical structure of community is diversified. There are the third and forth class stands in community. The tree layer is divided into three sub-layers. The individual density declines rapidly because of self-thinning. In the mixed forest the vertical stmcture is relatively stable. The abundance of the fifth class stands and area of breast height reach the first peak in the succession serial. The individual density increases rapidly. In stage of evergreen broad-leaved forest dominated by heliophytes, the vertical structure changes largely. The abundance of the fifth class and area of breast height decline rapidly, but the individual density changes slowly. In the stage of evergreen broad-leaved forest dominated by mesophytes, the vertical structure of community is stable and the composition of every stand class becomes more stable. The area of breast height is the biggest in the succession serial. When succession develops, the coverage of communities increases gradually but the turnover rate of species declines. The species composition tends to be stabilized. The diversity of species and community evenness increase gradually thus, the ecological dominance declines gradually.