首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 109 毫秒
1.
This investigation determined the response of soil microbial communities to enhanced UV‐B radiation and disturbance in upland grassland. A factorial field experiment encompassing two levels of UV‐B supplementation (simulating ambient and a 30% increase in stratospheric ozone) and two levels of disturbance (disturbed and undisturbed) was established at Buxton Climate Change Impacts Laboratory, Derbyshire, UK, and maintained for 7 years prior to sampling. Enhanced UV‐B increased microbial utilization of carbohydrates, carboxylic acids, polymers and aromatic compounds present in Biolog® GN plates when inoculated with soils taken from disturbed plots, but did not affect carbon utilization of soil microbial communities associated with undisturbed plots (UV‐B×Disturbance interaction, P<0.05 for each substrate type). UV‐B treatment did not affect numbers of bacteria or fungi. Direct microscopic counts showed fewer bacteria in soil originating from disturbed plots than from undisturbed plots (Disturbance, P<0.001), although a greater number of culturable bacteria and fungi were isolated from disturbed than from undisturbed soils (Disturbance, P<0.001). No UV‐B‐ or disturbance‐related differences in protein, starch or urea hydrolysis were exhibited by bacterial isolates. UV‐B treatment did not affect total plant biomass within undisturbed plots or the biomass of individual groupings of grasses, forbs and mosses. Per cent root length colonized by arbuscular mycorrhizal fungi (AMF) was not affected by enhanced UV‐B radiation in the undisturbed plots. Neither AMF nor plant biomass was measured in disturbed plots. The key findings of this study show that UV‐B‐mediated alterations in carbon utilization occurred in soil microbial communities subjected to disturbance, but such changes were not observed in communities sampled from undisturbed grassland. Differences in the catabolic potential of microbial communities from disturbed grassland subjected to enhanced UV‐B are probably related to plant‐mediated changes in resource availability or quality.  相似文献   

2.
The effects of intensive recreation impacts and restoration amendments on soil parameters were assessed at four campsites in the Eagle Cap Wilderness, northeastern Oregon. Sites (2,215‐ to 2,300‐m elevation) are characterized by shallow granitic soils, an Abies lasiocarpa/Pinus albicaulis overstory, and a Vaccinium scoparium understory. In fall 1995, plots were established at four campsites on three subalpine lakes in which soils were scarified, compost amended, and planted to native species. In summer 1998, we sampled surface soils (0–15 cm) on undisturbed sites (between and under vegetation) and unamended and compost‐amended campsite soils. Samples were analyzed for total organic C, total N, potentially mineralizable N (PMN), NH4, soil moisture, microbial biomass, basal 5‐day respiration rates, and microbial community carbon utilization profiles. Unamended campsite soils had significantly lower levels of PMN, microbial biomass, basal respiration, and number of substrates metabolized in carbon utilization profiles. Compost addition elevated all these impacted parameters on campsite soils, although the increase in basal respiration rate was neither statistically significant nor sufficient to approach rates found underneath vegetation on undisturbed soils. Only the number of substrates metabolized in the carbon utilization profiles was significantly higher on compost‐amended soils than on undisturbed soils. Levels of PMN indicate that campsite soils may lack sufficient N for rapid plant regeneration, whereas amended and undisturbed soils contained adequate quantities of available N. This work suggests that compost amendments can ameliorate impacts to soil chemistry and microbial populations caused by camping, without exceeding the N fertility found on undisturbed soils.  相似文献   

3.
Soil microbial communities in Chihuahuan Desert grasslands generally experience highly variable spatiotemporal rainfall patterns. Changes in precipitation regimes can affect belowground ecosystem processes such as decomposition and nutrient cycling by altering soil microbial community structure and function. The objective of this study was to determine if increased seasonal precipitation frequency and magnitude over a 7‐year period would generate a persistent shift in microbial community characteristics and soil nutrient availability. We supplemented natural rainfall with large events (one/winter and three/summer) to simulate increased precipitation based on climate model predictions for this region. We observed a 2‐year delay in microbial responses to supplemental precipitation treatments. In years 3–5, higher microbial biomass, arbuscular mycorrhizae abundance, and soil enzyme C and P acquisition activities were observed in the supplemental water plots even during extended drought periods. In years 5–7, available soil P was consistently lower in the watered plots compared to control plots. Shifts in soil P corresponded to higher fungal abundances, microbial C utilization activity, and soil pH. This study demonstrated that 25% shifts in seasonal rainfall can significantly influence soil microbial and nutrient properties, which in turn may have long‐term effects on nutrient cycling and plant P uptake in this desert grassland.  相似文献   

4.
Liming is a forestry practice used to correct tree cation deficiency induced by soil acidity. Ectomycorrhizal (ECM) community structure and functioning is closely linked to soil nutrient availability, which is strongly affected by liming. The aim of this study was to assess the impact of liming on ECM community structure depending on soil horizon and tree host. Acidophilic species occurring in untreated plots, such as Russula ochroleuca, were absent from limed plots and were replaced by more generalist morphtoypes. The abundance of ECM root tips in the untreated plots was higher in topsoil layers, whereas most of the ECM root tips in the limed plots were in the organomineral layer, whatever the tree host. Liming was the major determinant of fungal community structure, then tree host.  相似文献   

5.
Specialist plant species in calcareous sandy grasslands are threatened by acidification and high nutrient levels in the topsoil. We investigated whether topsoil removal and soil perturbation in degraded sandy grasslands could lead to establishment of specialist species belonging to the threatened xeric sand calcareous grassland habitat. Restoration actions performed in 2006 resulted in increased soil pH and reduced nitrogen availability. We found early colonisztion of the perennial key species Koeleria glauca after both deep perturbation and topsoil removal, and high seedling establishment in topsoil removal plots 5 and 6 years following the restoration treatment (2011–2012). After topsoil removal, overall vegetation composition in 2012 had developed toward the undegraded community, with target species accounting for 20% of the community after topsoil removal, compared to 30% in the undegraded vegetation, and less than 1% in untreated controls. Deep perturbation led to 7% target species, while there were almost no effects of shallow perturbation 6 years following treatment. These results demonstrate that topsoil removal can promote colonization of target species of calcareous sandy grassland and highlights the importance of considering the regeneration niche for target species when implementing restoration measures .  相似文献   

6.
The goal of the present study was to assess a soil seed bank as an input seed source for revegetating lead/zinc (Pb/Zn) mine tailings. The seed bank source was abandoned farmland, whose top 10‐cm layer of topsoil contained 6,850 ± 377 seeds/m2 from 41 species. The seeds in the soil were principally distributed in the upper 0–2 cm, which held 75.8% of total seeds and 92.7% of species composition. The top 2‐cm layer of topsoil may be sufficient to serve the purpose of providing a seed source for revegetation on derelict lands, including mined lands. Four different thicknesses of topsoil (1, 2, 4, and 8 cm, redistributed from the total 0–10‐cm layer from the farmland) were field‐tested on the Pb/Zn mine tailings. There was no significant difference in seedling density among the 4 thickness treatments. Many seeds in the treatments with more than 1‐cm of topsoil were unable to emerge from the deeper layer. Seedlings in plots with topsoil of 1‐, 2‐ and 4‐cm failed to establish within 1 year due to the extremely high acidity (pH 2.39 to 2.76). A shallow layer of topsoil cannot neutralize the sulfuric acid generated from oxidation of pyrites in the tailings. For establishment of seedlings on metalliferous lands, an insulating layer such as subsoil, building rubble, or domestic refuse is necessary before covering with valuable topsoil. The woody legume Leucaena leucocephala grown on the tailings with a topsoil cover of 8‐cm was the most dominant species. Lead was accumulated in root, branch, stem bark, and xylem, which accounted for more than 80% of the total metal concentration in the plant. This portion of Pb will reside in the plant for a long period, while the smaller portion of Pb in the leaf (about 15%) could be returned to the environment as litter during growth. Woody plants may have an advantage in metal‐phyto‐remediation over herbaceous plants.  相似文献   

7.
Using undisturbed sandy loam soil cores heavily infested with mycorrhizae, the effects of the antibiotic-producing Pseudomonas fluorescens strain F113 and its non-antibiotic derivative Ps. fluorescens F113G22 on nodulation by introduced and indigenous Rhizobium were studied. Furthermore, the effects of the different microbial inocula on the colonization of the pea roots by mycorrhizae were studied. It was found that Ps. fluorescens F113 enhanced nodulation by Rhizobium fourfold, while the nodules produced were much larger and strongly pigmented (pink) compared with those in other treatments. The proportion of roots colonized by arbuscular mycorrhizae was not significantly affected by the different treatments.  相似文献   

8.
 Tecomán, in the Mexican state of Colima, had the world's greatest production of lime Citrus aurantifolia Swingle. Typical farming systems in the area include: (a) high-input monoculture, (b) a high-input system in which lime trees grow together with coconut palms, (c) a low-input system called "Family Farms" or "Family Gardens". In the Family Gardens, cultural practices are minimal and other fruit trees (about 16 species) coexist with the lime trees. This traditional minimal input system makes use of locally available resources and they are structurally very diverse. Arbuscular mycorrhizae may be crucial for sustainable production in Family Gardens. Root colonization and spore populations of fungi were scored at 2-week intervals in the three agroecosystems during a 6-month period. First samples were taken after the application of chemical fertilizer and irrigation in the high-input systems. Root colonization of lime was much higher and consistent in the low-input plots than in conventionally farmed plots, with colonization levels of 50–62% that remained the same throughout the sampling time; the high-input systems showed a high variation and lower level of colonization, 36% and 27% in associated and monoculture systems, respectively. Spore abundance was higher in the high-input systems but showed constant variation. The results suggest a strong effect of agroecosystem on mycorrhizal colonization of lime roots. Accepted: 12 September 1995  相似文献   

9.
Study plots with ten types of disturbances were established in a Solidago-Aster community in western Pennsylvania. One year after disturbance, 93% of all species had vesicular-arbuscular mycorrhizae (VAM) and accounted for 92% of all plant cover. After 3 yr, 96% of the species had VAM and 96% canopy coverage. An adjacent 10-yr Solidago-Aster community had 100% VAM species. The VAM annuals, Ambrosia artemisiifolia and Setaria glauca, were major first year dominants while VAM perennials, Agropyron repens, Solidago canadensis, and Aster ericoides, dominated at 3 yr. The mean percent mycorrhizae of all dominants at 1 yr was 39% and 34% at 3 yr. Four disturbed sites had 100% VAM colonization after 1 yr and six sites after 3 yr. Severe physical disturbances (topsoil removed and topsoil-subsoil removed) resulted in complete colonization by VAM species and mean mycorrhizal infections of more than 75%. The plowed-disked-prometone and plowed-disked-vapam disturbances resulted in low levels of mycorrhizae after 3 yr. The plowed-disked-atrazine plot showed an initial severe decrease in percentage of mycorrhizae, but doubled its infection rate by 3 yr. Three non-mycorrhizal species (Chenopodium album, Rumex acetosella, and Polygonuspersicaria) were observed during the 3-yr period. C. album was the major dominant after 1 yr in the plowed-disked-fertilized site and R. acetosella a dominant in the plowed-disked-prometone plot.  相似文献   

10.
Invasion by woody alien plants, construction, and mining operations are among the major disturbances degrading vegetation in the Cape Floristic Kingdom, South Africa. The aim of this study was to assess whether native fynbos shrubland vegetation could be restored following dense alien invasion and disturbance by mining. An area supporting dense alien trees was cleared and topsoil was stripped and stockpiled to simulate mining disturbance. A field trial investigated the effects of topsoil depth, seed mix application, and fertilizer on native species recruitment and vegetation development over a three‐year period. Soil‐stored seed banks contributed 60% of the species recruited, indicating that areas invaded for three decades have good restoration potential. The addition of a fynbos seed mix, which included serotinous overstory species, improved both the richness and structural composition of the vegetation. Most species sown in untopsoiled plots established, but survival and growth was low compared to topsoil plots. Poor growth in combination with a lack of soil seed bank species, indicate that restoring a diverse and functional cover of indigenous vegetation on subsoil is not possible in the short‐term. Soil amelioration is required to improve rooting conditions and initiate ecosystem processes. Shallow and deep topsoil treatments yielded high plant density, richness, and projected canopy cover, but canopy cover was higher in deep topsoil plots throughout the trial. Fertilizer addition increased canopy cover in untopsoiled and shallow topsoil plots via an increase in alien annual species. Fertilizer addition ultimately may lead to increased native vegetation cover in untopsoiled areas, but as it increased proteoid mortality on deep topsoil plots, it is not recommended for sites where topsoil is available. A species‐rich and structurally representative fynbos community may be restored on topsoiled areas provided that the native disturbance regime is simulated and seeds of major structural guilds not present in the soil seed bank are included in the seed mix.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号