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1.
《Applied soil ecology》2001,16(3):209-217
The position of weed seeds within the soil matrix plays an important role in seedling emergence and seed survival. The relationship of weed seeds with soil aggregates and soil depth was evaluated in a Waukegon silt loam soil that had been under a long-term, conventional tillage, annual crop management system. Soil aggregates were separated and classified into eight size classes from ≤5 to >12 mm and weed seeds were extracted from the aggregates. Amaranthus spp., Chenopodium album L. (common lambsquarters), Polygonum pensylvanicum L. (Pennsylvania smartweed), Setaria faberi Herrm. (giant foxtail), and Solanum ptycanthum Dun. (eastern black nightshade) accounted for the majority of seeds recovered. In general, seed viability declined from April to June, but increased in October following seed deposition. Seeds of individual species were most abundant in the aggregate size class most closely matching its seed size. However, seeds were commonly found associated with aggregates larger than 9 mm. Highest seed viability was found in the aggregate fraction closest to the seed size, however, S. faberi viability was also high in the >12 mm aggregate size class. Regardless of aggregate size, seed numbers were generally greatest in the upper 5 cm of soil. The results of this research were species-dependent and variable and demonstrated the complexity of weed seed/soil aggregate associations. However, they did show that seed placement within the soil matrix may play an important role in weed population dynamics.  相似文献   

2.
Long-distance dispersal of wind dispersed plant seed is dependent on seeds ascending in the atmosphere's surface boundary layer (SL). However, seed dispersal research often focuses on the near-surface dynamics of abscission and deposition, with little attention paid to seed ascent and transport beyond the surface boundary layer. Our research sought to estimate the vertical seed density flux of Conyza canadensis, a common agricultural weed, in the surface boundary layer. Using a 2.7 ha field infested with Conyza canadensis, the vertical seed concentration profile was measured on 5 days, three times per day while simultaneously monitoring micrometeorological conditions to connect the mechanisms of release with the process of ascent. Vertical seed sampling was conducted from two to six meters above ground level using removable screen frames. Remotely piloted airplanes were used to quantify seed concentration at 68 and 120 m above ground level and provide a connection between near surface dynamics and dynamics higher in the SL. Seed flux density (area under seed concentration curve) decreased with height and decreased from morning to afternoon. The seed flux density was significantly correlated with mean mechanical turbulence and the interaction of mean mechanical and mean thermal turbulence, supporting earlier research of meteorological effects on seed dispersal. While fewer total seeds were collected in the afternoon, more seeds were collected at 68 and 120 m during this period and may suggest more seeds were present in the upper SL where dispersal distance may be greater. Seeds collected above the SL will potentially be carried for hours before descending, depositing seeds in the range of 2–122 m, and influencing a much greater area than seeds unable to ascend through the lower SL. While this range is very wide, the dispersal distances reported herein are several orders of magnitude greater than previously reported for plants. These findings are all the more striking since the study species has evolved resistance to glyphosate herbicide, an herbicide now widely used in soybean, cotton, and corn crops in the US. Therefore, aerial transport of C. canadensis seeds carrying genes coding for glyphosate resistance enables seed to move tens or hundreds of kilometers in a single dispersal event, a spread rate corroborated by number of cases of reported glyphosate resistance occurrences in North America.  相似文献   

3.
Whilst considerable research effort in Europe has linked agricultural intensification with dramatic declines of seed-feeding birds, surprisingly little is known about the wider importance of seeds in animal food-webs. Moreover, understanding the dynamics of farmland seed food resources for species of conservation concern is of considerable research interest.We examined the distribution of berries and soil-surface seeds in the managed and unmanaged habitats of a 125 ha organic farm. We took soil suction-samples over a year, counted and identified all seeds, and compared abundances and species-richness between habitats. We constructed ecological networks from literature records and by rearing insects to investigate the importance of these seeds for insects, birds and mammals. We predicted the impacts of management on seed biomass, energy and the ecosystem service of pest control across the whole farm.We estimated seed and berry food resources of up to 33 metric tons of biomass and 560 GJ of energy on the farm. Potentially, more than 330 species use the seeds as a food resource, the overwhelming majority of which are invertebrates (82%) relying predominantly on non-crop and weed species. Generally, uncultivated semi-natural habitats such as woodland and mature hedgerows were more species-rich and had higher seed biomass and energy than crop habitats throughout the year, but fallow land was disproportionately important for seeds during the summer. Models of increased management intensity revealed declines of up to 19% in seed biomass and energy and cascades through the network that resulted in a substantial decrease in potentially pest-controlling parasitoids.  相似文献   

4.
Energy crops are of growing importance in agriculture worldwide. This field study aimed to investigate earthworm communities of different intensively cultivated soils during a 2-year period, with special emphasis on annual and perennial energy crops like rapeseed, maize, and Miscanthus. These were compared with cereals, grassland, and fallow sites. Distribution patterns of earthworm abundance, species, and ecological categories were analysed by constrained ordination procedures (redundancy analysis; CANOCO) using a set of environmental variables as predictors, such as CN value of harvest residues, SOC and Nt content, soil pH, soil texture, and land-use intensity. The latter was determined by principal component analysis using average soil coverage and intensity of tillage, weed control, and fertilisation as input variables. It was clearly found that land-use intensity was the dominant regressor for earthworm abundance and total number of species. The diversity of earthworm communities was especially enhanced and showed a more balanced species composition in extensively managed soils under grassland, fallow, and Miscanthus. For the total number of species, Miscanthus (5.1 ± 0.9) took a medium position and neither differed significantly from intensively managed rapeseed (4.0 ± 0.9), cereals (3.7 ± 1.1), and maize sites (3.0 ± 1.4), nor from grassland (6.8 ± 1.5) and fallow (6.4 ± 1.0) sites. Total earthworm abundance ranged between 355 (±132) and 62 (±49) individuals m−2 in fallow and maize sites, respectively.Interestingly, Miscanthus had quite positive effects on earthworm communities although the CN value of harvest residues was very high. It is recommended that Miscanthus may facilitate a diverse earthworm community even in intensive agricultural landscapes.  相似文献   

5.
Globally, bird numbers are declining, with potentially serious flow-on effects on ecosystem processes, such as seed dispersal mutualisms. However, management to maintain seed dispersal may be inappropriate if unexpected animals are the most important dispersers. Numbers of the world’s only alpine parrot, the New Zealand kea (Nestor notabilis), have declined drastically over the last 120 years after an intense period of official persecution. Today <5000 kea remain in the wild. Previously it has been assumed that like other parrots, kea would destroy most of the seeds they eat, thereby contributing little to seed dispersal. The New Zealand alpine flora is rich in fleshy-fruited species yet has a limited disperser fauna. Consequently, we investigated the relevance of kea as a seed disperser in New Zealand’s alpine ecosystems. Field-based foraging observations coupled with faecal analyses showed kea were by far the most important extant alpine avian frugivore. Kea selected more fruiting species (21 vs. 17 species), consumed more fruit, and dispersed more seeds (8137 vs. 795) than all other birds combined. Rates of seed predation by kea were extremely low, and evident in only 25% of species eaten. Kea are the only species that make frequent long-distance flights within and between mountain ranges. Hence, much of the effective long-distance dispersal of the alpine flora may be currently performed by kea. Conservation of kea is therefore important both for ensuring the survival of the species and for their role in seed-dispersal mutualisms for which there are few extant substitutes.  相似文献   

6.
《Applied soil ecology》2007,35(1):128-139
We tested the effect of soil moisture on the performance of four entomopathogenic nematodes species that have recently shown promise for the control of white grubs, i.e., Heterorhabditis bacteriophora, H. zealandica, Steinernema scarabaei, and S. glaseri. Experiments for all four nematodes were conducted in sandy loam, for S. scarabaei also in loamy sand and silt loam. Infectivity was tested by exposing third-instar Japanese beetle, Popillia japonica, to nematodes in laboratory experiments and determining nematode establishment in the larvae and larval mortality. Nematode infectivity was the highest at moderate soil moistures (−10 to −100 kPa), and tended to be lower in wet (−1 kPa) and moderately dry (−1000 kPa) soil. In dry soil (−3000 kPa), only S. scarabaei showed some activity. S. scarabaei was active from −1 to −3000 kPa in all soil types but the range of highest activity was wider in loamy sand (−1 to −1000 kPa) than in loamy sand and silt loam (−10 to −100 kPa). Persistence was determined in laboratory experiments by baiting nematode-inoculated soil with larvae of the greater wax moth, Galleria mellonella. For both Heterorhabditis spp. persistence was short at −10 kPa, improved slightly at −100 kPa, significantly at −1000 kPa, and was the highest at −3000 kPa. Both Steinernema spp. persisted very well at −10 kPa. However, S. glaseri persistence was the shortest at −10 kPa but did not differ significantly at −100 to −3000 kPa, whereas S. scarabaei persistence was not affected by soil moisture. Our observations concur with previous observations on the effect of soil moisture on entomopathogenic nematodes but also show that moisture ranges for infectivity and persistence vary among species. Differences among species may be based on differences in size and behavioral and physiological adaptations.  相似文献   

7.
Salinity is the major environmental factor limiting crop production. Alfalfa is a legume with high nutritional value that establishes a symbiosis relation with Ensifer meliloti. Under saline conditions the alfalfa yield decreases and this symbiosis is affected. The aim of this work is to study the effect of the co-inoculation of alfalfa plants with Halomonas maura (a moderately halophile bacterium) and E. meliloti in saline soils to improve their productivity and growth under greenhouse and field conditions. Alfalfa plants were grown in Leonard jar under greenhouse conditions, using a N-free mineral solution to mimic the conditions of an Orthic Solonchak. Then alfalfa plants were grown in the field in the same soil type. Seeds were inoculated with E. meliloti, H. maura, co-inoculated with E. meliloti and H. Maura, or non-inoculated as a control in both experiments. In greenhouse experiments the co-inoculation of alfalfa plants increased significantly the shoot dry weight (0.64 ± 0.02 vs. 0.79 ± 0.02), the leghaemoglobin content (10.17 ± 0.03 vs. 11.25 ± 0.06) and water potential (−3.12 ± 0.02 vs. −2.79 ± 0.02) compared with the single inoculation with E. meliloti. In the field experiments, biomass of co-inoculated plants clearly outyielded those of plants inoculated with any inoculant. The co-inoculation of H. maura and E. meliloti enhances alfalfa productivity in saline soils, thus contributing to the agricultural exploitation of low productive areas. H. maura and E. meliloti could be considered in formulation of bioinoculants to contribute in the reduction of the overuse of chemical fertilizers and their environmental impacts.  相似文献   

8.
The distribution, density and biomass of earthworms were investigated at the copper polluted site, Hygum (Denmark). In 1994, shortly after farming of the area was abandoned, only four earthworm species were present and their distribution was restricted to areas where copper concentration did not exceed 200 mg kg?1 dry soil. Sixteen years later (in 2010), without any agricultural activity, ten species of earthworms were found, in particular, epigeic species were present where soil copper concentrations reached >1000 mg kg?1 dry soil.  相似文献   

9.
In the state of Tabasco, South-eastern, Mexico, land-use changes such as the conversion of natural into agricultural systems, modify soil quality and the abundance of soil macrofauna, including earthworms. The aim of this study was to characterize by near-infrared spectroscopy (NIRS) the earthworms’ fingerprint in soil, in six sites including natural and agricultural ecosystems with low and high earthworm biomass and low and high earthworm diversity, in order to identify specific wavelengths that discriminate the presence/abundance of earthworm species and functional groups. The spectral region of 1860–1870 nm was significantly correlated with total earthworm density, particularly at one of the sites (Cedar polyculture; r = 0.8, p < 0.05). Earthworm biomass had a specific NIRS wavelength according to the earthworm species and feeding category: 1820 and1860–1870 nm wavelengths were significantly correlated with Polypheretima elongata (r2 = 0.7, p < 0.05; mesohumic species) biomass and 2090 nm for biomass of all Lavellodrilus species (polyhumics). Two species had a much wider spectral range: L. bonampakensis and Dichogaster saliens (an epigeic worm; 1690–2300 nm, r2 = 0.7, p < 0.05). Biomasses of Periscolex brachysistis and Diplotrema murchiei were not significantly correlated with any near infrared wavelength spectra analyzed. Combining a maximum of 4 species per wavelength, mesohumic earthworms had a wider wavelength spectrum than polyhumics. Therefore, earthworm species diversity, biomass and abundance are associated with soil quality (as measured by NIR spectra) and this relationship varies with species and ecological category. Sites with lower and higher earthworm diversity have lower and higher soil organic matter quality, respectively, as observed by the wider or narrower spectral range with which earthworm biomasses are correlated.  相似文献   

10.
《Applied soil ecology》1999,11(1):35-42
Intact seeds and seed and seedling root exudates of birdsfoot trefoil (Lotus corniculatus L.) were used as chemoattractants in experiments to determine the relative importance of chemotaxis in spermosphere and rhizosphere colonization by selected rhizobacteria. Results for soft-agar, capillary tube and soil chemotaxis assays indicated that selected deleterious rhizobacteria were attracted to seed and seedling root exudates. Several sugars and phenolic fractions detected in exudates were chemoattractants for these rhizobacteria. Using soil-chemotaxis assemblies, migration of rhizobacterial isolates through 2 cm distances of soil toward birdsfoot trefoil seeds was detected within 24 h. Isolates were not detected at the same site in soils without seeds until 72 h after inoculation. These results suggest that attraction of deleterious rhizobacteria toward seeds and seedling roots mediated by exudates (chemotaxis) might be the first step in the establishment and subsequent colonization of bacteria involved in soilborne disease complexes of birdsfoot trefoil.  相似文献   

11.
Cover crops have traditionally been used to reduce soil erosion and build soil quality, but more recently cover crops are being used as an effective tool in organic weed management. Many studies have demonstrated microbial community response to individual cover crop species, but the effects of mixed species cover crop communities have received less attention. Moreover, the relationship between arable weeds and soil microbial communities is not well understood. The objective of this study was to determine the relative influence of cover crop diversity, early-season weed communities, and tillage on soil microbial community structure in an organic cropping system through the extraction of fatty acid methyl esters (FAMEs). A field experiment was conducted between 2009 and 2011 near Mead, NE where spring-sown mixtures of zero (control), two, and eight cover crop species were included in a sunflower–soybean–corn crop rotation. A mixture of four weed species was planted in all experimental units (excluding the no-cover control), and also included as an individual treatment. Cover crops and weeds were planted in late-March, then terminated in late-May using a field disk or sweep plow undercutter, and main crops were planted within one week of termination. Three (2009) or four (2010–11) soil cores were taken to a depth of 20 cm in all experimental units at 45, 32, and 25 days following cover crop termination in 2009, 2010, and 2011, respectively. Total FAMEs pooled across 2009 and 2010 were greatest in the two species mixture–undercutter treatment combination (140.8 ± 3.9 nmol g−1) followed by the eight species mixture–undercutter treatment combination (132.4 ± 3.9 nmol g−1). Abundance of five (2009 and 2010) and seventeen (2011) FAME biomarkers was reduced in the weedy treatment relative to both cover-cropped treatments and the no-cover control. In 2009 and 2010, termination with the undercutter reduced abundance of most actinomycete biomarkers while termination with the field disk reduced abundance of C18:1(cis11) and iC16:0. Canonical discriminant analysis of the microbial community successfully segregated most cover crop mixture by termination method treatment combinations in 2009 and 2010. Microbial communities were most strongly influenced by the presence and type of early-spring plant communities, as weeds exerted a strong negative influence on abundance of many key microbial biomarkers, including the AMF markers C16:1(cis11) and C18:1(cis11). Weeds may alter soil microbial community structure as a means of increasing competitive success in arable soils, but this relationship requires further investigation.  相似文献   

12.
A dual-beam surface layer scintillometer (SLS), for the estimation of sensible heat flux density H for a path length of 101 m, was used in a mixed grassland community in the eastern seaboard of South Africa for 30 months. Measurements also included Bowen ratio (BR) and eddy covariance (EC) estimates of H. Acceptable SLS data between 0600 h and 1800 h, judged by the percent of error-free 1 kHz data exceeding 25% and an inner scale of turbulence exceeding 2 mm, showed little seasonal variation and was consistently high—between 86.7% and 94.8%. An analysis of the various Monin–Obukhov similarity theory (MOST) empirical dimensionless stability functions used for estimating H from the SLS measurements showed percent differences in H that varied from ?30% to 28% for neutral to unstable conditions, respectively and for stable continuous conditions the differences in H were within 60 W m?2 with much larger differences for stable sporadic conditions. The good agreement in measurements of H over an extended period for the SLS, BR and EC methods demonstrates the applicability and robustness of the SLS method and the associated MOST empirical functions used for estimating H for a range of canopy heights, stability conditions and diurnal and seasonal weather conditions. Furthermore, there was no evidence for an underestimation in EC sensible heat compared to SLS and BR measurements, which implies that any lack of energy balance closure points to possible latent energy EC underestimation or due to energy fluxes not included in the shortened energy balance if the net irradiance and soil heat flux components are correct. A sensitivity analysis was used to determine the relative importance of the SLS data inputs of air temperature, atmospheric pressure, beam path length and beam height on H estimates. Worst-case errors in air temperature, atmospheric pressure, beam path length and beam height resulted in errors in H within 1.0%, 1.3%, 3.0% and 4.0%, respectively. Overall, the worst-case total percent error in SLS-estimated H is within 5.3% and the typical percent error is within 3.9%. Accounting for the error in net irradiance and soil heat flux measurements, the seasonal variation in the error in daily evaporation estimated as a residual of the energy balance is generally less than 0.2 mm (0.49 MJ m?2) in winter when the daily evaporation was about 1 mm (2.45 MJ m?2) and typically less than 0.4 mm (0.98 MJ m?2) when the evaporation exceeded 4 mm (9.8 MJ m?2). Soil heat flux density measurements can contribute significantly to the overall error.  相似文献   

13.
Impact of Pheidole sp., reportedly important in insect pest suppression in agroecosystems was studied on supporting agroecosystem services. This tropical ant species was found to be common and abundant in agroecosystems, with a high nest density and preference for the central, crop-growing zone of annual cropping systems. Physico-chemical characteristics of the debris soil were examined from nests located by the roadside and within two managed ecosystems. The debris soil had significantly higher concentrations of total C, N, P and NO3-N along with higher water-holding capacity and moderate-sized soil particles in comparison to the control soil. The pH of the Pheidole sp. debris soil was shifted towards reduced alkaline conditions. Results reveal that annually, 2.44 kg/ha C, 0.071 kg/ha P, 0.628 kg/ha N and 0.009 kg/ha NO3-N are added to the soil through the accumulation of organic refuse at the nest rim. This contributes to soil nutrient enhancement and is suggested to enhance ecosystem productivity. The high nutrient content of nest debris soil is linked to the predominance of arthropod carcasses (93.7% of the total organic refuse) in the refuse piles derived from the animal-based food (70.3%) brought to the nests by the foragers. Plant-based food was 29.6% (seeds, leaves, roots, etc.) of the total indicating a minor role of Pheidole sp. as a seed harvester. The results suggest an important role of Pheidole sp. in regulating the soil nutrients as an ecosystem engineer.  相似文献   

14.
《Applied soil ecology》2007,35(1):46-56
A study on the widespread earthworm Dendrobaena octaedra was conducted to determine which individual life history traits were the most sensitive to copper and to determine the contribution of changes in individual traits to changes in the population growth rate (λ). The study showed that the effect of copper on population growth rate mirrored the effects seen on growth, maturation and reproductive output, with stimulation at the lowest concentrations and inhibition at the highest concentration. A decomposition analysis showed that the mean change in λ was mainly driven by time between consecutive cocoon productions, except at the highest copper concentration (200 mg/kg dry soil) where decreased production of fertile cocoons also contributed to the reductions in λ. The highest population growth rate (λ = 1.18 week−1) occurred at 80 mg Cu/kg dry soil. At higher concentrations λ became gradually smaller, and was almost 1 week−1 (where no population increase or decrease occurs) at the highest exposure concentration of 200 mg Cu/kg dry soil suggesting that extinction would occur if a population of D. octaedra were to be exposed to copper concentrations only slightly higher than this level.  相似文献   

15.
Inoculants are biological formulations that combine a stable microorganism population and various types of compounds produced and released during fermentation, such as phytohormones and plant growth regulators. Azospirillum brasilense strain Az39 and Brayrhizobium japonicum strain E109 were previously shown to produce indole 3-acetic acid (IAA), gibberellic acid (GA3) and zeatin (Z). We tested the hypothesis that such compounds are responsible for early growth promotion in inoculated corn (Zea mays L.) and soybean (Glycine max L.) seedlings. Seeds were inoculated with Az39, E109, or both, and kept in a chamber at 20–30 °C under a controlled photoperiod to evaluate seed germination. To evaluate root and shoot length and dry weight, and number of nodules and percentage of nodulated seedlings, in soybean, seedlings were kept in a growth chamber for 14 days under similar photoperiod and temperature conditions. Az39 and E109, singly or in combination, showed the capacity to promote seed germination, nodule formation, and early development of corn and soybean seedlings. Both strains were able to excrete IAA, GA3 and Z into the culture medium, at a concentration sufficient to produce morphological and physiological changes in young seed tissues.  相似文献   

16.
Fertilization with animal residues together with no-tillage is being widely used in dryland Mediterranean agriculture. The aim of this work is to assess the potential impacts of these combined management practices on oribatid mite species, and to evaluate their potential use as bioindicators of soil disturbances. From an experiment established ten years ago, eight fertilization treatments (including minerals or pig slurries), all combined with minimum tillage (MT) and no-tillage (NT), were studied. Four of these combinations were sampled three times during the winter cereal cropping season. The rest, and a neighbouring oak forest, were only sampled close to the end of the season (May). In total, 34 oribatid species and 4140 individuals were recovered. Oribatid abundance responded positively (p < 0.05) to the reduction of tillage intensity (NT) and marginally (p < 0.1) to slurry fertilization at sowing (close to maximum legislation allowed rate: <210 kg N ha−1 yr−1). At this slurry rate, Shannon index of diversity varied through the season, and was higher in May in MT than in NT plots. The Berger–Parker index of abundance signals plots without slurries as the most disturbed (compared with the forest). Nitrogen slurry over-fertilization reduced abundance of Oribatula (Zygoribatula) connexa connexa , but the impact on the most relevant species depended on the tillage system: Epilohmannia cylindrica cylindrica dominated in MT plots; under NT it was balanced by Tectocepheus velatus sarekensis and Passalozetes (Passalozetes) africanus. Scutovertex sculptus is also very negatively affected by tillage. Oribatida are a good target for the biological indication of soil disturbances associated to agricultural management.  相似文献   

17.
《Soil biology & biochemistry》2001,33(7-8):913-919
A reliable and simple technique for estimating soil microbial biomass (SMB) is essential if the role of microbes in many soil processes is to be quantified. Conventional techniques are notoriously time-consuming and unreproducible. A technique was investigated that uses the UV absorbance at 280 nm of 0.5 M K2SO4 extracts of fumigated and unfumigated soils to estimate the concentrations of carbon, nitrogen and phosphorus in the SMB. The procedure is based on the fact that compounds released after chloroform fumigation from lysed microbial cells absorb in the near UV region. Using 29 UK permanent grassland soils, with a wide range of organic matter (2.9–8.0%) and clay contents (22–68%), it was demonstrated that the increase in UV absorbance at 280 nm after soil fumigation was strongly correlated with the SMB C (r=0.92), SMB N (r=0.90) and SMB P (r=0.89), as determined by conventional methods. The soils contained a wide range of SMB C (412–3412 μg g−1 dry soil), N (57–346 μg g−1 dry soil) and P (31–239 μg g−1 dry soil) concentrations. It was thus confirmed that the UV absorbance technique described was a rapid, simple, precise and relatively inexpensive method of estimating soil microbial biomass.  相似文献   

18.
《Applied soil ecology》1999,11(2-3):189-197
Senescent leaves of Miscanthus sinensis contained 36% soluble polysaccharides, 26% cellulose and had a C/N ratio of 45. In 11 wild flower species contents of soluble polysaccharides (21–30%), cellulose (3–16%) and C/N ratio (13–31) were lower. Decomposing leaves of M. sinensis lost weight at a rate of 0.002 day−1, increased the C/N ratio from 45 to about 100, the bacterial biomass from 0.4 to 1 μg C mg−1 dry weight, and decreased the tensile strength from 35 to 10 N. The withdrawal rate of Lumbricus terrestris with senescent leaves of M. sinensis was 30 mg g−1 week−1; the feeding rate was lower. With most senescent wild flowers withdrawal and feeding rates were higher. During decomposition of M. sinensis withdrawal rates increased to about 90, and feeding rates to about 30 mg g−1 week−1. The rates were not related to soluble polysaccharides, cellulose, acid-insoluble residue, C/N ratio and the presence of trichomes on the leaves. The abundance of L. terrestris decreased in a meadow turned into a field of M. sinensis from 55 to 26 earthworms m−2 and increased in a rotational maize field turned into wild flower strips from 28 to 46 earthworms m−2. The species richness of earthworms decreased with M. sinensis from 7.2 to 4.7 and increased with wild flowers from 4.7 to 6.7 species per sampling unit.  相似文献   

19.
Growth and symbiotic activity of legumes are reduced by high soil compaction and mediated by Nod factors (LCO, lipo-chitooligosaccharides) application. Our objective was to assess the combined effects of soil compaction and Nod factors application on growth and symbiotic activity of pea. The experiment was two factorial and included soil compaction (1.30 g cm−3 – not compacted (control) and 1.55 g cm−3 – compacted soil), and Nod factors concentration (control without addition of Nod factors and use of 260 nM Nod solution) for each soil compaction. The soil (Haplic Luvisol) was packed into pots, pea (Pisum sativum L.) seeds were soaked with Nod factors solution or water and then plants were grown for 46 days. This study has shown that soil compaction and treatments of pea seeds with Nod factors influenced pea growth and symbiotic activity. Soil compaction significantly reduced pea growth parameters, namely plant height, dry mass, leaf area, root mass and root length and symbiotic parameters, namely mass of nodules, dry mass of an individual nodule, nitrogenase activity and total nitrogen content in plant in comparison to the non-compacted treatment. Treatment of seeds with Nod factors generally improved nearly all of the above parameters. Nitrogenase activity per pot and total plant nitrogen content were significantly reduced by soil compaction and increased by application of Nod factors in plants grown in not compacted soil. Our results demonstrate that increased symbiotic activity resulting from Nod factors addition may mitigate adverse effect of soil compaction on plant growth.  相似文献   

20.
Impacts of management and land use on soil bacterial diversity have not been well documented. Here we present the application of the bacterial tag encoded FLX amplicon pyrosequencing (bTEFAP) diversity method, which will promote studies in soil microbiomes. Using this modified FLX pyrosequencing approach we evaluated bacterial diversity of a soil (Pullman soil; fine, mixed, thermic Torrertic Paleustolls) with 38% clay and 34% sand (0–5 cm) under four systems. Two non-disturbed grass systems were evaluated including a pasture monoculture (Bothriochloa bladhii (Retz) S.T. Blake) [P] and a diverse mixture of grasses in the Conservation Reserve Program (CRP). Two agricultural systems were evaluated including a cotton (Gossypium hirsutum L.) -winter wheat (Triticum aestivum L.)-corn (Zea mays L.) rotation [Ct–W–Cr] and the typical practice of the region, which is continuous monoculture cotton (Ct–Ct). Differences due to land use and management were observed in soil microbial biomass C (CRP > P = Ct–W–Cr > Ct–Ct). Using three estimators of diversity, the maximum number of unique sequences operational taxonomic units (OTU; roughly corresponding to the species level) never exceeded 4500 in these soils at the 3% dissimilarity level. The following trend was found using the most common estimators of bacterial diversity: Ct–W–Cr > P = CRP > Ct–Ct. Predominant phyla in this soil were Actinobacteria, Bacteriodetes and Fermicutes. Bacteriodetes were more predominant in soil under agricultural systems (Ct–W–Cr and Ct–Ct) compared to the same soil under non-disturbed grass systems (P and CRP). The opposite trend was found for the Actinobacteria, which were more predominant under non-disturbed grass systems (P and CRP). Higher G? bacteria and lower G+ bacteria were found under Ct–W–Cr rotation and highest abundance of actinomycetes under CRP. The bTEFAP technique proved to be a powerful method to characterize the bacterial diversity of the soil studied under different management and land use in terms not only on the presence or absence, but also in terms of distribution.  相似文献   

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