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1.
Summary Selective grazing of fungi by soil microarthropods may affect decomposition rates of litter materials and the structure of microarthropod and fungal communities. We developed laboratory methods to assay feeding selectivity and investigated the preferences of the collembolan Folsomia candida on three fungi: Acremonium sp., Paecilomyces varioti, and Penicillium citrinum. F. candida showed stronger preference for Acremonium sp. than for P. varioti and P. citrinum. Oviposition site selection followed the same pattern. Actively metabolizing hyphae of Acremonium sp. and P. varioti were preferred over senescent hyphae, while spores of P. citrinum were preferred over active hyphae. If microarthropod preference for active hyphae is extensive, microarthropod regulation of decomposition could be more important than their biomass indicates. Furthermore, as the P. citrinum results indicate, mechanisms of microbial dissemination may include selective grazing.Contribution in part to International Symposium on Faunal Influences on Soil Structure, Edmonton, Alberta, Canada (11–13 June 1984), organized by W. B. McGill; and the annual meeting of the Ecological Society of America, Minneapolis, Minnesota (17–21 June 1985)  相似文献   

2.
Summary The aim of this study was to investigate the environmental requirements of Eisenia fetida (Lumbricidae) and its relation to Enchytraeus albidus (Enchytraeidae). Specimens of Eisenia fetida were cultured at two different temperatures (15°C and 25°C) and moisture conditions (50% and 80%) in presence or absence of Enchytraeus albidus. Eisenia fetida grew best at the higher temperature and amount of moisture. Enchytraeus albidus impaired the growth of Eisenia fetida at the higher temperature. When Enchytraeus albidus was present, the mortality of Eisenia fetida increased.Interaction between Eisenia fetida and Enchytraeus albidus was shown, although the mechanisms remain unclear. These species, coexisting in the same habitat (compost), appear to have slightly different niches: Eisenia fetida favours warmer, moister conditions than Enchytraeus albidus.Dedicated to the late Prof.Dr. M.S. Ghilarov  相似文献   

3.
Summary Application to soil of 1 g (recommended rate) or 10 g l-1 of phosphonate did not affect the numbers of bacteria and fungi nor the proportions of actinomycetes and fungi antagonistic to Phytophthora cinnamomi. Foliar phosphonate applications to avocado seedlings (Persea americana) did not affect microbial numbers or the proportions of microbes in the rhizosphere capable of antagonizing P. cinnamomi. Mycelium of P. cinnamomi and zoospores of P. palmivora did not appear to respond to diffusates from excised roots of phosphonate-treated avocado and pepper-corn tree (Schinus molle) seedlings, respectively. However, less extensive lesions were observed on the roots of fungicide-treated avocado and pepper-corn tree seedlings exposed to P. cinnamomi and P. palmivora, respectively. The reduction in P. cinnamomi infection on pepper-corn tree seedlings appears to be brought about by additive rather than interactive effects of the resident soil microflora and foliar-applied phosphonate.  相似文献   

4.
A common garden crop grown in the coastal plain region of North and South Carolina (United States) is the non-heading, leafy green type of Brassica oleracea L. known as collard (B. oleracea L. subsp. oleracea convar. acephala (DC.) Alef. var. viridis L.). Predominantly a fall and winter vegetable in this region, collard is often the only green planting to be found in the yard or garden of a rural home during these cool seasons. Historically, the traditional collard patch and even commercial fields were planted with unique varieties perpetuated by individual seed savers, and collectively, the regional diversity for this crop was probably very significant for well over a century. Genetic erosion of this collard germplasm pool has been severe in recent decades as commercial hybrids have been adopted by both large-scale producers and home gardeners. Although a significant number of collard landraces are being perpetuated to this day, existing diversity among landraces still grown in the region is now in the hands of an aging population of seed savers who maintain germplasm through on-farm preservation. From 2003 to 2006, we explored the coastal plain region of North and South Carolina in search of collard gardens containing traditional landraces. Exploration trips were conducted mid-winter to early spring. About 90 samples of collard were obtained from seed savers during the course of this exploration. Observations of morphological differences of these landraces indicate that significant diversity exists in this group. Obtained landraces are being deposited into the U.S. plant introduction collection and will be available for future use. This preserved collection could prove to be an important new source of genes for B. oleracea improvement.  相似文献   

5.
Summary Rye-grass (Lolium perenne) is known to be a strong competitor to red clover (Trifolium pratense) for soil K+ under conditions of low K availability in the soil. The objective of this study was to clarify whether this competitive behaviour of the two species can be explained by root morphology. Total K+ uptake ofL. perenne andT. pratense was studied under field conditions in relation to root fresh weight, root density, root cation exchange capacity, root surface and root length. The soil was an Alfisol, Udalf. All root parameters, when calculated per unit soil surface (M2), were higher inL. perenne than inT. pratense. In addition,L. perenne had longer root hairs and a denser root hair system thanT. pratense. The greatest difference in root morphology between species was root length, withL. perenne roots averaging 4–6 times longer than those ofT. pratense.Significant correlations were found between the total K+ uptake and all root parameters examined, with highest correlationsforroot fresh weight (r,0.92***T. pratense; 0.94***L. perenne) and root length (r, 0.91***T. pratense;r, 0.93***L. perenne). Potassium uptake per unit root fresh weight, root surface and root length were all significantly higher forT. pratense than for L. perenne. Differences in the rate of K+ uptake between species were particularly high when expressed per unit root length. Because of its greater root length and surface area,L. perenne can take up more soil K+ thanT. pratense, particularly where there is a low K– supply in the soil. Under such conditionsL. perenne will be a particularly strong competitor toT. pratense.  相似文献   

6.
Diversity of native rice (Oryza Poaceae:) species of Costa Rica   总被引：1，自引：0，他引：1  
We found several populations of wild Oryza species in the lowlands of Costa Rica. The plants showed extensive morphological variation, suggesting the presence of several species. In the morphologic study, 33 traits were scored for plants of all the species. A principal component analysis revealed the significant morphological separation of the different species. The analyses indicated that there are three species, O. grandi­glumis, O. latifolia and O. glumaepatula. Two putative hybrid types were found, both significantly differing in their morphology from the known species and intermediate at several traits. O. grandi­glumis is a new record for Costa Rican flora. Its main population is located in Caño Negro Wildlife Refuge, Los Chiles, Alajuela. O. latifolia is distributed throughout the lowlands of the country and the plants of the Atlantic slope are significantly bigger in general habit than those of the Guanacaste area. During this study a population of O. glumaepatula of hundreds of thousands of plants was discovered in the Medio Queso River wetland, Los Chiles, Alajuela. This population is the most important source of genes for cultivar's improvement from the primary gene pool of rice in Costa Rica. The small ligule and the wide flag leaf characteristic of the two CCDD species separated them from the AA diploid O. glumaepatula. Seed size, ligule size, number of branches in the panicle, plant height and sterile lemma length are all bigger in O. grandi­glumis, and influenced the second factor that separated the CCDD species in two discrete clusters. The species found offer great possibilities for the improvement of rice cultivars and they should be thoroughly studied and appropriately protected.  相似文献   

7.
Summary The major agronomic concern with NH3 loss from urea-containing fertilizers is the effect of these losses on crop yields and N fertilizer efficiency. In this 2-year study, NH3 volatilization from surface-applied N fertilizers was measured in the field, and the effects of the NH3 losses detected on corn (Zea mays L.) and orchardgrass (Dactylis glomerata L.) yield and N uptake were determined. For corn, NH4NO3 (AN), a urea-AN solution (UAN), or urea, were surface-broadcast at rates of 0, 56 and 112 kg N ha–1 on a Plano silt loam (Typic Argiudoll) and on a Fayette silt loam (Typic Hapludalf). Urea and AN (0 and 67 kg N ha–1) were surface-applied to grass pasture on the Fayette silt loam. Significant NH3 losses from urea-containing N sources were detected in one of four corn experiments (12%–16% of applied N) and in both experiments with grass pasture (9%–19% of applied N). When these losses occurred, corn grain yields with UAN and urea were 1.0 and 1.5 Mg ha–1, respectively, lower than yields with AN, and orchardgrass dry matter yields with urea were 0.27 to 0.74 Mg ha–1 lower than with AN. Significant differences in crop N uptake between N sources were detected, but apparent NH3 loss based on N uptake differences was not equal to field measurements of NH3 loss. Rainfall following N application markedly influenced NH3 volatilization. In corn experiments, NH3 loss was low and yields with all N sources were similar when at least 2.5 mm of rainfall occurred within 4 days after N application. Rainfall within 3 days after N application did not prevent significant yield reductions due to NH3 loss from urea in grass pasture experiments.  相似文献   

8.
Summary Kleptocopry is the behaviour of adults or larvae of a certain species whereby dung masses are utilized which had been provisioned by individuals of another species for the latter's own brood. Aphodius coenosus is a kleptocoprid in nests of Typhaeus typhoeus. This is the first record of kleptocopry by A. coenosus and of a kleptocoprid in the nest of T. typhoeus. In the laboratory, newly emerged A. coenosus adults moved to the surface while back-filling their burrows. Back-filled burrows (approximately 3 mm in diameter) were also found in the field, together with back-filled burrows from T. typhoeus (approximately 14 mm in diameter). Ancient (ca. 10 000 years old) back-filling traces of the Typhaeus type reported earlier were also accompanied by small back-filling traces, similar to those made by A. coenosus. The traces made by kleptocoprid A. coenosus thus offer support to the hypothesis that the ancient large traces originate from large geotrupid dung beetles.Dedicated to the late Prof. Dr. M.S. Ghilarov  相似文献   

9.
Summary A study was undertaken to investigate arylsulphatase activity in 15 soils cropped to cocoa (Theobroma cacao) and coffee (Coffea canephora var. robusta) in Ghana. The arylsulphatase activity was correlated positively and significantly with organic C, total N, and cation exchange capacity, and correlated negatively with acetate soluble sulphate. The enzyme was deactivated at an incubation temperature of over 60°C. Preheating and oven-drying of soils decreased arylsulphatase activity. Addition of 1.0 ml toluene during the assay resulted in a sharp decline in arylsuphatase activity. The addition of trace elements at a concentration of 1 ppm caused a reduction in soil arylsulphatase activity compared with that of the untreated samples.  相似文献   

10.
In a greenhouse study, the effect of the earthwormAporrectodea trapezoides on root nodulation in seedlings of subterranean clover (Trifolium subterraneum) was examined in the presence and absence of addedRhizobium leguminosarium biovartrifolii (strain NA 30). WhenR. trifolii NA 30 was inoculated into dung and placed on the soil surface, the total number of root nodules was five times greater (P<0.001) in the presence of earthworms than without earthworms and the number of nodules on the primary root of the plants 2–8 cm below the soil surface was 4 to 6 times greater (P<0.001) in the presence of earthworms. The additional nodulation did not affect plant growth or foliar N. When NA30 was dispersed through the soil at the beginning of the experiment, the presence of earthworms did not influence the level of root nodulation. The presence of earthworms increased root dry weight by 20–30%, plant top weight by up to 125% (P<0.001), and foliar N by 5–25% (P<0.001). Surface-applied dung increased the dry weight of plant tops (2-to 3-fold,P<0.001) but did not affect the concentration of foliar N (P<0.005).  相似文献   

11.
Summary In an outdoor experiment the distribution of earthworms (Lumbricus spp., Allolobophora spp.) under different plant species was studied. Earthworms avoid uncovered areas, but show different reactions under vegetation. This effect reappears in the same manner every year. A particular preference was shown for clover whereas onion was least preferred. Possible reasons for this behaviour are the extent of covering, the moisture regime and exudates of the plants. According to the results obtained the deciding factor seems to be the extent of cover whereas odorous substances are of secondary importance.Dedicated to the late Prof. Dr. M.S. Ghilarov  相似文献   

12.
采前苯丙噻重氮处理抑制厚皮甜瓜采后挥发性物质的释放   总被引：4，自引：1，他引：4  
用50 mg/L苯丙噻重氮(BTH)于采前1周喷洒“银帝”甜瓜植株和果实，采收后采用固相微萃取(SPME)结合气-质联用(GC-MS)技术分析果实常温贮藏期间挥发性物质的释放变化。结果表明：BTH处理可明显抑制果实挥发性物质的释放，处理者挥发性物质的释放随贮藏时间的延长而逐渐增加，而对照果实挥发性物质的释放呈单峰形变化，至采后第7 d达到高峰。BTH处理者挥发性物质的释放总量也明显低于对照。此外，BTH处理对10种甜瓜特征成分的释放也存在不同程度的影响。  相似文献   

13.
Summary Spores of the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus clarum obtained from sweet potatoes grown in soil inoculated with this fungus and with an enrichment culture of Acetobacter diazotrophicus contained A. diazotrophicus and several other bacteria, including a diazotrophic Klebsiella sp. Inoculation of micropropagated sweet potatoes with G. clarum and A. diazotrophicus enhanced spore formation in soil compared to VAM inoculation alone. Plants inoculated with VAM spores containing the bacteria showed additional increases in the number of spores formed within roots. A. diazotrophicus infected aerial plant parts only when inoculated together with VAM or when present within VAM spores. Micropropagated sugarcane seedlings inoculated with the same VAM spores containing the diazotrophs also contained much higher numbers of A. diazotrophicus in aerial parts than seedlings inoculated in vitro with the bacteria alone. When grown in non-sterile soil, the sugarcane seedlings again showed the greatest infection of aerial parts after inoculation with VAM spores containing the diazotrophs. This treatment also increased VAM colonization and the numbers of spores formed within roots. Similar effects were observed in sweet sorghum except that the aerial plant parts were not infected by A. diazotrophicus.  相似文献   

14.
Summary The connection between faunal composition and soil factors is discussed in this study on vertical distribution of soil nematodes under grass and barley. The investigation was undertaken on the field site of a Swedish integrated research project Ecology of Arable Land. The Role of Organisms in Nitrogen Cycling. Higher nematode number (7.6 × 106 m–2) and biomass (340 mg dry wt. m–2) were found under a 4-year-old grass ley than under barley (5.0 × 106 m–2; biomass, 136 mg dry wt. m–2). Plant feeders dominated under the grass ley (3.2 × 106 m–2 whereas under barley the bacterial feeders (2.4 × 106 m–2) were the most abundant feeding group. Number, biomass, mean individual size and various community parameters indicated a much better nutritive situation for the nematodes under grass than under barley. The vertical changes in the various parameters, including proportion of egg-carrying females, indicated an increasing food shortage for the nematode populations towards greater depths. In the top soil, predation could be an important factor in regulating nematode number.Dedicated to the late Prof. Dr. M.S. Ghilarov  相似文献   

15.
Summary Three field experiments with wheat were conducted in 1983, 1984, and 1985 in Terra Roxa soil in Paraná, the major Brazilian wheat-growing region, to study inoculation effects of various strains of Azospirillum brasilense and A. amazonense. In all three experiments inoculation with A. brasilense Sp 245 isolated from surface-sterilized wheat roots in Paraná produced the highest plant dry weights and highest N% in plant tops and grain. Grain yield increases with this strain were up to 31 % but were not significant. The application of 60 or 100 kg N ha–1 to the controls increased N accumulation and produced yields less than inoculation with this strain. Another A. brasilense strain from surface-sterilized wheat roots (Sp 107st) also produced increased N assimilation at the lower N fertilizer level but reduced dry weights at the high N level, while strain Sp 7 + Cd reduced dry weights and N% in the straw at both N levels. The A. amazonense strain isolated from washed roots and a nitrate reductase negative mutant of strain Sp 245 were ineffective. Strains Sp 245 and Sp 107st showed the best establishment within roots while strain Cd established only in the soil.  相似文献   

16.
We investigated the diversity of rhizobia isolated from different indigenous legumes in Flanders (Belgium). A total of 3810 bacterial strains were analysed originating from 43 plant species. Based on rep-PCR clustering, 16S rRNA gene and recA gene sequence analysis, these isolates belonged to Bradyrhizobium, Ensifer (Sinorhizobium), Mesorhizobium and Rhizobium. Of the genera encountered, Rhizobium was the most abundant (62%) and especially the species Rhizobiumleguminosarum, followed by Ensifer (19%), Bradyrhizobium (14%) and finally Mesorhizobium (5%). For two rep-clusters only low similarity values with other genera were found for both the 16S rRNA and recA genes, suggesting that these may represent a new genus with close relationship to Rhodopseudomonas and Bradyrhizobium. Primers for the symbiotic genes nodC and nifH were optimized and a phylogenetic sequence analysis revealed the presence of different symbiovars including genistearum, glycinearum, loti, meliloti, officinalis, trifolii and viciae. Moreover, three new nodC types were assigned to strains originating from Ononis, Robinia and Wisteria, respectively. Discriminant and MANOVA analysis confirmed the correlation of symbiosis genes with certain bacterial genera and less with the host plant. Multiple symbiovars can be present within the same host plant, suggesting the promiscuity of these plants. Moreover, the ecoregion did not contribute to the separation of the bacterial endosymbionts. Our results reveal a large diversity of rhizobia associated with indigenous legumes in Flanders. Most of the legumes harboured more than one rhizobial endosymbiont in their root nodules indicating the importance of including sufficient isolates per plant in diversity studies.  相似文献   

17.
Inter-Simple Sequence Repeat (ISSR) and Randomly Amplified Polymorphic DNA (RAPD) markers were used to analyze genetic distance among H. vulgare subsp. spontaneum populations from west Turkey. Fifty-five RAPD and 10 ISSR primers were used to detect variation among sample. A total of 55 polymorphic loci were found using 65 primers. Two distinct cluster groups were clearly established among populations. The minimum variation was detected between Pinarbasi and Bornova (GD = 0.192) populations and the maximum was found between Icmeler and Aydin populations (GD = 0.926). As two dominant markers, RAPD and ISSRs are effective and promising marker systems for detecting genetic variation.  相似文献   

18.
To study the magnitude and nature of genetic variation in E. fibrosus, the levels and distribution of allozyme and RAPD variations were investigated in populations collected from Finland and Russia. The results obtained from the allozyme and RAPD studies were compared to each other in 10 of the populations. The allozyme analysis showed that 6 of 12 presumed loci (50%) were polymorphic within the species, while the mean number of polymorphic loci within populations was 4.8%. The mean number of allele per locus for the species was 1.5 and 1.05 across the populations. Genetic diversity at the species level was low (H es = 0.025), and the mean population genetic diversity was even lower (H ep = 0.007). Both these values were much lower than the average for other Elymus and self-fertilising species. The largest proportion of the total allozyme diversity was found among, rather than within the populations (G ST = 0.70). The allozyme genetic distances between the populations did not reflect geographic distances. Cluster and principal coordinates analyses revealed the same allozyme relationship patterns among the populations. A comparison of allozyme and RAPD variation in 10 of the populations showed differences in the amount of genetic variation. The RAPD analysis revealed higher levels of variation (A p = 1.19, P p = 20.3 and H ep = 0.09) than the allozyme one) A p = 1.06, P p = 5.8 and H ep = 0.008). For both markers, the largest proportion of the total gene diversity was found among the populations studied (G st = 0.63 for RAPDs and G st = 0.65 for allozyme). In contrast to the allozyme analysis, the RAPD based genetic distances did reflect geographic distances. The cluster and principal coordinates analyses showed different grouping of populations for each data set. There was a positive, but not significant, correlation (r = 0.41) between the genetic distance matrices resulting from these markers. Regional comparison revealed that the Finnish populations had a higher diversity than the Russian ones. Generally, this study indicates that E. fibrosus contains low genetic variation in its populations. The results are discussed in the context of conservation of the species.  相似文献   

19.
Summary An investigation was conducted during the summer months of 1986–1987 and 1987–1988 in Western Australia to evaluate the effect of soil solarization on the control of root rot of gerbera an also on the microbial and nutrient status of the soil. Infested soil cores were sampled from a site where root-rot was a severe problem and were removed to a non-infested site where they were subjected to soil solarization or fumigation. Soil solarization resulted in reduced root rot (root disease index 28.6%) in comparison to the untreated control (52.0%) 8 months after planting. Plants in the fumigated plots had 15.8% less disease than those in solarized plots. Solarization increased the total numbers of bacteria and actinomycetes, and the proportion of bacteria and fungi antogonistic to Fusarium oxysporum, F. solani and Rhizoctonia solani. The proportion of actinomycetes antagonistic to these fungi, however, did not differ between solarized and control soil treatments. There was a significant reduction in disease in plants grown in infested fumigated soil to which a 10% concentration of solarized soil had been added, suggesting the development of microbial suppression in solarized soil. Phytophthora cryptogea was eradicated to 30 cm by solarization as well as by fumigation. Solarization eliminated R. solani but not F. oxysporum to a soil depth of 10 cm. Solarization increased the levels of NO n3 – -N and NH4 +-N in soil, but did not affect the concentrations of PO4 3–, K+, Fe2+, organic C and pH. Yield (as number of flowers per plant) was increased by soil solarization and by fumigation.Increased yields and decreased disease severity in the solarized plots could have been caused by (1) a reduction in the infectivity of the infested soils, (2) an increase in the suppressiveness of the soil, and (3) an increased available of plant nutrients.  相似文献   

20.
Summary An extensive crossing program including 10 wild taxa and 23 accessions representing 6 major cultivated forms and landraces of theBrassica oleracea group was carried out. Data for crossability, germination, viability, fertility inF 1 andF 2 were studied as well as the meiotic chromosomal pairing inF 1 hybrids in some combinations. The fertility of hybrids between all cultivated forms and wild populations ofB. oleracea was high and it was concluded that all, including the Chinese endemicalboglabra form, belong to the same biological species. Among the other species,B. macrocarpa, B. montana, andB. rupestris had the lowest andB. cretica the highest fertility values in crosses with cultivated forms. The crossing data do not give any further information as to the genetic differentiation ofB. oleracea during the course of domestication. Introgression between wild and cultivated forms has probably occurred frequently. All members of theB. oleracea cytodeme belong to the primary and secondary gene pools of the 18 chromosomic crops and are as such of great importance for breeding purposes.  相似文献   

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