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1.
This work analyzes the direct effect of soil management practices on soil microbial communities, which may affect soil productivity and sustainability. The experimental design consisted of two tillage treatments: reduced tillage (RT) and zero tillage (ZT), and three crop rotation treatments: continuous soybean (SS), corn–soybean (CS), and soybean–corn (SC). Soil samples were taken at soybean planting and harvest. The following quantifications were performed: soil microbial populations by soil dilution plate technique on selective and semi-selective culture media; microbial respiration and microbial biomass by chloroform fumigation-extraction; microbial activity by fluorescein diacetate hydrolysis; and fatty acid methyl ester (FAME) profiles. Soil chemical parameters were also quantified. Soil organic matter content was significantly lower in RT and SS sequence crops, whereas soil pH and total N were significantly higher in CS and SC sequence crops. Trichoderma and Gliocladium populations were lower under RTSS and ZTSS treatments. Except in a few cases, soil microbial respiration, biomass and activity were higher under zero tillage than under reduced tillage, both at planting and harvest sampling times. Multivariate analyses of FAMEs clearly separated both RT and ZT management practices at each sampling time; however, separation of sequence crops was less evident. In our experiments ZT treatment had highest proportion of 10Me 16:0, an actinomycetes biomarker, and 16:1ω9 and 18:1ω7, two fatty acids associated with organic matter content and substrate availability. In contrast, RT treatment had highest content of branched biomarkers (i15:0 and i16:0) and of cy19:0, fatty acids associated with cell stasis and/or stress. As cultural practices can influence soil microbial populations, it is important to analyze the effect that they produce on biological parameters, with the aim of conserving soil richness over time. Thus, in a soybean-based cropping system, appropriate crop management is necessary for a sustainable productivity without reducing soil quality.  相似文献   

2.
The herbicide, glyphosate [N-(phosphonomethyl) glycine] is extensively used worldwide. Long-term use of glyphosate can cause micronutrient deficiency but little is known about potassium (K) interactions with glyphosate. The repeated use of glyphosate may create a selection pressure in soil microbial communities that could affect the nutrient dynamics such as K. The objective of this study was to determine the effect of single or repeated glyphosate applications on microbial and K properties of soils. A 54 day incubation study (Exp I) had a 3 × 5 factorial design with 3 soils (silt loam: fine, illitic, mesic Aeric Epiaqualf) of similar physical and chemical characteristics, that varied in long-term glyphosate applications (no, low, and high glyphosate field treatments) and five glyphosate rates (0, 0.5×, 1×, 2×, and 3× recommended field rates applied once at time zero). A second 6 month incubation study (Exp II) had a 3 × 3 factorial design with three soils (as described above) and three rates of glyphosate (0, 1×, and 2× recommended field application rates applied monthly). For each study microbial properties [respiration; community structure measured by ester linked fatty acid methyl ester (EL-FAME) analysis and microbial biomass K] and K fractions (exchangeable and non-exchangeable) were measured periodically. For Exp I, glyphosate significantly increased microbial respiration that was closely related to glyphosate application rate, most notably in soils with a history of receiving glyphosate. For Exp II, there was no significant effect of repeated glyphosate application on soil microbial structure (EL-FAME) or biomass K. We conclude that glyphosate: (1) stimulates microbial respiration particularly on soils with a history of glyphosate application; (2) has no significant effect on functional diversity (EL-FAME) or microbial biomass K; and (3) does not reduce the exchangeable K (putatively available to plants) or affect non-exchangeable K. The respiration response in soils with a long-term glyphosate response would suggest there was a shift in the microbial community that could readily degrade glyphosate but this shift was not detected by EL-FAME.  相似文献   

3.
The objectives of this work were to (a) investigate the short-term effects of applications of mineral fertilizer, municipal solid waste (MSW) compost, and two sewage sludges (SSs) subjected to different treatments (composting and thermal drying) on microbial biomass and activity of soil by measuring microbial biomass C, adenosine 5′-triphosphate content, basal respiration, and dehydrogenase, catalase, urease, phosphatase, β-glucosidase, and N-α-benzoyl-l-argininamide-hydrolyzing activities and (b) explore the relationships between soil microbiological, biochemical, and chemical properties and wheat yields under semiarid field conditions by principal component analysis. The additions of MSW compost, SS compost, and thermally dried SS did not affect significantly soil microbial biomass, as compared to mineral fertilization and no amendment. However, microbial activity increased in organically amended soils, probably due to the stimulating effect of the added decomposing organic matter. Changes in soil microbiological and biochemical properties showed no significant relationships with wheat yields, probably because plant growth was primarily water-limited, as typically occurs in semiarid regions.  相似文献   

4.
Drying and rewetting (D/W) of soils often leads to a pulse of total dissolved phosphorus (TDP) by lysis of sensitive microorganisms. The relevance of D/W on the P cycle in ecosystems depends on the duration of the TDP release. In forest soils, the forest floor represents a hotspot of microbial activity and is often prone to D/W. Here, we investigated the dynamics of TDP, the microbial P pool (Pmic), and the composition of microbial communities after D/W. Samples were taken from Oi and Oe layers of a European beech and a Norway spruce site and desiccated up to ??100 MPa (pF 6) at 20 °C, while controls were kept moist. TDP and Pmic were measured 0, 1, 3, 7, and 14 days after rewetting and the composition of microbial communities was analyzed by automated ribosomal intergenic spacer analysis after 14 days. After D/W, the largest TDP net release (D/W-control) was from Oe layers with 40–50 mg P kg?1 and inorganic P as the dominant fraction. The TDP concentrations decreased strongly in Oi layers within 1 (beech) to 4 (spruce) days, while remaining stable in Oe layers. The TDP dynamics were linked to the decrease and recovery of Pmic after D/W. Pmic dynamics differed between layers and stand types, suggesting the influence of microbial communities with different D/W sensitivities. The composition of microbial communities varied strongly among sites and layers, while D/W only affected the composition of bacterial and fungal communities in the spruce Oe layer. D/W of forest floors increases the plant available P and affects the P cycle in forest ecosystems.  相似文献   

5.
The composition of microbial communities and the level of enzymatic activity in the soil are both important indicators of soil quality, but the mechanisms by which a soil bacterial community is generated and maintained are not yet fully understood. Two soil samples were collected from the same location, but each had been subjected to a different long-term fertilization treatment and was characterized by different microbial diversity, biomass and physicochemical properties. These samples were γ-sterilized and swap inoculated. Non-sterilized soil samples along with sterilized and inoculated soil samples were incubated for eight months before their nutrient content, microbial biomass, enzymatic activity and bacterial composition were analyzed. Total phosphorus, and potassium concentrations along with the overall organic matter content of the non-sterilized soil were all equal to those of the same soil that had been sterilized and self/swap inoculated. Additionally, the microbial biomass carbon concentration was not affected by the specific inoculum and varied only by soil type. The activities of catalase, invertase, urease, protease, acid phosphatase and phytase were smaller in the sterilized soils that had been inoculated with organisms from chemical fertilizer amended soil (NPK) when compared to sterilized soil inoculated with organisms from manure and chemical fertilizer amended soil (NPKM) and non-sterilized soil samples. Bacterial 16S rRNA examined by 454-pyrosequencing revealed that the composition of bacterial community reconstructed by immigrant microbial inoculum in the soil was mainly influenced by its physicochemical properties, although the microbial inoculum contained different abundances of bacterial taxa. For example, the pH of the soil was the dominant factor in reconstructing a new bacterial community. Taken together, these results demonstrated that both soil microbial composition and functionality were primarily determined by soil properties rather than the microbial inoculum, which contributed to our understanding of how soil microbial communities are generated and maintained.  相似文献   

6.
The study dealt with the assessment of the impact of deforestation on tropical soil through a comparative analysis of physicochemical and microbiological parameters of natural forest and a deforested barren site. With significant decline in clay, texturally the soil of the deforested barren site was observed to be different from that of natural forest. Bulk density and porosity data revealed structural deterioration of deforested barren soil. The soil hydrological regime was also adversely affected by the deforestation. Levels of soil organic carbon, total nitrogen, microbial biomass C, N and microfungal biomass also exhibited significant decline in deforested site. Analysis of microbial respiratory quotient (q CO2) was also observed to be impaired in the deforested site. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

7.
We investigated the interactions of altitude and artificial warming on the soil microbial community structure in a subalpine Abies faxoniana forest in southwestern China after four years of warming. Open top chambers (OTCs) at two elevations (3000 m and 3500 m) were established, and their soil microbial characteristics, organic carbon (C) and nitrogen (N) were measured. The microbial community structure was quantified by phospholipid fatty acid (PLFA) analysis. A two-step sulfuric acid hydrolysis was used to quantify the labile and recalcitrant C fractions in the soil organic matter. The results showed that bacterial PLFAs and gram-negative bacterial PLFAs increased and the fungal PLFAs and the fungi/bacteria ratio decreased with warming at the high altitude. By contrast, the warming effects on those parameters at low altitude were small. The higher proportion of labile easily decomposable soil C may explain the different responses of the microbial community composition at the two altitudes. An RDA analysis confirmed that the variations in the soil community structure were significantly associated with soil organic matter properties such as the sizes of the soil labile N pool (LP-N), the recalcitrant N pool (RP-N), and the labile C pool as well as dissolved organic C (DOC) and dissolved organic N concentrations (DON). Our results also showed that labile C and N pools increased with the altitude, but the microbial biomass C as measured with chloroform fumigation techniques decreased. Warming increased only the recalcitrant C pools at the high altitude. Given the longer mean residence time for recalcitrant C and the much greater size of this soil organic carbon pool, the results indicated that a rise in temperature in our case increased soil C pools at higher altitudes, at least during the early stages of experimental soil warming. Warming could also cause changes in the composition of the microbial community and enzyme activities, consequently leading to functional changes in soil ecosystem processes at the high altitude.  相似文献   

8.
A combination of molecular and classical techniques was used to study the composition, structure, diversity, and dynamics of an aerobic heterotrophic cultivable bacterial community isolated from five different soil samples treated with the fumigant agent 1,3-dichloropropene (1,3-D) and further subjected to nitrogen–phosphorous–potassium (NPK) fertigation (F), amendment (C 2 and C 4), and NPK fertigation plus amendment (F + C) in two different periods (May and July). The restriction and sequence analysis of 16S rDNA from 189 isolates revealed a very high percentage (94%) of Gram-positive bacterial isolates, most of which (83%) belonging to the genus Bacillus. The degree of intraspecific genetic diversity was high, as shown by random amplified polymorphic DNA analysis. These data seem to be related with the increase in microbial biomass C (C mic) content and the decrease in the total organic C (C org) and metabolic quotient (qCO2) values, especially in amended soils (C 2, C 4) where soil microflora mineralized the organic matter of the added fertilizers. In a short term, it is suggested that the presence of very high percentage of Gram-positive bacteria might be related to the ability of these bacteria to form spores so as to be resistant to fumigants rather than being the result of a selective pressure in the predominance of microbial species with a set of genes involved in biodegradation of 1,3-D. Stefano Mocali and Donatella Paffetti contributed equally to this work.  相似文献   

9.
《Applied soil ecology》2007,35(2):281-290
As a result of many decades of fire suppression and atmospheric deposition the deciduous forests of eastern North America have changed significantly in stem density, basal area, tree size-frequency distribution, and community structure. Consequently, soil organic matter quality and quantity, nutrient availability, and microbial activity have likely been altered. This study evaluated the effects of four alternative forest ecosystem restoration strategies on soil microbial activity, microbial functional diversity, soil organic C, and soil N status in two mixed-oak (Quercus spp.) forests in southern Ohio, USA. The soils of these forests were sampled during the fourth growing season after application of (1) prescribed fire, (2) thinning of the understory and midstory to pre-settlement characteristics, (3) the combination of fire and thinning, and (4) an untreated control. Prescribed fire, with or without thinning, resulted in increased bacterial but not fungal activity when assessed using Biolog®. In contrast, assays of acid phosphatase and phenol oxidase activity indicated greater microbial activity in the thinning treatment than in the other three treatments. Functional diversity of both bacteria and fungi was affected by restoration treatment, with the bacterial and fungal assemblages present in the thin + burn sites and the fungal assemblage present in the thinned sites differing significantly from those of the control and burned sites. Treatments did not result in significant differences in soil organic C content among experimental sites; however, the soil C:N ratio was significantly greater in thinned sites than in sites given the other three treatments. Similarly, there were no significant differences in dissolve inorganic N, dissolved organic N, or microbial biomass N among treatments. Bacterial and fungal functional diversity was altered significantly. Based on Biolog® utilization treatments the bacterial assemblage in the thin-only treatment appeared to be relatively N-limited and the fungal assemblage relatively C-limited, whereas in the thin + burn treatment this was reversed. Although effects of restoration treatments on soil organic matter and overall microbial activity may not persist through the fourth post-treatment year, effects on microbial functional diversity are persistent.  相似文献   

10.
《Applied soil ecology》2006,34(3):258-268
The potential negative impact of agricultural practices on soil and water quality is of environmental concern. The associated nutrient transformations and movements that lead to environmental concerns are inseparable from microbial and biochemical activities. Therefore, biochemical and microbiological parameters directing nitrogen (N) transformations in soils amended with different animal manures or inorganic N fertilizers were investigated. Soils under continuous corn cultivation were treated with N annually for 5 years at 56, 168, and 504 kg N ha−1 in the form of swine effluent, beef manure, or anhydrous ammonia. Animal manure treatments increased dehydrogenase activity, microbial biomass carbon (Cmic) and N (Nmic) contents, and activities of amidohydrolases, including l-asparaginase, urease, l-glutaminase, amidase, and β-glucosaminidase. Soils receiving anhydrous ammonia demonstrated increased nitrate contents, but reduced microbiological and biochemical activities. All treatments decreased Cmic:organic C (Corg) ratios compared with the control, indicating reduced microbial C use efficiency and disturbance of C equilibrium in these soil environments. Activities of all enzymes tested were significantly correlated with soil Corg contents (P < 0.001, n = 108), but little correlation (r = 0.03, n = 36) was detected between Cmic and Corg. Activities of amidase and β-glucosaminidase were dominated by accumulated enzymes that were free of microbial cells, while activities of asparaginase and glutaminase were originated predominately from intracellular enzymes. Results indicated that soil microbial and biochemical activities are sensitive indicators of processes involved in N flow and C use efficiency in semiarid agroecosystems.  相似文献   

11.
Field and pot experiments showed that the P demand of wheat is highest in early stages of growth (up to 1.67 μg P per cm2 root surface and day). The needed orthophosphate ions H2PO4? and HPO42-move from soil to the root by diffusion. This process is controlled by the concentration gradient of the diffusible phosphate and the effective diffusion coefficient according to Pick's first law. Root excretions (rhizodeposition) are able to affect both characteristics. The water soluble portion of rhizodeposition contains more than 50% of up to 8 different sugars, 10–40% carboxylic acids and 10–15 amino acids and amides. The composition varies in dependence on the age of the root parts and on nutrition (Zea mays L., Brassica napus L., Pisum sativum L.). Diffusion experiments using small soil blocks showed that 50–75% of the root exudates were decomposed by respiration within 3 days. The rest was largely chemically converted. Originally present sugars disappeared. Due to the biosynthesis of different organic acids from the individual sugars the mobilisation of Ca3(PO4)2 by Pantoea agglomerans increased when the sugar mixture was derived from the rhizodeposition of P deficient plants with more pentoses instead of glucose and fructose (mainly effect of anions). In the rhizosphere therefore a mixture of rhizodeposition and its conversion products exists which affects the binding of phosphorus in soil and the P transport to the root. This should be considered both for the development of new soil extractants and for modelling the P supply to plants.  相似文献   

12.
The most intensive degradation of polysaccharides takes place upon low and moderate temperatures in typical chernozems and gray forest soils and upon high temperatures in brown desert-steppe soils. This regularity is related to the structure of soil microbial complexes. The soil water content exerts a more pronounced effect on chitin decomposition in comparison with cellulose and pectin decomposition. The most favorable conditions for pectin decomposition by microbes are created at the water content close to the field capacity. Model experiments indicate that the range of moisture, upon which the transformation of chitin by microbes is most active, is wider in clay and loamy soils than in sandy soils. Direct study of microorganisms in the investigated soils under microscope has shown that actinomycetes, bacteria, and fungi participate in the transformation of polysaccharides. The role of actinomycetes in chitin decomposition increases in parallel with the rise in the soil water content and temperature. The role of fungi in pectin decomposition becomes higher under higher moistening and lower temperatures. The use of the FISH method makes it possible to reveal differences in the structure and number of metabolically active representatives of Bacteria and Archaea chitinolytic and pectinolytic prokaryotic complexes in the investigated soils under the impact of different ecological factors.  相似文献   

13.
《Soil biology & biochemistry》2008,40(6):1269-1271
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14.
The effects of 11 different 2- and 3-yr potato crop rotations on soil microbial communities were characterized over three field seasons using several techniques. Assessments included microbial populations determined by soil dilution plate counts on various general and selective culture media, microbial activity by fluorescein diacetate (FDA) hydrolysis, single carbon source substrate utilization (SU) profiles, and fatty acid methyl ester (FAME) profiles. Potato rotation crops evaluated in research plots at Newport, ME, included barley/clover, canola, green bean, millet, soybean, sweet corn, and a continuous potato control. Soil populations of culturable bacteria and overall microbial activity tended to be highest following barley, canola, and sweet corn rotations, and lowest with continuous potato. Differences among rotations were less apparent during the potato phase of the rotations. Populations of actinomycetes and fluorescent pseudomonads tended to be greater in barley rotations than in most other rotations. SU profiles derived from BIOLOG GN2 plates indicated that certain rotations, including barley, canola, and sweet corn tended to have higher overall microbial activity, and barley and sweet corn rotations averaged higher substrate richness and diversity. Soybean and potato rotations tended to have lower substrate richness and diversity. Principal component analyses of SU data revealed differences among rotation soil communities in their utilization of individual carbon sources and substrate guilds, including carbohydrates, carboxylic acids, amines/amides, and amino acids. Analyses of soil FAME profiles demonstrated distinct differences among all the rotation soils in their relative composition of fatty acids, indicating differences in their microbial community structure. Fatty acids most responsible for differentiation among rotation soils included 16:1 ω5c, 16:1 ω7c, 18:2 ω6c, 18:1 ω9c, 12:0, and 13:0 anteiso, with 16:1 ω5c being the single greatest determinant. Overall, monounsaturated fatty acids, particularly 16:1 ω5c, were most prevalent in sweet corn rotations and polyunsaturates were highest in barley and millet rotations. Straight chain saturated fatty acids comprised the greatest proportion of fatty acids in soils under continuous potato. FAME biomarkers for microorganism groups indicated barley and millet rotations had the highest ratio of fungi to bacteria, and soybean and continuous potato had the lowest ratio. This research has demonstrated that different crop rotations have distinctive effects on soil microbial communities that are detectable using a variety of techniques. Further studies will identify more specific changes associated with particular rotations and relate these changes to potential effects on disease management, crop health, and crop productivity.  相似文献   

15.
We studied the reactions of humus layer (F/H) microbial respiratory activity, microbial biomass C, and the fungal biomass, measured as the soil ergosterol content, to the application of three levels of wood ash (1000, 2500, and 5000 kg ha-1) and to fire treatment in a Scots pine (Pinus sylvestris L.) stand. Physicochemical measurements (pH, organic matter content, extractable and total C content, NH 4 + and total N content, cation-exchange capacity, base saturation) showed similarity between the fire-treated plots and those treated with the lowest dose of wood ash (1000 kg ha-1). The ash application did not change the level of microbial biomass C or fungal ergosterol when compared to the control, being around 7500 and 350 g g-1 organic matter for the biomass C and ergosterol, respectively. The fire treatment lowered the values of both biomass measurements to about half that of the control values. The fire treatment caused a sevenfold fall in the respiration rate of fieldmoist soil to 1.8 l h-1 g-1 organic matter compared to the values of the control or ash treatments. However, in the same soils adjusted to a water-holding capacity of 60%, the differences between the fire treatment and the control were diminished, and the ash-fertilized plots were characterized by a higher respiration rate compared to the control plots. The glucose-induced respiration reacted in the same way as the water-adjusted soil respiration. The metabolic quotient, qCO2, gradually increased from the control level with increasing applications of ash, reaching a maximum in the fire treatment. Nitrification was not observed in the treatment plots.  相似文献   

16.
Proteolysis of milk proteins can be attributed to both native proteases and the proteases produced by psychrotrophic bacteria during storage of fresh raw milk. These proteases cause beneficial or detrimental changes, depending on the specific milk product. Plasmin, the major native protease in milk, is important for cheese ripening. Milk storage and cheese-making conditions can affect the level of plasmin in the casein and whey fractions of milk. A microbial protease from a psychrotrophic microorganism can indirectly increase plasmin levels in the casein curd. This relationship between the plasmin system and microbial proteases in milk provides a means to control levels of plasmin to benefit the quality of dairy products. This paper is a short review of both the plasmin system and microbial proteases, focusing on their characteristics and relationship and how the quality of dairy products is affected by their proteolysis of milk proteins.  相似文献   

17.
Plant effects on ecosystem processes are mediated through plant-microbial interactions belowground and soil enzyme assays are commonly used to directly relate microbial activity to ecosystem processes. Live plants influence microbial biomass and activity via differences in rhizosphere processes and detrital inputs. I utilized six grass species of varying litter chemistry in a factorial greenhouse experiment to evaluate the relative effect of live plants and detrital inputs on substrate-induced respiration (SIR, a measure of active microbial biomass), basal respiration, dissolved organic carbon (DOC), and the activities of β-glucosidase, β-glucosaminidase, and acid phosphatase. To minimize confounding variables, I used organic-free potting media, held soil moisture constant, and fertilized weekly. SIR and enzyme activities were 2-15 times greater in litter-addition than plant-addition treatments. Combining live plants with litter did not stimulate microbial biomass or activity above that in litter-only treatments, and β-glucosidase activity was significantly lower. Species-specific differences in litter N (%) and plant biomass were related to differences in β-glucosaminidase and acid phosphatase activity, respectively, but had no apparent effect on β-glucosidase, SIR, or basal respiration. DOC was negatively related to litter C:N, and positively related to plant biomass. Species identity and living plants were not as important as litter additions in stimulating microbial activity, suggesting that plant effects on soil enzymatic activity were driven primarily by detrital inputs, although the strength of litter effects may be moderated by the effect of growing plants.  相似文献   

18.
The effects of timber harvesting and the resultant soil disturbances (compaction and forest floor removal) on relative soil water content, microbial biomass C and N contents (Cmic and Nmic), microbial biomass C:N ratio (Cmic-to-Nmic), microbial respiration, metabolic quotient (qCO2), and available N content in the forest floor and the uppermost mineral soil (0-3 cm) were assessed in a long-term soil productivity (LTSP) site and adjacent mature forest stands in northeastern British Columbia (Canada). A combination of principal component analysis and redundancy analysis was used to test the effects of stem-only harvest, whole tree harvest plus forest floor removal, and soil compaction on the studied variables. Those properties in the forest floor were not affected by timber harvesting or soil compaction. In the mineral soil, compaction increased soil total C and N contents, relative water content, and Nmic by 45%, 40%, 34% and 72%, respectively, and decreased Cmic-to-Nmic ratio by 29%. However, these parameters were not affected by stem only harvesting or whole tree harvesting plus forest floor removal, contrasting the reduction of white spruce and aspen growth following forest floor removal and soil compaction reported in an earlier study. Those results suggest that at the study site the short-term effects of timber harvesting, forest floor removal, and soil compaction are rather complex and that microbial populations might not be affected by the perturbations in the same way as trees, at least not in the short term.  相似文献   

19.
The interaction between protein and phytate was investigated in vitro using proteins extracted from five common feedstuffs and from casein. The appearance of naturally present soluble protein-phytate complexes in the feedstuffs, the formation of complexes at different pHs, and the degradation of these complexes by pepsin and/or phytase were studied. Complexes of soluble proteins and phytate in the extracts appeared in small amounts only, with the possible exception of rice pollards. Most proteins dissolved almost completely at pH 2, but not after addition of phytate. Phytase prevented precipitation of protein with phytate. Pepsin could release protein from a precipitate, but the rate of release was increased by phytase. Protein was released faster from a protein-phytate complex when phytase was added, but phytase did not hydrolyze protein. Protein was released from the complex and degraded when both pepsin and phytase were added. It appears that protein-phytate complexes are mainly formed at low pH, as occurs in the stomach of animals. Phytase prevented the formation of the complexes and aided in dissolving them at a faster rate. This might positively affect protein digestibility in animals.  相似文献   

20.
Forest management practices often generate clear-cut patches, which may be colonized by ants not present in the same densities in mature forests. In addition to the associated changes in abiotic conditions ants can initiate processes, which do not occur in old-growth stands. Here, we analyse the effects of ants and aphid honeydew on litter solution of Norway spruce, microbial enzyme activities, and needle decomposition in a field and greenhouse experiment during summer 2003. In the field, low ant densities had relatively little effects on litter solution 30 cm away from a tree trunk, but significantly increased organic carbon concentrations and decreased inorganic nitrogen concentrations next to a trunk where ants tend to build their nests. In a greenhouse experiment, the addition of ants to lysimeters containing spruce litter significantly increased dissolved organic carbon (DOC), dissolved organic nitrogen (DON), NH4-N, NO3-N and K concentrations in litter solutions compared to the control treatment, while the simulation of aphid infestation (addition of honeydew) significantly increased DOC as a direct result of honeydew leaching, and decreased inorganic N concentrations in leachates. The presence of ants resulted in a changed composition of dissolved organic matter (DOM) with more aromatic and complex compounds, and microbial enzyme activity was significantly higher in litter extracts from the ant treatment compared to the honeydew and control treatment. However, mass loss, litter %C and %N were not affected by ants or honeydew. Our results suggest that ants have a distinct and immediate effect on solution composition and microbial activity in the litter layer indicating accelerated litter decay whereas the effect of honeydew was insignificant.  相似文献   

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