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1.
Grazing animals recycle a large fraction of ingested C and N within a pasture ecosystem, but the redistribution of C and N via animal excreta is often heterogeneous, being highest in stock camping areas, i.e., near shade and watering sources. This non-uniform distribution of animal excreta may modify soil physical and chemical attributes, and likely affect microbial community eco-physiology and soil N cycling. We determined microbial population size, activity, N mineralization, and nitrification in areas of a pasture with different intensity of animal excretal deposits (i.e., stock camping, open grazing and non-grazing areas). The pasture was cropped with coastal bermudagrass (Cynodon dactylon L.) and subjected to grazing by cattle for 4 y. Soil microbial biomass, activity and N transformations were significantly higher at 0-5 cm than at 5-15 cm soil depth, and the impacts of heterogeneous distribution of animal excreta were more pronounced in the uppermost soil layer. Microbial biomass, activity and potential net N mineralization were greater in stock camping areas and were significantly correlated (r2≈0.50, P<0.05) with the associated changes in total soil C and N. However, gross N mineralization and nitrification potential tended to be lower in stock camping areas than in the open grazing areas. The lower gross N mineralization, combined with greater net N mineralization in stock camping areas, implied that microbial N immobilization was lower in those areas than in the other areas. This negative association between microbial N immobilization and soil C is inconsistent with a bulk of publications showing that microbial N immobilization was positively related to the amount of soil C. We hypothesized that the negative correlation was due to microbial direct utilization of soluble organic N and/or changes in microbial community composition towards active fungi dominance in stock camping areas.  相似文献   

2.
The decomposition in soil of plant material from the stems of uniformly grown tobacco plants with genetic modifications to lignin biosynthesis was investigated by measuring CO2 production over 74 days. The effect on decomposition of readily available C, N and combined C plus N (as glucose, NH4NO3 and alanine, respectively) were determined by adding these compounds to the soil before the addition of plant materials. The genetic modifications to tobacco were the introduction of partial or antisense transgenes for cinnamyl alcohol dehydrogenase (CAD), caffeic acid O‐methyl transferase (COMT) and cinnamoyl CoA reductase (CCR), which are all enzymes that catalyse key steps in the monolignol pathway. In line with previous reports, reduced CCR material decomposed significantly faster than the reduced CAD or reduced COMT materials, which decomposed significantly faster than the unmodified material. All the plant materials had large C‐to‐N ratios (58, 72, 61 and 52 for the unmodified, reduced CAD, reduced COMT and reduced CCR materials, respectively), but the relationships between C‐to‐N ratio and decomposition rate were not consistent across all materials. Addition of glucose slowed the decomposition rate of all the materials. This is consistent with the additional C leading to a surplus of C relative to other nutrients at the sites of plant residue decomposition, but the reduction in decomposition rate was directly related to the combined C‐to‐N ratio of the plant material and soil amendment. In the case of reduced CCR material, addition of N as either NH4NO3 or alanine led to an increase in decomposition rate, indicating that a constraint on decay of this material was alleviated by N addition. However, addition of N did not increase the decomposition of the unmodified, reduced CAD and reduced COMT materials, which indicates that their decomposition was constrained by factors other than N. We have shown significant effects of targeted lignin modification on decomposition in laboratory studies over a relatively short period (< 74 days). However, longer‐term and more detailed field‐based investigations are needed before the wider ecological significance of the differences in decomposition can be properly assessed.  相似文献   

3.
《Soil biology & biochemistry》2001,33(4-5):583-591
Short-term effects of actively burrowing Octolasion lacteum (Örl.) (Lumbricidae) on the microbial C and N turnover in an arable soil with a high clay content were studied in a microcosm experiment throughout a 16 day incubation. Treatments with or without amendment of winter wheat straw were compared under conditions of a moistening period after summer drought. The use of 14C labeled straw allowed for analyzing the microbial use of different C components. Microbial biomass C, biomass N and ergosterol were only slightly affected by rewetting and not by O. lacteum in both cases. Increased values of soil microbial biomass were determined in the straw treatments even after 24 h of incubation. This extra biomass corresponded to the initial microbial colonization of the added straw. O. lacteum significantly increased CO2 production from soil organic matter and from the 14C-labeled straw. Higher release rates of 14C-CO2 were recorded shortly after insertion of earthworms. This effect remained until the end of the experiment. O. lacteum enhanced N mineralization. Earthworms significantly increased both mineral N content of soil and N leaching in the treatments without straw addition. Moreover, earthworms slightly reduced N immobilization in the treatments with straw addition. The immediate increase in microbial activity suggests that perturbation of soil is more important than substrate consumption for the effect of earthworms on C and N turnover in moistening periods after drought.  相似文献   

4.
Microbial activity in Arctic tundra ecosystems continues through the winter and is an important component of the annual C budget. This activity is sensitive to climatic variation, particularly snow depth because that regulates soil temperature. The influence of winter conditions on soil N cycling is poorly understood. In this study, we used intact core incubations sampled periodically through the winter and following growing season to measure net N mineralization and nitrification in dry heath and in moist tussock tundra under ambient and experimentally increased snow depths (by use of a snowfence). In dry heath, we sampled soils under Dryas octopetela or Arctostaphylos alpine, while in tussock tundra, we sampled Eriophorum vaginatum tussocks and Sphagnum dominated areas between tussocks. Our objectives were to: (1) examine how different winter snow regimes influenced year-round N dynamics in the two tundra types, and (2) evaluate how these responses are affected by dominant species present in each system. In tussock tundra, soils with increased winter snow cover had high net N mineralization rates during the fall and winter, followed by immobilization during thaw. In contrast, N mineralization only occurred during the autumn in soils with ambient snow cover. During the growing season when N immobilization dominated in areas with ambient snow cover, soils with increased winter snow cover had positive net mineralization and nitrification rates. In dry heath tundra, soils with increased snow depth had high late winter net N mineralization rates, but these rates were: (a) comparable to early winter rates in soils under Arctostaphylos plants with ambient snow cover; (b) greater in soils under Arctostaphylos plants than in soils under Dryas plants; and (c) less than the rates found in tussock tundra. Our findings suggest under ambient snow conditions, low soil temperatures limit soil N mineralization, but that deeper snow conditions with the associated warmer winter soil temperatures dramatically increase over-winter N mineralization and thereby alter the amount and timing of plant-available N in tundra ecosystems.  相似文献   

5.
Summary The effects of plant roots on net N mineralization were examined by comparing soil microcosms with and without plants. Additionally, inorganic N amendments were used to test for competition for N between plants and microorganisms. Daily watering and the application of suction to microcosms eliminated the effects of transpiration on soil moisture content. Monthly litter collections reduced the influence of the aboveground portions of plants. Plants decreased net N mineralization by 23% during days 0–114 and then increased net mineralization by the same amount during days 144–124. Root-free soil collected from with-plant microcosms on day 244 evolved 24% more CO2 in laboratory incubations than soil from without-plant microcosms. This indicates that plants had increased substrate availability to soil microorganisms. Inorganic N amendments had no significant effects on the microcosms or on laboratory soil incubations. Evidence is most consistent with the hypothesis that plant roots increased microbial activity due to the increased substrate availability. Different net N mineralization rates probably resulted from changes in the substrate C : N ratio.  相似文献   

6.
Atrazine is a widely used herbicide and is often a contaminant in terrestrial and freshwater ecosystems. It is uncertain, however, how the activity of soil macrofauna affects atrazine fate and transport. Therefore, we investigated whether earthworms enhance atrazine biodegradation by stimulating herbicide degrading soil microflora, or if they increase atrazine persistence by facilitating herbicide sorption. Short (43 d) and medium term (86 d) effects of the earthworms Lumbricus terrestris and Aporrectodea caliginosa on mineralization, distribution, and sorption of U-ring-14C atrazine and on soil C mineralization was quantified in packed-soil microcosms using silt loam soil. A priming effect (stimulation of soil C mineralization) caused by atrazine supply was shown that likely lowered the earthworm net effect on soil C mineralization in atrazine-treated soil microcosms. Although earthworms significantly increased soil microbial activity, they reduced atrazine mineralization to 14CO2-C from15.2 to 11.7% at 86 d. Earthworms facilitated formation of non-extractable atrazine residues within C-rich soil microsites that they created by burrowing and ingesting soil and organic matter. Atrazine sorption was highest in their gut contents and higher in casts than in burrow linings. Also, gut contents exhibited the highest formation of bound atrazine residues (non-extractable atrazine). Earthworms also promoted a deeper and patchier distribution of atrazine in the soil. This contributed to greater leaching losses of atrazine in microcosms amended with earthworms (3%) than in earthworm-free microcosms (0.003%), although these differences were not significant due to high variability in transport from earthworm-amended microcosms. Our results indicated that earthworms, mainly by casting activity, facilitated atrazine sorption, which increased atrazine persistence. As a consequence, this effect overrode any increase in atrazine biodegradation due to stimulation of microbial activity by earthworms. It is concluded that the affect of earthworms of atrazine mineralization is time-dependent, mineralization being slightly enhanced in the short term and subsequently reduced in the medium term.  相似文献   

7.
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8.
The decomposition in soil of pieces of stem and different fractions of stems from uniformly-grown tobacco plants with genetic modifications to lignin biosynthesis was investigated by measuring CO2 production over 74 d. The fractions used were intact stems, the insoluble fraction obtained by washing the stems with water, the lignin-rich fraction obtained by dissecting away the epidermis and cortex from the stems to leave a fraction in which the vascular tissue was concentrated, and the lignin-rich, insoluble fraction obtained by washing the lignin-rich fraction in water. The genetic modifications were the introduction of partial or antisense transgenes for cinnamyl alcohol dehydrogenase (CAD), caffeic acid O-methyl transferase (COMT) and cinnamoyl CoA reductase (CCR), which are all enzymes that catalyse key steps in the monolignol pathway. The total CO2 produced during decomposition declined in the following order: intact stem>insoluble stem fraction>lignin-rich fraction>lignin-rich, insoluble fraction, for all plant lines except the lignin-rich fraction from the reduced CCR plants. There was an initial flush of CO2 production that peaked between 2 and 4 d and which subsided within 20 d for both the intact stems and the lignin-rich fractions from all lines. There was no such flushes of CO2 release from the corresponding insoluble fractions. For the intact stems, the amount of CO2 released during the initial 20 d was significantly greater for the reduced COMT plants, than for the reduced CAD or reduced CCR plants, both of which released significantly more CO2 than the unmodified plants. Liquid-state 13C nuclear magnetic resonance spectroscopy of the water-soluble material from all lines showed that it was dominated by soluble sugars, but that there were no clear differences in the composition of the soluble fractions between the different lines of plants. Furthermore, the timing of the initial flush of CO2 release from the intact plant materials corresponded to that from glucose when incubated in the same soil indicating that sugars probably fuelled the initial flush of CO2 from the intact stems. Over 74 d, significantly more CO2 was released from the reduced CCR plant stems than from the reduced CAD and reduced COMT plants, which did not differ significantly from each other, but which were significantly greater than the unmodified stems. The total CO2 production from the lignin-rich fractions did not differ significantly between the unmodified, the reduced CAD and the reduced COMT plants, but the total CO2 production from the lignin-rich fraction from the reduced CCR plants was substantially greater than that from the other lines.We have shown significant effects of targeted lignin modification on decomposition in laboratory studies over a relatively short period (<74 d). The effects of genetic modification can be explained in part at least by alterations in the amount, composition and conformation of the lignin and the effect it has on other, more labile, components. However, longer-term and more detailed field-based investigations are needed before the wider ecological significance of the differences in decomposition can be properly assessed.  相似文献   

9.
Plant roots can increase microbial activity and soil organic matter (SOM) decomposition via rhizosphere priming effects. It is virtually unknown how differences in the priming effect among plant species and soil type affect N mineralization and plant uptake. In a greenhouse experiment, we tested whether priming effects caused by Fremont cottonwood (Populus fremontii) and Ponderosa pine (Pinus ponderosa) grown in three different soil types increased plant available N. We measured primed C as the difference in soil-derived CO2-C fluxes between planted and non-planted treatments. We calculated “excess plant available N” as the difference in plant available N (estimated from changes in soil inorganic N and plant N pools at the start and end of the experiment) between planted and non-planted treatments. Gross N mineralization at day 105 was significantly greater in the presence of plants across all treatments, while microbial N measured at the same time was not affected by plant presence. Gross N mineralization was significantly positively correlated to the rate of priming. Species effects on plant available N were not consistent among soil types. Plant available N in one soil type increased in the P. fremontii treatment but not in the P. ponderosa treatment, whereas in the other two soils, the effects of the two plant species were reversed. There was no relationship between the cumulative amount of primed C and excess plant available N during the first 107 days of the experiment when inorganic N was still abundant in all planted soils. However, during the second half of the experiment (days 108-398) when soil inorganic N in the planted treatments was depleted by plant N uptake, the cumulative amount of primed C was significantly positively correlated to excess plant available N. Primed C explained 78% of the variability in plant available N for five of the six plant-soil combinations. Excess plant available N could not be predicted from cumulative amount of primed C in one species-soil type combination. Possibly, greater microbial N immobilization due to large inputs of rhizodeposits with low N concentration may have reduced plant available N or we may have underestimated plant available N in this treatment because of N loss through root exudation and death. We conclude that soil N availability cannot be determined by soil properties alone, but that is strongly influenced by root-soil interactions.  相似文献   

10.
The immobilization and mineralization of N following plant residue incorporation were studied in a sandy loam soil using15N-labelled field pea (Pisum sativum L.) and spring barley (Hordeum vulgare L.) straw. Both crop residues caused a net immobilization of soil-derived inorganic N during the complete incubation period of 84 days. The maximum rate of N immobilization was found to 12 and 18 mg soil-derived N g?1 added C after incorporation of pea and barley residues, respectively. After 7 days of incubation, 21% of the pea and 17% of the barley residue N were assimilated by the soil microbial biomass. A comparison of the15N enrichments of the soil organic N and the newly formed biomass N pools indicated that either residue N may have been assimilated directly by the microbial biomass without entering the soil inorganic N pool or the biomass had a higher preference for mineralized ammonium than for soil-derived nitrate already present in the soil. In the barley residue treatment, the microbial biomass N was apparently stabilized to a higher degree than the biomass N in the pea residue treatment, which declined during the incubation period. This was probably due to N-deficiency delaying the decomposition of the barley residue. The net mineralization of residue-derived N was 2% in the barley and 22% in the pea residue treatment after 84 days of incubation. The results demonstrated that even if crop residues have a relative low C/N ratio (15), transient immobilization of soil N in the microbial biomass may contribute to improved conservation of soil N sources.  相似文献   

11.
Legume-based pastures generally rely on soil biological activity to provide nitrogen (N) for plants. This study examined seasonal pasture growth in nine adjacent hill pastures, under sheep or beef, with different long-term managements, including certified organic, no fertilizer, and conventional fertilizer application, that formed a soil-fertility sequence. We determined relationships between net N mineralization, as a measure of soil biological activity and N availability, and microbial biomass, soil organic matter, and fauna. Net N mineralization generally explained differences in pasture production (r = 0.87). On an areal basis, net N mineralization was strongly related (r = 0.93) to total soil N (0–200 mm depth) and negatively related (r = −0.92) to soil C:N ratio, but not to soil C. Total N and C:N ratios were related to soil phosphorus (P) status and probably past N fixation by legumes. Where labile P was low, the N:P ratios of both soil microbes and enchytraeids were wide, and the organisms appeared to be P limited, possibly competing with plants for P. Faunal grazing on soil micro-organisms appeared to release P. We could find no convincing evidence that net N mineralization, pasture growth or soil biological diversity increased under organic farming. Rather, the data from organic pastures followed similar trend lines to data from pastures under conventional management.  相似文献   

12.
This study assessed the respective roles of biochemical quality and N content of plant residues on C and N dynamics in a soil. Both 15N- and 13C-labeled oilseed rape residues (roots, seedpod walls) combining different biochemical characteristics and similar N content or the same biochemical characteristics and different N contents were used as amendments. These treatments were combined with two levels of soil inorganic N to ensure that decomposition was not limited by N availability. The soil was incubated under laboratory conditions for 134 days. Soil amended with residues of similar biochemical quality (i.e. the two pod walls) displayed similar C mineralization dynamics when the initial N availability (residue+soil N) ranged from 1.7 to 3.2% of residue dry matter. The roots showed poorer decomposition than the pod walls, lower cumulative C mineralization and greater accumulation of root-derived C in the >50 μm coarse fraction of the soil organic matter. The N content of the residues influenced mineral N accumulation in the soil with a lower net immobilization of residues with low C-to-N ratios. Adding an exogenous source of inorganic N had no effect on C dynamics but modified the remineralization kinetics of the previously immobilized N, suggesting changes in the microbial community involved.  相似文献   

13.
The objectives of our study were to quantify the impact of endogeic earthworms Aporrectodea caliginosa (Savigny) on iron (Fe), manganese (Mn) and zinc (Zn) mobility and availability in soil. Dried rye straw (Cecale cereale L.), clover aboveground parts (Trifolium pratense L.) or calcium carbonate were added to determine the effects on soil micronutrient mobility. To test the importance of soil–water saturation mediated by earthworms, soil samples were modified to 60% (control) and 100% (as in casts) water holding capacity (WHC). To assess availability of micronutrients, a cucumber plant (Cucumis sativus L.) bioassay were used. Earthworm casts had generally higher amounts of water-soluble micronutrients compared with bulk soils regardless of their moisture contents. The increased micronutrient mobility was more pronounced in casts from soil samples amended with plant residues (especially with straw) and was significantly higher than mobility in control soil for at least 1 week after the casts were deposited. Pre-incubation of soils amended with clover or straw with living earthworms for 4 weeks produced an increase in both shoot biomass and translocation rate of micronutrients (Mn, Zn) into xylem sap of cucumber compared to soils not worked by earthworms. The earthworm-mediated plant performances were determined 4 weeks after the earthworms were removed. The results demonstrated that earthworms can significantly impact the formation of mobile and available micronutrients in a soil. The relationship between micronutrient availability to cucumber plants and earthworm contribution to nitrogen (N) mineralization and micronutrient mobility are discussed.  相似文献   

14.
We examined the hypothesis that changes in the quality and/or quantity of soil particulate organic matter (POM) after afforestation of pasture land with Eucalyptus globulus Labill. plantations caused increased nitrogen (N) immobilization and a decline in N availability. The quantity of POM was measured on soils from 10 paired pasture/plantation sites in south-western Australia. Net mineralization of C and N were measured over a 14-day incubation of POM, whole soil, and a mix of POM (33%) and whole soil (67%) at 25 °C and optimal moisture content (matric potential of 25 kPa). There was no significant difference in total organic C between pasture and plantation. However, the POM fraction C was higher in plantation soils (75%) than under pasture (62%), reflecting the coarser nature of organic inputs under plantation. Total soil N concentration was 20% lower under plantation compared to pasture, and the proportion in the POM was higher (74% compared to 57% for pasture soil). The C:N ratios in POM under both pasture and plantation, and in the whole soil under plantation were around 19, but C:N ratios of whole soil under pasture was 17. Average C mineralization was 13% lower in plantation relative to that in pasture soil. The isolated POM fraction had 18% higher C mineralization rate than that in whole soil. The change in net N mineralization with afforestation was marked, with 50% lower net N mineralization in plantation than pasture whole soils. Net N mineralization in the isolated POM fraction was also about 50% of that in the whole soil for both pasture and plantation soils. Although, the pasture and plantation POM had similar C:N ratios, the net N mineralization was 2-fold greater in pasture POM than in plantation POM, suggesting that biochemical characteristics other than the C:N ratio had the main influence on net N mineralization rates. The POM fraction did not significantly immobilize N from the whole soil when placed in a mixture of POM and whole soil, suggesting that N immobilization was not the main mechanism for POM to influence N availability in these soils.  相似文献   

15.
N mineralization capacity and its main controlling factors were studied in a large variety (n=112) of native (forest, bush) and agricultural (pasture, cultivated) soils from several climatic zones in Spain. The available inorganic N content, net N mineralization, and net N mineralization rate were determined after 6 weeks of aerobic incubation. NH inf4 sup+ –N largely predominated over NO inf3 sup- -N (ratio near 10:1) except in some agricultural soils. Net N mineralization predominated (83% of soils) over net N immobilization, which was more frequent in agricultural soils (25%) than in native soils (9%). In forest soils, both net N mineralization and the net N mineralization rate were significantly higher than in the other soil groups. The net N mineralization rate of pasture and cultivated soils was similar to that of bush soils, but available inorganic N was lower. The net N mineralization rate decreased in the order: soils over acid rocks>soils over sediments>soils over basic rocks or limestone; moreover, the highest net N mineralization and available inorganic N were found in soils over acid rocks. The highest N mineralization was found in soils with low C and N contents, particularly in the native soils, in which N mineralization increased as the C:N ratio increased. N mineralization was higher in soils with a low pH and base saturation than in soils with high pH and base saturation values, which sometimes favoured N immobilization. Soils with an Al gel content of >1% showed lower net N mineralization rates than soils with Al gel contents of <1%, although net N mineralization and available inorganic N did not differ between these groups. The net N mineralization rate in silty soils was significantly lower than in sandy and clayey soils, although soil texture only explained a low proportion of the differences in N mineralization between soils.  相似文献   

16.
Understanding the chronological changes in soil microbial properties of turfgrass ecosystems is important from both the ecological and management perspectives. We examined soil microbial biomass, activity and N transformations in a chronosequence of turfgrass systems (i.e. 1, 6, 23 and 95 yr golf courses) and assessed soil microbial properties in turfgrass systems against those in adjacent native pines. We observed age-associated changes in soil microbial biomass, CO2 respiration, net and gross N mineralization, and nitrification potential. Changes were more evident in soil samples collected from 0 to 5 cm than the 5 to 15 cm soil depth. While microbial biomass, activity and N transformations per unit soil weight were similar between the youngest turfgrass system and the adjacent native pines, microbial biomass C and N were approximately six times greater in the oldest turfgrass system compared to the adjacent native pines. Potential C and N mineralization also increased with turfgrass age and were three to four times greater in the oldest vs. the youngest turfgrass system. However, microbial biomass and potential mineralization per unit soil C or N decreased with turfgrass age. These reductions were accompanied by increases in microbial C and N use efficiency, as indicated by the significant reduction in microbial C quotient (qCO2) and N quotient (qN) in older turfgrass systems. Independent of turfgrass age, microbial biomass N turnover was rapid, averaging approximately 3 weeks. Similarly, net N mineralization was ∼12% of gross mineralization regardless of turfgrass age. Our results indicate that soil microbial properties are not negatively affected by long-term management practices in turfgrass systems. A tight coupling between N mineralization and immobilization could be sustained in mature turfgrass systems due to its increased microbial C and N use efficiency.  相似文献   

17.
Laboratory incubation experiments were conducted to study the C and N mineralization dynamics of crop residues (fine roots and straw) of the two main crops (winter wheat and peanut) in the Chinese Loess Plateau under different ways of incorporation. The C mineralization patterns of the soil amended with winter wheat residues differed greatly, and the highest C mineralization was observed in the treatment with winter wheat straw incorporated (39% of the total added C mineralized). The way of straw placement had only a minor effect on the pattern of C mineralization for peanut. Generally, winter wheat residues showed a stronger immobilization than peanut residues during the incubation period, without any net N release. Winter wheat straw incorporated showed the strongest N immobilization with 35 mg kg−1 (equivalent to 27% of added N) immobilized at the eighth week. This study indicated that retaining crop residues at the soil surface in the dry land soils of the Chinese Loess Plateau is beneficial for C sequestration. It also showed that N immobilization occurs only during a limited period of time, sufficient to prevent part of the mineral N pool from leaching, and that net N mineralization can be expected during the subsequent cropping season, thus enhancing synchronization of N supply and demand.  相似文献   

18.
The interactive impacts of arbuscular mycorrhizal fungi (AMF, Glomus intraradices) and earthworms (Aporrectodea trapezoides) on maize (Zea mays L.) growth and nutrient uptake were studied under near natural conditions with pots buried in the soil of a maize field. Treatments included maize plants inoculated vs. not inoculated with AMF, treated or not treated with earthworms, at low (25 mg kg−1) or high (175 mg kg−1) P fertilization rate. Wheat straw was added as feed for earthworms. Root colonization, mycorrhiza structure, plant biomass and N and P contents of shoots and roots, soil available P and NO3−–N concentrations, and soil microbial biomass C and N were measured at harvest. Results indicated that mycorrhizal colonization increased markedly in maize inoculated with AMF especially at low P rate, which was further enhanced by the addition of earthworms. AMF and earthworms interactively increased maize shoot and root biomass as well as N and P uptake but decreased soil NO3−–N and available P concentrations at harvest. Earthworm and AMF interaction also increased soil microbial biomass C, which probably improved root N and P contents and indirectly increased the shoot N and P uptake. At low P rate, soil N mobilization by earthworms might have reduced potential N competition by arbuscular mycorrhizal hyphae, resulting in greater plant shoot and root biomass. Earthworms and AMF interactively enhanced soil N and P availability, leading to greater nutrient uptake and plant growth.  相似文献   

19.
Abstract

We compared estimates of soil nitrogen (N) mineralization rates using the buried bag and PVC core methods in an ongoing investigation of the effects of earthworms and N fertilizer sources on agroecosystem N dynamics. Over a seven‐month period, we paired monthly buried bag and PVC core soil incubations within research plots receiving one of three N treatments (inorganic, legume, or manure fertilizers) and with manipulated earthworm populations (reduced, ambient, or increased numbers). Soil moisture within both the buried bags and the PVC cores fluctuated in response to changes in the surrounding soil, violating assumptions of the buried bag method that soil moisture remains constant during incubation. For both methods, overall CV's for net ammonification, nitrification, and N mineralization rates were very high (104 ‐ 628%). Overall, results for the two methods were significantly correlated for net ammonification (r = 0.89), net nitrification (r = 0.58), and net N mineralization (r = 0.24). In general, the two methods yielded similar seasonal estimates of net N mineralization and nitrification. However, on one occasion in the plots with the inorganic N treatment, buried bag estimates of net N mineralization were significantly higher than the PVC core estimates (1.5 versus ‐0.4 mg N‐kg‐1 soil‐d1, respectively). Under some conditions, the two methods may lead to quite different interpretations of soil N mineralization processes.  相似文献   

20.
To evaluate the effect of climate change on ecosystem functioning, the temperature and moisture response of microbial C, N, and P transformations during decomposition of Calluna vulgaris (L.) Hull. litter was studied in a laboratory incubation experiment. The litter originated from a dry heathland in the Netherlands where P limited vegetation growth. Fresh litter was incubated at 5, 10, 15, or 20°C and at a moisture content of 50, 100, or 200% in a full factorial design. Microbial nutrient transformations and activity were evaluated during two successive periods: an initial period of 48 days characterized by microbial growth and a second period from 48 to 206 days in which microbial growth declined significantly. Temperature and moisture response of respiration rate, the metabolic quotient (qCO2), C, N, and P immobilization, net N and P mineralization and nitrification rates were evaluated by performing linear regressions. Microbial nutrient transformations and microbial activity depended both on temperature and moisture. In the first period, the respiration rate, qCO2, microbial C and N immobilization, net P mineralization, net N mineralization and net nitrification rates were more strongly affected by temperature, while the microbial P immobilization rate was more strongly affected by moisture. The respiration rate, qCO2, P immobilization rate, net P and N mineralization rate, and nitrification rate increased with temperature and moisture, while the C and N immobilization rate decreased with increasing temperature and increased with moisture. In the second period, C, N, and P immobilization and net N and P mineralization rates were significantly lower. The respiration rate and qCO2 continued to increase with temperature and moisture, but C and N immobilization rates increased with temperature and declined with increasing moisture. Net P mineralization rate decreased at higher temperature and moisture, and nitrification rate declined with increasing temperature and increased with moisture. It was concluded that plant growth in these P-limited systems is very sensitive to climate change as it strongly relies on the competition for P with microbes, and temperature and moisture have a large effect on the immobilization rate of available P.  相似文献   

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