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1.
A laboratory experiment was performed to assess the impact of ecologically different earthworm species on soil water characteristics, such as soil tension, water content, and water infiltration rate. Three earthworm species (Lumbricus rubellus, Aporrectodea caliginosa, Lumbricus terrestris) were exposed in soil columns (diameter 30 cm, height 50 cm) for 100 days with a total fresh earthworm biomass of 22.7 ± 0.4 g per column, each in duplicate. Each column was equipped with tensiometers at 10 and 40 cm and FD-probes at 10 cm depth, to continuously measure the temporal development of soil tension and soil moisture. Additionally, 30 g of sieved and rewetted horse manure was placed on the soil surface as a food source. Precipitation events (10 mm) were simulated at day 28 and day 64. At the end of the experiment the water infiltration rate and the runoff at 55 cm depth were determined.The results showed considerable evidence, that ecologically different earthworms modify soil water characteristics in different ways. The anecic L. terrestris and the endogeic A. caliginosa showed the tendency to enhance the drying of the topsoil and subsoil. Their intensive and deep burrowing activity might enhance the exchange of water vapor due to a better aeration in soil. In contrast, the epigeic L. rubellus tended to enhance the storage of soil moisture in the topsoil, which might be linked to lower rates of litter loss from soil surface and thus a thicker litter layer remaining. A. caliginosa led to considerable higher water infiltration rates and faster water discharges in the subsoil, relative to the other species, probably due to a high soil dwelling activity.  相似文献   

2.
《Applied soil ecology》2011,48(3):210-216
Labile soil organic matter (SOM) can sensitively respond to changes in land use and management practices, and has been suggested as an early and sensitive indicator of SOM. However, knowledge of effects of forest vegetation type on labile SOM is still scarce, particularly in subtropical regions. Soil microbial biomass C and N, water-soluble soil organic C and N, and light SOM fraction in four subtropical forests were studied in subtropical China. Forest vegetation type significantly affected labile SOM. Secondary broadleaved forest (SBF) had the highest soil microbial biomass, basal respiration and water-soluble SOM, and the pure Cunninghamia lanceolata plantation (PC) the lowest. Soil microbial biomass C and N and respiration were on average 100%, 104% and 75%, respectively higher in the SBF than in the PC. The influence of vegetation on water-soluble SOM was generally larger in the 0–10 cm soil layer than in the 10–20 cm. Cold- and hot-water-soluble organic C and N were on average 33–70% higher in the SBF than in the PC. Cold- and hot-soluble soil organic C concentrations in the coniferous-broadleaved mixed plantations were on average 38.1 and 25.0% higher than in the pure coniferous plantation, and cold- and hot-soluble soil total N were 51.4 and 14.1% higher, respectively. Therefore, introducing native broadleaved trees into pure coniferous plantations increased water-soluble SOM. The light SOM fraction (free and occluded) in the 0–10 cm soil layer, which ranged from 11.7 to 29.2 g kg−1 dry weight of soil, was strongly affected by vegetation. The light fraction soil organic C, expressed as percent of total soil organic C, ranged from 18.3% in the mixed plantations of C. lanceolata and Kalopanax septemlobus to 26.3% in the SBF. In addition, there were strong correlations among soil organic C and labile fractions, suggesting that they were in close association and partly represented similar C pools in soils. Our results indicated that hot-water-soluble method could be a suitable measure for labile SOM in subtropical forest soils.  相似文献   

3.
《Pedobiologia》2014,57(4-6):263-269
Nitrogen (N) availability is an important factor that determines ecosystem productivity and respiration, especially in N-limited alpine ecosystems. However, the magnitude of this response depends on the timing and amounts of N input. Moreover, we have only a limited understanding of the potential effects of the timing of N fertilization on ecosystem carbon (C) and N processes, and activities of the soil microbes. A nitrogen fertilization experiment was conducted in an alpine meadow on the Tibetan Plateau to determine how plant productivity and ecosystem respiration (RE) respond to the timing and amount of N application. In this study, half of the N was added either in the early spring (ES), before the growing season, or in the late fall (LF), after the growing season. All treatments received the other half of the N in mid-July. Three N levels (10, 20, 40 kg N hm−2 yr−1) were used for each of two N treatments, with no N addition used as a control. Plant aboveground biomass, ecosystem respiration (RE) and soil respiration (RS) were measured for the 2011 and 2012 growing seasons. The LF treatment enhanced ecosystem CO2 efflux compared with the ES treatment at high N addition levels, resulting from an increase of soil dissolved organic C (DOC) and soil microbial activity. The ES treatment resulted in increased plant aboveground biomass when compared with LF during both growing seasons, although this increase accounted for little variation in ecosystem and soil respiration. Overall, the ES treatment is likely to increase the ecosystem C pool, while the LF treatment could accelerate ecosystem C cycling, especially for the high N treatment. Our results suggest that supplying N during the early stage of the growing season benefits both forage production and soil C sequestration in this alpine ecosystem.  相似文献   

4.
Soil organic matter (SOM) status was evaluated using the relationships between two independent soil variables, i.e., C respiration and the weight of particulate organic matter POM (4000–50 μm) under different vegetation covers and ecosystems of central Belgium. A positive relationship was found between the weight of the finest POM fraction, i.e., fine POM fraction (250–50 μm) and C respiration after 1 week (R2 = 0.34, n = 120, p < 0.0001) and 2 weeks (R2 = 0.28, n = 120, p < 0.0001) of incubation. Therefore, we assumed that the C respiration and the weight of fine POM might be used to evaluate the SOM status under different vegetation covers and ecosystems.  相似文献   

5.
Earlier research with endogeic and epigeic earthworm species in loamy arable soil has shown that both earthworm groups can increase nitrous oxide (N2O) emissions, provided that crop residue placement matches the feeding strategy of the earthworm ecological group(s). However, it is not yet clear whether these effects also occur in sandy soils which typically contain less soil organic matter and have low soil aggregation levels. Here, we aimed to quantify N2O emissions as affected by endogeic and/or epigeic earthworm species, and to relate changes in N2O emissions to earthworm-induced changes in soil properties in a sandy soil. A 90 day mesocosm study was conducted with sandy soil and 15N-labeled radish (Raphanus sativus cv. Adagio L.) residue applied on top. Treatments included: (i) no earthworm addition, (ii) addition of the endogeic species Aporrectodea caliginosa (Savigny), (iii) addition of the epigeic species Lumbricus rubellus (Hoffmeister), and (iv) both species combined. An additional treatment was included without earthworms and with residue manually incorporated into the soil. L. rubellus significantly increased cumulative N2O emissions from 228 to 859 μg N2O–N kg?1 (F1,12 = 83.12, P < 0.001), whereas A. caliginosa did not affect N2O emissions. In contrast to earlier studies in loamy soil, no positive interaction between both species with regard to N2O emissions was found. This was probably related to high competition for organic resources in the relatively poor soil and a low potential for stable soil aggregate formation (and associated anaerobic microsites) by endogeic worms in sandy soil. 15N isotope analysis revealed that the activity of L. rubellus significantly increased (F1,12 = 6.20, P = 0.028) the recovery of 15N in the 250–8000 μm size fraction, indicating incorporation of crop residues into the mineral soil. When residues were manually incorporated, N2O emissions were significantly (P < 0.008) lower (509 μg N2O–N kg?1) than when incorporated by L. rubellus. The high N2O emissions in the presence of L. rubellus, when compared to manual mixing, suggest a stimulation of microbial activity and/or changes in the microbial community composition. Insights on the earthworm effects on N2O emission from such soils are discussed.  相似文献   

6.
《Soil biology & biochemistry》2001,33(12-13):1641-1652
We tested whether inputs from canopy herbivores would affect soil processes such as respiration, nutrient cycling, and decomposition along an elevation gradient. The five treatments we used were frass additions, throughfall additions, removal of all litter that fell during the study, removal of greenfall that fell during the study, and controls. Soil respiration was significantly reduced on low and mid elevation sites in litter exclusion, greenfall exclusion and throughfall addition treatments (from 0.846 g CO2/m2/h for controls to 0.618, 0.667, and 0.708 g CO2/m2/h, respectively, for the three treatments). Throughfall additions containing PO4 and NH4 contributed to significant increases in PO4 (as much as 0.737 mg/l in 100 ml KCl extract greater then controls), but decreases in NO3, (0.306  mg/l in 100 ml KCl extract less than con trols), in soil solution samples compared to controls. We observed no significant treatment effects on litter decomposition. Precipitation and temperature influenced soil respiration, but both factors showed a significant interaction with elevation. Phosphate concentrations in soil solutions differed significantly with elevation (low elevation mean 0.097 mg/l, mid elevation mean 0.192 mg/l). Elevation had no significant effect on decomposition.  相似文献   

7.
We studied a semi-natural forest in Northern Italy that was set aside more than 50 years ago, in order to better understand the soil carbon cycle and in particular the partitioning of soil respiration between autotrophic and heterotrophic respiration. Here we report on soil organic carbon, root density, and estimates of annual fluxes of soil CO2 as measured with a mobile chamber system at 16 permanent collars about monthly during the course of a year. We partitioned between autotrophic and heterotrophic respiration by the indirect regression method, which enabled us to obtain the seasonal pattern of single components.The soil pool of organic carbon, with 15.8 (±4.5) kg m?2, was very high over the entire depth of 45 cm. The annual respiration rates ranged from 0.6 to 6.9 μmol CO2 m?2 s?1 with an average value of 3.4 (±2.3) μmol CO2 m?2 s?1, and a cumulative flux of 1.1 kg C m?2 yr?1. The heterotrophic component accounted for 66% of annual CO2 efflux. Soil temperature largely controlled the heterotrophic respiration (R2 = 0.93), while the autotrophic component followed irradiation, pointing to the role of photosynthesis in modulating the annual course of soil respiration.Most studies on soil respiration partitioning indicate autotrophic root respiration as a first control of the spatial variability of the overall respiration, which originates mainly from the uppermost soil layers. Instead, in our forest the spatial variability of soil respiration was mainly linked to soil carbon, and deeper layers seemed to provide a significant contribution to soil respiration, a feature that may be typical for an undisturbed, naturally maturing ecosystem with well developed pedobiological processes and high carbon stocks.  相似文献   

8.
Net ecosystem exchange of carbon (FNEE) was estimated for a temperate broadleaf, evergreen eucalypt forest ecosystem at Tumbarumba in south-eastern Australia to investigate the processes controlling forest carbon sinks and their response to climate. Measurements at a range of temporal and spatial scales were used to make three different estimates of FNEE based on: (1) the difference between fluxes of carbon input by photosynthesis and output by autotrophic plus heterotrophic respiration, (2) changes over time in the carbon pools in the above- and below-ground biomass, soil and litter, and (3) micrometeorological flux measurements that provide a continuous estimate of the net exchange. A rigorous comparison of aggregated component fluxes and the net eddy fluxes within a flux tower source area was achieved based on an inventory of the site and a detailed sampling strategy. Measurements replicated in space and time provided mean values, confidence limits and patterns of variation of carbon pools and fluxes that allowed comparisons within known limits of uncertainty. As a result of comparisons between nighttime eddy flux and chamber measurements of respiration, a revised micrometeorological method was developed for estimating nighttime carbon flux using flux tower measurements. Uncertainty in the final estimate of FNEE was reduced through mutual constraints of each of these measurement approaches. FNEE for the period October 2001–September 2002, with average rainfall, was an uptake of 6.7 (5.1–8.3) tC ha?1 yr?1 estimated from component fluxes, and 5.4 (3.0–7.5) tC ha?1 yr?1 estimated from the revised eddy flux method. Biomass increment was 4.5 (3.7–5.4) tC ha?1 yr?1 and the remaining 0.9–2.2 tC ha?1 yr?1 could represent a carbon sink in the soil and litter pools or lie within the confidence limits of the measured fluxes. FNEE was reduced to ?0.1 to 2.4 tC ha?1 yr?1 during a period of drought and insect disturbance in October 2002–September 2003, with biomass increment being the main component reduced. The forest is a large carbon sink compared with other forest ecosystems, but this is subject to high-annual variability in response to climate variability and disturbance.  相似文献   

9.
《Soil biology & biochemistry》2001,33(4-5):503-509
The distribution of vegetation types in Venezuelan Guyana (in the ‘Canaima’ National Park) represents a transitional stage in a long term process of savannization, a process considered to be conditioned by a combined chemical and intermittent drought stress. All types of woody vegetation in this environment accumulate large amounts of litter and soil organic carbon (SOC). We hypothesized that this accumulation is caused by low microbial activity. During 1 year we measured microbial biomass carbon (Cmic), microbial respiration and soil respiration of stony Oxisols (Acrohumox) at a tall, a medium and a low forest and with three chemical modifications of site conditions by the addition of NO3−, Ca2+ and PO43− as possible limiting elements. Due to high SOC contents, mean Cmic was 1 mg g soil−1 in the mineral topsoil and 3 mg g soil−1 in the forest floor. Mean microbial respiration in the mineral topsoil and the forest floor were 165 and 192 μg CO2-C g soil−1 d−1, respectively. We calculated high mean metabolic quotients (qCO2) of 200 mg CO2-C g Cmic−1 d−1 in the litter layer and 166 mg CO2-C g Cmic−1 d−1 in the mineral topsoil, while the Cmic-to-SOC ratios were as low as 1.0% in the litter layer and 0.8% in the mineral topsoil. Annual soil respiration was 9, 12 and 10 Mg CO2-C ha−1 yr−1 in the tall, medium and low forest, respectively. CO2 production was significantly increased by CaHPO4 fertilization, but no consistent effects were caused by Ca2+ and NO3−, fertilization. Our findings indicate that Cmic and microbial respiration are reduced by low nutrient concentrations and low litter and SOC quality. Reduced microbial decomposition may have contributed to SOC accumulation in these forests.  相似文献   

10.
This study investigates how carbon sources of soil microbial communities vary with soil depth. Microbial phospholipid fatty acids (PLFA) were extracted from 0–20, 20–40 and 40–60 cm depth intervals from agricultural soils and analysed for their stable carbon isotopes (δ13C values). The soils had been subjected to a vegetation change from C3 (δ13C≈?29.3‰) to C4 plants (δ13C≈?12.5‰) 40 years previously, which allowed us to trace the carbon flow from plant-derived input (litter, roots, and root exudates) into microbial PLFA. While bulk soil organic matter (SOM) reflected ≈12% of the C4-derived carbon in top soil (0–20 cm) and 3% in deeper soil (40–60 cm), the PLFA had a much higher contribution of C4 carbon of about 64% in 0–20 cm and 34% in 40–60 cm. This implies a much faster turnover time of carbon in the microbial biomass compared to bulk SOM. The isotopic signature of bulk SOM and PLFA from C4 cultivated soil decreases with increasing soil depth (?23.7‰ to ?25.0‰ for bulk SOM and ?18.3‰ to ?23.3‰ for PLFA), which demonstrates decreasing influence of the isotopic signature of the new C4 vegetation with soil depth. In terms of soil microbial carbon sources this clearly shows a high percentage of C4 labelled and thus young plant carbon as microbial carbon source in topsoils. With increasing soil depth this percentage decreases and SOM is increasingly used as microbial carbon source. Among all PLFA that were associated to different microbial groups it could be observed that (a) depended on availability, Gram-negative and Gram-positive bacteria prefer plant-derived carbon as carbon source, however, (b) Gram-positive bacteria use more SOM-derived carbon sources while Gram-negative bacteria use more plant biomass. This tendency was observed in all three-depth intervals. However, our results also show that microorganisms maintain their preferred carbon sources independent on soil depth with an isotopic shift of 3–4‰ from 0–20 to 40–60 cm soil depth.  相似文献   

11.
Earthworms are important engineering species of many terrestrial ecosystems as they play a significant role in regulating C turnover. The effects of earthworms on moderating C decomposition processes differ across species and with interactions between species, which is not fully understood. We carried out an experiment to study the interactions of Lumbricus rubellus and Octolasion lacteum, and their effects on soil respiration. Laboratory mesocosms were set up using tulip poplar (Liriodendron tulipifera) leaf litter and varying densities of earthworms in single and combined species treatments. CO2 efflux rate was used as an indicator of C decomposition rates, and measured with CO2 sensors every five days over one month. L. rubellus induced higher leaf consumption rate and higher CO2 efflux than O. lacteum; meanwhile O. lacteum grew more than L. rubellus. Both litter consumption rate and growth rate of earthworms decreased with increasing earthworm density. Soil CO2 efflux increased with increasing earthworm density (from ∼1-2 μg CO2 g−1 hr−1 with no earthworms to ∼ 4 μg CO2 g−1 hr−1 with 8 earthworms). Combining the two species had a synergistic effect on leaf litter consumption, and neutralizing effects on soil respiration. The data suggest that the strength of intra- and inter-specific interactions among earthworm ecological groups varies at different absolute and relative densities, leading to altered leaf litter decomposition and C cycling.  相似文献   

12.
Little is know on the impact of biosolids application on soil organic matter (SOM) stability, which contributes to soil C sequestration. Soil samples were collected in 2006 at plow layer from fields that received liquid and dry municipal biosolids application from 1972 to 2004 at the cumulative rate of 1416 Mg ha−1 in mined soil and 1072 Mg ha−1 in nonmined soil and control fields that received chemical fertilizer at Fulton County, western Illinois. The biosolids application increased the soil microbial biomass C (SMBC) by 5-fold in mined soil and 4-fold in nonmined soil. The biosolids-amended soils showed a high amount of basal respiration and N mineralization, but low metabolic quotient, and low rate of organic C and organic N mineralization. There was a remarkable increase in mineral-associated organic C from 6.9 g kg−1 (fertilizer control) to 26.6 g kg−1 (biosolids-amended) in mined soil and from 8.9 g kg−1 (fertilizer control) to 23.1 g kg−1 (biosolids-amended) in nonmined soil. The amorphous Fe and Al, which can improve SOM stability, were increased by 2–7 folds by the long-term biosolids application. It is evident from this study that the biosolids-modified SOM resists to decomposition more than that in the fertilizer treatment, thus long-term biosolids application could increase SOM stability.  相似文献   

13.
The species Chromolaena odorata (Asteraceae) is a notorious invasive shrub spreading throughout West and Central Africa and as such, there is a need to determine its environmental impact, particularly on soil biodiversity and functioning. Indeed, soil organisms such as earthworms are known to strongly influence soil properties and biogeochemical cycles. This study, conducted in Central Côte d’Ivoire, aims to investigate the temporal dynamics of earthworm communities in C. odorata fallows of different ages and to identify associated indicators and persistent species. Three distinct classes of fallows identified by local farmers, were considered: young (1–3 years, C1), medium-aged (4–8 years, C2) and old (>9 years, C3). Each of the classes included four plot replicates where earthworms were sampled using the Tropical Soil Biology and Fertility (TSBF) 25 cm × 25 cm × 30 cm soil monolith method. The study of earthworm communities was focused on density, biomass, diversity and complementarity. Indicator values (IndVals) were used to identify indicator species of the classes of fallows. The shrub exerted a mixed influence on earthworms depending on the functional group, with litter feeders and polyhumics declining over time as a result of a reduction of the litter availability on the soil surface. The species richness was significantly greater in C1 than in the other classes although the Shannon–Weaver's index did not vary significantly. However, a cluster analysis performed on densities highlighted marked differences between C2 and the two other classes in terms of community composition. Indicator species were found for C1 and C2. The geophagous Millsonia omodeoi has emerged as a persistent species as its density and biomass steadily increased so that it became the dominant species in old fallows. The roles of litters and soil parameters in influencing earthworm communities are discussed.  相似文献   

14.
We used natural gradients in soil and vegetation δ13C signatures in a savannah ecosystem in Texas to partition soil respiration into the autotrophic (Ra) and heterotrophic (Rh) components. We measured soil respiration along short transects from under clusters of C3 trees into the C4 dominated grassland. The site chosen for the study was experiencing a prolonged drought, so an irrigation treatment was applied at two positions of each transect. Soil surface CO2 efflux was measured along transects and CO2 collected for analysis of the δ13C signature in order to: (i) determine how soil respiration rates varied along transects and were affected by localised change in soil moisture and (ii) partition the soil surface CO2 efflux into Ra and Rh, which required measurement of the δ13C signature of root- and soil-derived CO2 for use in a mass balance model.The soil at the site was unusually dry, with mean volumetric soil water content of 8.2%. Soil respiration rates were fastest in the centre of the tree cluster (1.5 ± 0.18 μmol m?2 s?1; mean ± SE) and slowest at the cluster–grassland transition (0.6 ± 0.12 μmol m?2 s?1). Irrigation produced a 7–11 fold increase in the soil respiration rate. There were no significant differences (p > 0.5) between the δ13C signature of root biomass and respired CO2, but differences (p < 0.01) were observed between the respired CO2 and soil when sampled at the edge of the clusters and in the grassland. Therefore, end member values were measured by root and soil incubations, with times kept constant at 30 min for roots and 2 h for soils. The δ13C signature of the soil surface CO2 efflux and the two end member values were used to calculate that, in the irrigated soils, Rh comprised 51 ± 13.5% of the soil surface CO2 efflux at the mid canopy position and 57 ± 7.4% at the drip line. In non-irrigated soil it was not possible to partition soil respiration, because the δ13C signature of the soil surface CO2 efflux was enriched compared to both the end member values. This was probably due to a combination of the very dry porous soils at our study site (which may have been particularly susceptible to ingress of atmospheric CO2) and the very slow respiration rates of the non-irrigated soils.  相似文献   

15.
《Applied soil ecology》2007,35(2-3):258-265
We examined the relationship between soil respiration rate and environmental determinants in three types of tropical forest ecosystem—primary forest, secondary forest, and an oil palm plantation in the Pasoh Forest Reserve on the Malaysian Peninsula. In August 2000, the soil respiration rate and environmental factors (soil temperature, soil water content, soil C and N contents, biomass of fine roots, and microbes) were measured at 12–16 points in research quadrats. Soil respiration rates were 831 ± 480, 1104 ± 995, 838 ± 143, 576 ± 374, and 966 ± 578 (mean ± S.D.) mg CO2 m−2 h−1 in the primary forest canopy and gap site, secondary forest canopy and gap site, and oil palm plantation, respectively. Although the mean soil respiration rates in the three forest ecosystems did not differ significantly, differences were evident in the environmental factors affecting the soil respiration. The major causes of spatial variation in soil respiration were fine root biomass, soil water content, and soil C content in the primary and secondary forests and oil palm plantation, respectively.  相似文献   

16.
Earthworms are key regulators of soil structure and soil organic matter (SOM) dynamics in many agroecosystems. They are greatly impacted by agricultural management, yet little is known about how these factors interact to control SOM dynamics. This study sought to explore linkages between agricultural management, earthworms and aggregate associated SOM dynamics through a survey of tomato (Solanum lycopersicum L.) cropping systems in northern California. Earthworms and soil samples were collected between February and April of 2005 from 16 fields under one of three types of residue management: (1) tomato mulch – no postharvest tillage and tomato residues left on the soil surface, (2) cover crop – tomato residues tilled in and leguminous cover crop planted, and (3) bare fallow – tomato residues tilled in and soil surface left exposed throughout the winter. Earthworms were collected via hand-sorting and identified to species, while soils were wet sieved to yield four aggregate size classes: large macroaggregates (>2000 μm), small macroaggregates (250–2000 μm), microaggregates (53–250 μm) and the silt and clay fraction (<53 μm). The combined large and small macroaggregate fraction was then fractionated into coarse particulate organic matter (cPOM; 250 μm), microaggregates within macroaggregates (mM; 53–250 μm) and macroaggregate occluded silt and clay (Msc; <53 μm). The earthworms identified in this survey were composed entirely of exotic species and were dominated by Aporrectodea caliginosa. Earthworm abundance was related to residue management, with the tomato mulch systems averaging 4.5 times greater fresh earthworm biomass than bare fallow (P = 0.024). Aggregate stability and total soil C and N also appeared to be influenced by residue management, such that the tomato mulch system displayed significantly greater mean weight diameters than the bare fallow system (P = 0.049), as well as more than 50% greater total soil C and N (P = 0.049 and P = 0.036; respectively). Earthworm biomass was also found to be positively correlated with total soil C (P = 0.009, R2 = 0.39) and N (P = 0.010, R2 = 0.039) as well as the proportion of macroaggregate C in the cPOM fraction (P = 0.028, R2 = 0.30). Our findings suggest that residue handling and the associated management practices (e.g., tillage, organic vs. conventional agriculture) are important for both earthworm populations and SOM storage. Although earthworms are known to influence SOM in many ways, other factors appear to play a more prominent role in governing aggregate associated SOM dynamics.  相似文献   

17.
We investigated the fate of root and litter derived carbon in soil organic matter and dissolved organic matter in soil profiles, in order to explain mechanisms of short-term soil carbon storage. A time series of soil and soil solution samples was investigated at the field site of The Jena Experiment between 2002 and 2004. In addition to the main experiment with C3 plants, a C4 species (Amaranthus retroflexus L.) naturally labeled with 13C was grown on an extra plot. Changes in organic carbon concentration in soil and soil solution were combined with stable isotope measurements to follow the fate of plant carbon into the soil and soil solution. A split plot design with plant litter removal versus double litter input simulated differences in biomass input. After 2 years, the no litter and double litter treatment, respectively, showed an increase of 381 g C m?2 and 263 g C m?2 to 20 cm depth, while 71 g C m?2 and 393 g C m?2 were lost between 20 and 30 cm depth. The isotopic label in the top 5 cm indicated that 115 g C m?2 and 156 g C m?2 of soil organic carbon were derived from C4 plant material on the no litter and the double litter treatment, respectively. Without litter, this equals the total amount of 97 g C m?2 that was newly stored in the same soil depth, whereas with double litter this clearly exceeded the stored amount of 75 g C m?2. Our results indicate that litter input resulted in lower carbon storage and larger carbon losses and consequently accelerated turnover of soil organic carbon. Isotopic evidence showed that inherited soil organic carbon was replaced by fresh plant carbon near the soil surface. Our results suggest that primarily carbon released from soil organic matter, not newly introduced plant organic matter, was transported in the soil solution. However, the total flow of dissolved organic carbon was not sufficient to explain the observed carbon storage in deeper soil layers, and the existence of additional carbon uptake mechanisms is discussed.  相似文献   

18.
Application of earthworm in soil re-cultivation and re-creation in post-industrial ecosystems make a big challenge for temporal applied zoology. The sediments of the Krakow Soda Works “Solvay” have undergone land reclamation in different ways: older sediments traps were left without any re-cultivation practices; meanwhile the newest ones were reclaimed using standard method (new soil cover planted with combination of grass and leguminous plants). The effect of different treatments on community and population structure of earthworm was estimated during consecutive years 1999–2000. Six localities differing in time of establishment, reclamation processes, vegetation type and soil properties were chosen. Nine species were recorded, among which Aporrectodea caliginosa occurred in all localities, being also the most abundant. Two other species, Lumbricus rubellus and Dendrobaena octaedra, which are epigeic species, become most important in forest assemblages and were characteristic for communities of older succession processes. Abundance of adult forms as well as total biomass were significantly affected by soil depth (r = 0.75, P < 0.05, r = 0.917, P < 0.001, respectively). Species richness however was connected with higher amount of macroelements and average plant height. Shannon diversity index and its evenness negatively correlated only with forestation (r = –0.67, P < 0.05, r = –0.68, P < 0.05, respectively). Niche overlap (α Pianka) for all analysed species extracted two groups differing in environmental requirements. First contained epigeic earthworms, closely related to plant succession (PCA results), the other one grouped endogeic and anecique species correlated significantly with soil depth and plant density. Community structure of earthworms do not reflects succession changes in post-industrial habitats, but is strongly affected by microhabitat factors in local scale (mainly soil depth and plant density).  相似文献   

19.
《Applied soil ecology》2006,31(1-2):32-42
Microcosm and litterbag experiments were conducted to determine the effects of litter quality, soil properties and microclimate differences on soil carbon (C) and nitrogen (N) mineralization in alley cropping systems. Bulk soils were collected from 0 to 20 cm depth at three sites: a 21-year old pecan (Carya illinoinensis)/bluegrass (Poa trivialis) intercrop (Pecan site) in north-central Missouri, a 12-year old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (Maple site) in northeastern Missouri and a restored prairie site (MDC site) in southwestern Missouri. Seven tree and crop litters with varying composition were collected, including pecan, silver maple, chestnut and walnut leaf litter (tree litter) and maize, soybean and bluegrass residues (crop litter). Aerobic microcosm incubations were maintained at 25 °C and a soil water potential of −47 kPa. Unamended MDC soil mineralized 24 and 18% more CO2 than the Pecan and Maple soils, respectively. Soil amended with crop litter mineralized on average 32% more CO2 than when amended with tree litter. Net N mineralization from soybean litter was 40 mg kg−1, while all other litter immobilized N for various durations. A double pool and a single pool model best described C and N mineralization from amended soils, respectively. Cumulative CO2 mineralized, labile C fraction (C1) and potentially mineralizable C (C0) were correlated to litter total N and lignin contents and to (lignin + polyphenol):N ratio. In the field, bluegrass litter decomposed and released N twice as fast as pecan leaf litter. Soybean, maize and silver maple litter released 84, 75 and 63% of initial N, respectively, 308 days after field placement, while no differences in mass loss was observed among the three litter materials. At the Maple site, mass and N remaining, 308 days after field placement was lower at the middle of the alley, corresponding to higher soil temperature and water content. No differences in mass loss and N release patterns were observed at the Pecan site. Microclimate and litter quality effects can lead to differences in nutrient availability in alley cropping systems.  相似文献   

20.
Eddy covariance measurements and estimates of biomass net primary production (NPP) in combination with soil carbon turnover modelled by the Roth-C model were used to assess the ecosystem carbon balance of an agricultural ecosystem in Thuringia, Germany, growing winter wheat in 2001. The eddy CO2 flux measurements indicate an annual net ecosystem exchange (NEE) uptake in the range from −185 to −245 g C m−2 per year. Main data analysis uncertainty in the annual NEE arises from night-time u1 screening, other effects (e.g. coordinate rotation scheme) have only a small influence on the annual NEE estimate. In agricultural ecosystems the fate of the carbon removed during harvest plays a role in the net biome production (NBP) of the ecosystem, where NBP is given by net ecosystem production (NEP=−NEE) minus non-respiratory losses of the ecosystem (e.g. harvest). Taking account of the carbon removed by the wheat harvest (290 g C m−2), the agricultural field becomes a source of carbon with a NBP in the order of −45 to −105 g C m−2 per year. Annual carbon balance modelled with the Roth-C model also indicated that the ecosystem was a source for carbon (NBP −25 to −55 g C m−2 per year). Based on the modelling most of carbon respired resulted from changes in the litter and fast soil organic matter pool. Also, the crop and management history, particularly the C input to soil in the previous year, significantly affect next year’s CO2 exchange.  相似文献   

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