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1.
To date our knowledge is limited with regard to the cycling of ethylene (C2H4) in temperate forest soils containing volcanic ash, and the effect of forest‐to‐orchard conversion on its cycling. We studied ethylene accumulation in such forest soils by oxic and anoxic incubations, along with the stimulatory effect of glucose addition on soil C2H4 accumulation. We also studied the effect of antibiotics and autoclaving on C2H4 production and consumption by volcanic forest soils, and the cycling of C2H4 and CH4 in surface soils after conversion of a Japanese cedar forest to an orchard. Ethylene production and consumption by forest surface soils results from a microbial process, and soil streptomycin‐sensitive bacteria make a minor contribution. Soil C2H4 accumulation was much larger during anoxic than during oxic incubation, which indicates that anoxic conditions can induce C2H4 accumulation in forest soils. Glucose addition as a carbon source can sharply increase C2H4 accumulation rates in the anoxic and oxic forest soils during the first week of incubation. However, there was no difference in total C2H4 accumulation in the amended and non‐treated soils after 35 days of anoxic incubation. Ethylene production of the 0–5 cm and 5–10 cm soils beneath forest and orchard showed the greatest rate after 2 weeks of anoxic incubation when soil CH4 production started to increase sharply, and later it was strongly suppressed. The forest‐to‐orchard conversion showed little influence on the CH4 production of surface soils during short‐term anoxic incubation, but significantly reduced soil C2H4 production. The conversion also significantly decreased the consumption of soil CH4 and C2H4, the former more than the latter. Soil properties such as total C, water‐soluble organic C and pH contribute to the consumption and production of C2H4 in the 0–5 cm and 5–10 cm soils, and there are the parallels between CH4 and C2H4 consumption in soils, which suggests the presence of similar microorganisms. Long‐term anoxic conditions of in situ surface upland soils are normally not prevalent, so it can be reasonably concluded that there is a larger C2H4 accumulation rather than CH4 accumulation in surface soils beneath forest and orchard after heavy rainfall, especially beneath forest.  相似文献   

2.
A 100-day incubation experiment was conducted to (i) trace the fate of rice residue-derived 13C in the amino sugar (AS) pool in 0–1-cm (oxic) and 1–5-cm (anoxic) layers of paddy soil and (ii) evaluate the effects of inorganic N ((NH4)2SO4) fertilization on the formation of AS at early and late incubation times (5 and 100 days, respectively). The accumulation of rice residue-derived AS occurred at 5 and 100 days in both soil layers as a result of AS stabilization. Inorganic N addition increased the contents of rice residue-derived muramic acid, glucosamine, and galactosamine in the 0–1-cm soil layer for both incubation times by average on 14.7–20.8%, 23.7–31.8%, and 11.6–23.3%, respectively. In contrast, no effects of N fertilization on AS content in the 1–5-cm soil layer were found. The amount of rice residue-derived AS was higher in the 1–5-cm than in the 0–1-cm soil layer at early incubation time, probably due to the higher contents of ammonium here compared to the upmost oxic layer where nitrate was the dominated N form. Thus, the preferential uptake of ammonium but not nitrate by microorganisms led to the higher formation of rice residue-derived AS in the anoxic soil layer. The ratio of fungal to bacterial residues (fungal glucosamine/muramic acid) ranged between 1.0 and 1.7 for rice residue-derived AS and was 12.5–14.6 for total AS, indicating that fungi and bacteria have similar contributions to the decomposition of fresh rice residue whereas native soil organic matter (SOM) is a fungi-predominated process. This study emphasized that coupling of C and N cycles in paddy soils is different in oxic and anoxic layers, resulting in variation of plant residue decomposition and formation of SOM.  相似文献   

3.
Biological degradation rates of estrogen compounds and common pharmaceutical and personal care products (PPCPs) were examined in soils with a long history of exposure to these compounds through wastewater effluent and in soil not previously exposed. Biological degradation rates over 14 days were compared under aerobic and anaerobic conditions. Estrogen compounds including estrone, 17??-estradiol, estriol, and 17??-ethinylestradiol exhibited rapid degradation by soil microorganisms in both aerobic and anaerobic conditions. Rapid degradation rates for estrone, estriol, and 17??-ethinylestradiol occurred in pre-exposed soil under aerobic conditions; half-lives calculated under these conditions were 0.6, 0.7, and 0.8 day, respectively. Unexposed soil showed similar or slightly longer half-lives than pre-exposed soil under aerobic conditions. The exception was 17??-estradiol; in all treatments, degradation in unexposed soil resulted in a shorter half-life (2.1 versus 2.3 days). Anaerobic soils exhibited high biological degradation of estrogens as well. Half-lives of all estrogens ranged from 0.7 to 6.3 days in anaerobic soils. Triclosan degraded faster under aerobic conditions with half-lives of 5.9 and 8.9 days in exposed and unexposed soil. Under anaerobic conditions, triclosan half-lives were 15.3 days in unexposed and 28.8 days in exposed soil. Ibuprofen showed the least propensity toward biological degradation than other chemicals tested. Biological degradation of ibuprofen was only observed in unexposed soil; a half-life of 41.2 days was determined under anaerobic conditions and 121.9 days under aerobic conditions. Interestingly, unexposed soil exhibited a greater ability under anaerobic conditions to biologically degrade tested compounds than previously exposed soil.  相似文献   

4.
The microbial activity and bacterial community structure were investigated in two types of peat soil in a temperate marsh. The first, a drained grassland fen soil, has a neutral pH with partially degraded peat in the upper oxic soil horizons (16% soil organic carbon). The second, a bog soil, was sampled in a swampy forest and has a very high soil organic carbon content (45%), a low pH (4.5), and has occasional anoxic conditions in the upper soil horizons due to the high water table level. The microbial activity in the two soils was measured as the basal and substrate-induced respiration (SIR). Unexpectedly, the SIR (μl CO2 g−1 dry soil) was higher in the bog than in the fen soil, but lower when CO2 production was expressed per volume of soil. This may be explained by the notable difference in the bulk densities of the two soils. The bacterial communities were assessed by terminal restriction fragment length polymorphism (T-RFLP) profiling of 16S rRNA genes and indicated differences between the two soils. The differences were determined by the soil characteristics rather than the season in which the soil was sampled. The 16S rRNA gene libraries, constructed from the two soils, revealed high proportions of sequences assigned to the Acidobacteria phylum. Each library contained a distinct set of phylogenetic subgroups of this important group of bacteria.  相似文献   

5.
In forested catchments, retention and remobilization of S in soils and wetlands regulate soil and water acidification. The prediction of long‐term S budgets of forest ecosystems under changing environmental conditions requires a precise quantification of all relevant soil S pools, comprising S species with different remobilization potential. In this study, the S speciation in topsoil horizons of a soil toposequence with different groundwater influence and oxygen availability was assessed by synchrotron‐based X‐ray absorption near‐edge spectroscopy (XANES). Our investigation was conducted on organic (O, H) and mineral topsoil (A, AE) horizons of a Cambisol–Stagnosol–Histosol catena. We studied the influence of topography (i.e., degree of groundwater influence) and oxygen availability on the S speciation. Soil sampling and pretreatment were conducted under anoxic conditions. With increasing groundwater influence and decreasing oxygen availability in the sequence Cambisol–Stagnosol–Histosol, the C : S ratio in the humic topsoil decreased, indicating an enrichment of soil organic matter in S. Moreover, the contribution of reduced S species (inorganic and organic sulfides, thiols) increased systematically at the expense of intermediate S species (sulfoxide, sulfite, sulfone, sulfonate) and oxidized S species (ester sulfate, SO ). These results support the concept of different S‐retention processes for soils with different oxygen availability. Sulfur contents and speciation in two water‐logged Histosols subject to permanently anoxic and temporarily oxic conditions, respectively, were very different. In the anoxic Histosol, reduced S accounted for 57% to 67% of total S; in the temporarily oxic Histosol, reduced S was only 43% to 54% of total S. Again, the extent of S accumulation and the contribution of reduced S forms to total S closely reflected the degree of O2 availability. Our study shows that XANES is a powerful tool to elucidate key patterns of the biogeochemical S cycling in oxic and anoxic soil environments. In contrast to traditional wet‐chemical methods, it particularly allows to distinguish organic S compounds in much more detail. It can be used to elucidate microbial S‐metabolism pathways in soils with different oxygen availability by combining soil inventories and repeated analyses of a sample in different stages of field or laboratory incubation experiments under controlled boundary conditions and also to study (sub)microspatial patterns of S speciation in aggregated soils.  相似文献   

6.
Biological degradation rates of six pharmaceuticals and personal care products were examined in soil from a land application site and in adjacent soil with no prior history of effluent exposure. Microbial degradation rates were compared over 2 weeks under standing water or saturated conditions and draining conditions after having been saturated for 3 days. Biological degradation of 17??-estradiol exhibited rapid rates of biological degradation under both saturated and draining conditions. Half-lives for 17??-estradiol ranged from 1.5 to 4 days; 66?C97% was lost from the soils. Estriol showed a pattern of biological degradation in both saturated and draining conditions though the half-lives were longer (8.7?C25.9 days) than those observed for 17??-estradiol. Twenty-eight percent to 73% of estriol was lost over the 14 days treatment period. Estrone and 17??-ethinylestradiol exhibited slower rates of biological transformation under saturated and draining conditions. Half-lives for estrone ranged between 27.5 and 56.8 days with loss of at most 21%. 17??-ethinylestradiol exhibited half-lives of 22.6?C207 days. Half-life data for ibuprofen ranged from 30.4 to 1,706.4 days in this experiment. Losses of up to 17% were observed in draining soils. Triclosan loss was at most 10%, and half-lives were 70.9?C398.8 days. In all cases, soils that were draining from saturated conditions exhibited faster degradation rates than soils that remained saturated. Prior exposure of the soil to effluent did not always result in higher biological degradation rates.  相似文献   

7.
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8.
Floodplain soils are characterized by frequent and extreme redox changes caused by inundation with river water or imbibition of groundwater. Depending on the duration and extent of inundation, biogeochemical processes run at sub‐/anoxic conditions, which may result in the mobilization and relocation of dissolved and particulate matter within the soil. In this study, we investigated the effect of inundation events on the composition of mobilized matter in the topsoil horizon of a floodplain soil. We conducted experiments with soil columns in the laboratory and gravitational lysimeters in the field to identify redox‐mediated (im)mobilization processes and to estimate their relevance under field conditions. The lysimeters were filled with topsoil monoliths and run under in situ conditions during a ≈ 2.5‐y period. The soil columns were run with the same soil material either under strictly anoxic or mixed oxic–anoxic conditions. Effluents from mixed oxic–anoxic soil were composed fundamentally different [comparably high: Mn, Al, nitrate, sulfate; comparably low: pH, organic C (OC); not detected: Fe, As] compared to effluents from strictly anoxic soil (comparably high: pH, Fe, Mn, OC, As; comparably low: Al; not detected: nitrate, sulfate). Matter, which was mobile under anoxic conditions (e.g., Fe, As, OC), was effectively immobilized as soon as the mobile phase passed anoxic–oxic boundaries within soil (exception: Mn). We assume that the solution in the soil monoliths always passed such anoxic–oxic boundaries during downwards migration independent of lysimeter flooding with river water. This is indicated by the similar composition of the lysimeter seepage water and the effluents from mixed oxic–anoxic soil columns. Both solutions contained “fingerprints” from anoxic (Mn) and oxic conditions (nitrate). Inundations with river water and the duration of these floods (1–22 d) did not affect the composition of the lysimeter seepage water. In conclusion, immediate changes in the composition of the solution, which enters either the subsoil or nearby receiving waters, cannot be expected from regular topsoil flooding.  相似文献   

9.

Purpose

The application of roxarsone (ROX), an arsenic-containing compound, as a feed additive in the animal production industry results in elevated soil levels of ROX and its metabolites, namely, monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenate (As(V)), and arsenite (As(III)). This study was conducted to study the extraction and speciation analysis of ROX-related arsenicals in soils with different physicochemical properties and the possible effects of soil properties on the extraction of ROX and its metabolites.

Materials and methods

Analytical method based on high-performance liquid chromatography (HPLC)-inductively coupled plasma–mass spectrometry (ICP-MS) was employed to determine the concentrations of As(III), DMA, MMA, As(V), and ROX extracted by different extraction solvents from different soils spiked by arsenicals. Validity of the developed method was assessed by the recovery efficiencies of arsenic species in soil-dissolved matter solutions containing 20 μg As?·?L?1 of each arsenic species. Effects of soil properties on the extraction of ROX and its metabolites were analyzed by Pearson’s correlation.

Results and discussion

Arsenic species were separated using gradient elution of water and 20 mmol?·?L?1 (NH4)2HPO4 + 20 mmol?·?L?1 NH4NO3 + 5 % methanol (v/v) within 27 min. The linear ranges of all arsenicals were 0–200 μg As?·?L?1 with R 2?>?0.9996. The developed method provided lower limits of detection for As(III), DMA, MMA, As(V), and ROX (0.80, 0.58, 0.35, 0.24, and 1.52 μg As?·?L?1, respectively) and excellent recoveries (92.52–102.2 %) for all five species. Arsenic speciation was not altered by 0.1 mol?·?L?1 NaH2PO4 + 0.1 mol?·?L?1 H3PO4 (9:1, v/v), which offered better average extraction efficiencies for As(III), As(V), DMA, MMA, and ROX (32.49, 92.50, 78.24, 77.64, and 84.54 %, respectively). Extraction performance of arsenicals was influenced by soil properties, including pH, cation exchange capacity (CEC), total Fe, and amorphous Fe.

Conclusions

ROX and its metabolites from soils could be satisfactorily separated by the developed method for the studied arsenicals. To extract arsenic species from soils, 0.1 mol?·?L?1 NaH2PO4 + 0.1 mol?·?L?1 H3PO4 (9:1, v/v) was recommended. Extraction efficiencies of arsenicals were influenced more by solvent composition than soil physicochemical properties. The present study provides a valuable tool and useful information for determining the concentrations of ROX and its metabolites in contaminated soils.
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10.
《Applied soil ecology》2009,41(3):499-509
Redox states affect substrate availability and energy transformation, and, thus, play a crucial role in regulating soil microbial abundance, diversity, and community structure. We evaluated microbial communities in soils under oxic, intermittent, and anoxic conditions along a river floodplain continuum using fatty acid methyl ester (FAME) and 16S rRNA genes-based terminal-restriction fragment length polymorphism (T-RFLP) bacterial fingerprints. In all the soils tested, microbial communities clustered according to soil redox state by both evaluation techniques. Bacteria were dominant components of soil microbial communities, while mycorrhizal fungi composed about 12% of the microbial community in the oxic soils. Gram-positive bacteria consisted >10% of the community in all soils tested and their abundance increased with increasing soil depth when shifting from oxic to anoxic conditions. In the anoxic soils, Gram-positive bacteria composed about 16% of the total community, suggesting that their growth and maintenance were not as sensitive to oxygen supply as for other microbes. In general, microorganisms were more abundant and diverse, and distributed more evenly in the oxic layers than the anoxic layers. The decrease in abundance with increasing oxygen and substrate limitation, however, was considerably more drastic than the decrease in diversity, suggesting that growth of soil microorganisms is more energy demanding than maintenance. The lower diversity in the anoxic than the oxic soils was attributed primarily to the differences in oxygen availability in these soils.  相似文献   

11.
Boron detection in soil extracts by inductively-coupled plasma optical-emission spectrometry (ICP-OES) can be influenced by iron interference, particularly in strongly weathered tropical forest soils. Boron concentrations in Mehlich-III extracts of 230 soils under lowland tropical forest in Panama were markedly overestimated at the most sensitive ICP-OES wavelength (249.772 nm) compared to a less sensitive but interference-free wavelength (208.957 nm) due to iron interference. Hot-water extracts contained insufficient iron to interfere in boron detection, but boron quantification in total element digests was affected strongly by iron interference at 249.772 nm. The relationship between boron overestimation and iron was used to correct a database of 300 Mehlich-III extractable boron measurements made at 249.772 nm for soils from a large forest dynamics plot. We recommend that boron measurements in tropical forest soils by ICP-OES should use the less sensitive 208.957 nm wavelength to avoid interference by extracted iron.  相似文献   

12.
Experiments were conducted to evaluate the arsenic toxicity, its accumulation and phytoremediation potential of bean plants (Phaseolus vulgaris) grown in soils contaminated with different species of arsenic such as arsenite (As(III)), arsenate (As(V)) and dimethylarsinic acid (DMA). Bean plants were grown in soils amended by aqueous solutions of 20 and 50 mg kg?1 of As (III), As(V) or DMA. Arsenic species negatively affected the yield and growth of the plant. The study demonstrated arsenic accumulation in the plant parts. The concentration of arsenic compounds in the shoots decreased in the order arsenate > arsenite > dimethylarsinic acid while in the roots as arsenite > arsenate > dimethylarsinic acid. Most arsenic is accumulated in the roots with limited transfer to shoots. Thus, bean plants can be considered as an arsenic excluder and has the potential for phytostabilization of arsenic contaminated sites. The study also reveals that removal of arsenic by boiling the vegetables with excess of water is not possible.  相似文献   

13.
On 1998, a settling pond of a pyrite mine in Aznalcóllar (SW Spain) broke open, spilling some 3.6?×?106 m3 of water and 0.9?×?106 m3 of toxic tailings into the Agrio and Guadiamar river basin 40 km downstream, nearly to Doñana National Park. The soils throughout the basin were studied for arsenic pollution. Almost all the arsenic penetrated the soils in the solid phase (tailings) in variable amounts, mainly as a result of the different soil structure. The chemical oxidation of the tailings was the main cause of the pollution in these soils. A study of the relationships between the main soil characteristics and arsenic extracted with different reagents (water, CaCl2, acetic acid, oxalic–oxalate and EDTA) indicates a direct relationship with the total arsenic concentration. The highest amount of arsenic was extracted by oxalic–oxalate (24%–36% of the total arsenic), indicating the binding with the iron oxides.  相似文献   

14.
Abstract

To evaluate arsenic (As) levels in agricultural soils of the Red River Delta in northern Vietnam, surface (0–5 cm) and subsurface (20–25 cm) soil samples were collected from 18 paddy and six upland fields on both sides of the river. As a reference, forest soils were also sampled at two sites of the upper river basin. The total As contents of approximately 80% of the surface paddy and upland soils exceeded the maximum allowable limit for Vietnamese agricultural soils (12 mg kg?1). Arsenic contents higher than 35 mg kg?1 were found in soils from the Hungyen and Hanam provinces, where high As levels in the groundwater have also been reported. Sequential fractionation of As in these soils indicated that the amounts of As in the phosphate-extractable and residual fractions were higher than those in the forest soils. Elevated total As contents were also detected in the surface soil of a paddy field near a fertilizer factory in Hanoi (site P10). The amount of HCl-extractable As in the surface soil at P10 corresponded to 84% of the total As, while the proportion never exceeded 40% at other locations. In the surface soil at P10, most of the As was part of the phosphate-extractable fraction. Significant correlations between the total As contents of the upland soils and their non-crystalline Fe oxide contents (r = 0.652, P ≤ 0.05) and between As levels of paddy soils and their crystalline Fe oxide contents (r = 0.544, P ≤ 0.01) were observed. Overall, the present study indicated that although serious As pollution was not found in the studied area, there were some point pollutions caused by industrial activities, in addition to some non-point pollutions resulting from high As concentrations in the groundwater. In addition, Fe oxides in the soils are important factors affecting the As contents of agricultural soils in the Red River Delta.  相似文献   

15.
Application of iron (Fe) -rich amendments to soils has been proposed as a means of decreasing phosphorus (P) losses from soils. However, anoxic conditions following soil saturation are known to increase Fe and P solubility in soils, thus cancelling out the potential benefits. Our aim was to evaluate the effects of continuous oxic, continuous anoxic and alternating anoxic/oxic conditions on P exchangeability and Fe forms in soil amended with Ca(OH)2 and FeSO4. We incubated amended and unamended soils under these conditions for 8 weeks and measured Fe forms and P exchangeability. Under oxic conditions, addition of Ca(OH)2 and FeSO4 resulted in a strong decrease in P exchangeability and an increase in oxalate-extractable Fe. Mössbauer analyses suggested that an unidentified Fe oxide (D1oxide) with a strong sorbing capacity for P was precipitated. Under continuously anoxic conditions, P exchangeability and oxalate-extractable Fe increased with or without the amendments. Mössbauer analyses suggested that there was a partial dissolution of the D1oxide phase, precipitation of another unidentified Fe oxide (S3) and a reduction of structural Fe3+ in phyllosilicate, thereby increasing soil negative charge. These transformations resulted in a strong increase in rapidly exchangeable P. Alternating anoxic and oxic periods induced the dissolution and precipitation of iron oxides and the increase and decrease in P exchangeability. Implications of the results for limiting P losses from grassland soils are discussed.  相似文献   

16.
Estimating future fluxes of CH4 between land and atmosphere requires well-conceived process-based biogeochemical models. Current models do not represent the anaerobic oxidation of methane (AOM) in land surface soils, in spite of increasing evidence that this process is widespread. Our objective was to determine whether AOM, or potential AOM, commonly occurs in 20 hydromorphic soils spanning a wide range of chemical properties. Bulk soil samples were collected under shallow water near the shoreline of 15 recently drained fish ponds in southern Bohemia (Czech Republic), as well as from below the water table at 3 peatland locations in northeast Scotland and 2 acid sulfate soils on the southern coast of Finland. Each soil slurry was incubated under both oxic and anoxic conditions, with or without the addition of alternative electron acceptors (SO42− and NO3−) or H2PO4−. Here, “oxic” and “anoxic” conditions refer to anoxic soil respectively incubated in a headspace containing air or argon. Using the isotope dilution method, we determined the gross production and oxidation rates of CH4 after 2 days incubation under oxic headspace conditions, and after 2, 21 and 60 days incubation under anoxic conditions. Large differences in net CH4 fluxes were observed between soil types and between incubation conditions. AOM was detected in each of the 20 bulk soil samples, which spanned >6 pH units and 2 orders of magnitude in organic C content. Significant positive relationships were found between AOM and gross CH4 production rates under anoxic conditions, resulting in AOM rates that were sometimes higher than CH4 oxidation rates under oxic headspace conditions. There was no relationship between net and gross CH4 production rates, such that 2 soil types could display similar low net rates, yet conceal very large differences in gross rates. The effects of alternative electron acceptors on AOM were idiosyncratic and resulted in no net trend. We did find, however, a negative effect of SO42− and H2PO4− on gross CH4 production rates under anoxic and oxic conditions respectively. Under oxic headspace conditions, CH4 oxidation was related to soil organic C content. Taken collectively, our results suggest that AOM, or potential AOM, is prevalent over a wide range of soil types, that AOM may contribute substantially to CH4 oxidation in soils, and that AOM in soils should be integrated to current process-based CH4 cycling models.  相似文献   

17.
Wetlands are considered to be the biggest unknowns regarding the influence of global climate change on element dynamics, so knowledge of processes and conditions controlling sink and source functions of redox processes is crucial. The aim of this study was to investigate the sink/source function of nitrate, Fe, sulfate reduction and methanogenesis of an upland and a lowland fen within a boreal spruce catchment, southern Germany. We used suction cups and anaerobic dialysis chambers for soil solution sampling, FeS probes for the determination of S oxidation potential and stability of anoxic conditions and analysis of the soil solid phase (contents of C, S and Fe species). Both fens had high rates of nitrate reduction and potentially high rates of CH4 production. The upper few cm of all profiles were oxic with low CH4 concentrations, suggesting low CH4 emission rates from the soil, though emission by vascular plants cannot be excluded. Sulfate and Fe reduction processes differed significantly in the fens. The upland fen was characterized by relatively stable anoxic conditions, low Fe contents but high contents of organic S and low C/S ratios. We concluded that the upland fen is an effective sink for sulfate with long-term S storage. In contrast, the lowland fen was characterized by alternating oxidation-reduction cycles with high Fe contents, lower contents of organic S and higher C/S ratios. Thus, even though low sulfate and high Fe concentrations in soil solutions indicated high reduction rates in the lowland fen, long-term storage of S is not likely in this fen. Differences in biogeochemical processes between sites are most likely not associated with hydrology but rather with the role of vascular plants.  相似文献   

18.
Abstract

The present study described the relationship between growth and soil physico-chemical properties in Eucalyptus camaldulensis (Myrtaceae) and Pinus caribaea (Pinaceae), two important species in Nigerian forest recovery programs. The study sites were located in a 17-year-old plantation in a Northern Nigeria forest reserve. The soils at the study sites were nutrient poor compared with other plantations. Growth of E. camaldulensis was positively correlated with exchangeable K content in soils 0–20 cm deep, and negatively correlated with total N and exchangeable Na in soils 20–150 cm deep. Growth of P. caribaea was positively correlated with available P in soils 0–20 cm deep, and volumetric water content in soils 20–150 cm deep. Soils in the top layers were very hard and plinthite layers were well developed at shallow soil depths at most sites. E. camaldulensis exhibited a comparatively high survival rate, and its growth was comparable to that in other plantations. However, the survival rates of P. caribaea were low and its growth was lower than that in other plantations. The survival rate of E. camaldulensis was lower at sites where plinthite layers were found within 50.8 cm of the surface. These results indicated that E. camaldulensis is suitable for afforestation in Northern Nigeria. However, it is not recommended for sites where the plinthite layer occurs at shallow soil depths.  相似文献   

19.
Abstract

We measured the concentration and composition (sensu Leenheer, 1981) of dissolved organic carbon (DOC) in lysimeter solutions from the forest floor of a spruce stand in Maine and in laboratory extracts of organic (Oa horizon) and mineral soils collected from various forests in Maine, New Hampshire, and Vermont. All soils were acid Spodosols developed from glacial till. The effects of different storage, extraction and filtration methods were compared. Extracts from Oa horizons stored fresh at 3°C contained a larger fraction of hydrophobic neutrals than lysimeter forest floor solutions (31 and 4% of DOC in stored and lysimeter solutions, respectively), whereas extracts from Oa horizons which had been extracted, incubated at 10–15°C, and extracted again had DOC compositions similar to that in lysimeter solutions. Mechanical vacuum and batch extractions of Oa horizons yielded DOC similar in concentration and composition if the extracts were filtered through glass fiber filters. Nylon membrane filters, however, removed more hydrophobic acids from batch extracts. Dissolved organic carbon extracted from frozen, air‐dry, and oven‐dry Oa and Bh horizons was relatively rich in hydrophilic bases and neutrals and was similar to that released after chloroform fumigation, indicating that common soil‐storage methods disrupt microbial biomass.  相似文献   

20.
In order to determine the effect of land use on forest floor and soil, two adjacent sites with different land use were investigated in Gallura (northern Sardinia, Italy). One site is a Quercus suber L. forest mainly used for cork production and the other is an open Quercus suber L. forest where livestock is put out to graze. In each site one soil profile was studied to characterize the mineral soil, and five humus profiles were opened along a vegetation transect, were studied to characterize the forest floor. Samples of L, F and H horizons of the forest floor and of the A mineral horizons were collected and analysed for each profile. In the site mainly used for cork production well‐developed ectorganic (L, F and H) horizons are always present, with a total thickness ranging from 5·2 to 9·5 cm. Humus profile is of the Moder type, while mineral soils have an A–C profile, generally 50 cm deep. Organic matter content in the forest floor ranges from 1·76–3·72 kg m−2 and nutrients content in the mineral soil is high. In the site used chiefly for grazing the ectorganic horizons are very poorly developed, with a total thickness ranging from 1–3 cm, except for some islands under the Quercus suber L. canopy where the total thickness may reach 5·3 cm. Humus profile is of the Mull type, but the used classification system seems not appropriate when the tree density is below a critical limit. Mineral soils have an A–C profile 20–25 cm deep. The organic matter content in the forest floor ranges from 0·45 to 1·84 kg m−2, while nutrient content in the mineral soil maintains at high level, even higher than in the former case for C, N and Ca, probably in relation with higher supply of cattle excreta. Sheet erosion is evident in the site. It is concluded that cork production will maintain a sustainable forest floor development in cork–oak forest ecosystem, whereas cattle grazing, fires and ploughing in cork–oak forests may be considered to trigger off severe soil degradation processes. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

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