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1.
Quinone profile analysis of stored air-dried soils gave an approximation of the long-term changes in the microbial community structure in four soils subjected to different types of fertilizer application from 1987 to 1997: unfertilized soil (NF-soil), soil amended with chemical fertilizers (CF-soil), soil amended with chemical fertilizers and 40 t ha-1 y-1 of farmyard manure (CF+ FYM-soil), and soil amended with 400 t ha-1 y-1 of farmyard manure (FYM-soil). The carbon content increased, and the soil pH remained higher in the soils receiving farmyard manure. Principal component analysis of the quinone profiles of the soils indicated that the microbial community structure showed a high similarity among the four soils before the onset of cultivation and changed to a different community structure specific to the respective fertilizing practices except for the NF-soil. The specific quinone profile became stable after two cropping seasons in the FYM-soil, after 10 cropping seasons in the CF+ FYM-soil and after 15 cropping seasons in the CF-soil, respectively. The quinone profile of the NF-soil did not become stable, and no specific profile was developed. The specific quinone profiles in the FYM- and CF+ FYM-soils were both characterized by large mole fractions of menaquinone with seven isoprenoid units (MK-7). Farmyard manure itself contained a large mole fraction of MK-7. It was suggested that the amount of MK-7 increased due to the application of farmyard manure. MK-7 indicates the presence of Gram-positive bacteria with low guanine plus cytosine contents such as Bacillus and Gram-negative bacteria of the Cytophaga-Flavobacterium complex. The specific quinone profile in the CF-soil was characterized by the presence of menaquinone with seven isoprenoid units dihydrated (MK-7(H2)and MK-7(H4). Although Brevibacterium and Kocuria contain MK-7(H2), no microorganisms are known to have MK- 7(H.) as major quinone. The common major quinones were MK-8, MK-10(H4) and a mixture of MK-8(H4) and MK-9, suggesting the predominance of Grampositive bacteria in all the soils. Mole fractions of Ubiquinone with 8 isoprenoid units (Q-8) and Q-10 increased at various times in all the soils, indicating the sporadic growth of Gram-negative bacteria.  相似文献   

2.
The tall, aerodynamically rough surfaces of forests provide for the efficient exchange of heat and momentum between terrestrial surfaces and the atmosphere. The same properties of forests also provide for large potential rates of deposition of pollutant gases, aerosols and cloud droplets. For some reactive pollutant gases, including SO2, HNO3 and NH3, rates of deposition may be large and substantially larger than onto shorter vegetation and is the cause of the so called "filtering effect" of forest canopies. Pollutant inputs to moorland and forest have been compared using measured ambient concentrations from an unpolluted site in southern Scotland and a more polluted site in south eastern Germany. The inputs of S and N to forest at the Scottish site exceed moorland by 16% and 31% respectively with inputs of 7.3 kg S ha-1 y and 10.6 kg N ha-1 y-1. At the continental site inputs to the forest were 43% and 48% larger than over moorland for S and N deposition with totals of 53.6 kg S ha-1 y-1 and 69.5 kg N ha-1 y-1 respectively. The inputs of acidity to global forests show that in 1985 most of the areas receiving > 1 kg H+ ha-1 y-1 as S are in the temperate latitudes, with 8% of total global forest exceeding this threshold. By 2050, 17% of global forest will be receiving > 1 kg H-1 ha-1 as S and most of the increase is in tropical and sub-tropical countries. Forests throughout the world are also exposed to elevated concentrations of ozone. Taking 60 ppb O3 as a concentration likely to be phytotoxic to sensitive forest species, a global model has been used to simulate the global exposure of forests to potentially phytotoxic O3 concentrations for the years 1860, 1950, 1970, 1990 and 2100. The model shows no exposure to concentrations in excess of 60 ppb in 1860, and of the 6% of global forest exposed to concentrations > 60 ppb in 1950, 75% were in temperate latitudes and 25% in the tropics. By 1990 24% of global forest is exposed to O3 concentrates > 60 ppb, and this increases to almost 50% of global forest by 2100. While the uncertainty in the future pollution climate of global forest is considerable, the likely impact of O3 and acid deposition is even more difficult to assess because of interactions between these pollutants and substantial changes in ambient CO2 concentration, N deposition and climate over the same period, but the effects are unlikely to be beneficial overall.  相似文献   

3.
Coastal areas in the southeastern USA are prone to hurricanes and strong storms that may cause salt-water influx to freshwater aquatic sediments. These changes in environmental conditions may impact sediment processes including nitrogen (N) cycling. The relative abilities of sediment microbial communities from two freshwater golf course retention ponds that drain into the adjacent wetlands, and two proximal saline wetland ponds, to remove nitrate (NO3−) were compared to assess whether low concentrations of sulfide changed N-transformation processes. Microcosms were incubated with NO3-N (300 μg g dw−1) alone, and with NO3-N and sulfide (H2S) (100 and 200 μg g dw−1). Nitrous oxide (N2O), nitrite (NO2−), NO3−, ammonium (NH4+), SO42− and acid volatile sulfides were analyzed over time. The acetylene block technique was used to measure denitrification in sediment microcosms with no added H2S. Denitrification was measured without acetylene (C2H2) addition in microcosms with added H2S. With no added H2S, denitrification was greater in the freshwater retention ponds than in the wetland ponds. Although low H2S concentrations generally increased NO3-N removal rates at all sites, lag periods were increased and denitrification was inhibited by low sulfide in the freshwater sediments, as evidenced by the greater concentrations of N2O that accumulated compared to those in the wetland sediments. In addition to the inability of the freshwater sediments to convert N2O to N2 in the absence of C2H2, anomalously high transient NO2-N concentrations accumulated in the retention pond samples. NH4-N formation generally decreased due to H2S addition at the freshwater sites; NH4-N formation increased initially at the wetland sites, but was greater when no H2S was added. Storm events that allow influx of SO42−-containing seawater into freshwater systems may change the dominant N species produced from nitrate reduction. Even low concentrations of sulfide produced incomplete denitrification and decreased formation of NH4+ in these coastal freshwater sediments.  相似文献   

4.
Analysis of [l4C]respiratory Quinones synthesized in soil for 6 h after spiking with [U-14C]glucose, [U-l4C]glycine, and [1,2-l4C]acetate enabled to fingerprint the microorganisms metabolizing each substrate in soil and to determine the whole structure of the microbial communities at the same time. The [l4C]- Quinones synthesized from [U-l4C] glucose were the same as those from [U-l4C] gIycinc in soil, suggesting that the same microbial groups metabolized glucose and glycine under the given conditions. No [l4C]quinones from [1,2- 14C] acetate were detected in soil, indicating that the metabolism of acetate by microorganisms is negligible. The profiles of [l4C]quinones from [U-l4C]- glucose were compared between Nagoya University Farm soils subjected to 4 different fertilizing practices. The soils receiving farmyard manure contained [l4C]menaquinones with highly hydrated isoprenoid units, which indicated the presence of Actinobacteria metabolizing glucose. The soil receiving only chemical fertilizers contained [14C]ubiquinone with 8 isoprenoid units (Q-8), indicating the presence of beta and gamma subdivisions of Proteobacteria. All the 4 soils were characterized by the high proportions of [14C] MK-6 and a mixture of [l4C]MK-8(H4) and [l4C]MK-9. The Q-9 and Q-10(H2) indicators of fungi, were not labeled under most of the conditions.  相似文献   

5.
Purpose

Prescribed burning is a forest management practice which can lead to nitrogen (N)-limited conditions. This study aimed to explore whether biological N2 fixation (BNF) remained the main source of N acquisition for two understorey Acacia species in a Eucalyptus-dominated suburban forest of subtropical Australia, 3 to 6 years after prescribed burning. Root-nodule bacteria associated with these acacias were also characterised to unravel the differences in rhizobial communities between sites and species.

Material and methods

Two sites, burned 3 and 6 years before sample collection, were selected within a dry subtropical forest of south-east Queensland, Australia. Leaves were collected from individuals of Acacia disparrima and A. leiocalyx at each site to determine leaf total carbon (C) and N content, C and N isotope composition (δ13C and δ15N) and the percentage of N derived from atmospheric N2. Nodules were harvested from both acacia species at each site to isolate root nodule bacteria. Bacterial isolates were processed for 16S rDNA gene sequencing.

Results and discussion

Generally, no differences were found in plant physiological variables between the two acacia species. Six years after the fire, both species still depended upon BNF for their N supply, with a higher dependence in winter than in summer. Fire, although of low intensity, was likely to have created a N-limited environment which induced the reliance of legumes on BNF. Root nodule bacteria were dominated by non-rhizobial endophytes, mainly from the Firmicutes phylum. No difference in nodule bacterial diversity was found between sites. The relative abundance of rhizobial genera varied amongst plant species and sites, with a shift in dominance from Bradyrhizobium to Rhizobium species between sites 1 and 2.

Conclusions

Our results show that even 6 years after burning, ecosystem remained under N stress and BNF was still the main mechanism for N acquisition by the understorey legumes.

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6.
Samples of organic (F/H) and mineral soil (to approximately 8 cm depth) were collected from three ‘ecologically analogous’ sites in a boreal forest at intervals of 2.8 km (site 1), 6.0 km (site 2) and 9.6 km (site 3) from a ‘sour gas’ plant emitting S02. The organic soil of site 1 was characterized by a lower basal respiration rate, smaller microbial biomass, and a longer time to attain the peak rate of CO2 efflux following enrichment with glucose or vanillin (0.15 and 0.1 g (15 g soil)?1, respectively). No significant differences were detected between the mineral soils of the 3 sites in terms of the rate or extent of glucose decomposition (0.1 g (100 g soil)?1), but there was a significant retardation in vanillin decomposition in the mineral soil of site 1 (0.05 g (100 g soil)?1). Concentrations of 0.075 and 0.1 g vanillin (100 g soil)?1 were decomposed in the mineral soil of sites 2 and 3, but not at site 1. Following incubation with vanillin, fewer bacteria were isolated from both the organic and mineral soils of site 1, and a greater proportion of these were spore formers and bisulfite-tolerant isolates compared with those from sites 2 and 3.  相似文献   

7.
Mexico City experiences some of the most severe air pollution in the world. Ozone injury has been documented in sensitive tree species in urban and forested areas in the Valley of Mexico. However, little is known of the levels of other atmospheric pollutants and their ecological effects on forests in the Valley of Mexico. In this study bulk throughfall deposition of inorganic nitrogen (N) and sulfur (S) was measured for one year at a forested site upwind (east) and downwind (southwest) of Mexico City. Edaphic and plant (Pinus hartwegii Lindl.) indicators of N and S nutrient status were also measured. Streamwater NO3 - and SO4 2- concentrations were also determined as an indicator of watershed-level N and S loss. Annual bulk throughfall deposition of inorganic N and S at the high-pollution forested site 23 km southwest of Mexico City (Desierto de los Leones National Park; DL) was 18.5 and 20.4 kg ha-1. Values for N and S deposition at Zoquiapan (ZOQ), a relatively low-pollution site 53 km east of Mexico City, were 5.5 and 8.8 kg ha-1 yr-1. Foliar concentrations of N, foliar N:P and C:N ratios, extractable soil NO3 -, and streamwater NO3 - concentrations indicate that the forest at DL is N enriched, possibly as a result of chronic N deposition. Sulfur concentrations in current-year foliage were also slightly greater at DL than at ZOQ, but S concentrations in one-year-old foliage were not statistically different between the two sites. Streamwater concentrations of NO3 - ranged from 0.8 to 44.6 μEq L-1 at DL compared to 0.0 to 11.3 μEq L-1 at ZOQ. In summary, these findings support the hypothesis that elevated N deposition at DL has increased the level of available N, increased the N status of P. hartwegii, and resulted in export of excess N as NO3 - in streamwater.  相似文献   

8.
To evaluate the effect of tillage intensity on the N mineralization pattern of winter wheat residues, sugar beet residues, Italian ryegrass and maize residues undisturbed soil samples were taken from six sites under different tillage management. Site NTK had been managed for 10 years under reduced tillage (RT), whereby the last 4 years the crops were sown using direct seeding (NT). Site RTCSE had been managed for 20 years under reduced tillage (RT) and site RTH for 3 years. For each site under RT a nearby site under conventional tillage (CT) was selected (CTK, CTCSE and CTH). On site NTK and site RTCSE a significantly higher amount of SOC in the 0–10 cm was accumulated compared to the respective CT sites. Between site RTH and site CTH no such significant difference was found. However, the content of microbial biomass C (MB-C) and the β-glucosidase and urease activities were higher on all RT sites compared to the respective CT sites. This indicates that these microbiological and biochemical parameters seem to be very sensitive for alterations in management intensity. After 98 days, more N was immobilized under NTK than under CTK by adding winter wheat residues (expressed as kg ha−1 and as % of total added N). This higher immobilization potential can be explained by a higher microbial activity and a change in microbial population. Under RTCSE and RTH net N immobilization of the winter wheat residues was found, but the pattern was less pronounced than for NTK. However, when expressed as % of total N added, N immobilization of winter wheat residues was higher under CT than under RT, which indicates that high C:N residues when incorporated, decompose more slowly under RT than under CT. Similar results were found comparing the N mineralization pattern of maize residues under RTH and CTH. The residues of sugar beet and Italian ryegrass at site CTH released N more rapidly and to a higher extent, 74.1% and 66.2%, respectively (expressed as % of total N added) than under RTH at the end of the incubation. The slower mineralization of N rich crop residues under RT compared to CT means that there is less potential risk for nitrate leaching to occur, which may result in a higher N efficiency in RT compared to CT.  相似文献   

9.
Surface mineral horizons from four ecosystems sampled in the northwestern Italian Alps were incubated at −3 and +3°C to simulate subnivial and early thaw period temperatures for a seasonally snow-covered area. The soil profiles at these sites represent extreme examples of management, grazed meadow (site M) and extensive grazing beneath larch (site L) or naturally disturbed by avalanche and colonized by alder (site A) and the expected forest climax vegetation beneath fir (site F). Changes in labile pools of nitrogen (N) and phosphorus (P) were active at all sites at both temperatures during 14 days of laboratory incubation. Ammonium was the dominant inorganic form of total dissolved N (TDN), being equivalent to 1.8–9.8 g N m−2 within the mineral horizon. Gross rates of ammonification were similar at the two temperatures but significantly (p<0.05) greater in soil from beneath fir than in the other three. Nitrification occurred in all soils and displayed a wide range in rates, from 2 to 85 mg N m−2 day−1, and was least in the two most acid soils, A and F. Immobilization of NH4 + as microbial N was greater in the fir soil than in the other three. Also, the fir soil showed greatest gross ammonification and least accumulation of NO3 − and greatest tendency to retain N. This high N retention capacity in the climax ecosystem contrasted with the managed systems characterized by higher nitrification rates and greater potential spring NO3 − loss. Dissolved organic N ranged between 30 and 50% of the TDN, while dissolved organic P was greater than 70% of total dissolved P (TDP). The dissolved organic compounds were important components of the labile pool, in equilibrium with a large reserve of organic N, and may significantly contribute to the soil N availability at low temperatures.  相似文献   

10.
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11.
A major forest disturbance such as clearcutting may bring on a flush of mineral N in organic forest floor horizons, but the magnitude of this flush can vary markedly from one ecosystem to another. For example, it was previously established that clearcutting in a high elevation Engelmann spruce-subalpine fir (ESSF) ecosystem results in significantly higher NH4+ and NO3− concentrations, whereas clearcutting in an old-growth coastal western hemlock (CWH) ecosystem has little effect on mineral N dynamics. We hypothesized that the higher mineral N flush observed in the ESSF ecosystem is due to a greater temperature sensitivity of mineral N transformation rates, and to a lower proportion of heterotrophic nitrifiers, compared to the CWH ecosystem. To test these two hypotheses, we sampled forest floors several times over the growing season from clearcut and old-growth plots in both ecosystems, and measured gross mineral N transformation rates at field temperatures and at 10 °C above field temperatures, as well as with and without acetylene to inhibit autotrophic nitrifiers. Gross NH4+ transformations rates ranged between 20 and 120 μg N (g forest floor)−1 day−1 at the ESSF site, and between 15 and 40 μg N (g forest floor)−1 day−1 at the CWH site. Higher temperature increased gross NH4+ transformation rates in forest floor samples at both sites, but the average Q10 value was higher at the ESSF site (3.15) than at the CWH site (1.25). Temperature sensitivity at the ESSF site was greater in clearcut plots (Q10=4.31) than in old-growth plots (Q10=1.98). Gross NO3− transformation rates ranged between 10 and 32 μg N (g forest floor)−1 day−1 at the ESSF site, and between 10 and 24 μg N (g forest floor)−1 day−1 at the CWH site, but there were no significant effects of temperature or clearcutting on gross NO3− transformation rates at either site. Likewise, there were no significant differences in the proportion of heterotrophic nitrifiers between sites. Overall, our results support the view that the temperature sensitivity of microbial processes may explain the magnitude of the NH4+ flush in some coniferous ecosystems, but we lack the evidence relating the magnitude of the NO3− flush to the proportion of heterotrophic nitrifiers.  相似文献   

12.
Abstract

Phosphorus and sulfur deficiencies have been observed on many of the volcanic ash derived soils in Central America. One exploratory experiment was initiated in 1987 to examine maize (Zea mays L.) grain yield response to phosphorus, sulfur and nitrogen applied together on a volcanic ash derived soil in the Pacific coastal plain of Guatemala. Four cycles of yield data were collected in 2 rainy and 2 dry seasons. Treatments consisted of rate combinations of N (0, 100 kg ha‐1 as urea), P (0, 22 kg ha‐1 as triple superphosphate) and S (0, 57 and 114 kg ha‐1 as CaSO4.2H2O) applied together in continuous bands in a randomized complete block design. Residual P and S response was measured during the last two cycles, whereby only urea was applied at a constant rate to all plots. The combined analysis of the first two cycles demonstrated a linear response of yield to applied S when no P was applied (4.95, 5.75 and 5.95 Mg ha‐1 at 0, 57 and 114 kg S ha‐1 respectively), while yield response was quadratic when S as CaSO42H2O and P as triple superphosphate were applied together in a continuous band at 100 kg N ha‐1 (5.38, 6.38 and 5.48 Mg ha‐1 at the same S rates respectively). Response of yield to S was linear without and with P for the combined residual analysis of the last two cycles at the same N rate (4.65, 4.94, 5.26 and 4.68, 5.53, 5.56 Mg ha‐1 respectively). Grain yields were maximized over the four cycle period using a joint N, P, S band (100 kg of N as urea, 22 kg P as triple superphosphate, and 57 kg S as CaSO4.2H2O ha‐1). It is hypothesized that precipitation of dicalcium phosphate dihydrate (DCPD) and dicalcium phosphate (DCP) took place within the joint N‐P‐S band subsequently reducing the amount of P fixed as Fe or Al hydroxides and/or amounts of P complexed with amorphous allophane. The precipitation and subsequent dissolution of DCPD and DCP within the band could have increased P availability with time. Alternatively, SO4 = blocking of adsorption sites could have increased P availability by reducing the amount of P fixed by the soil. It is possible that both of the previously mentioned mechanisms played a role in first cycle yield responses since increases were noted at the low S rate (57 kg S ha‐1), while reductions were found when the S rate was doubled (114 kg S ha‐1). Significant residual response for the last two cycles was observed for the joint triple superphosphate, CaSO4.2H2O, urea band, especially at the high S rate. This suggests that excess precipitation of DCP and DCPD could have occurred and that this provided delayed dissolution of the precipitated P reaction products. Chemical characterization of precipitated reaction products within the band is needed as well as further verification on similar soils in order to validate the observed response.  相似文献   

13.
Cyanobacteria are important for global nitrogen cycle and often form complex associations referred to as cyanobacterial mats or periphyton that are common in tropical, limestone-based wetlands. The objective of this study was to monitor the nitrogen fixation rate using the acetylene reduction assay of these cyanobacterial mats in a tropical, unfertilized, and protected wetland. To account for temporal and spatial variation of nitrogenase activity, we were interested in seasons in a hydrological cycle (dry, rains, and end of rains), sites with different vascular vegetation, and rates of nitrogenase activity in a 24-h cycle. The annual average of nitrogenase activity was 22 nmol C2H4 cm−2 h−1, with a range of <6 to 35 nmol C2H4 cm−2 h−1, and the annual nitrogen fixation rate of our study site (9.0 g N m−2 year−1) is higher than similar estimates from other freshwater wetlands. There was a clear temporal pattern in nitrogenase activity with a maximum rate occurring during the rainy season (August) and a maximum nitrogenase activity occurring between 0600 and 1200 hours. We found spatial differences in nitrogenase activity among the four sites that could be attributed to variations in species composition within the periphyton.  相似文献   

14.
Cores of podzolic soil (monolith lysimeters) were treated for 4.8 yr with 1500 mm yr?1 of either 0.5 mM H2SO4 at pH 3, equivalent to 24 g S m?2 yr?1 (acid treated) or distilled water (controls). The acid treatment was about 37 times greater than the average annual input of H3O+ from rain at the site from which the monoliths were taken. Acid treatment acidified the litter (from pH(CaCl2)3.4 to pH(CaCl2)2.6) and the mineral soil to a depth of 80 cm (mean pH(CaCl2) decrease of 0.2 unit). In the litter and upper A horizon, ion-exchange reactions provided the main neutralizing mechanism, resulting in a decrease in the reserves of extractable (in 2.5 % acetic acid) Ca, Mg, and Mn of about 70 to 80 %. Dissolution of solid phase Al from hydrous oxides provided most neutralization below this depth. Al3+ was the principal soluble Al species throughout the profile. In the litter and upper A horizon, some of the mobilized Al3+ was retained on cation exchange sites resulting in an increase in exchangeable Al. Deeper in the profile, where the exchange sites were effectively saturated with Al3+, no increase in exchangeable Al occurred, and Al3+ was, therefore, available for leaching. Some reversible adsorption of SO4 2?, associated with hydrous Al oxides, occurred in the Bs and C horizons. The results are discussed in relation to possible effects of acid deposition over regions of Europe and N. America.  相似文献   

15.
The effect of harvesting bamboo savanna on the dynamics of soil nutrient pools, N mineralization, and microbial biomass was examined. In the unharvested bamboo site NO inf3 sup- -N in soil ranged from 0.37 to 3.11 mg kg-1 soil and in the harvested site from 0.43 to 3.67 mg kg-1. NaHCO3-extractable inorganic P ranged from 0.55 to 3.58 mg kg-1 in the unharvested site and from 1.01 to 4.22 mg kg-1 in the harvested site. Over two annual cycles, the N mineralization range in the unharvested and harvested sites was 0–19.28 and 0–24.0 mg kg-1 soil month-1, respectively. The microbial C, N, and P ranges were 278–587, 28–64, and 12–26 mg kg-1 soil, respectively, with the harvested site exhibiting higher values. Bamboo harvesting depleted soil organic C by 13% and total N by 20%. Harvesting increased N mineralization, resulting in 10 kg ha-1 additional mineral N in the first 1st year and 5 kg ha-1 in the 2nd year following the harvest. Microbial biomass C, N and P increased respectively by 10, 18, and 5% as a result of bamboo harvesting.  相似文献   

16.
太行山低山丘陵区不同植物群落物种多样性研究   总被引：2，自引：0，他引：2       下载免费PDF全文
 通过样地法对小浪底水库库区山地生态系统不同群落间的Shannon-Wiener指数(H′)、Simpson指数(D1)、Margalef物种丰富度(D2)、种间相遇概率(P)和Pielou均匀度指数(Jsw)等多样性指数进行研究,利用统计方法分析不同群落的物种多样性指数与其所处环境的关系。结果表明:1)物种多样性指数和丰富度指数与群落类型有密切关系,同一类型的群落中,多样性指数随演替时间表现出复杂的关系;2)土壤含水量对H′、P、Jsw、D1等呈极显著的正相关性,土壤厚度与H′、D1、P呈显著正相关性;多样性指数与坡度无相关性;土壤有机质、速效氮、速效磷等养分指标与多样性指数H′、D1有显著的正相关;3)多样性指数H′与乔木、灌木群落生物量表现为正相关关系,草本群落与D1相关性不显著;4)乔木林群落的恢复时间与Jsw、H′呈正相关关系,其余多样性指数(P、D1、D2)与恢复时间关系不显著(P>0.05);恢复时间每增加10a,群落物种数平均增加约6种;5)物种多样性指数H′与灌木的盖度和高度呈极显著正相关性;有些单优群落随高度增加和盖度提高,多样性指数反而表现出降低;6)草本植物群落的高度和盖度与物种丰富度指数D2与呈显著的负相关关系,与H′相关性不显著。  相似文献   

17.
 The 15N isotope dilution method was combined with a field incubation technique to provide simultaneous measurements of gross and net rates of N turnover in three long-term swards: unfertilized (Z) or receiving N either from N fixation as clover (C), or as 200 kg fertilizer N ha–1 year–1 (F). Uniform N enrichment of soil microplots was achieved with a multi-point soil injector to measure mineralization/immobilization turnover and nitrification over a 4-day incubation. Net rates of mineralization ranged between 0.6 and 2.9 μg N g–1 day–1 and in all three treatments were approximately half the gross rates. Nitrification rates (gross) were between 1.0 and 1.6 μg N g–1 day–1. In the F treatment, the turnover of NH4 +-N and NO3 –-N pools was on a 2- and 4-day cycle, respectively, whereas in the N-limited treatments (C and Z) turnover rates were faster, with the NO3 –-N pools turning over twice as fast as the NH4 +-N pools. Therefore, available N was recycled more efficiently in the C and Z treatments, whereas in the F treatment a higher N pool size was maintained which would be more vulnerable to leakage. A large proportion of the added 15N was recovered in the soil microbial biomass (SMB), which represented a 4–5 times larger sink for N than the plant biomass. Although the C treatment had a significantly lower SMB than the grass-only treatments, there were no differences in microbial activity. Gross rates of nitrification increased along the gradient of N input intensity (i.e. Z<C<F), and the addition of a nitrification inhibitor (C2H2) tended to increase microbial immobilization, but did not influence plant N uptake. In this study, the value of combining different techniques to verify net rates was demonstrated and the improved methodology for 15N labelling of soil enabled measurements to be obtained from relatively undisturbed soil under natural field conditions. Received: 25 May 1999  相似文献   

18.
The major part of Venezuela oil production is located in and around the Lake Maracaibo Basin. The samples were collected over a 1-year period at Catatumbo and La Esperanza sites. The rainwater was acidic, with a VWA-pH of 4.6 for Catatumbo and 4.2 for La Esperanza. This acidity is made up in 93% by inorganic acids (mainly H2SO4), and NH4 + is the major cation which buffer the acidity of precipitation. An excess of sulfate (SO2 *) > 96% was obtained in both sites. Correlation analysis shows that H+ is strongly correlated with SO4 x. Anthropogenic air pollution from oil fields (H2S) and the burning of sulphur-bearing fuels (SO2) are probably the dominant sources; however, the lack of correlation between the H+ and NO3 – levels would appear to indicate that the SO4 * is also of biogenic origin (H2S-DMS from Sinamaica Lagoon-Lake Maracaibo- and the Caribbean). Statistical analysis of the pooled data indicated that the concentration differences between Catatumbo and La Esperanza sites are not significant at 99% confidence level.  相似文献   

19.
Abstract

The amount of sulphur (S), nitrogen (N), and organic carbon (C) in different layers of soils from some Alfisols varied considerably with location. The amount of S extracted by different extractants as a percentage of the total S was in the order of organic (3.5%)>0.05 (N) NH4OAc+0.25 (N) HOAc (1.9%)>0.1 (N) H3PO4 (1.8%)>0.025 (N) CaCl2 (1.8%)>0.03 (N) NaH2PO4 (1.7%)>0.001 (N) HCl (0.6%). In all the soil series SO4 2?‐S mineralization decreased up to the second week after incubation, followed by a slight increase up to the fourth week, a subsequent decline up to the sixth week, and a slight increase up to the eighth week. The C:N, C:S, N:S, and C:N:S ratios averaged 9.4:1, 63.7:1, 6.9:1, and 94:10:2.08, respectively.  相似文献   

20.
Invasive exotic plants can modify soil organic matter (SOM) dynamics and other soil properties. We evaluated changes in particulate organic matter (POM) and carbon (C) mineralisation in adjacent plots invaded by Solidago gigantea, Prunus serotina, Heracleum mantegazzianum and Fallopia japonica, and non-invaded control plots on different soils in Belgium. Litter decomposition of S. gigantea and P. serotina was compared to that of the native species Epilobium hirsutum, Betula pendula and Fagus sylvatica. Disregarding the differences in site characteristics (soil texture, parental material and plant species), we argued that the invasion by S. gigantea and P. serotina enhance SOM dynamics by increasing C mineralisation in 2 out of 3 sites invaded by S. gigantea and in 1 out of 3 sites invaded by P. serotina; C in coarse POM (cPOM, 4,000–250 μm) and fine POM (fPOM, 250–50 μm) in 1 site invaded by S. gigantea and C content in total POM (tPOM, 4,000–50 μm) and the organo-mineral fraction (OMF, 0–50 μm) in 1 site invaded by P. serotina. H. mantegazzianum and F. japonica slowed down SOM dynamics by reducing C mineralisation in three out of four sites; C and nitrogen (N) of fPOM in the invaded compared with the non-invaded plots at one site invaded by H. mantegazzianum. However, N content of cPOM (4,000–250 μm) was higher in the invaded sites by F. japonica compared with the non-invaded plots. Our results indicated that the effects of invasion by exotic plant species were not species-specific but site-specific.  相似文献   

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