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1.
The ability of an ecosystem to retain anthropogenic nitrogen (N) deposition is dependent upon plant and soil sinks for N, the strengths of which may be altered by chronic atmospheric N deposition. Sugar maple (Acer saccharum Marsh.), the dominant overstory tree in northern hardwood forests of the Lake States region, has a limited capacity to take up and assimilate NO3. However, it is uncertain whether long-term exposure to NO3 deposition might induce NO3 uptake by this ecologically important overstory tree. Here, we investigate whether 10 years of experimental NO3deposition (30 kg N ha−1 y−1) could induce NO3 uptake and assimilation in overstory sugar maple (approximately 90 years old), which would enable this species to function as a direct sink for atmospheric NO3 deposition. Kinetic parameters for NH4+ and NO3 uptake in fine roots, as well as leaf and root NO3 reductase activity, were measured under conditions of ambient and experimental NO3 deposition in four sugar maple-dominated stands spanning the geographic distribution of northern hardwood forests in the Upper Lake States. Chronic NO3 deposition did not alter the V max or K m for NO3 and NH4+ uptake nor did it influence NO3 reductase activity in leaves and fine roots. Moreover, the mean V max for NH4+ uptake (5.15 μmol 15N g−1 h−1) was eight times greater than the V max for NO3 uptake (0.63 μmol 15N g−1 h−1), indicating a much greater physiological capacity for NH4+ uptake in this species. Additionally, NO3 reductase activity was lower than most values for woody plants previously reported in the literature, further indicating a low physiological potential for NO3 assimilation in sugar maple. Our results demonstrate that chronic NO3 deposition has not induced the physiological capacity for NO3 uptake and assimilation by sugar maple, making this dominant species an unlikely direct sink for anthropogenic NO3 deposition.  相似文献   

2.
Sugar maple (Acer saccharum Marsh.)-dominated northern hardwood forests in the upper Lakes States region appear to be particularly sensitive to chronic atmospheric NO3 deposition. Experimental NO3 deposition (3 g NO3 N m−2 y−1) has significantly reduced soil respiration and increased the export of DOC/DON and NO3 across the region. Here, we evaluate the possibility that diminished microbial activity in mineral soil was responsible for these ecosystem-level responses to NO3 deposition. To test this alternative, we measured microbial biomass, respiration, and N transformations in the mineral soil of four northern hardwood stands that have received 9 years of experimental NO3 deposition. Microbial biomass, microbial respiration, and daily rates of gross and net N transformations were not changed by NO3 deposition. We also observed no effect of NO3 deposition on annual rates of net N mineralization. However, NO3 deposition significantly increased (27%) annual net nitrification, a response that resulted from rapid microbial NO3 assimilation, the subsequent turnover of NH4+, and increased substrate availability for this process. Nonetheless, greater rates of net nitrification were insufficient to produce the 10-fold observed increase in NO3 export, suggesting that much of the exported NO3 resulted directly from the NO3 deposition treatment. Results suggest that declines in soil respiration and increases in DOC/DON export cannot be attributed to NO3-induced physiological changes in mineral soil microbial activity. Given the lack of response we have observed in mineral soil, our results point to the potential importance of microbial communities in forest floor, including both saprotrophs and mycorrhizae, in mediating ecosystem-level responses to chronic NO3 deposition in Lake States northern hardwood forests.  相似文献   

3.
Levanon  Dan  Levin  Israel 《Plant and Soil》1989,120(1):65-68
The effect of nitrate concentration in the nutrient solution, on yields and nitrate accumulation in the plant, was studied in Rhodes grass grown in sand culture. The results showed that optimal yield was achieved in the 7.5meq.L−1 N solution. The optimal NO3−N concentration in the plant canopy may be an indicator of effective N fertilizer use. Increasing N fertilization will only increase the NO3−N concentration in the plant. A.R.O. Contribution no. 2244-E, 1987 series.  相似文献   

4.
The biological reduction of Fe(III) ethylenediaminetetraacetic acid (EDTA) is a key step for NO removal in a chemical absorption–biological reduction integrated process. Since typical flue gas contain oxygen, NO2 and NO3 would be present in the absorption solution after NO absorption. In this paper, the interaction of NO2 , NO3 , and Fe(III)EDTA reduction was investigated. The experimental results indicate that the Fe(III)EDTA reduction rate decrease with the increase of NO2 or NO3 addition. In the presence of 10 mM NO2 or NO3 , the average reduction rate of Fe(III)EDTA during the first 6-h reaction was 0.076 and 0.17 mM h−1, respectively, compared with 1.07 mM h−1 in the absence of NO2 and NO3 . Fe(III)EDTA and either NO2 or NO3 reduction occurred simultaneously. Interestingly, the reduction rate of NO2 or NO3 was enhanced in presence of Fe(III)EDTA. The inhibition patterns observed during the effect of NO2 and NO3 on the Fe(III)EDTA reduction experiments suggest that Escherichia coli can utilize NO2 , NO3 , and Fe(III)EDTA as terminal electron acceptors.  相似文献   

5.
天山林区不同类型群落土壤氮素对冻融过程的动态响应   总被引:1,自引:0,他引:1  
季节性冻融过程对北方温带森林土壤氮素的转化与流失具有重要影响,但不同类型群落对冻融过程响应的差异尚不明确。通过在林地、草地、灌丛上设置系列监测样地,采用原位培养的方法,利用林冠遮挡形成的自然雪被厚度差异,监测分析了冻融期天山林区不同群落表层土壤(0—15 cm)的氮素动态及净氮矿化速率间的差异。结果表明:(1)不同类型群落土壤的铵态氮(NH+4-N)含量、微生物量氮(MBN)含量基本与土壤(5 cm)温度呈正相关,深冻期林地土壤铵态氮含量低于其他群落类型而硝态氮含量高于其他群落类型;(2)硝态氮(NO-3-N)为天山林区季节性冻融期间土壤矿质氮的主体,占比达78.4%。灌丛土壤硝态氮流失风险较大,融化末期较融化初期灌丛土壤硝态氮含量下降了64.6%;(3)冻融时期对整体氮素矿化速率影响显著,群落类型对氨化速率影响显著;(4)天山林区土壤氮素在冻结期主要以氮固持为主。通过揭示不同类型群落土壤氮素对冻融格局的响应,能够助益于对北方林区冬季土壤氮素循环的认识。  相似文献   

6.
Nitrite (NO2 ) is an intermediate in a variety of soil N cycling processes. However, NO2 dynamics are often not included in studies that explore the N cycle in soil. Within the presented study, nitrite dynamics were investigated in a Nothofagus betuloides forest on an Andisol in southern Chile. We carried out a 15N tracing study with six 15N labeling treatments, including combinations of NO3 , NH4 + and NO2 . Gross N transformation rates were quantified with a 15N tracing model in combination with a Markov chain Monte Carlo optimization routine. Our results indicate the occurrence of functional links between (1) NH4 + oxidation, the main process for NO2 production (nitritation), and NO2 reduction, and (2) oxidation of soil organic N, the dominant NO3 production process in this soil, and dissimilatory NO3 reduction to NH4 + (DNRA). The production of NH4 + via DNRA was approximately ten times higher than direct mineralization from recalcitrant soil organic matter. Moreover, the rate of DNRA was several magnitudes higher than the rate of other NO3 reducing processes, indicating that DNRA is able to outcompete denitrification, which is most likely not an important process in this ecosystem. These functional links are most likely adaptations of the microbial community to the prevailing pedo-climatic conditions of this Nothofagus ecosystem.  相似文献   

7.
The kinetics of NH4 + and NO3 uptake in young Douglas fir trees (Pseudotsuga menziesii [Mirb.] Franco) were studied in solutions, containing either one or both N species. Using solutions containing a single N species, the Vmax of NH4 + uptake was higher than that of NO3 uptake. The Km of NH4 + uptake and Km of NO3 uptake differed not significantly. When both NH4 + and NO3 were present, the Vmax for NH4 + uptake became slightly higher, and the Km for NH4 + uptake remained in the same order. Under these conditions the NO3 uptake was almost totally inhibited over the whole range of concentrations used (10–1000 μM total N). This inhibition by NH4 + occurred during the first two hours after addition. ei]{gnA C}{fnBorstlap}  相似文献   

8.
Urban streams often contain elevated concentrations of nitrogen (N) which can be amplified in systems receiving effluent from wastewater treatment plants (WWTP). In this study, we evaluated the importance of denitrification in a stream draining urban Greensboro, NC, USA, using two approaches: (1) natural abundance of 15N–NO3 in conjunction with background NO3–N concentrations along a 7 km transect downstream of a WWTP; and (2) C2H2 block experiments at three sites and at three habitat types within each site. Overall lack of a longitudinal pattern of δ15N–NO3 and NO3–N, combined with high concentrations of NO3–N suggested that other factors were controlling NO3–N flux in the study transect. However, denitrification did appear to be significant along one portion of the transect. C2H2 block experiments showed that denitrification rates were much higher downstream of the WWTP compared to upstream, and showed that denitrification rates were highest in erosional and depositional areas downstream of the WWTP and in erosional areas upstream of the plant. Thus, the combination of the two methods for evaluating denitrification provided more insight into the spatial dynamics of denitrification activity than either approach alone. Denitrification appeared to be a significant sink for NO3–N upstream of the WWTP, but not downstream. Approximately 46% of the total NO3–N load was removed via denitrification in the upstream, urban section of the stream, while only 2.3% of NO3–N was lost downstream of the plant. This result suggests that controlling NO3–N loading from the plant could result in considerable improvement of downstream water quality.  相似文献   

9.
Sehtiya  H. L.  Goyal  Sham S. 《Plant and Soil》2000,227(1-2):185-190
The effect of light and exogenously supplied sucrose on NO3 uptake was studied in 9-day-old intact C3 (barley) and C4 (corn) seedlings. The seedlings used were uninduced for nitrate uptake system (i.e. had never seen nitrogen during germination and growth) and were exposed to continuous light for 3 days to avoid any diurnal variation and to load the seedlings fully with photosynthates. The uptake assay was conducted either in light or in darkness. Prior to assay, seedlings were treated with darkness or light for 24 h. Accordingly, four sets of seedlings, i.e. pretreated with light and assayed in light (LL); pretreated and assayed in darkness (DD); pretreated with light and assayed in darkness (LD); and pretreated with darkness and assayed in light (DL) were formed. Barley exhibited 55% higher NO3 uptake than corn during light (LL) and 91% higher during darkness (DD). Shifting barley seedlings from light to dark (LD) or dark to light (DL) for uptake assay, did not affect NO3 uptake, i.e. in LD the uptake was similar to LL and in DL it was similar to DD. However, in corn, the light conditions during the assay determined the uptake regardless of the conditions during the period preceding the assay. One percent sucrose in the medium increased NO3 uptake by 31% in barley and 70% in corn during light (LL). The corresponding increase during darkness (DD) was 38% in both barley and corn. Removal of the corn residual endosperm decreased NO3 uptake by 40% during darkness. Etiolated seedlings (those having never seen light) of both barley and corn were able to take up significant amount of NO3 during darkness. Externally supplied sucrose in the assay medium of etiolated seedlings increased the NO3 uptake to about 4 and 2 fold in barley and corn, respectively. The data presented here provide evidence that: 1. In intact seedlings, light per se is not obligatory for NO3 uptake and that the carbohydrate supply may mimic light. 2. Light affected the NO3 uptake differently in barley and corn. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

10.
Summary The purpose of this study was to investigate the phytotoxicity of nitrapyrin 2-chloro-6-(trichloromethyl)pyridine to sunflower (Helianthus annuus L.) under different N regimes and to see if N forms affect the phytotoxicity of nitrapyrin. Sunflower was grown in pot culture for 21 days and was fertilized with (NH4)2SO4, NH4NO3 and NaNO3 to provide 0, 100 and 200 ppm N and with nitrapyrin application of 0 and 20 ppm. All N-treated sunflower plants in all N regimes and regardless of titrapyrin treatment produced more root and shoot dry weights and contained a significantly higher N than untreated check. Nitrapyrin toxicity appeared as a curling of leaf margin and a tendril type of stem growth, the visible toxicity symptoms decreased in the order: (NH4)2SO4>NH4NO3>NaNO3. Furthermore nitrapyrin addition suppressed sunflower growth in each N regime, the suppressing effect being greater with (NH4)2SO4 and NH4NO3 than as with NaNO3. Although, shoot growth from plants receiving nitrapyrin was not significantly affected by any N regime, root growth of nitrapyrin-treated plants was somewhat restricted by NH4 +−N nutrition relative to NO3 −N nutrition.  相似文献   

11.
Labelled fertilizer N applied to winter wheat as Na15NO3 and (15NH4)2SO4 at a total N dressing of 100kg ha−1 was used in a microplot balance study to investigate the fate of each split fraction at three growth stages: end of tillering, heading and beginning of flowering. Results indicated that while the percentage utilization of the applied N by the grain and total crop increased considerably from the first to the third split application, these values diminished steadily in the straw. Grain recovery values for the first, second and third split applications were 34.2%, 51.5% and 55.7% for the NO3 and 32.3%, 48.4% and 52.5% for the NH4 carrier, respectively. The corresponding recovery values for the whole plant were 54.6%, 67.8% and 69.9% for the NO3 and 51.7%, 63.5% and 66.1% for the NH4 carrier. A greater proportion of the fertilizer N applied at the end of tillering stage was found in the vegetative plant components as compared with the grain. The reverse occurred for the N applied at the heading and at the beginning of the flowering stages. The residual fertilizer N found in the soil amounted to 18.0%, 10.4% and 11.6% of the applied NO3−N and to 22.5%, 12.7% and 15.2% of the applied NH4−N for the respective split applications. No differences were found for each split application between the two carriers as far as the unaccounted fertilizer N was concerned. The losses were 26.6%, 22.3% and 18.6% of the applied N for the three split applications, respectively. The application of fertilizer N did not lead to any increase in soil N uptake by the crop.  相似文献   

12.
Summary A procedure for the rapid determination of EUF-extractable nitrogen (NH4 +, NO3 and easily soluble organic N compounds) is described. In this procedure the EUF-N fractions are oxidized to NO3. The oxidation with peroxodisulfate is accelerated by ultraviolet (UV) radiation. This reduces the time of digestion to about 15 minutes. The contents of EUF-extractable N are on the average only between 2–8 mg/100 g soil. Their determination by the new procedure in the form of NO3 is more precise than the results obtained by digestion according to Kjeldahl. The sum of EUF-extractable N fractions obtained by the new procedure allows to assess the N fertilizer requirements more precisely than is possible when using the EUF-NO3 fractions alone. Therefore this new procedure constitutes a considerable advantage when working out fertilizer recommendations for agricultural practice.  相似文献   

13.
Abstract Sugar maple (Acer saccharum Marsh.)-dominated northern hardwood forests of the Great Lakes Region commonly receive elevated levels of atmospheric nitrate (NO3) deposition, which can alter belowground carbon (C) cycling. Past research has demonstrated that chronic experimental NO3 deposition (3 g N m−2 y−1 above ambient) elicits a threefold increase in the leaching loss of dissolved organic carbon (DOC). Here, we used DOC collected from tension-cup lysimeters to test whether increased DOC export under experimental NO3 deposition originated from forest floor or mineral soil organic matter (SOM). We used DOC radiocarbon dating to quantify C sources and colorimetric assays to measure DOC aromaticity and soluble polyphenolic content. Our results demonstrated that DOC exports are primarily derived from new C (<50-years-old) in the forest floor under both ambient and experimental NO3 deposition. Experimental NO3 deposition increased soluble polyphenolic content from 25.03 ± 4.26 to 49.19 ± 4.23 μg phenolic C mg DOC−1, and increased total aromatic content as measured by specific UV absorbance. However, increased aromatic compounds represented a small fraction (<10%) of the total observed increased DOC leaching. In combination, these findings suggest that experimental NO3 deposition has altered the production or retention as well as phenolic content of DOC formed in forest floor, however exact mechanisms are uncertain. Further elucidation of the mechanism(s) controlling enhanced DOC leaching is important for understanding long-term responses of Great Lakes forests to anthropogenic N deposition and the consequences of those responses for aquatic ecosystems.  相似文献   

14.
Summary A cotton and a wheat experiment were conducted in sequence to evaluate the effect of residual and fertilizer N on wheat with a water table fluctuating between 65 and 125 cm. Cotton treatments, replicated four times, consisted of 3 irrigation treatments as main plots and 6 N levels as subplots (0, 25, 50, 75, 100, 125 kg N/ha). After cotton the plots were planted to wheat and each subplot was divided into two equal sub-subplots. One received N at a rate similar to that previously applied to cotton and the other sub-subplot was left without N application for evaluating the residual effect. Determination of N forms in the soil before wheat indicated that NO3-N content of the top 25 cm increased from 4.4 to 16.3 ppm as N applied to cotton increased from 0 to 125 kg/ha. On the other hand, mineralizable-N was greater in the control than in the fertilized treatments, suggesting a priming effect on the mineralization of soil N. The residual effect on wheat was related to mineralizable-N rather than to NO3-N as grain yield was higher for the control than for the residual fertilizer N treatments. The yield was also higher for the more frequent than for the less frequent irrigation treatments, which may be attributed to increase in mineralization with soil water content. Wheat response to N application was significant. But high N levels accompanied by frequent irrigation enhanced lodging with subsequent reduction in yield. Measuring N uptake by grain and straw indicated 37% recovery of fertilizer N. It was concluded that under the prevailing conditions of high water table wheat response was largely dependent on the applied fertilizer due to insignificant residual N availability.  相似文献   

15.
Nitrogen fertilization is a key factor for coffee production but creates a risk of water contamination through nitrate (NO3) leaching in heavily fertilized plantations under high rainfall. The inclusion of fast growing timber trees in these coffee plantations may increase total biomass and reduce nutrient leaching. Potential controls of N loss were measured in an unshaded coffee (Coffea arabica L.) plot and in an adjacent coffee plot shaded with the timber species Eucalyptus deglupta Blume (110 trees ha−1), established on an Acrisol that received 180 kg N ha−1 as ammonium-nitrate and 2,700 mm yr−1 rainfall. Results of the one year study showed that these trees had little effect on the N budget although some N fluxes were modified. Soil N mineralization and nitrification rates in the 0–20 cm soil layer were similar in both systems (≈280 kg N ha−1 yr−1). N export in coffee harvest (2002) was 34 and 25 kg N ha−1 yr−1 in unshaded and shaded coffee, and N accumulation in permanent biomass and litter was 25 and 45 kg N ha−1 yr−1, respectively. The losses in surface runoff (≈0.8 kg mineral N ha−1 yr−1) and N2O emissions (1.9 kg N ha−1 yr−1) were low in both cases. Lysimeters located at 60, 120, and 200 cm depths in shaded coffee, detected average concentrations of 12.9, 6.1 and 1.2 mg NO3-N l−1, respectively. Drainage was slightly reduced in the coffee-timber plantation. NO3leaching at 200 cm depth was about 27 ± 10 and 16 ± 7 kg N ha−1 yr−1 in unshaded and shaded coffee, respectively. In both plots, very low NO3 concentrations in soil solution at 200 cm depth (and in groundwater) were apparently due to NO3 adsorption in the subsoil but the duration of this process is not presently known. In these conventional coffee plantations, fertilization and agroforestry practices must be refined to match plant needs and limit potential NO3 contamination of subsoil and shallow soil water.  相似文献   

16.
A sterile hydroponic culture system suitable for studying nitrogen (N) uptake ofLagerstroemia indica L.in vitro was developed. Four different treatments were assayed: with and without activated charcoal (AC and NAC, respectively), with and without 50 μM of 6-benzyladenine (+BA and −BA, respectively). Medium pH, electrical conductivity (EC), NO3 and NH4 + concentrations were measured weekly. At the end of the culture, propagules were sampled and SPAD indices, and shoot and root fresh weights were determined. Explants grown in media with activated charcoal were able to take up both NO3 and NH4 +, although NH4 + uptake was lower. Subsequently the pH of the media was maintained between 5.5–6.0. In treatments with no addition of activated charcoal, NH4 + uptake was preferential and the pH dropped to 3.1. Explants in these conditions were unable to raise the pH by taking up NO3 , especially when root morphogenesis was inhibited by addition of BA. Supply of this PGR produced root growth inhibition, which was almost complete in the treatment without activated charcoal. This component significantly reduced the inhibitory effect of 50 μM BA on root growth. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

17.
Wetlands are often highly effective nitrogen (N) sinks. In the Lake Waco Wetland (LWW), near Waco, Texas, USA, nitrate (NO3) concentrations are reduced by more than 90% in the first 500 m downstream of the inflow, creating a distinct gradient in NO3 concentration along the flow path of water. The relative importance of sediment denitrification (DNF), dissimilatory NO3 reduction to ammonium (DNRA), and N2 fixation were examined along the NO3 concentration gradient in the LWW. “Potential DNF” (hereafter potDNF) was observed in all months and ranged from 54 to 278 μmol N m−2 h−1. “Potential DNRA” (hereafter potDNRA) was observed only in summer months and ranged from 1.3 to 33 μmol N m−2 h−1. Net N2 flux ranged from 184 (net denitrification) to −270 (net N2 fixation) μmol N m−2 h−1. Nitrogen fixation was variable, ranging from 0 to 426 μmol N m−2 h−1, but high rates ranked among the highest reported for aquatic sediments. On average, summer potDNRA comprised only 5% (±2% SE) of total NO3 loss through dissimilatory pathways, but was as high as 36% at one site where potDNF was consistently low. Potential DNRA was higher in sediments with higher sediment oxygen demand (r 2 = 0.84), and was related to NO3 concentration in overlying water in one summer (r 2 = 0.81). Sediments were a NO3 sink and accounted for 50% of wetland NO3 removal (r 2 = 0.90). Sediments were an NH4+ source, but the wetland was often a net NH4+ sink. Although DNRA rates in freshwater wetlands may rival those observed in estuarine systems, the importance of DNRA in freshwater sediments appears to be minor relative to DNF. Furthermore, sediment N2 fixation can be extremely high when NO3 in overlying water is consistently low. The data suggest that newly fixed N can support sustained N transformation processes such as DNF and DNRA when surface water inorganic N supply rates are low.  相似文献   

18.
川西北高寒草地沙化过程中土壤氮素变化特征   总被引:7,自引:0,他引:7  
蒋双龙  胡玉福  蒲琴  舒向阳  袁铖铭  余倩 《生态学报》2016,36(15):4644-4653
草地沙化是我国最严重的环境问题之一,但关于草地沙化过程中氮素变化特征的研究报道多集中于干旱半干旱地区,而半湿润地区的相关报道还比较缺乏。通过野外调查,研究了川西北半湿润地区高寒沙质草地沙化过程中土壤氮素变化特征。结果表明,草地沙化对0—100cm土层土壤氮素具有显著影响,全氮、碱解氮、铵态氮(NH_4~+-N)、硝态氮(NO_3~--N)和微生物量氮(MBN)均呈现极显著下降的变化特征,极度沙化阶段较未沙化阶段分别减少了73.95%、77.72%、76.75%、79.77%和84.12%。其中,0—20cm土层变化最显著,全氮、碱解氮、NH_4~+-N、NO_3~--N和MBN含量分别减少了86.43%、83.52%、82.11%、88.82%和91.77%。随着土层深度增加,不同程度沙化草地土壤氮素含量及其变化量逐渐减少;草地沙化过程中,不同沙化阶段土壤氮素损失数量不尽相同,其中,以轻度沙化阶段氮素损失最严重,全氮、碱解氮、NH_4~+-N、NO-3-N和MBN含量分别降低了41.18%、35.17%、46.74%、43.46%和46.88%。草地沙化过程中,土壤全氮、碱解氮、NH_4~+-N、NO_3~--N和MBN含量与土壤粉粒、粘粒含量和植被群落盖度均呈极显著正相关特征,与土壤沙粒含量呈极显著负相关特征。研究区土壤氮素损失与风蚀选择性吹蚀土壤粉粒、粘粒及地表植物覆盖状况逐渐变差密切相关,因此该区域治沙的关键是采取措施降低风蚀对地表土壤吹蚀作用,提高沙化草地地表植被覆盖。同时,还应及时对沙化前期阶段及潜在沙化的草地进行生态治理,从而避免草地沙化继续恶化。  相似文献   

19.
Three-year-old Scots pine (Pinus sylvestris) trees were grown on a sandy forest soil in pots, with the objective to determine their NH4/NO3 uptake ratio and proton efflux. N was supplied in three NH4-N/NO3-N ratios, 3:1, 1:1 and 1:3, either as 15NH4+14NO3 or as 14NH4+15NO3. Total N and 15N acquisition of different plant parts were measured. Averaged over the whole tree, the NH4/NO3 uptake ratios throughout the growing season were found to be 4.2, 2.5, and 1.5 for the three application ratios, respectively. The excess cation-over-anion uptake value (Ca-Aa) appeared to be linearly related to the natural logarithm of the NH4/NO3 uptake ratio. Further, this uptake ratio was related to the NH4/NO3 ratio of the soil solution. From these relationship it was estimated that Scots pine exhibits an acidifying uptake pattern as long as the contribution of nitrate to the N nutrition is lower than 70%. Under field circumstances root uptake may cause soil acidification in the topsoil, containing the largest part of the root system, and soil alkalization in deeper soil layers.  相似文献   

20.
Large inputs of atmospheric N from dry deposition accumulate on vegetation and soil surfaces of southern Californian chaparral and coastal sage scrub (CSS) ecosystems during the late-summer and early-fall and become available as a pulse following winter rainfall; however, the fate of this dry season atmospheric N addition is unknown. To assess the potential for dry season atmospheric N inputs to be incorporated into soil and/or vegetation N pools, an in situ N addition experiment was initiated in a post-fire chaparral and a mature CSS stand where 10 × 10 m plots were exposed to either ambient N deposition (control) or ambient +50 kg N ha−1 (added N) added as NH4NO3 during a single application in October 2003. After 1 year of N addition, plots exposed to added N had significantly higher accumulation of extractable inorganic N (NH4−N + NO3−N) on ion exchange resins deployed in the 0–10 cm mineral soil layer and higher soil extractable N in the subsurface (30–40 cm) mineral soil than plots exposed to ambient N. Chaparral and CSS shrubs exposed to added N also exhibited a significant increase in tissue N concentration and a decline in the tissue C:N ratio, and added N significantly altered the shrub tissue δ 15N natural abundance. Leaching of inorganic N to 1 m below the soil surface was on average 2–3 times higher in the added N plots, but large within treatment variability cause these differences to be statistically insignificant. Although a large fraction of the added N could not be accounted for in the shrub and soil N pools investigated, these observations suggest that dry season N inputs can significantly and rapidly alter N availability and shrub tissue chemistry in Mediterranean-type chaparral and CSS shrublands of southern California.  相似文献   

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