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1.
Fertilization rates and clay fixed ammonium in two Quebec soils 总被引:5,自引:0,他引:5
Clay fixed NH4
+ can provide a significant sink for fertilizer N, as well as a source of N for plant uptake. Knowledge or soil NH4
+ fixing capacity and release for crops is necessary to develop long-term fertilizer programs. Field experiments with corn (Zea mays L.) were carried out to investigate soil NH4
+ fixing capacity and subsequent release as influenced by fertilizer rates using 15N in a Ste. Rosalie clay (fine, mixed, frigid, Typic Humaquept) and a Chicot sandy clay loam (fine-loamy, mixed, frigid, Typic Hapludalf). With high N rates increased NH4
+ fixation occurred only in the Ste. Rosalie soil. At the end of the first growing season, fertilizer N recovery as clay fixed NH4
+ for high and normal rates of fertilizer in the Ste. Rosalie soil was 17.8% and 28.7%, respectively and the recovery for the high and normal rates in the Chicot soil was 4.6 and 10.5%, respectively. Significant amounts of clay fixed NH4
+-N were released in the soil profile in the second year after 15N application on the Chicot soil. Recently clay fixed fertilizer NH4
+N was released more rapidly than that of the native fixed NH4
+, from the surface layer of the Ste. Rosalie soil. The fertilizer fixed NH4
+ seems to be in a more labile N pool than the native fixed NH4
+-N in the Chicot soil. 相似文献
2.
Impacts of Soil Nitrogen and Carbon Additions on Forest Understory Communities with a Long Nitrogen Deposition History 总被引:1,自引:0,他引:1
Samantha K. Chapman Kathryn A. Devine Courtney Curran Rachel O. Jones Frank S. Gilliam 《Ecosystems》2016,19(1):142-154
Rates of nitrogen (N) deposition have been historically high throughout much of the northeastern United States; thus, understanding the legacy of these high N loads is important for maintaining forest productivity and resilience. Though many studies have documented plant invasions due to N deposition and associated impacts on ecosystems, less is known about whether invasive plants will continue to increase in dominance with further shifting nutrient regimes. Using soil N and carbon additions, we examined the impact of both increasing and decreasing soil N on native and invasive understory plant dynamics over 4 years in a northeastern deciduous forest with a long history of N deposition. Despite applying large quantities of N, we found no difference in soil nitrate (NO3) or ammonium (NH4 +) pools in N addition plots over the course of the study. Indicative of the potential N saturation in these forest soils, resin-available NO3 ? and NH4 + showed evidence that the added N was rapidly moving out of the soil in N addition plots. Accordingly, we also found that adding N to soil altered neither invasive nor native plant abundance, though adding N temporally increased invasive plant richness. Carbon additions decreased soil N availability seasonally, but did not alter the total percent cover of invasive or native plants. Rather than being suppressed by excess N availability, native plant species in this ecosystem are primarily inhibited by the invasive species, which now dominate this site. In conclusion, understory plant communities in this potentially N-saturated ecosystem may be buffered to future alterations in N availability. 相似文献
3.
The effect of incorporating cattle slurry in soil, either by mixing or by simulated injection into a hollow in soil, on the ryegrass uptake of total N and 15NH4
+-N was determined in three soils of different texture. The N accumulation in Italian ryegrass (Lolium multiflorum L.) from slurry N and from an equivalent amount of NH4
+-N in (15NH4) SO4 (control) was measured during 6 months of growth in pots. After this period the total recovery of labelled N in the top soil plus herbage was similar in the slurry and the control treatments. This indicated that gaseous losses from slurry NH4
+-N were insignificant. Consequently, the availability of slurry N to plants was mainly influenced by the mineralization-immobilization processes. The apparent utilization of slurry NH4
+-N mixed into soil was 7%, 14% and 24% lower than the utilization of (NH4)2SO4-N in a sand soil, a sandy loam soil and a loam soil, respectively. Thus, the net immobilization of N due to slurry application increased with increasing soil clay content, whereas the recovery in plants of 15N-labelled NH4
+-N from slurry was similar on the three soils. A parallel incubation experiment showed that the immobilization of slurry N occurred within the first week after slurry application. The incorporation of slurry N by simulated injection increased the plant uptake of both total and labelled N compared to mixing the slurry into the soil. The apparent utilization of injected slurry NH4
+-N was 7% higher, 8% lower and 4% higher than the utilization of (NH4)2SO4-N in the sand, the sandy loam and the loam soil, respectively. It is concluded that the spatial distribution of slurry in soil influenced the net mineralization of N to the same degree as did the soil type. 相似文献
4.
H. W. Scherer 《Plant and Soil》1982,64(1):67-71
Summary Representative arable soils from Hesse were investigated for their contents of fixed NH4
+ and EUF-extractable potassium in the rooting zone. Alluvial soils were found to be rich in fixed ammonium and low in EUF-extractable
potassium, while soils of basaltic origin were low in fixed ammonium and rich in EUF-extractable potassium. A negative correlation
(r=0.79*) was found between fixed NH4
+ and EUF-extractable soil K+. The content of fixed NH4
+ in the soil profile showed considerable and significant changes during the growing season, which finding is supposed to be
due to NH4
+ uptake by the crop. 相似文献
5.
Although the inhibitory effects of high concentrations of mineral N (> 1.0 mM) on nodule development and function have often been studied, the effects of low, static concentrations of NH4+ (< 1.0 mM) on nodulation are unknown. In the present experiments we examine the effects of static concentrations of NH4+ at 0, 0.1 and 0.5 mM in flowing, hydroponic culture on nodule establishment and nitrogenase activity in field peas [Pisum sativum L. cv. Express (Svalöf AB)] for the initial 28 days after planting (DAP). Peas grown in the presence of low concentrations of NH4+ had significantly greater nodule numbers (up to 4-fold) than plants grown without NH4+. Nodule dry weight per plant was significantly higher at 14, 21 and 28 DAP in plants grown in the presence of NH4+, but individual nodule mass was lower than in plants grown without NH4+. The nodulation pattern of the plants supplied with NH4+ was similar to that often reported for supernodulating mutants, however the plants did not express other growth habits associated with supernodulation. Estimates of N2 fixation indicate that the plus-NH4+ peas fixed as much or more N2 than the plants supplied with minus-NH4+ nutrient solution. There were no significant differences in nodule numbers, nodule mass or NH4+ uptake between the plants grown at the two concentrations of NH4+. Nodulation appeared to autoregulate by 14 DAP in the minus-NH4+ treatment. Plant growth and N accumulation in the minus-NH4+ plants lagged behind those of the plus-NH4+ treatments prior to N2 fixation becoming well established in the final week of the experiment. The plus-NH4+ treatments appeared not to elicit autoregulation and plants continued to initiate nodules throughout the experiment. 相似文献
6.
增氮对青藏高原东缘高寒草甸土壤甲烷吸收的早期影响 总被引:1,自引:0,他引:1
研究大气氮沉降对青藏高原高寒草甸土壤CH4吸收的影响,对于揭示氮素调节土壤CH4吸收的机制和评价氮沉降增加背景下大气CH4收支平衡至关重要.通过构建多形态、低剂量的增氮控制试验,测定土壤CH4净交换通量和相关土壤理化性质,分析高寒草甸土壤CH4通量变化特征及其主要驱动因子.研究结果表明:自然状态下高寒草甸土壤是大气CH4汇,CH4平均吸收量为(35.40±1.92) μg· m-2· h-1.土壤CH4吸收主要受水分驱动,其次为土壤NH4+-N和NO3-N含量.NH4+-N抑制CH4吸收,NO3--N促进CH4吸收;不同剂量氮素输入对土壤CH4吸收影响也不尽相同,低氮处理促进土壤CH4吸收,而中氮和高氮处理抑制土壤CH4吸收.结果显示青藏高原高寒草甸土壤是重要的大气CH4汇,在未来大气氮沉降加倍的情景下CH4汇功能增强,但当氮沉降量增加两倍以上时CH4汇功能将会减弱. 相似文献
7.
NH4 +-fixation by inorganic and organic soil components and crop utilization of fertilier nitrogen was studied in a number of Carbbean soils using15N fertilizers. At moderate rates of nitrogen application, NH4 +-fixation by clays during several-week laboratory incubations was rapid and highly vaiable, ranging from less than 10% to over 70% of the NH4 + added. The 2: 1 lattice types were the most reactive, and the process were almost complete by one week after fertilization. Fixation increased with rate of NH4 +-N application and was higher at elevated temperatures in soils that were allowed to air-dry during incubation. NH4 +-N fixation was more active in the fulvic fractions of the soil organic matter than in the humuc fractions (25–69%vs0–3% of the added NH4 + was fixed in each, respectively). There was little incorporation of fertilizer-N by the N-containing fractions of soil organic matter. Plant uptake of added NH4 +-N in greenhouse pot experiments showed that a greater percentalte of fertilizer-N was taken up by Sudan grass (Sourghum sudanese) at a fertilizer rate of 40 kg NH4 +-N ha?1 than at a rate of 200n kg NH4 +N ha?1. howver, the recovery was low, ranging from 10 to 25 percent of that applied. In field experiments with maize (Zea mays), urea-N was rapidly lost when applied to soils in a wet tropical environment. At normal rates of application (100 kg urea-N ha?1) only about half of the fertilizer was utilized by the crop. Mulches did not significantly affect the fate of added nitrogen; however, mulching did result in increased yields for dry-season cropping, due probably to water conservation effects. There is good indication that for conditions in Trinidad, NH4 +-N is better utilzed and less subject to unidentified losses than is urea. Addition of fertilizer-N resulted in crop uptake of important quantities of native soil nitrogen. The Caribbean Andepts were outstanding in that the showed very little NH4 +-fixation under all experimental conditions and very little tendency for apparent nitrification of added NH4 +-N. 相似文献
8.
氮素类型和剂量对寒温带针叶林土壤N2O排放的影响 总被引:1,自引:0,他引:1
大气氮沉降输入会增加森林生态系统氮素有效性,进而改变土壤N_2O产生与排放,然而有关不同氮素离子(氧化态NO_3~--N与还原态NH_4~+-N)沉降对土壤N_2O排放的影响知之甚少。以大兴安岭寒温带针叶林为研究对象,构建了3种类型(NH_4Cl、KNO_3、NH_4NO_3)和4个施氮水平(0、10、20、40 kg N hm~(-2)a~(-1))的增氮控制试验,利用流动化学分析仪和静态箱-气相色谱法4次/月测定凋落物层和矿质层土壤无机氮含量、土壤-大气界面N_2O净交换通量以及相关环境因子,分析施氮类型和剂量对土壤氮素有效性、土壤N_2O通量的影响探讨氮素富集条件下土壤N_2O通量的环境驱动机制。结果表明:施氮类型和剂量均显著影响土壤无机氮含量,土壤NH_4~+-N的积累效应显著高于NO_3~--N。施氮一致增加寒温带针叶林土壤N_2O排放,NH_4NO_3促进效应最为明显,增幅为442%-677%,高于全球平均水平(134%)。土壤N_2O通量与土壤温度、凋落物层NH_4~+-N含量正相关,且随着施氮水平增加而增加。结果表明大气氮沉降短期内不会导致寒温带针叶林土壤NO_3~--N大量流失,但会显著促进土壤N_2O的排放。此外,外源性NH_4~+和NO_3~-输入对土壤N_2O排放的促进作用具有协同效应,在未来森林生态系统氮循环和氮平衡研究中应该区分对待。 相似文献
9.
C. Vega-Jarquin M. Garcia-Mendoza N. Jablonowski M. Luna-Guido L. Dendooven 《Plant and Soil》2003,256(2):379-388
The dynamics of inorganic N are important in soil, and this applies particularly to the saline–alkaline soils of the former lake Texcoco in Mexico with high pH and salinity where a forestation program was started in the 1970s. In soils of lake Texcoco, in Mexico, more than 50% of applied N could not be accounted for one day after application of 200 mg kg–1 soil along with glucose amendment. It was not clear whether this was due to abiotic or biotic processes, the form of inorganic N applied or the result of applying an easily decomposable substrate. We investigated this by adding glucose and 200 mg kg–1 soil as (NH4)2SO4-N or KNO3-N to sterilized and unsterilized soil. The changes in inorganic and ninhydrin N, microbial biomass C and production of CO2 were then monitored. Between the time of applying N and extraction with 0.5 M K2SO4, i.e., after ca 2 h, approximately 110 mg NH4
+-N kg–1 dry soil could not be accounted for in the unsterilized and sterilized soil and that remained so for the entire incubation in the sterilized soil. After 1 day this increased to 140 mg NH4
+-N kg–1 dry soil in the unsterilized control and 170 mg NH4
+-N kg–1 dry soil in C amended soil. Volatilization of NH3 accounted for 56 mg NH4
+-N kg–1 so the rest appeared to be adsorbed on the soil matrix. The NH3 volatilization and NH4
+ fixed in the soil matrix remained constant over time and no oxidation to NO2
– or NO3
– had occurred, so unaccounted N in unsterilized soil was probably incorporated into the microbial biomass in excess of what was required for metabolic activity. The unaccounted N was ca 70 mg NO3
––N in nitrate amended soil after 3 days and 138 NO3
––N when glucose was additionally added. Losses through abiotic processes were absent as inferred from changes in sterilized soil and the aerobic incubation inhibited possible losses through denitrification. It was inferred that NO3
– that could not be accounted for was taken up by micro-organisms in excess of what was required for metabolic activity. 相似文献
10.
K. L. Sahrawat 《Plant and Soil》1980,55(2):225-233
Summary A study of changes in NH4
+ and NO3
––N in Maahas clay amended with (NH4)2SO4 and subjected to 4 water regimes in the presence and absence of the nitrification inhibitor N-Serve (Nitrapyrin) showed that the mineral N was well conserved in the continoous regimes of 50% and 200% (soil weight basis) but suffered heavy losses due to nitrification-denitrification under alternate drying and flooding. N-Serve was effective in minimizing these losses.Another incubation study with 3 soils showed that after 10 cycles of flooding and drying (either at 60°C or 25°C), the ammonification of soil N was enhanced. Nitrification of soil as well as fertilizer NH4
+ was completely inhibited upto 4 weeks by the treatments involving drying at high temperature. Flooding and air drying at 25°C, on the other hand, enhanced ammonification of soil N but retarded nitrification. These treatments, however, enhanced both ammonification and nitrification of the applied NH4
+ fertilizer N. Under flooded conditions rate of NH4
+ production was faster in soils that were dried at 60°C or 25°C and then flooded as compared to air dried soils.It is concluded that N losses by nitrification-denitrification and related N transformations may be considerably altered by alternating moisture regimes. Flooding and drying treatments seem to retard nitrification of soil N but conserve that of fertilizer NH4
+ applied after these treatments. 相似文献
11.
Tree growth and soil acidification in response to 30 years of experimental nitrogen loading on boreal forest 总被引:23,自引:0,他引:23
PETER HÖGBERG HOUBAO FAN † MAUD QUIST ‡ DAN BINKLEY§ CARL OLOF TAMM¶ 《Global Change Biology》2006,12(3):489-499
Relations among nitrogen load, soil acidification and forest growth have been evaluated based on short‐term (<15 years) experiments, or on surveys across gradients of N deposition that may also include variations in edaphic conditions and other pollutants, which confound the interpretation of effects of N per se. We report effects on trees and soils in a uniquely long‐term (30 years) experiment with annual N loading on an un‐polluted boreal forest. Ammonium nitrate was added to replicated (N=3) 0.09 ha plots at two doses, N1 and N2, 34 and 68 kg N ha?1 yr?1, respectively. A third treatment, N3, 108 kg N ha?1 yr?1, was terminated after 20 years, allowing assessment of recovery during 10 years. Tree growth initially responded positively to all N treatments, but the longer term response was highly rate dependent with no gain in N3, a gain of 50 m3 ha?1 stemwood in N2 and a gain of 100 m3 ha?1 stemwood in excess of the control (N0) in N1. High N treatments caused losses of up to 70% of exchangeable base cations (Ca2+, Mg2+, K+) in the mineral soil, along with decreases in pH and increases in exchangeable Al3+. In contrast, the organic mor‐layer (forest floor) in the N‐treated plots had similar amounts per hectare of exchangeable base cations as in the N0 treatment. Magnesium was even higher in the mor of N‐treated plots, providing evidence of up‐lift by the trees from the mineral soil. Tree growth did not correlate with the soil Ca/Al ratio (a suggested predictor of effects of soil acidity on tree growth). A boron deficiency occurred on N‐treated plots, but was corrected at an early stage. Extractable NH4+ and NO3?were high in mor and mineral soils of on‐going N treatments, while NH4+ was elevated in the mor only in N3 plots. Ten years after termination of N addition in the N3 treatment, the pH had increased significantly in the mineral soil; there were also tendencies of higher soil base status and concentrations of base cations in the foliage. Our data suggest the recovery of soil chemical properties, notably pH, may be quicker after removal of the N‐load than predicted. Our long‐term experiment demonstrated the fundamental importance of the rate of N application relative to the total amount of N applied, in particular with regard to tree growth and C sequestration. Hence, experiments adding high doses of N over short periods do not mimic the long‐term effects of N deposition at lower rates. 相似文献
12.
H+ production due to N uptake in a mature Scots pine stand subjected to high NH4
+ deposition was previously estimated to amount to approx. 2.2 kmol ha-1 y-1. The question whether H+ transfers related to N mineralization (ammonification and nitrification) offset or corroborate this proton production is investigated in the present research. To determine N mineralization, soil cores were used of which both ends were closed with layers of ion exchange resin (IER) to prevent influx and efflux of ions. The effect of liming on N mineralization and the resulting H+ production was investigated in 7 incubation periods of each ca. 8 wk. Because of its high mobility NO3 accumulated in both IER layers at the expense of that in the incubated forest floor and mineral soil. Net N mineralization in the soil cores as a whole amounted to 40 and 77 kg N ha-1 in 384 d in the control and limed plots, respectively. In both treatments ca. 65% of mineralized N was nitrified. H+ production due to N mineralization amounted to approx. 1.2 kmol ha-1 y-1 in the control and limed plots. Liming reduced the amount of C in the forest floor, but not forest floor mass, because of an increased mixing with mineral particles. 相似文献
13.
Spatial variability of soil total nitrogen (N), available N (KCl extractable NH4+ and NO3−), and spatial patterns of N mineralization and nitrification at a stand scale were characterized with geostatistical and
univariate analysis. Two extensive soil spatial samplings were conducted in an evergreen broadleaf forest in Sichuan province,
southwestern China in June and August 2000. In a study area of 90 × 105 m2, three soil samples were collected from each 5 × 5 m2 plot (n = 378) in June and August, and were analyzed for total N and available N contents. Net N mineralization and nitrification
were measured by in situ core incubation and the rates were estimated based on the difference of NH4+ and NO3− contents between the two sampling dates. Total N, NH4+, and NO3− were all spatially structured with different semivariogram ranges (from high to low: NH4+, NO3−, and total N). The semivariograms of mineralization and nitrification were not as spatially structured as available N. NH4+ was the dominant soil inorganic N form in the system. Both NH4+ and NO3− affected spatial patterns of soil available N, but their relative importance switched in August, probably due to high nitrification
as indicated by greatly increased soil NO3− content. High spatial auto-correlations (>0.7) were found between available N and NH4+, available N and NO3− on both sampling dates, as well as total N measurements between both sampling dates. Although significant, the spatial auto-correlation
between NH4+ and NO3− were generally low. Topography had significant but low correlations with mineralization (r = −0.16) and nitrification (r = −0.14), while soil moisture did not. The large nugget values of the calculated semivariograms and high-semivariance values,
particularly for mineralization and nitrification, indicate that some fine scale (<5 m) variability may lie below the threshold
for detection in this study. 相似文献
14.
Summary Tracer studies were made on balance and chemical distribution of added fertilizer under field conditions using a modified type of lysimeter at different moisture regimes. A modified chemical method was also used for the determination of different forms of organic N.An average of 25 per cent of the isotope enriched nitrogen applied to soil could not be accounted for at the end of the 3 years of experiment. The amount of residual added N in soil was around 33 per cent of which 27 per cent was in 0–20 cm layers and only 6 per cent was found in 20–50 cm layers. The average crop recoveries were around 43 per cent. Only 0.18 per cent of NO3–N was leached from the irrigated plots.The alkali-stable N (amino acid-N) fraction was higher for irrigated (19 per cent) than nonirrigated plots (15 per cent). There were no difference in the amounts of fixed NH4, non-hydrolyzed and alkali-labile N fractions for irrigated and non-irrigated plots. Only an average of 1.5 per cent of total fertilizer N was found as fixed NH4–N form but the total fixed NH4–N was higher (10–13 per cent) than that reported by other workers for surface soil layers. The sum of different soil-nitrogen fractions were always higher than the total nitrogen in soil. 相似文献
15.
青藏高原高寒草甸土壤CO2排放对模拟氮沉降的早期响应 总被引:5,自引:0,他引:5
研究大气氮沉降输入对青藏高原高寒草甸土壤-大气界面CO2交换通量的影响,对于准确评价全球变化背景下区域碳平衡至关重要。通过构建多形态、低剂量的增氮控制试验,利用静态箱-气相色谱法测定土壤CO2排放通量,同时测定相关土壤变量和地上生物量,分析高寒草甸土壤CO2排放特征及其主要驱动因子。研究结果表明:低、高剂量氮输入倾向于消耗土壤水分,而中剂量氮输入有利于土壤水分的保持;施氮初期总体上增加了土壤无机氮含量,铵态氮累积效应更为显著;施氮显著增加地上生物量和土壤CO2排放通量,铵态氮的促进效应显著高于硝态氮。另外,土壤CO2排放通量主要受土壤温度驱动,其次为地上生物量和铵态氮储量。上述结果反映了氮沉降输入短期内可能刺激了植物生长和土壤微生物活性,加剧了土壤-大气界面CO2排放。 相似文献
16.
Yongsheng Wang Shulan Cheng Huajun Fang Guirui Yu Minjie Xu Xusheng Dang Linsen Li Lei Wang 《PloS one》2014,9(4)
To date, few studies are conducted to quantify the effects of reduced ammonium (NH4
+) and oxidized nitrate (NO3
−) on soil CH4 uptake and N2O emission in the subtropical forests. In this study, NH4Cl and NaNO3 fertilizers were applied at three rates: 0, 40 and 120 kg N ha−1 yr−1. Soil CH4 and N2O fluxes were determined twice a week using the static chamber technique and gas chromatography. Soil temperature and moisture were simultaneously measured. Soil dissolved N concentration in 0–20 cm depth was measured weekly to examine the regulation to soil CH4 and N2O fluxes. Our results showed that one year of N addition did not affect soil temperature, soil moisture, soil total dissolved N (TDN) and NH4
+-N concentrations, but high levels of applied NH4Cl and NaNO3 fertilizers significantly increased soil NO3
−-N concentration by 124% and 157%, respectively. Nitrogen addition tended to inhibit soil CH4 uptake, but significantly promoted soil N2O emission by 403% to 762%. Furthermore, NH4
+-N fertilizer application had a stronger inhibition to soil CH4 uptake and a stronger promotion to soil N2O emission than NO3
−-N application. Also, both soil CH4 and N2O fluxes were driven by soil temperature and moisture, but soil inorganic N availability was a key integrator of soil CH4 uptake and N2O emission. These results suggest that the subtropical plantation soil sensitively responses to atmospheric N deposition, and inorganic N rather than organic N is the regulator to soil CH4 uptake and N2O emission. 相似文献
17.
High δ15N of tree foliage in forests subject to high N supply has been attributed to 15N enrichment of plant available soil N pools after losses of N through processes involving N isotope fractionation (ammonia volatilization, nitrification followed by leaching and denitrification, and denitrification in itself). However, in a long-term experiment with high annual additions of NH4NO3, we found no change in the weighted average δ15N of the soil, but attributed the high δ15N of trees to loss of ectomycorrhizal fungi and their function in tree N uptake, which involves redistribution of N isotopes in the ecosystem (Högberg et al. New Phytol 189:515–525, 2011), rather than a loss of isotopically light N. Here, we compare the effects of additions of urea and NH4NO3 on the δ15N of trees and the soil profile, because we have previously found higher δ15N in tree foliage in trees in the urea plots. Doing this, we found no differences between the NH4NO3 and urea treatments in the concentration of N in the foliage, or the amounts of N in the organic mor-layer of the soil. However, the foliage of trees receiving the highest N loads in the urea treatment were more enriched in 15N than the corresponding NH4NO3 plots, and, importantly, the weighted average δ15N of the soil showed that N losses had been associated with fractionation against 15N in the urea plots. Thus, our results in combination with those of Högberg et al. (New Phytol 189:515–525, 2011) show that high δ15N of the vegetation after high N load may be caused by both an internal redistribution of the N isotopes (as a result of change of the function of ectomycorrhiza) and by losses of isotopically light N through processes fractionating against 15N (in case of urea ammonia volatilization, nitrification followed by leaching and denitrification). 相似文献
18.
To study the long-term fate of deposited ammonium (NH4 +) in a Scots pine forest stand under high nitrogen (N) deposition in the Netherlands we re-sampled the plots of a 15N tracer experiment with high (i.e. ambient) and lowered N deposition in this stand 8 years after application of the tracer. The results were compared with results obtained 7 years earlier. In the 7 years between the samplings the 15N deltas of needles, twigs and upper organic soil layer had converged to similar values still above the natural 15N abundance, suggesting equilibration as a result of intensive cycling of N among these pools. Bark and wood had lower deltas than needles and twigs, but if the label found was attributed to tissue synthesized since the start of the labeling only, bark values were similar to needles and twigs, whereas wood values were higher indicating retranslocation of N into older wood. Mineral soil lost all 15N label it had accumulated after 1 year indicating that this label had not been strongly bound. The first year the low N treatment had retained more of the labeled NH4 + deposition than the high N treatment, but in the seven subsequent years relatively more label was retained in the latter. This better retention after 7 years was ascribed to a larger fraction of label taken up by the vegetation in the high N treatment. This shows that the vegetation can affect the label dynamics despite the fact that only a relatively small amount of label was present in the aboveground vegetation. 相似文献
19.
The seasonal dynamics of amino acids and other nutrients in Alaskan Arctic tundra soils 总被引:4,自引:0,他引:4
Past research strongly indicates the importance of amino acids in the N economy of the Arctic tundra, but little is known about the seasonal dynamics of amino acids in tundra soils. We repeatedly sampled soils from tussock, shrub, and wet sedge tundra communities in the summers of 2000 and 2001 and extracted them with water (H2O) and potassium sulfate (K2SO4) to determine the seasonal dynamics of soil amino acids, ammonium (NH4+), nitrate (NO3–), dissolved organic nitrogen (DON), dissolved organic carbon (DOC), and phosphate (PO42–). In the H2O extractions mean concentrations of total free amino acids (TFAA) were higher than NH4+ in all soils but shrub. TFAA and NH4+ were highest in wet sedge and tussock soils and lowest in shrub soil. The most predominant amino acids were alanine, arginine, glycine, serine, and threonine. None of the highest amino acids were significantly different than NH4+ in any soil but shrub, in which NH4+ was significantly higher than all of the highest individual amino acids. Mean NO3– concentrations were not significantly different from mean TFAA and NH4+ concentrations in any soil but tussock, where NO3– was significantly higher than NH4+. In all soils amino acid and NH4+ concentrations dropped to barely detectable levels in the middle of July, suggesting intense competition for N at the height of the growing season. In all soils but tussock, amino acid and NH4+ concentrations rebounded in August as the end of the Arctic growing season approached and plant N demand decreased. This pattern suggests that low N concentrations in tundra soils at the height of the growing season are likely the result of an increase in soil N uptake associated with the peak in plant growth, either directly by roots or indirectly by microbes fueled by increased root C inputs in mid-July. As N availability decreased in July, PO42– concentrations in the K2SO4 extractions increased dramatically in all soils but shrub, where there was a comparable increase in PO42– later in the growing season. Previous research suggests that these increases in PO42– concentrations are due to the mineralization of organic phosphorus by phosphatase enzymes associated with soil microbes and plant roots, and that they may have been caused by an increase in organic P availability. 相似文献
20.
Two experiments were conducted where Cucumis sativus were grown in uncompartmented pots either alone or in symbiosis with
Glomus intraradices Schenck and Smith (Experiment 1) or Glomus sp. (Experiment 2) in order to investigate if root colonization
by arbuscular mycorrhizal (AM) fungi has an effect on depletion of the soil mineral N pool. All pots were gradually supplied
with 31 mg NH4NO3-N kg-1 dry soil from 12–19 days after planting and an additional 50 mg (NH4)2SO4-N kg-1 dry soil (15N-labelled in Experiment 1) was supplied at 21 or 22 days after planting in Experiments 1 and 2, respectively. Dry weight
of plant parts, total root length, mycorrhizal colonization rate and soil concentration of NH
4
+
and NO
3
-
were recorded at five sequential harvest events: 21, 24, 30, 35 and 42 days (Experiment 1) and 22, 25, 28, 31 and 35 days
(Experiment 2) after planting. In Experiment 1, plants were also analysed for total content of N and 15N.
The mycorrhizal colonization rate increased during time: from 25 to 40% in Experiment 1 and from 50 to 60% in Experiment 2.
Plant dry matter accumulation was unaffected by mycorrhizal colonization, except in Experiment 1 where shoot dry weights were
slightly increased and in Experiment 2 where root dry weights were slightly decreased compared to non-mycorrhizal control
plants. The total root length was similar in the control and mycorrhizal treatments in Experiment 1, while it was decreased
(20–30%) by mycorrhizal colonization in the last two harvest in Experiment 2. Mycorrhizal colonization affected the rate of
depletion of soil mineral N in Experiment 1, where both NH
4
+
and NO
3
-
concentrations were markedly lower in the first two harvests, when plants were mycorrhizal. As the root length was similar
in mycorrhizal and control treatments, this may indicate that the external AM hyphae contributed to the depletion of the soil
mineral N pool. A similar pattern was observed in Experiment 2, although the effect was less pronounced. The 15N enrichment in mycorrhizal plants (Experiment 1) also indicated a faster NH
4
+
uptake than in the non-mycorrhizal controls in the first two harvests after application of the 15N-labelled N source. However, the external hyphae and roots seemed to have access to the same N sources as the 15N enrichment and total N content were similar in mycorrhizal and control plants at the end of the experiment.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献