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1.
In a greenhouse study, with and without rice plants, of five flooded Philippine rice soils whose organic C (OC) content varied
from 0.5 to 3.6%, incorporation ofSesbania rostrata, Azolla microphylla and rice straw affected the kinetics of soil solution NH
4
+
−N, K+, Fe2+, Mn2+, Zn2+, and P. Sesbania and Azolla increased NH
4
+
−N concentration above the control treatment, whereas rice straw depressed it. In all soils Azolla released less NH
4
+
−N than Sesbania. The apparent net N release depended on the soil and ranged from 44–81% for Sesbania and 27–52% for Azolla.
These effects persisted throughout the growth of IR36. Soil solution and exchangeable NH
4
+
−N increased initially but levelled off between 30 to 80 days and between 20 to 40 days after flooding (DF), respectively.
With rice, soil solution NH
4
+
−N concentration, reached a peak at 15–40 DF and declined to very low levels (<4mg L−1). In the 3 soils of low OC content nitrogen derived from green manure ranged from 34–53% and the apparent revovery of added
green manure N varied from 29–67%. Almost all N released from both Azolla and Sesbania were recovered in the rice plant in
all soils except Concepcion with only 77%. The concentration of K+, Fe2+, Mn2+ and P in the soil solution were higher with rice straw than Sesbania and Azolla in all soils except Hanggan which showed
no change in Fe2+ and Mn2+ but increased K+ and P. In general, rice straw, Sesbania and Azolla decreased Zn2+ concentration in all soils. 相似文献
2.
Old growth forest soils are large C reservoirs, but the impacts of tree-fall gaps on soil C in these forests are not well
understood. The effects of forest gaps on soil C dynamics in old growth northern hardwood–hemlock forests in the upper Great
Lakes region, USA, were assessed from measurements of litter and soil C stocks, surface C efflux, and soil microbial indices
over two consecutive growing seasons. Forest floor C was significantly less in gaps (19.0 Mg C ha−1) compared to gap-edges (39.5 Mg C ha−1) and the closed forest (38.0 Mg C ha−1). Labile soil C (coarse particulate organic matter, cPOM) was significantly less in gaps and edges (11.1 and 11.2 Mg C ha−1) compared to forest plots (15.3 Mg C ha−1). In situ surface C efflux was significantly greater in gaps (12.0 Mg C ha−1 y−1) compared to edges and the closed forest (9.2 and 8.9 Mg C ha−1 y−1). Microbial biomass N (MBN) was significantly greater in edges (0.14 Mg N ha−1) than in the contiguous forest (0.09 Mg N ha−1). The metabolic quotient (qCO2) was significantly greater in the forest (0.0031 mg CO2 h−1 g−1/mg MBC g−1) relative to gaps or edges (0.0014 mg CO2 h−1 g−1/mg MBC g−1). A case is made for gaps as alleviators of old growth forest soil C saturation. Relative to the undisturbed closed forest,
gaps have significantly less labile C, significantly greater in situ surface C efflux, and significantly lower decreased qCO2 values. 相似文献
3.
CO2 applied for Free-Air CO2 Enrichment (FACE) experiments is strongly depleted in 13C and thus provides an opportunity to study C turnover in soil organic matter (SOM) based on its δ
13C value. Simultaneous use of 15N labeled fertilizers allows N turnover to be studied. Various SOM fractionation approaches (fractionation by density, particle
size, chemical extractability etc.) have been applied to estimate C and N turnover rates in SOM pools. The thermal stability
of SOM coupled with C and N isotopic analyses has never been studied in experiments with FACE. We tested the hypothesis that
the mean residence time (MRT) of SOM pools is inversely proportional to its thermal stability. Soil samples from FACE plots
under ambient (380 ppm) and elevated CO2 (540 ppm; for 3 years) treatments were analyzed by thermogravimetry coupled with differential scanning calorimetry (TG-DSC).
Based on differential weight losses (TG) and energy release or consumption (DSC), five SOM pools were distinguished. Soil
samples were heated up to the respective temperature and the remaining soil was analyzed for δ
13C and δ
15N by IRMS. Energy consumption and mass losses in the temperature range 20–200°C were mainly connected with water volatilization.
The maximum weight losses occurred from 200–310°C. This pool contained the largest amount of carbon: 61% of the total soil
organic carbon in soil under ambient treatment and 63% in soil under elevated CO2, respectively. δ
13C values of SOM pools under elevated CO2 treatment showed an increase from −34.3‰ of the pool decomposed between 20–200°C to −18.1‰ above 480°C. The incorporation
of new C and N into SOM pools was not inversely proportional to its thermal stability. SOM pools that decomposed between 20–200
and 200–310°C contained 2 and 3% of the new C, with a MRT of 149 and 92 years, respectively. The pool decomposed between 310–400°C
contained the largest proportion of new C (22%), with a MRT of 12 years. The amount of fertilizer-derived N after 2 years
of application in ambient and elevated CO2 treatments was not significantly different in SOM pools decomposed up to 480°C having MRT of about 60 years. In contrast,
the pool decomposed above 480°C contained only 0.5% of new N, with a MRT of more than 400 years in soils under both treatments.
Thus, the separation of SOM based on its thermal stability was not sufficient to reveal pools with contrasting turnover rates
of C and N.
Responsible Editor: Bernard Nicolardot. 相似文献
4.
Kristell Hergoualc’h Ute Skiba Jean-Michel Harmand Catherine Hénault 《Biogeochemistry》2008,89(3):329-345
The objective of this study was to evaluate the effect of N fertilization and the presence of N2 fixing leguminous trees on soil fluxes of greenhouse gases. For a one year period, we measured soil fluxes of nitrous oxide
(N2O), carbon dioxide (CO2) and methane (CH4), related soil parameters (temperature, water-filled pore space, mineral nitrogen content, N mineralization potential) and
litterfall in two highly fertilized (250 kg N ha−1 year−1) coffee cultivation: a monoculture (CM) and a culture shaded by the N2 fixing legume species Inga densiflora (CIn). Nitrogen fertilizer addition significantly influenced N2O emissions with 84% of the annual N2O emitted during the post fertilization periods, and temporarily increased soil respiration and decreased CH4 uptakes. The higher annual N2O emissions from the shaded plantation (5.8 ± 0.3 kg N ha−1 year−1) when compared to that from the monoculture (4.3 ± 0.1 kg N ha−1 year−1) was related to the higher N input through litterfall (246 ± 16 kg N ha−1 year−1) and higher potential soil N mineralization rate (3.7 ± 0.2 mg N kg−1 d.w. d−1) in the shaded cultivation when compared to the monoculture (153 ± 6.8 kg N ha−1 year−1 and 2.2 ± 0.2 mg N kg−1 d.w. d−1). This confirms that the presence of N2 fixing shade trees can increase N2O emissions. Annual CO2 and CH4 fluxes of both systems were similar (8.4 ± 2.6 and 7.5 ± 2.3 t C-CO2 ha−1 year−1, −1.1 ± 1.5 and 3.3 ± 1.1 kg C-CH4 ha−1 year−1, respectively in the CIn and CM plantations) but, unexpectedly increased during the dry season. 相似文献
5.
Carbon isotopic composition of soils subjected to C3–C4 vegetation change can be used to estimate C turnover in bulk soil and in soil organic matter (SOM) pools with fast and intermediate
turnover rates. We hypothesized that the biological availability of SOM pools is inversely proportional to their thermal stability,
so that thermogravimetry can be used to separate SOM pools with contrasting turnover rates. Soil samples from a field plot
cultivated for 10.5 years with the perennial C4 plant Miscanthus×gigantheus were analyzed by thermogravimetry coupled with differential scanning calorimetry (DSC). Three SOM fractions were distinguished
according to the differential weight losses and exothermic or endothermic reactions measured by DSC. The δ13C and δ15N values of these three fractions obtained by gradual soil heating were measured by IRMS. The weight losses up to 190 °C mainly
reflected water evaporation because no significant C and N losses were detected and δ13C and δ15N values of the residual SOM remained unchanged. The δ13C values (−16.4‰) of SOM fraction decomposed between 190 and 390 °C (containing 79% of total soil C) were slightly closer
to that of the Miscanthus plant tissues (δ13C = −11.8‰) compared to the δ13C values (−16.8‰) of SOM fraction decomposed above 390 °C containing the residual 21% of SOM. Thus, the C turnover in the
thermally labile fraction was faster than that in thermally stable fractions, but the differences were not very strong. Therefore,
in this first study combining TG-DSC with isotopic analysis, we conclude that the thermal stability of SOM was not very strongly
related to biological availability of SOM fractions. In contrast to δ13C, the δ15N values strongly differed between SOM fractions, suggesting that N turnover in the soil was different from C turnover. More
detailed fractionation of SOM by thermal analysis with subsequent isotopic analysis may improve the resolution for δ13C. 相似文献
6.
Site-dependent N uptake from N-form mixtures by arctic plants,soil microbes and ectomycorrhizal fungi 总被引:1,自引:0,他引:1
Soil microbes constitute an important control on nitrogen (N) turnover and retention in arctic ecosystems where N availability
is the main constraint on primary production. Ectomycorrhizal (ECM) symbioses may facilitate plant competition for the specific
N pools available in various arctic ecosystems. We report here our study on the N uptake patterns of coexisting plants and
microbes at two tundra sites with contrasting dominance of the circumpolar ECM shrub Betula nana. We added equimolar mixtures of glycine-N, NH4+–N and NO3−–N, with one N form labelled with 15N at a time, and in the case of glycine, also labelled with 13C, either directly to the soil or to ECM fungal ingrowth bags. After 2 days, the vegetation contained 5.6, 7.7 and 9.1% (heath
tundra) and 7.1, 14.3 and 12.5% (shrub tundra) of the glycine-, NH4+- and NO3−–15N, respectively, recovered in the plant–soil system, and the major part of 15N in the soil was immobilized by microbes (chloroform fumigation-extraction). In the subsequent 24 days, microbial N turnover
transferred about half of the immobilized 15N to the non-extractable soil organic N pool, demonstrating that soil microbes played a major role in N turnover and retention
in both tundra types. The ECM mycelial communities at the two tundras differed in N-form preferences, with a higher contribution
of glycine to total N uptake at the heath tundra; however, the ECM mycelial communities at both sites strongly discriminated
against NO3−. Betula nana did not directly reflect ECM mycelial N uptake, and we conclude that N uptake by ECM plants is modulated by the N uptake
patterns of both fungal and plant components of the symbiosis and by competitive interactions in the soil. Our field study
furthermore showed that intact free amino acids are potentially important N sources for arctic ECM fungi and plants as well
as for soil microorganisms.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
7.
Harrison Ifeanyichukwu Atagana 《World journal of microbiology & biotechnology》2006,22(11):1145-1153
The effect of a combination of biostimulation, bioaugmentation and the presence of CuSO4 on the biodegradation of the polycyclic aromatic hydrocarbons (PAHs) dibenzofuran 210 mg kg−1, benzo(a)anthracene 200 mg kg−1, dibenzo-p-dioxine 100 mg kg−1 and 9-fluorenone 100 mg kg−1 in a sandy loam soil was studied. The pH of the soil was raised from 5 to 7 with agricultural lime. The soil was then divided into two sets labelled Treatments A and B. Six subsets numbered 1–6 were established for each of Treatments A and B. Treatment A was not amended with CuSO4 while Treatment B was amended with 5% CuSO4. Sterile control was established for both sets of treatment by adding 75 g sodium azide twice during the treatment period to Treatment 1. Treatment 2 was established as a natural control, without further amendments. Treatments 3–6 were tilled daily and maintained at 70% moisture. Mono-ammonium phosphate (MAP) (1 g kg−1 soil) was added to Treatments 4–6 twice during the treatment period. H2O2 at 500 mg l−1 (600 μl of a 39% solution) was added weekly to Treatment 5. A biosupplement was added to Treatment 6 every week. The experiments were incubated for 10 weeks at ambient temperature. The C:N:P ratio of the soil after the addition of MAP was 38:1:2.2. Counts of microorganisms were larger in the treatments not amended with CuSO4. For example counts were 77×106 in A6, as compared to 61×106 in B6. CO2 evolution was also consistently lower in the CuSO4-amended treatments. Reduction in the concentrations of the PAHs in the treatments without CuSO4 reached a maximum of 28.6% (dibenzofuran) in the sterile control and 39.1% (dibenzofuran) in the natural control. In contrast, maximum reduction in Treatment 3 reached 85% (dibenzofuran). Reduction in Treatments 4, 5 and 6 was between 90% and 100% in both Treatments A and B after 10 weeks. The combination of biostimulation and bioaugmentation (Treatment 6) enhanced PAH reduction by 100% reduction of all PAHs tested, better than only biostimulation (Treatments 4 & 5), which reduced the PAHs concentrations by between 90% and 100%. The effect of CuSO4 on the biodegradation of the tested PAHs was more prominent during the early stages of the experiment. However, there was no significant difference in the overall residual concentrations of the PAHs in both treatments A and B at the end of the treatment period. 相似文献
8.
Impact of long-term nitrogen addition on carbon stocks in trees and soils in northern Europe 总被引:4,自引:2,他引:2
The aim of this study was to quantify the effects of fertiliser N on C stocks in trees (stems, stumps, branches, needles,
and coarse roots) and soils (organic layer +0–10 cm mineral soil) by analysing data from 15 long-term (14–30 years) experiments
in Picea abies and Pinus sylvestris stands in Sweden and Finland. Low application rates (30–50 kg N ha−1 year−1) were always more efficient per unit of N than high application rates (50–200 kg N ha−1 year−1). Addition of a cumulative amount of N of 600–1800 kg N ha−1 resulted in a mean increase in tree and soil C stock of 25 and 11 kg (C sequestered) kg−1 (N added) (“N-use efficiency”), respectively. The corresponding estimates for NPK addition were 38 and 11 kg (C) kg−1 (N). N-use efficiency for C sequestration in trees strongly depended on soil N status and increased from close to zero at
C/N 25 in the humus layer up to 40 kg (C) kg−1 (N) at C/N 35 and decreased again to about 20 kg (C) kg−1 (N) at C/N 50 when N only was added. In contrast, addition of NPK resulted in high (40–50 kg (C) kg−1 (N)) N-use efficiency also at N-rich (C/N 25) sites. The great difference in N-use efficiency between addition of NPK and
N at N-rich sites reflects a limitation of P and K for tree growth at these sites. N-use efficiency for soil organic carbon
(SOC) sequestration was, on average, 3–4 times lower than for tree C sequestration. However, SOC sequestration was about twice
as high at P. abies as at P. sylvestris sites and averaged 13 and 7 kg (C) kg−1 (N), respectively. The strong relation between N-use efficiency and humus C/N ratio was used to evaluate the impact of N
deposition on C sequestration. The data imply that the 10 kg N ha−1 year−1 higher deposition in southern Sweden than in northern Sweden for a whole century should have resulted in 2.0 ± 1.0 (95% confidence
interval) kg m−2 more tree C and 1.3 ± 0.5 kg m−2 more SOC at P. abies sites in the south than in the north for a 100-year period. These estimates are consistent with differences between south
and north in tree C and SOC found by other studies, and 70–80% of the difference in SOC can be explained by different N deposition. 相似文献
9.
Sandy clay loam soil was contaminated with 5000 mg kg−1 diesel, and amended with nitrogen (15.98 atom% 15N) at 0, 250, 500, and 1000 mg kg−1 to determine gross rates of nitrogen transformations during diesel biodegradation at varying soil water potentials. The observed
water potential values were −0.20, −0.47, −0.85, and −1.50 MPa in the 0, 250, 500, and 1000 mg kg−1 nitrogen treatments respectively. Highest microbial respiration occurred in the lowest nitrogen treatment suggesting an inhibitory
osmotic effect from higher rates of nitrogen application. Microbial respiration rates of 185, 169, 131, and 116 mg O2 kg−1 soil day−1 were observed in the 250, 500, control and 1000 mg kg−1 nitrogen treatments, respectively. Gross nitrification was inversely related to water potential with rates of 0.2, 0.04,
and 0.004 mg N kg−1 soil day−1 in the 250, 500, and 1000 mg kg−1 nitrogen treatments, respectively. Reduction in water potential did not inhibit gross nitrogen immobilization or mineralization,
with respective immobilization rates of 2.2, 1.8, and 1.8 mg N kg−1 soil day−1, and mineralization rates of 0.5, 0.3, and 0.3 mg N kg−1 soil day−1 in the 1000, 500, and 250 mg kg−1 nitrogen treatments, respectively. Based on nitrogen transformation rates, the duration of fertilizer contribution to the
inorganic nitrogen pool was estimated at 0.9, 1.9, and 3.2 years in the 250, 500, and 1000 mg kg−1 nitrogen treatments, respectively. The estimation was conservative as ammonium fixation, gross nitrogen immobilization, and
nitrification were considered losses of fertilizer with only gross mineralization of organic nitrogen contributing to the
most active portion of the nitrogen pool. 相似文献
10.
Plant and Soil N Response of Southern Californian Semi-arid Shrublands After 1 Year of Experimental N Deposition 总被引:1,自引:0,他引:1
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
11.
Eva Ritter 《Plant and Soil》2007,295(1-2):239-251
Afforestation has become an important tool for soil protection and land reclamation in Iceland. Nevertheless, the harsh climate
and degraded soils are growth-limiting for trees, and little is know about changes in soil nutrients in maturing forests planted
on the volcanic soils. In the present chronosequence study, changes in C, N and total P in soil (0–10 and 10–20 cm depth)
and C and N in foliar tissue were investigated in stands of native Downy birch (Betula pubescens Enrh.) and the in Iceland introduced Siberian larch (Larix sibirica Ledeb.). The forest stands were between 14 and 97 years old and were established on heath land that had been treeless for
centuries. Soils were Andosols derived from basaltic material and rhyolitic volcanic ash. A significant effect of tree species
was only found for the N content in foliar tissue. Foliar N concentrations were significantly higher and foliar C/N ratios
significantly lower in larch needles than in birch leaves. There was no effect of stand age. Changes in soil C and the soil
nutrient status with time after afforestation were little significant. Soil C concentrations in 0–10 cm depth in forest stands
older than 30 years were significantly higher than in heath land and forest stands younger than 30 years. This was attributed
to a slow accumulation of organic matter. Soil N concentrations and soil Ptot were not affected by stand age. Nutrient pools in the two soil layers were calculated for an average weight of soil material
(400 Mg soil ha−1 in 0–10 cm depth and 600 Mg soil ha−1 in 10–20 cm depth, respectively). Soil nutrient pools did not change significantly with time. Soil C pools were in average
23.6 Mg ha−1 in the upper soil layer and 16.9 Mg ha−1 in the lower soil layer. The highest annual increase in soil C under forest compared to heath land was 0.23 Mg C ha−1 year−1 in 0–10 cm depth calculated for the 53-year-old larch stand. Soil N pools were in average 1.0 Mg N ha−1 in both soil layers and did not decrease with time despite a low N deposition and the uptake and accumulation of N in biomass
of the growing trees. Soil Ptot pools were in average 220 and 320 kg P ha−1 in the upper and lower soil layer, respectively. It was assumed that mycorrhizal fungi present in the stands had an influence
on the availability of N and P to the trees.
Responsible Editor: Hans Lambers. 相似文献
12.
Effects of N-fertilizers,straw, and dry fallow on the nitrogen balance of a flooded soil planted with rice 总被引:1,自引:0,他引:1
Teresita Santiago-Ventura Marjorie Bravo C. Daez V. Ventura I. Watanabe A. A. App 《Plant and Soil》1986,93(3):405-411
Summary Nitrogen balance studies were made on rice (Oryza sativa) grown in flooded soil in pots. A low rate of fertilizer (5.64 mg N. kg−1 soil) did not depress the N gain, but a high rate (99.72 mg N. kg−1 soil) elminated the N gain. Soil N loss was negligible since15N applied as ammonium sulfate and thoroughly mixed with the soil was recovered from the soil-plant system after 3 crops. The
observed N gain, therefore, was caused by N2-fixation, not by a reduction of soil N loss.
Straw enhanced N gain at the rate of 2–4 mg per g straw. However, this gain was not observed when soil N availability was
high. Dry fallow between rice crops decreased the N gain. 相似文献
13.
A portion of nitrate (NO
3
−
), a final breakdown product of nitrogen (N) fertilizers, applied to soils and/or that produced upon decomposition of organic
residues in soils may leach into groundwater. Nitrate levels in water excess of 10 mg L−1 (NO3–N) are undesirable as per drinking water quality standards. Nitrate concentrations in surficial groundwater can vary substantially
within an area of citrus grove which receives uniform N rate and irrigation management practice. Therefore, differences in
localized conditions which can contribute to variations in gaseous loss of NO
3
−
in the vadose zone and in the surficial aquifer can affect differential concentrations of NO3–N in the groundwater at different points of sampling. The denitrification capacity and potential in a shallow vadose zone
soil and in surficial groundwater were studied in two large blocks of a citrus grove of ‘Valencia’ orange trees (Citrus sinensis
(L.) Obs.) on Rough lemon rootstock ( Citrus jambhiri (L.)) under a uniform N rate and irrigation program. The NO3–N concentration in the surficial groundwater sampled from four monitoring wells (MW) within each block varied from 5.5- to
6.6-fold. Soil samples were collected from 0 to 30, 30 to 90, or 90 to 150 cm depths, and from the soil/groundwater interface
(SGWI). Groundwater samples from the monitoring wells (MW) were collected prior to purging (stagnant water) and after purging
five well volumes. Without the addition of either C or N, the denitrification capacity ranged from 0.5 to 1.53, and from 0.0
to 2.25 mg N2O–N kg−1 soil at the surface soil and at the soil/groundwater interface, respectively. The denitrification potential increased by
100-fold with the addition of 200 mg kg−1 each of N and C. The denitrification potential in the groundwater also followed a pattern similar to that for the soil samples.
Denitrification potential in the soil or in the groundwater was greatest near the monitor well with shallow depth of vadose
zone (MW3). Cumulative N2O–N emission (denitrification capacity) from the SGWI soil samples and from stagnant water samples strongly correlated to
microbial most probable number (MPN) counts (r2 = 0.84 – 0.89), and dissolved organic C (DOC) (r2 = 0.96 – 0.97). Denitrification capacity of the SGWI samples moderately correlated to water-filled pore space (WFPS) (r2 = 0.52). However, extractable NO3-N content of the SGWI soil samples poorly (negative) correlated to denitrification capacity (r2 = 0.35). However, addition C, N or both to the soil or water samples resulted in significant increase in cumulative N2O emission. This study demonstrated that variation in denitrification capacity, as a result of differences in denitrifier
population, and the amount of readily available carbon source significantly (at 95% probability level) influenced the variation
in NO3–N concentrations in the surficial groundwater samples collected from different monitoring wells within an area with uniform
N management.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
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
15.
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
16.
Elevated [CO2], temperature increase and N supply effects on the turnover of below-ground carbon in a temperate grassland ecosystem 总被引:5,自引:0,他引:5
The effects of elevated [CO2] (700 μl l-1 CO2) and temperature increase (+3 °C) on carbon turnover in grassland soils were studied during 2.5 years at two N fertiliser
supplies (160 and 530 kg N ha-1 y-1) in an experiment with well-established ryegrass swards (Lolium perenne) supplied with the same amounts of irrigation water.
During the growing season, swards from the control climate (350 μl l-1 [CO2] at outdoor air temperature) were pulse labelled by the addition of 13CO2. The elevated [CO2] treatments were continuously labelled by the addition of fossil-fuel derived CO2 (13
C of -40 to -50 ‰). Prior to the start of the experimental treatments, the carbon accumulated in the plant parts and in the
soil macro-organic matter (‘old’ C) was at −32‰. During the experiment, the carbon fixed in the plant material (‘new’ C) was
at −14 and −54‰ in the ambient and elevated [CO2] treatments, respectively. During the experiment, the 13C isotopic mass balance method was used to calculate, for the top soil (0–15 cm), the carbon turnover in the stubble and roots
and in the soil macro-organic matter above 200 μ (MOM). Elevated [CO2] stimulated the turnover of organic carbon in the roots and stubble and in the MOM at N+, but not at N−. At the high N supply,
the mean replacement time of ‘old’ C by ‘new’ C declined in elevated, compared to ambient [CO2], from 18 to 7 months for the roots and stubble and from 25 to 17 months for the MOM. This resulted from increased rates
of ‘new’ C accumulation and of ‘old’ C decay. By contrast, at the low N supply, despite an increase in the rate of accumulation
of ‘new’ C, the soil C pools did not turnover faster in elevated [CO2], as the rate of ‘old’ C decomposition was reduced. A 3 °C temperature increase in elevated [CO2] decreased the input of fresh C to the roots and stubble and enhanced significantly the exponential rate for the ‘old’ C
decomposition in the roots and stubble. An increased fertiliser N supply reduced the carbon turnover in the roots and stubble
and in the MOM, in ambient but not in elevated [CO2]. The respective roles for carbon turnover in the coarse soil OM fractions, of the C:N ratio of the litter, of the inorganic
N availability and of a possible priming effect between C-substrates are discussed.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
The effects of forest management (thinning) on gross and net N conversion, the balance of inorganic N production and consumption, inorganic N concentrations and on soil microbial biomass in the Ah layer were studied in situ during eight intensive field measuring campaigns in the years 2002–2004 at three beech (Fagus sylvatica L.) forest sites. At all sites adjacent thinning plots (“T”) and untreated control plots (“C”) were established. Since the sites are characterized either by cool-moist microclimate (NE site and NW site) or by warm-dry microclimate (SW site) and thinning took place in the year 1999 at the NE and SW sites and in the year 2003 at the NW site the experimental design allowed to evaluate (1) short-term effects (years 1–2) of thinning at the NW site and (2) medium-term effects (years 4–6) of thinning under different microclimate at the SW and NE site. Microbial biomass N was consistently higher at the thinning plots of all sites during most of the field campaigns and was overall significantly higher at the SWT and NWT plots as compared to the corresponding untreated control plots. The size of the microbial biomass N pool was found to correlate positively with both gross ammonification and gross nitrification as well as with extractable soil NO3− concentrations. At the SW site neither gross ammonification, gross nitrification, gross ammonium (NH4+) immobilization and gross nitrate (NO3−) immobilization nor net ammonification, net nitrification and extractable NH4+ and NO3− contents were significantly different between control and thinning plot. At the NET plot lower gross ammonification and gross NH4+ immobilization in conjunction with constant nitrification rates coincided with higher net nitrification and significantly higher extractable NO3− concentrations. Thus, the medium-term effects of thinning varied with different microclimate. The most striking thinning effects were found at the newly thinned NW site, where gross ammonification and gross NH4+ immobilization were dramatically higher immediately after thinning. However, they subsequently tended to decrease in favor of gross nitrification, which was significantly higher at the NWT plot as compared to␣the␣NWC plot during all field campaigns after␣thinning except for April 2004. This increase␣in␣gross nitrification at the NWT plot (1.73 mg N kg−1 sdw day−1 versus 0.48 mg N kg−1 sdw day−1 at the NWC plot) coincided with significantly higher extractable NO3− concentrations (4.59 mg N kg−1 sdw at the NWT plot versus 0.96 mg N kg−1 sdw at the NWC plot). Pronounced differences in relative N retention (the ratio of gross NH4+ immobilization + gross NO3− immobilization to gross ammonification + gross nitrification) were found across the six research plots investigated and could be positively correlated to the soil C/N ratio (R = 0.94; p = 0.005). In sum, the results obtained in this study show that (1) thinning can lead to a shift in the balance of microbial inorganic N production and consumption causing a clear decrease in the N retention capacity in the monitored forest soils especially in the first two years after thinning, (2)␣the resistance of the investigated forest ecosystems to disturbances of N cycling by thinning may vary with different soil C contents and C/N ratios, e. g. caused by differences in microclimate, (3) thinning effects tend to decline with the growth of understorey vegetation in the years 4–6 after thinning. 相似文献
18.
Alfalfa (Medicago sativa L.) was grown in greenhouse sand culture to examine the effect of salinity composition and concentration on Se accumulation
by plants. In a 2×2×4 factorial experiment, salinity was added as either C1− or SO
4
2−
salts to the irrigating solution to achieve an electrical conductivity of 0.5, 1.5–3.0, or 6.0 dS m−1. Selenium was added to the nutrient solution at a concentration of 0.25 or 1.0 mg Se(VI)I−1. Following the third cutting, the roots were washed and all plant material analyzed for dry weight and Se. Plant biomass
production decreased with additions of either Se or salinity, regardless of composition. In the presence of Se, the yield
reduction was greater with Cl− salinity than with SO
4
2−
salinity. Plant Se accumulation was reduced from 948 mg Se kg−1 to 6 mg Se kg−1 in the presence of SO
4
2−
salts (0.5 mmol SO
4
2−
l−1
vs. 40 mmol SO
4
2−
l−1) due to an apparent Se(VI) −SO
4
2−
antagonism. This Se−SO
4
2−
antagonism prevented accumulation of Se and reduced Se-induced toxicity. A lesser antagonistic effect on Se accumulation
was observed between Cl−, and Se. A synergistic interaction between SO
4
2−
and Se(VI) increased plant S concentrations in the presence of the relatively low basal SO
4
2−
concentrations but not at the higher solution SO
4
2−
concentrations. In many areas, soil and water containing high Se concentrations also contain large amounts of SO
4
2−
. The occurrence of SO
4
2−
with Se reduces plant accumulation of Se(VI) and may lower the risk of Se overexposure to animals feeding on forage material
grown in high Se−SO
4
2−
regions. 相似文献
19.
T. Rütting D. Huygens C. Müller O. Van Cleemput R. Godoy P. Boeckx 《Biogeochemistry》2008,90(3):243-258
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
20.
Katja Pörtl Sophie Zechmeister-Boltenstern Wolfgang Wanek Per Ambus Torsten W. Berger 《Plant and Soil》2007,295(1-2):79-94
Natural 15N abundance measurements of ecosystem nitrogen (N) pools and 15N pool dilution assays of gross N transformation rates were applied to investigate the potential of δ15N signatures of soil N pools to reflect the dynamics in the forest soil N cycle. Intact soil cores were collected from pure
spruce (Picea abies (L.) Karst.) and mixed spruce-beech (Fagus sylvatica L.) stands on stagnic gleysol in Austria. Soil δ15N values of both forest sites increased with depth to 50 cm, but then decreased below this zone. δ15N values of microbial biomass (mixed stand: 4.7 ± 0.8‰, spruce stand: 5.9 ± 0.9‰) and of dissolved organic N (DON; mixed stand:
5.3 ± 1.7‰, spruce stand: 2.6 ± 3.3‰) were not significantly different; these pools were most enriched in 15N of all soil N pools. Denitrification represented the main N2O-producing process in the mixed forest stand as we detected a significant 15N enrichment of its substrate NO3− (3.6 ± 4.5‰) compared to NH4+ (−4.6 ± 2.6‰) and its product N2O (−11.8 ± 3.2‰). In a 15N-labelling experiment in the spruce stand, nitrification contributed more to N2O production than denitrification. Moreover, in natural abundance measurements the NH4+ pool was slightly 15N-enriched (−0.4 ± 2.0 ‰) compared to NO3− (−3.0 ± 0.6 ‰) and N2O (−2.1 ± 1.1 ‰) in the spruce stand, indicating nitrification and denitrification operated in parallel to produce N2O. The more positive δ15N values of N2O in the spruce stand than in the mixed stand point to extensive microbial N2O reduction in the spruce stand. Combining natural 15N abundance and 15N tracer experiments provided a more complete picture of soil N dynamics than possible with either measurement done separately. 相似文献