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1.
During 4 years continuous measurements of N-trace gas exchange were carried out at the forest floor-atmosphere interface at the Höglwald Forest that is highly affected by atmospheric N-deposition. The measurements included spruce control, spruce limed and beech sites. Based on these field measurements and on intensive laboratory measurements of N2-emissions from the soils of the beech and spruce control sites, a total balance of N-gas emissions was calculated. NO2-deposition was in a range of –1.6 –2.9 kg N ha–1 yr–1 and no huge differences between the different sites could be demonstrated. In contrast to NO2-deposition, NO- and N2O-emissions showed a huge variability among the different sites. NO emissions were highest at the spruce control site (6.4–9.1 kg N ha–1 yr–1), lowest at the beech site (2.3–3.5 kg N ha–1 yr–1) and intermediate at the limed spruce site (3.4–5.4 kg N ha–1 yr–1). With regard to N2O-emissions, the following ranking between the sites was found: beech (1.6–6.6 kg N ha–1 yr–1) >> spruce limed (0.7–4.0 kg N ha–1 yr–1) > spruce control (0.4–3.1 kg N ha–1 yr–1). Average N-trace gas emissions (NO, NO2, N2O) for the years 1994–1997 were 6.8 kg N ha–1 yr–1 at the spruce control site, 3.6 kg N ha–1 yr–1 at the limed spruce site and 4.5 kg N ha–1 yr–1 at the beech site. Considering N2-losses, which were significantly higher at the beech (12.4 kg N ha–1 yr–1) than at the spruce control site (7.2 kg N ha–1 yr–1), the magnitude of total gaseous N losses, i.e. N2-N + NO-N + NO2-N + N2O-N, could be calculated for the first time for a forest ecosystem. Total gaseous N-losses were 14.0 kg N ha–1 yr–1 at the spruce control site and 15.5 kg N ha–1 yr–1 at the beech site, respectively. In view of the huge interannual variability of N-trace gas fluxes and the pronounced site differences in N-gas emissions it is concluded that more research is needed in order to fully understand patterns of microbial N-cycling and N-gas production/emission in forest ecosystems and mechanisms of reactions of forest ecosystems to the ecological stress factor of atmospheric N-input. 相似文献
2.
A O Ejiofor Y Chisti M Moo-Young 《Journal of industrial microbiology & biotechnology》1996,16(2):102-109
A fermentation medium based on millet (Pennisetum typhoides) flour hydrolysate and a four-phase feeding strategy for fed-batch production of baker's yeast,Saccharomyces cerevisiae, are presented. Millet flour was prepared by dry-milling and sieving of whole grain. A 25% (w/v) flour mash was liquefied with a thermostable 1,4--d-glucanohydrolase (EC 3.2.1.1) in the presence of 100 ppm Ca2+, at 80°C, pH 6.1–6.3, for 1 h. The liquefied mash was saccharified with 1,4--d-glucan glucohydrolase (EC 3.2.1.3) at 55°C, pH 5.5, for 2 h. An average of 75% of the flour was hydrolysed and about 82% of the hydrolysate was glucose. The feeding profile, which was based on a model with desired specific growth rate range of 0.18–0.23 h–1, biomass yield coefficient of 0.5 g g–1 and feed substrate concentration of 200 g L–1, was implemented manually using the millet flour hydrolysate in test experiments and glucose feed in control experiments. The fermentation off-gas was analyzed on-line by mass spectrometry for the calculation of carbon dioxide production rate, oxygen up-take rate and the respiratory quotient. Off-line determination of biomass, ethanol and glucose were done, respectively, by dry weight, gas chromatography and spectrophotometry. Cell mass concentrations of 49.9–51.9 g L–1 were achieved in all experiments within 27 h of which the last 15 h were in the fedbatch mode. The average biomass yields for the millet flour and glucose media were 0.48 and 0.49 g g–1, respectively. No significant differences were observed between the dough-leavening activities of the products of the test and the control media and a commercial preparation of instant active dry yeast. Millet flour hydrolysate was established to be a satisfactory low cost replacement for glucose in the production of baking quality yeast.Nomenclature
C
ox
Dissolved oxygen concentration (mg L–1)
-
CPR
Carbon dioxide production rate (mmol h–1)
-
C
s0
Glucose concentration in the feed (g L–1)
-
C
s
Substrate concentration in the fermenter (g L–1)
-
C
s.crit
Critical substrate concentration (g L–1)
-
E
Ethanol concentration (g L–1)
-
F
s
Substrate flow rate (g h–1)
-
i
Sample number (–)
-
K
e
Constant in Equation 6 (g L–1)
-
K
o
Constant in Equation 7 (mg L–1)
-
K
s
Constant in Equation 5 (g L–1)
-
m
Specific maintenance term (h–1)
-
OUR
Oxygen up-take rate (mmol h–1)
-
q
ox
Specific oxygen up-take rate (h–1)
-
q
ox.max
Maximum specific oxygen up-take rate (h–1)
-
q
p
Specific product formation rate (h–1)
-
q
s
Specific substrate up-take rate (g g–1 h–1)
-
q
s.max
Maximum specific substrate up-take rate (g g–1 h–1)
-
RQ
Respiratory quotient (–)
-
S
Total substrate in the fermenter at timet (g)
-
S
0
Substrate mass fraction in the feed (g g–1)
-
t
Fermentation time (h)
-
V
Instantaneous volume of the broth in the fermenter (L)
-
V
0
Starting volume in the fermenter (L)
-
V
si
Volume of samplei (L)
-
x
Biomass concentration in the fermenter (g L–1)
-
X
0
Total amount of initial biomass (g)
-
X
t
Total amount of biomass at timet (g)
-
Y
p/s
Product yield coefficient on substrate (–)
-
Y
x/e
Biomass yield coefficient on ethanol (–)
-
Y
x/s
Biomass yield coefficient on substrate (–)
Greek letters
Moles of carbon per mole of yeast (–)
-
Moles of hydrogen atom per mole of yeast (–)
-
Moles of oxygen atom per mole of yeast (–)
-
Moles of nitrogen atom per mole of yeast (–)
-
Specific growth rate (h–1)
- crit
Critical specific growth rate (h–1)
-
E
Specific ethanol up-take rate (h–1)
- max.E
Maximum specific ethanol up-take rate (h–1) 相似文献
3.
Regional analysis of inorganic nitrogen yield and retention in high-elevation ecosystems of the Sierra Nevada and Rocky Mountains 总被引:4,自引:2,他引:2
Yields and retention of dissolved inorganic nitrogen (DIN: NO3
– + NH4
+) and nitrate concentrations in surface runoff are summarized for 28 high elevation watersheds in the Sierra Nevada of California and Rocky Mountains of Wyoming and Colorado. Catchments ranged in elevation from 2475 to 3603 m and from 15 to 1908 ha in area. Soil cover varied from 5% to nearly 97% of total catchment area. Runoff from these snow-dominated catchments ranged from 315 to 1265 mm per year. In the Sierra Nevada, annual volume-weighted mean (AVWM) nitrate concentrations ranged from 0.5 to 13 M (overall average 5.4 M), and peak concentrations measured during snowmelt ranged from 1.0 to 38 M. Nitrate levels in the Rocky Mountain watersheds were about twice those in the Sierra Nevada; average AVWM NO3
– was 9.4 M and snowmelt peaks ranged from 15 to 50 M. Mean DIN loading to Rocky Mountain watersheds, 3.6 kg ha–1 yr–1, was double the average measured for Sierra Nevada watersheds, 1.8 kg ha–1 yr–1. DIN yield in the Sierra Nevada, 0.69 kg ha–1 yr–1, was about 60% that measured in the Rocky Mountains, 1.1 kg ha–1 yr–1. Net inorganic N retention in Sierra Nevada catchments was 1.2 kg ha–1 yr–1 and represented about 55% of annual DIN loading. DIN retention in the Rocky Mountain catchments was greater in absolute terms, 2.5 kg ha–1 yr–1, and as a percentage of DIN loading, 72%.A correlation analysis using DIN yield, DIN retention and surface water nitrate concentrations as dependent variables and eight environmental features (catchment elevation, slope, aspect, roughness, area, runoff, soil cover and DIN loading) as independent variables was conducted. For the Sierra Nevada, elevation and soil cover had significant (p > 0.1) Pearson product moment correlations with catchment DIN yield, AVWM and peak snowmelt nitrate concentrations and DIN retention rates. Log-linear regression models using soil cover as the independent variable explained 82% of the variation in catchment DIN retention, 92% of the variability in AVWM nitrate and 85% of snowmelt peak NO3
–. In the Rocky Mountains, soil cover was significantly (p < 0.05) correlated with DIN yield, AVWM NO3
– and DIN retention expressed as a percentage of DIN loading (%DIN retention). Catchment mean slope and terrain roughness were positively correlated with steam nitrate concentrations and negatively related to %DIN retention. About 91% of the variation in DIN yield and 79% of the variability in AVWM NO3
– were explained by log-linear models based on soil cover. A log-linear regression based on soil cover explained 90% of the variation of %DIN retention in the Rocky Mountains. 相似文献
4.
Field experiments were conducted during the rainy reasons of 1989, 1990 and 1991 on an acid sandy soil in Niger, West Africa, to assess the effect of millet straw application (+CR) on growth and N2 fixation of groundnut (Arachis hypogaea L.).Three years of +CR (4 t ha–1 yr–1) increased symbiotic N2 fixation, total dry matter production (haulm plus pods) by 83% and total nitrogen (N) accumulation by 100%. Concentration of N in the shoot dry matter and total N in the soil were only slightly affected by the +CR treatment.Crop residue application increased the concentration of potassium (K) and molybdenum (Mo) and decreased the concentrations of aluminium (Al) and manganese (Mn) distinctly, both in the plant (shoot and nodule dry matter) and in the soil.The increase in dry matter production and N uptake was mainly due to improved N2 fixation reflected by enhanced formation and growth of nodules as well as nitrogenase activity. This was attributed to improved chemical soil conditions, particularly to the higher availability of Mo and the lowered content of available Al and Mn.Although with the application of 4 t CR ha–1, 60 kg K were supplied, increased growth could not be attributed to the additional supply of K.ICRISAT Journal Article No. 1229.ICRISAT Journal Article No. 1229. 相似文献
5.
Laboratory and field measurements of the flux of ammonia to forest floor canopies of spruce and beech stands at the Höglwald site in southern Bavaria are reported. Measurements were performed with an open chamber method. A linearity between ammonia concentration and ammonia flux from the atmosphere to the ground floor canopy was detected. Deposition of ammonia showed no saturation even at air concentrations up to 50 g NH3 m–3 air. Temperature, water content and the moss layer of the ground floor canopy had a minor influence on the deposition velocity in laboratory experiments. Deposition velocity of ammonia was higher to the spruce (1.3 cm s–1), and limed spruce ground floor canopy (1.17 cm s–1) compared to the beech stand (0.79 cm s–1). In field studies, a diurnal course of the deposition velocity was detected with highest velocities in midday and minor during night times, but not in the climatic chamber. The flux of ammonia to the ground floor canopy was estimated of app. 10 kg N ha–1 yr–1 for the soil under spruce, 9 kg N ha–1 yr–1 for the limed spruce and 6 kg N ha–1yr–1 for the soil under beech. The fluxes are interpreted as fluxes from the atmosphere to the ground canopies of the stands. 相似文献
6.
Globally, land-use change is occurring rapidly, and impacts on biogeochemical cycling may be influenced by previous land uses. We examined differences in soil C and N cycling during long-term laboratory incubations for the following land-use sequence: indigenous forest (soil age = 1800 yr); 70-year-old pasture planted after forest clearance; 22-year-old pine (Pinus radiata) planted into pasture. No N fertilizer had been applied but the pasture contained N-fixing legumes. The sites were adjacent and received 3–6 kg ha–1 yr–1volcanic N in rain; NO3
–-N leaching losses to streamwater were 5–21 kg ha–1 yr–1, and followed the order forest < pasture = pine. Soil C concentration in 0–10 cm mineral soil followed the order: pasture > pine = forest, and total N: pasture > pine > forest. Nitrogen mineralization followed the order: pasture > pine > forest for mineral soil, and was weakly related to C mineralization. Based on radiocarbon data, the indigenous forest 0–10 cm soil contained more pre-bomb C than the other soils, partly as a result of microbial processing of recent C in the surface litter layer. Heterotrophic activity appeared to be somewhat N limited in the indigenous forest soil, and gross nitrification was delayed. In contrast, the pasture soil was rich in labile N arising from N fixation by clover, and net nitrification occurred readily. Gross N cycling rates in the pine mineral soil (per unit N) were similar to those under pasture, reflecting the legacy of N inputs by the previous pasture. Change in land use from indigenous forest to pasture and pine resulted in increased gross nitrification, net nitrification and thence leaching of NO3
–-N. 相似文献
7.
Ulva rigida was cultivated in 7501 tanks at different densities with direct and continuous inflow (at 2, 4, 8 and 12 volumes d–1) of the effluents from a commercial marine fishpond (40 metric tonnes, Tm, of Sparus aurata, water exchange rate of 16 m3 Tm–1) in order to assess the maximum and optimum dissolved inorganic nitrogen (DIN) uptake rate and the annual stability of the Ulva tank biofiltering system. Maximum yields (40 g DW m–2 d–1) were obtained at a density of 2.5 g FW 1–1 and at a DIN inflow rate of 1.7 g DIN m–2 d–1. Maximum DIN uptake rates were obtained during summer (2.2 g DIN M–2 d–1), and minimum in winter (1.1 g DIN m–2 d–1) with a yearly average DIN uptake rate of 1.77 g DIN m–2 d–1 At yearly average DIN removal efficiency (2.0 g DIN m–2 d–1, if winter period is excluded), 153 m2 of Ulva tank surface would be needed to recover 100% of the DIN produced by 1 Tm of fish.Abbreviations DIN=
dissolved inorganic nitrogen (NH
inf4
sup+
+ NO
inf3
sup–
+ NO
inf2
sup–
);
- FW=
fresh weight;
- DW=
dry weight;
- PFD=
photon flux density;
- V=
DIN uptake rate 相似文献
8.
Spirulina platensis (= Arthrospira fusiformis) was isolated from Lake Chitu, a saline, alkaline lake in Ethiopia, where it forms an almost unialgal population. Optimum growth conditions were studied in a turbidostat. Cultures grown in modified Zarrouk's medium and exposed to a range of light intensities (20–500 µmol photons m–2s–1) showed a maximum specific growth rate (µmax) of 1.78 d–1. Quantum yield for growth (µ) was 3.8% at the optimum light for growth of 330 µmol photons m–2s–1, and ranged from 2.8 to 9.4%. With increase in irradiance, the chlorophyll a concentration decreased, and the carotenoids/chlorophyll a ratio increased by a factor of 2.4. The phosphorus to carbon ratio (P/C) showed some variation, while the nitrogen to carbon ratio (N/C) remained relatively constant, thus causing fluctuations in the N:P ratio (7–11) of cells. An optimum N:P ratio of about 7 was attained in cells growing at the optimum light for growth. Results from the continuous culture experiments agreed well with maximum values of photosynthetic efficiency given in the literature for natural populations of S. platensis in the soda lakes of East Africa, Lake Arenguade (Ethiopia), and Lake Simbi (Kenya). 相似文献
9.
The production of aboveground tissue of three alder species (Alnus crispa (Ait.) Pursh,A. rugosa (Du Roi) Spreng. andA. glutinosa (L) Gaertn.) on four sites ranged from 0.4 t ha–1 yr–1 to 4.0 t ha–1 yr–1 after four growing seasons. Large differences were observed among the four sites studied and among species. Soil nutrient levels affected the biomass production and foliar symptoms of P and Mg deficiency occurred withA. crispa andA. rugosa. Because of their poor aboveground biomass production (0.4–1.4 t ha–1 yr–1),A. crispa andA. rugosa should be used mainly as nurse trees. For its higher potential for biomass production (up to 4.0 t ha–1 yr–1), and its apparent higher ability to use P and Mg on deficient sites,A. glutinosa should be used preferably toA. crispa andA. rugosa for the production of biomass. 相似文献
10.
A family of 10 competing, unstructured models has been developed to model cell growth, substrate consumption, and product formation of the pyruvate producing strain Escherichia coli YYC202 ldhA::Kan strain used in fed-batch processes. The strain is completely blocked in its ability to convert pyruvate into acetyl-CoA or acetate (using glucose as the carbon source) resulting in an acetate auxotrophy during growth in glucose minimal medium. Parameter estimation was carried out using data from fed-batch fermentation performed at constant glucose feed rates of
qVG=10 mL h–1. Acetate was fed according to the previously developed feeding strategy. While the model identification was realized by least-square fit, the model discrimination was based on the model selection criterion (MSC). The validation of model parameters was performed applying data from two different fed-batch experiments with glucose feed rate
qVG=20 and 30 mL h–1, respectively. Consequently, the most suitable model was identified that reflected the pyruvate and biomass curves adequately by considering a pyruvate inhibited growth (Jerusalimsky approach) and pyruvate inhibited product formation (described by modified Luedeking–Piret/Levenspiel term).List of symbols cA
acetate concentration (g L–1)
- cA,0
acetate concentration in the feed (g L–1)
- cG
glucose concentration (g L–1)
- cG,0
glucose concentration in the feed (g L–1)
- cP
pyruvate concentration (g L–1)
- cP,max
critical pyruvate concentration above which reaction cannot proceed (g L–1)
- cX
biomass concentration (g L–1)
- KI
inhibition constant for pyruvate production (g L–1)
- KIA
inhibition constant for biomass growth on acetate (g L–1)
- KP
saturation constant for pyruvate production (g L–1)
- KP
inhibition constant of Jerusalimsky (g L–1)
- KSA
Monod growth constant for acetate (g L–1)
- KSG
Monod growth constant for glucose (g L–1)
- mA
maintenance coefficient for growth on acetate (g g–1 h–1)
- mG
maintenance coefficient for growth on glucose (g g–1 h–1)
- n
constant of extended Monod kinetics (Levenspiel) (–)
- qV
volumetric flow rate (L h–1)
- qVA
volumetric flow rate of acetate (L h–1)
- qVG
volumetric flow rate of glucose (L h–1)
- rA
specific rate of acetate consumption (g g–1 h–1)
- rG
specific rate of glucose consumption (g g–1 h–1)
- rP
specific rate of pyruvate production (g g–1 h–1)
- rP,max
maximum specific rate of pyruvate production (g g–1 h–1)
- t
time (h)
- V
reaction (broth) volume (L)
- YP/G
yield coefficient pyruvate from glucose (g g–1)
- YX/A
yield coefficient biomass from acetate (g g–1)
- YX/A,max
maximum yield coefficient biomass from acetate (g g–1)
- YX/G
yield coefficient biomass from glucose (g g–1)
- YX/G,max
maximum yield coefficient biomass from glucose (g g–1)
-
growth associated product formation coefficient (g g–1)
-
non-growth associated product formation coefficient (g g–1 h–1)
-
specific growth rate (h–1)
- max
maximum specific growth rate (h–1) 相似文献
11.
The biomass formation ofAzolla was greatly enhanced by water of the River Ganga and by prevailing environmental conditions. It increased gradually from January to April (first maximum 2.409 g.m–2.day–1), declined during June (1.185 g.m–2.day–1), and reached a second its maximum during September (2.629 g.m–2.day–1). The biomass formation was related to the nutrient availability in the medium in a particular season (measured were: nitrate-N, available phosphorus, total suspended solids, and conductivity). The average annual production of 6.73 ton.ha–1.yr–1 is equivalent to the average production of 0.025 ton.ha–1.yr–1 phosphorus, 0.252 ton.ha–1.yr–1 nitrogen, and 1.57 ton.ha–1.yr–1 crude protein. 相似文献
12.
Yukihiko Serisawa Yasutsugu Yokohama Yusho Aruga Alecia Bellgrove 《Journal of applied phycology》2004,16(3):227-235
Young sporophytes of short-stipe ecotype ofEcklonia cavafrom a warmer locality (Tei, Kochi Pref., southern Japan) and those of long-stipe ecotype from a cooler locality (Nabeta, Shizuoka Pref., central Japan) were transplanted in 1995 to artificial reefs immersed at the habitat of long-stipe ecotype in Nabeta Bay, Shizuoka Pref., central Japan. The characteristics of photosynthesis and respiration of bladelets of the transplanted sporophytes of the two ecotypes were compared in winter and summer 1997; the results were assessed per unit area, per unit chlorophyllacontent and per unit dry weight. In photosynthesis-light curves at 10–29 °C, light saturation occurred at 200–400 mol photon m–2s–1in sporophytes from both Tei and Nabeta. The maximum photosynthetic rate (P
max) at 10–29 °C and the light-saturation index (I
k) at 25–29 °C in sporophytes from both localities were generally higher in winter than in summer.P
maxat 25–29 °C (per unit area and chlorophylla) were higher in sporophytes from Tei than those from Nabeta in both seasons. The optimum temperature for photosynthesis was 25 °C in winter and 27 °C in summer at high light intensities of 100–400 mol photon m–2s–1. However, at lower light intensities of 12.5–50 mol photon m–2s–1, it was 20 °C in winter and 25–27 °C in summer for sporophytes from both locations. Dark respiration increased with temperature rise in the range of 10–29 °C in sporophytes from both locations in summer and winter. The sporophytes transplanted from Tei (warmer area) showed higher photosynthetic activities than those from Nabeta (cooler area) at warmer temperatures even under the same environmental conditions. This indicates that these physiological ecotypes have arisen from genetic differentiation. 相似文献
13.
Summary Permeabilities of ammonia (NH3), methylamine (CH3NH2) and ethylamine (CH3CH2NH2) in the cyanobacterium (cyanophyte)Synechococcus R-2 (Anacystis nidulans) have been measured. Based on net uptake rates of DCMU (dichlorophenyldimethylurea) treated cells, the permeability of ammonia was 6.44±1.22 m sec–1 (n=13). The permeabilities of methylamine and ethylamine, based on steady-state14C labeling were more than ten times that of ammonia (P
methylamine=84.6±9.47 m sec–1 (76),P
ethylamine=109±11 m sec–1 (55)). The apparent permeabilities based on net uptake rates of methylamine and ethylamine uptake were significantly lower, but this effect was partially reversible by ammonia, suggesting that net amine fluxes are rate limited by proton fluxes to an upper limit of about 700 nmol m–2 sec–1. Increasing concentrations of amines in alkaline conditions partially dissipated the pH gradient across the cell membrane, and this property could be used to calculate the relative permeabilities of different amines. The ratio of ethylamine to methylamine permeabilities was not significantly different from that calculated from the direct measurements of permeabilities; ammonia was much less effective in dissipating the pH gradient across the cell membrane than methylamine or ethylamine. An apparent permeability of ammonia of 5.7±0.9 m sec–1 could be calculated from the permeability ratio of ammonia to methylamine and the experimentally measured permeability of methylamine. The permeability properties of ammonia and methylamine are very different; this poses problems in the interpretation of experiments where14C-methylamine is used as an ammonia analogue. 相似文献
14.
The effect of long-term (1983–1988) applications of crop residues (millet straw, 2–4 t ha-1 yr–1) and/or mineral fertilizer (30 kg N, 13 kg P and 25 kg K ha-1 yr-1) on uptake of phosphorus (P) and other nutrients, root growth and mycorrhizal colonization of pearl millet (Pennisetum glaucum L.) was examined for two seasons (1987 and 1988) on an acid sandy soil in Niger. Treatments of the long-term field experiment were: control (–CR–F), mineral fertilizer only (–CR+F), crop residues only (+CR–F), and crop residues plus mineral fertilizer (+CR+F).In both years, total P uptake was similar for +CR–F and –CR+F treatments (1.6–3.5 kg P ha-1), although available soil P concentration (Bray I P) was considerably lower in +CR–F (3.2 mg P kg-1 soil) than in –CR+F (7.4) soil. In the treatments with mineral fertilizers (–CR+F; +CR+F), crop residues increased available soil P concentrations (Bray I P) from 7.4 to 8.9 mg kg-1 soil, while total P uptake increased from 3.6 to 10.6 kg P ha-1. In 1987 (with 450 mm of rainfall), leaf P concentrations of 30-day-old millet plants were in the deficiency range, but highest in the +CR+F treatment. In 1988 (699 mm), leaf P concentrations were distinctly higher, and again highest in the +CR+F treatment. In the treatments without crop residues (–CR–F; –CR+F), potassium (K) concentrations in the leaves indicated K deficiency, while application of crop residues (+CR–F; +CR+F) substantially raised leaf K concentrations and total K uptake. Leaf concentrations of calcium (Ca) and magnesium (Mg) were hardly affected by the different treatments.In the topsoil (0–30 cm), root length density of millet plants was greater for +CR+F (6.5 cm cm-3) than for +CR–F (4.5 cm cm-3) and –CR+F (4.2 cm cm-3) treatments. Below 30 cm soil depth, root length density of all treatments declined rapidly from about 0.6 cm cm-3 (30–60 cm soil depth) to 0.2 cm cm-3 (120–180 cm soil depth). During the period of high uptake rates of P (42–80 DAP), root colonization with vesicular-arbuscular mycorrhizal (VAM) fungi was low in 1987 (15–20%), but distinctly higher in 1988 (55–60%). Higher P uptake of +CR+F plants was related to a greater total root length in 0–30 cm and also to a higher P uptake rate per unit root length (P influx). Beneficial effects of crop residues on P uptake were primarily attributed to higher P mobility in the soil due to decreased concentrations of exchangeable Al, and enhancement of root growth. In contrast, the beneficial effect of crop residues on K uptake was caused by direct K supply with the millet straw. 相似文献
15.
Eurytemora affinis, a calanoid copepod, has been encountered in Volkerak-Zoommeer (Rhine delta region, S.W. Netherlands) both before this lake system was isolated in 1987 from the estuarine influence, and after. It was the main particle-feeding crustacean at all the 3 sampling stations in March–April 1990 when it reached densities of up to 215 ind.l–1. Its decline from mid April onwards, and low densities through summer, coincided with increase in cladocerans, especiallyDaphnia spp. (D. pulex andD. galeata), a decrease in seston (<33m) and chlorophyll concentrations and in primary production rates. The clearance rates (CR) ofEurytemora measured in the spring period varied enormously (0.6–24 ml.ind–1.d–1) depending mainly on size (0.44–1.06 mm), food concentration (0.8–2.2 mg C.l–1), and the water temperature which varied only narrowly (8.0–9.0°C). Mean ingestion rates of the animals measuring 0.68±0.02 mm during the study was 6.7±3.2 gC.ind–1.d–1; and assimilation efficiency varied between 27 and 53% (mean: 41±9%). The weight specific CR (SCR) varied between 0.96 and 6.4 litre.mg–1 body C.d–1. Pooled regression of SCR on the animal's body weight at the 3 study stations revealed a significant inverse relationship. Also daily ration and specific assimilation ofE. affinis varied greatly and inversely with the body weight. This calanoid contributed from about 50 to 100% to the zooplankton community grazing rates and assimilation rates, the former often exceeding the phytoplankton primary production. 相似文献
16.
Effects of soil freezing disturbance on soil solution nitrogen, phosphorus, and carbon chemistry in a northern hardwood ecosystem 总被引:21,自引:4,他引:17
Ross D. Fitzhugh Charles T. Driscoll Peter M. Groffman Geraldine L. Tierney Timothy J. Fahey Janet P. Hardy 《Biogeochemistry》2001,56(2):215-238
Reductions in snow cover undera warmer climate may cause soil freezing eventsto become more common in northern temperateecosystems. In this experiment, snow cover wasmanipulated to simulate the late development ofsnowpack and to induce soil freezing. Thismanipulation was used to examine the effects ofsoil freezing disturbance on soil solutionnitrogen (N), phosphorus (P), and carbon (C)chemistry in four experimental stands (twosugar maple and two yellow birch) at theHubbard Brook Experimental Forest (HBEF) in theWhite Mountains of New Hampshire. Soilfreezing enhanced soil solution Nconcentrations and transport from the forestfloor. Nitrate (NO3
–) was thedominant N species mobilized in the forestfloor of sugar maple stands after soilfreezing, while ammonium (NH4
+) anddissolved organic nitrogen (DON) were thedominant forms of N leaching from the forestfloor of treated yellow birch stands. Rates ofN leaching at stands subjected to soil freezingranged from 490 to 4,600 mol ha–1yr–1, significant in comparison to wet Ndeposition (530 mol ha–1 yr–1) andstream NO3
– export (25 mol ha–1yr–1) in this northern forest ecosystem. Soil solution fluxes of Pi from the forestfloor of sugar maple stands after soil freezingranged from 15 to 32 mol ha–1 yr–1;this elevated mobilization of Pi coincidedwith heightened NO3
– leaching. Elevated leaching of Pi from the forestfloor was coupled with enhanced retention ofPi in the mineral soil Bs horizon. Thequantities of Pi mobilized from the forestfloor were significant relative to theavailable P pool (22 mol ha–1) as well asnet P mineralization rates in the forest floor(180 mol ha–1 yr–1). Increased fineroot mortality was likely an important sourceof mobile N and Pi from the forest floor,but other factors (decreased N and P uptake byroots and increased physical disruption of soilaggregates) may also have contributed to theenhanced leaching of nutrients. Microbialmortality did not contribute to the acceleratedN and P leaching after soil freezing. Resultssuggest that soil freezing events may increaserates of N and P loss, with potential effectson soil N and P availability, ecosystemproductivity, as well as surface wateracidification and eutrophication. 相似文献
17.
In order to gain information about seasonal and interannual variations of CH4-fluxes at a spruce control site, a limed spruce site and a beech site of the Höglwald Forest, Bavaria, Germany, complete annual cycles of CH4-exchange between the soil and the atmosphere with 2-hourly resolution were followed for 4 consecutive years. The ranges of CH4 fluxes observed for the different sites were: +12.4 to –69.4 g CH4 m–2 h–1 (spruce control site), +11.7 to –51.4 g CH4 m–2 h–1 (limed spruce site), and –4.4 to –167.3 g CH4 m–2 h–1 (beech site). Lowest rates of atmospheric CH4-uptake or even a weak net-emission of CH4 by the soils were observed during winter/spring times, whereas highest rates of CH4-uptake were always found in summer/spring. Over the entire observation period of 4 years, mean CH4-uptake rates were –1.82 kg CH4-C ha–1 yr–1 at the spruce control site, –1.31 kg CH4-C ha–1 yr–1 at the limed spruce site, and –4.84 kg CH4-C ha–1 yr–1 at the beech site. The results obtained in this study demonstrate that in view of the huge interannual variations in CH4-fluxes of approx. 1 kg CH4-C ha–1 yr–1, multiple year measurements of CH4-fluxes are necessary to accurately characterize the sink strength of temperate forest for atmospheric CH4. By comparison of CH4-fluxes measured at the spruce control site and the limed spruce site, a significant negative effect of forest floor liming on CH4-uptake could be demonstrated. Compared to the spruce stand, the beech stand showed on average approx. 3 times higher rates of atmospheric CH4-uptake, most likely due to pronounced differences between both sites with regard to the organic layer structure and bulk density of the mineral soil. Regression analysis between CH4-fluxes and environmental parameters revealed that at all sites the dominating factors regulating temporal variations of CH4 fluxes were soil moisture and soil temperature. Field measurements of CH4 concentrations in the soil profile and laboratory measurements of CH4-oxidation and CH4-production activity on soil samples taken from different soil depths showed that the CH4-flux at the Höglwald Forest sites is the net-result of simultaneous occurring production and consumption of CH4 within the soil. Highest CH4-oxidation activity was found in the uppermost centimeters of the mineral soil, whereas highest potential CH4-production activity was found in the organic layer. 相似文献
18.
J.H. Jussy M. Colin-Belgrand É. Dambrine J. Ranger B. Zeller S. Bienaimé 《Biogeochemistry》2004,69(2):241-262
Nitrogen deposition, mineralisation, uptake and leaching were measured on a monthly basis in the field during 2 years in six forested stands on acidic soils under mountainous climate. Studies were conducted in three Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] plantations (D20: 20 year; D40: 40 yr; D60: 60 yr) on abandoned croplands in the Beaujolais Mounts; and two spruce (Picea abies Karst.) plantations (S45: 45 yr; S90: 90 yr) and an old beech (Fagus sylvatica L.) stand (B150: 150 yr) on ancient forest soils in a small catchment in the Vosges Mountains. N deposition in throughfall varied between 7–8 kg ha–1 year–1 (D20, B150, S45) and 15–21 kg ha–1 yr–1 (S90, D40, D60). N in annual litterfall varied between 20–29 kg ha–1 (D40, D60, S90), and 36–43 kg ha–1 (D20, S45, B150). N leaching below root depth varied among stands within a much larger range, between 1–9 kg ha–1 yr–1 (B150, S45, D60) and 28–66 kg ha–1 yr–1 (D40, S90, D20), with no simple relationship with N deposition, or N deposition minus N storage in stand biomass. N mineralisation was between 57–121 kg ha–1 yr–1 (S45, D40, S90) and between 176–209 kg ha–1 yr–1 in (B150, D60 and D20). The amounts of nitrogen annually mineralised and nitrified were positively related. Neither general soil parameters, such as pH, soil type, base saturation and C:N ratio, nor deposition in throughfall or litterfall were simply related to the intensity of mineralisation and/or nitrification. When root uptake was not allowed, nitrate leaching increased by 11 kg ha–1 yr–1 at S45, 36 kg ha–1 yr–1 at S90 and between 69 and 91 kg ha–1 yr–1 at D20, D40, B150 and D60, in relation to the nitrification rates of each plot. From this data set and recent data from the literature, we suggest that: high nitrification and nitrate leaching in Douglas-fir soils was likely related to the former agricultural land use. High nitrification rate but very low nitrate leaching in the old beech soil was related to intense recycling of mineralised N by beech roots. Medium nitrification and nitrate leaching in the old spruce stand was related to the average level of N deposition and to the deposition and declining health of the stand. Very low nitrification and N leaching in the young spruce stand were considered representative of fast growing spruce plantations receiving low N deposition on acidic soils of ancient coniferous forests. Consequently, we suggest that past land use and fine root cycling (which is dependent on to tree species and health) should be taken into account to explain the variability in the relation between N deposition and leaching in forests. 相似文献
19.
Effects of rate of nitrogen (N) fertilizer and stocking rate on production and N2 fixation by white clover (Trifolium repens L.) grown with perennial ryegrass (Lolium perenne L.) were determined over 5 years in farmlets near Hamilton, New Zealand. Three farmlets carried 3.3 dairy cows ha–1 and received urea at 0, 200 or 400 kg N ha–1 yr–1 in 8–10 split applications. A fourth farmlet received 400 kg N ha–1 yr–1 and had 4.4 cows ha–1.There was large variation in annual clover production and total N2 fixation, which in the 0 N treatment ranged from 9 to 20% clover content in pasture and from 79 to 212 kg N fixed ha–1 yr–1. Despite this variation, total pasture production in the 0 N treatment remained at 75–85% of that in the 400 N treatments in all years, due in part to the moderating effect of carry-over of fixed N between years.Fertilizer N application decreased the average proportion of clover N derived from N2 fixation (PN; estimated by 15N dilution) from 77% in the 0 N treatment to 43–48% in the 400 N treatments. The corresponding average total N2 fixation decreased from 154 kg N ha–1 yr–1 to 39–53 kg N ha–1 yr–1. This includes N2 fixation in clover tissue below grazing height estimated at 70% of N2 fixation in above grazing height tissue, based on associated measurements, and confirmed by field N balance calculations. Effects of N fertilizer on clover growth and N2 fixation were greatest in spring and summer. In autumn, the 200 N treatment grew more clover than the 0 N treatment and N2 fixation was the same. This was attributed to more severe grazing during summer in the 0 N treatment, resulting in higher surface soil temperatures and a deleterious effect on clover stolons.In the 400 N treatments, a 33% increase in cow stocking rate tended to decrease PN from 48 to 43% due to more N cycling in excreta, but resulted in up to 2-fold more clover dry matter and N2 fixation because lower pasture mass reduced grass competition, particularly during spring. 相似文献
20.
Leaching of nitrate and ammonium in heathland and forest ecosystems in Northwest Germany under the influence of enhanced nitrogen deposition 总被引:2,自引:0,他引:2
To study the impact of high atmospheric nitrogen deposition on the leaching of NO3– and NH4+ beneath forest and heathland vegetation, investigations were carried out in adjacent forest and heathland ecosystems in Northwest Germany. The study area is subjected to high deposition of nitrogen ranging from 15.9 kg ha–1 yr–1 in bulk precipitation to 65.3 kg ha–1 yr–1 beneath a stand of Pinus sylvestris L. with NH4–N accounting for 70–80% of the nitrogen deposited. Considerable leaching of nitrogen compounds from the upper horizons of the soil, mostly as nitrate, occurred at most of the forest sites and below a mixed stand of Calluna vulgaris (L.) Hull. and Erica tetralix, but was low in a Betula pubescens Ehrh. swamp forest as well as beneath Erica tetralix L. wet heath and heath dominated by Molinia caerulea(L.) Moench. Ground water concentrations of both NO3–N and NH4–N did not exceed 1 mg L–1 at most of the sites investigated. 相似文献