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991.
《Archives of animal nutrition》2013,67(6):478-491
The objective of this study was to evaluate the effects of diet composition on phytate (InsP6) degradation in dairy cows. In Experiment 1, four diets that differed in the amount and source of phosphorus (P) were fed to 24 lactating cows in a 4 × 4 Latin Square design. The control diet (Diet C) contained 4.18 g P/kg dry matter (DM). Diet MP contained additional mineral P (5.11 g P/kg DM), Diet RS contained rapeseed and rapeseed meal as organic P sources (5.26 g P/kg DM) and Diet RSM contained rapeseed meal and rapeseed oil (5.04 g P/kg DM). Total P (tP) and InsP6 excretion in faeces were measured. In Experiment 2, we used a rumen simulation technique (Rusitec) to estimate ruminal disappearance of tP and InsP6 from Diets C, MP and RSM. In Experiment 1, tP concentration in faeces increased with tP intake and was highest for Diets RS and RSM. The source of supplemented P had no influence on tP digestibility, but tP digestibility was reduced for Diets MP, RS and RSM in comparison to that for Diet C. InsP6 disappearance decreased in Diet MP (85.0%) and increased in Diets RS (92.7%) and RSM (94.0%) compared to that in Diet C (90.0%). In Experiment 2, P source influenced ruminal tP disappearance (Diet MP, 78.6%; Diet RSM, 75.3%). InsP6 disappearance for Diet C (98.1%) was higher than that for Diets MP (95.6%) and RSM (94.9%). The results confirmed the high potential of ruminants to degrade InsP6, but differences in diet composition influenced InsP6 disappearance. Further studies of the site of InsP6 degradation are required to understand the relevance of InsP6 degradation for the absorption of P. 相似文献
992.
This study was designed to quantify and model the effects of macrophytes on phosphorus retention in a lowland river. The seasonal
course of phosphorus retention was calculated from the measured difference in TP between beginning and end of a 30-km river
course and the estimated lateral P input. The coverage of submersed macrophytes was mapped and coincided with the difference
between theoretical water level (without vegetation) and the observed one. Therefore, the increase in water level was used
as measure of the macrophytes’ abundance. In years with rare vegetation (1991–1994), P was retained in winter and remobilized
in summer. In years with dense stands of macrophytes (1995–2002), net P retention was highest in summer and amounted up to
20% of TP load, and was negative during winter. The annual P budget was close to zero in both periods. The found sinusoidal
annual pattern of total phosphorus retention was used to create a retention model for vegetated lowland rivers. 相似文献
993.
The remains of cladocerans were examined from the surface sediments of 51 freshwater sites along a north–south transect spanning
Alaska. We identified 27 cladoceran taxa from the sediments, consisting primarily of littoral chydorid species. Variations
in cladoceran assemblages were related to measured physical and chemical variables using multivariate techniques. Redundancy
analysis (RDA) indicated that lake depth, total phosphorus (TP), and altitude all had a significant influence in determining
the composition of cladoceran assemblages. Cladoceran communities in tundra and forest-tundra lakes, which were relatively
shallow and nutrient-poor, had relatively low abundances of pelagic Cladocera, and were primarily composed of several littoral
chydorid species. Among pelagic cladoceran species, there was a distinct shift in dominance from the Bosminidae in lakes in
the southern boreal forest region to Daphniidae in lakes in the northern boreal forest. Daphnia dominated lakes had significantly higher total phosphorus, specific conductivity, and calcium concentrations than lakes dominated
by Eubosmina. Overall, the relative importance of physical and chemical factors in structuring cladocerans is similar to other previously
studied regions, and suggests the Cladocera may be useful as ecological and paleoenvironmental indicators in this region. 相似文献
994.
Hydraulic Phases, Persistent Stratification, and Phytoplankton
in a Tropical Floodplain Lake (Mary River, Northern Australia) 总被引:1,自引:0,他引:1
Simon Anthony Townsend 《Hydrobiologia》2006,556(1):163-179
The Mary River, in the Australian wet/dry tropics, flows seasonally. When the river ceases flowing in the dry season, a series
of isolated lakes remain along the river’s main floodplain channel. The limnology of a channel lake, which is 14 km long and
6-9 m deep in the dry season, was examined between April and December 2000. Four hydraulic phases were identified, these being
(1) riverine (April), (2) riverine to lake transition (May), (3) lake (June–late-November), and (4) lake to riverine transition
(late-November–December). These phases differ with respect to their duration and flow direction from lakes located on tropical
floodplains of perennially flowing rivers. Despite the variable hydraulic conditions, the main channel remained thermally
stratified, with only infrequent and short-lived deep mixing events, and sufficient light for photosynthesis in the diurnal
mixed layer. During the period of isolation and in contrast to floodplain lakes in tropical South America, the depth of the
Mary River channel lake always exceeded, by at least 2-fold, the depth of the diurnal mixed layer. The water quality (conductivity,
dissolved oxygen, pH, Si and water clarity) and phytoplankton assemblage of the channel lake was primarily driven by its hydraulics,
though this was not evident for the channel’s nutrient concentrations. Dissolved oxygen concentrations during lentic conditions
were double values during the riverine and transition phases. This was attributed to the cessation of inflowing waters with
a high biological oxygen demand, and enhanced photosynthetic activity of higher concentrations of phytoplankton retained under
lentic conditions. The channel’s phytoplankton assemblage reflected the channel’s hydraulics, with the most common phytoplankton
throughout the study period belonging to functional groups Lo(Peridinium inconspicuum), W1 (euglenoids), W2 (Trachelmonas) and Y (Cryptopmonas, Rhodomonas), with groups A (Acanthoceras) and D (Nitzschia agnita, Synedra alna) prominent during the lentic phase. Despite persistent stratification under lentic conditions, there was no clear evidence
of autogenic succession or domination by any single phytoplankton functional group. 相似文献
995.
Responses of maize grain yield to changes in acid soil characteristics after soil amendments 总被引:2,自引:0,他引:2
C. The H. Calba C. Zonkeng E. L. M. Ngonkeu V. O. Adetimirin H. A. Mafouasson S. S. Meka W. J. Horst 《Plant and Soil》2006,284(1-2):45-57
An experiment was conducted from 1997 to 2000 on an acid soil in Cameroon to assess the effectiveness of cultivating acid tolerant maize (Zea mays L.) cultivar and the use of organic and inorganic fertilizers as options for the management of soil acidity. The factors investigated were: phosphorus (0 and 60 kg ha?1), dolomitic lime (0 and 2 t ha?1), organic manure (no manure, 4 t ha?1 poultry manure, and 4 t ha?1 of leaves of Senna spectabilis), and maize cultivars (ATP-SR-Y – an acid soil-tolerant, and Tuxpeño sequia – an acid susceptible). On acid soil, maize grain yield of ATP-SR-Y was 61% higher than the grain yield of Tuxpeño sequia. Continuous maize cultivation on acid soil further increased soil acidity, which was manifested by a decrease in pH (0.23 unit), exchangeable Ca (31%) and Mg (36%) and by an increase in exchangeable Al (20%). Yearly application of 60 kg ha?1 of P for 3 years increased soil acidity through increases in exchangeable Al (8%) and H (16%) and a decrease in exchangeable Ca (30%), Mg (11%) and pH (0.07 unit). Lime application increased grain yield of the tolerant (82%) and susceptible (208%) cultivars. The grain yield increases were associated with a mean decrease of 43% in exchangeable Al, and 51% in H, a mean increase of 0.27 unit in pH, 5% in CEC, 154% in exchangeable Ca, and 481% in Mg contents of the soil. Poultry manure was more efficient than leaves of Senna producing 38% higher grain yield. This yield was associated with increases in pH, Ca, Mg and P, and a decrease in Al. The highest mean grain yields were obtained with lime added to poultry manure (4.70 t ha?1) or leaves of Senna (4.72 t ha?1). Grain yield increase was more related to the decrease in exchangeable Al (r = ?0.86 to ?0.95, P<0.01) and increase in Ca (r = 0.78–0.94, P<0.01), than to pH (r = ?0.57 (non-significant) to ?0.58 (P<0.05)). Exchangeable Al was the main factor determining pH (r = ?0.88 to ?0.92, P<0.01). The yield advantage of the acid tolerant cultivar was evident even after correcting for soil acidity. Acid soil-tolerant cultivars are capable of bringing unproductive acid soils into cultivation on the short run. The integration of soil amendments together with acid soil-tolerant cultivar offers a sustainable and comprehensive strategy for the management of acid soils in the tropics. 相似文献
996.
Soil Phosphorus Uptake by Continuously Cropped Lupinus albus: A New Microcosm Design 总被引:1,自引:0,他引:1
R. C. Le Bayon L. Weisskopf E. Martinoia J. Jansa E. Frossard F. Keller K. B. Föllmi J.-M. Gobat 《Plant and Soil》2006,283(1-2):309-321
When grown in soils with sparingly available phosphorus (P), white lupin (Lupinus albus L.) forms special root structures, called cluster roots, which secrete large amounts of organic acids and concomitantly acidify
the rhizosphere. Many studies dealing with the understanding of this P acquisition strategy have been performed in short time
experiments either in hydroponic cultures or in small microcosm designs with sand or sand:soil mixtures. In the present study,
we applied an experimental design which came nearer to the natural field conditions: we performed a one-year experiment on
large microcosms containing 7 kg of soil and allowing separation of rhizosphere soil and bulk soil. We planted six successive
generations of lupins and analysed P uptake, organic P desorption, phosphatase activities and organic acid concentrations
in different soil samples along a spatio-temporal gradient. We compared the rhizosphere soil samples of cluster (RSC) and
non-cluster roots (RSNC) as well as the bulk soil (BS) samples. A total shoot biomass of 55.69 ± 1.51 g (d.w.) y−1 was produced and P uptake reached 220.59 ± 5.99 mg y−1. More P was desorbed from RSC than from RSNC or BS (P < 0.05). RSC and RSNC showed a higher activity of acid and alkaline phosphatases than BS samples and a higher acid phosphatase
activity was observed in RSC than in RSNC throughout the one-year experiment. Fumarate was the most abundant organic acid
in all rhizosphere soil samples. Citrate was only present in detectable amounts in RSC while malate and fumarate were recovered
from both RSC and RSNC. Almost no organic acids could be detected in the BS samples. Our results demonstrated that over a
one-year cultivation period in the absence of an external P supply, white lupin was able to acquire phosphate from the soil
and that the processes leading to this P uptake took place preferentially in the rhizosphere of cluster roots. 相似文献
997.
Phytate, the major organic phosphorus in soil, is not readily available to plants as a source of phosphorus (P). It is either
complexed with cations or adsorbed to various soil components. The present study was carried out to investigate the extracellular
phytase activities of tobacco (Nicotiana tabacum variety GeXin No.1) and its ability to assimilate external phytate-P. Whereas phytase activities in roots, shoots and growth
media of Pi-fed 14-day-old seedlings were only 1.3–4.9% of total acid phosphatase (APase) activities, P starvation triggered an increase
in phytase secretion up to 914.9 mU mg−1 protein, equivalent to 18.2% of total APase activities. Much of the extracellular phytase activities were found to be root-associated
than root-released. The plants were not able to utilize phytate adsorbed to sand, except when insoluble phytate salts were
preformed with Mg2+ and Ca2+ ions for supplementation. Tobacco grew better in sand supplemented with Mg-phytate salts (31.9 mg dry weight plant−1; 0.68% w/w P concentration) than that with Ca-phytate salts (9.5 mg plant−1; 0.42%), presumably due to its higher solubility. We conclude that insolubility of soil phytate is the major constrain for
its assimilation. Improving solubility of soil phytate, for example, by enhancement of citrate secretion, may be a feasible
approach to improve soil phytate assimilation. 相似文献
998.
Nutrient uptake in streams draining agricultural catchments of the midwestern United States 总被引:2,自引:0,他引:2
MELODY J. BERNOT JENNIFER L. TANK TODD V. ROYER MARK B. DAVID 《Freshwater Biology》2006,51(3):499-509
1. Agriculture is a major contributor of non‐point source pollution to surface waters in the midwestern United States, resulting in eutrophication of freshwater aquatic ecosystems and development of hypoxia in the Gulf of Mexico. Agriculturally influenced streams are diverse in morphology and have variable nutrient concentrations. Understanding how nutrients are transformed and retained within agricultural streams may aid in mitigating increased nutrient export to downstream ecosystems. 2. We studied six agriculturally influenced streams in Indiana and Michigan to develop a more comprehensive understanding of the factors controlling nutrient retention and export in agricultural streams using nutrient addition and isotopic tracer studies. 3. Metrics of nutrient uptake indicated that nitrate uptake was saturated in these streams whereas ammonium and phosphorus uptake increased with higher concentrations. Phosphorus uptake was likely approaching saturation as evidenced by decreasing uptake velocities with concentration; ammonium uptake velocity also declined with concentration, though not significantly. 4. Higher whole‐stream uptake rates of phosphorus and ammonium were associated with the observed presence of stream autotrophs (e.g. algae and macrophytes). However, there was no significant relationship between measures of nutrient uptake and stream metabolism. Water‐column nutrient concentrations were positively correlated with gross primary production but not community respiration. 5. Overall, nutrient uptake and metabolism were affected by nutrient concentrations in these agriculturally influenced streams. Biological uptake of ammonium and phosphorus was not saturated, although nitrate uptake did appear to be saturated in these ecosystems. Biological activity in agriculturally influenced streams is higher relative to more pristine streams and this increased biological activity likely influences nutrient retention and transport to downstream ecosystems. 相似文献
999.
1. Studies of aquatic environments have shown that community organisation may strongly affect ecosystem functioning. One common phenomenon is a change in nutrient level following a shift in the fish community composition. Although several hypotheses have been suggested, there is no consensus on which mechanisms are involved. Our study evaluated indirect effects of benthivorous fish on the biogeochemical processes at the sediment–water interface separately from direct effects caused by nutrient excretion or sediment resuspension. 2. We assigned field enclosures to three treatments representing typical pond communities; without fish, addition of approximately 10 small tench or addition of one large bream. After one summer, we monitored the water chemistry, benthic invertebrates and periphyton in the enclosures and sampled sediment cores for laboratory analysis of biochemical process rates (oxygen, phosphorus and nitrogen exchange between sediment and water, and denitrification rate). 3. Fish had strong negative effects on benthic invertebrates, but weaker effects on periphyton, organic content and porosity of the sediment. Moreover, there were significant positive fish effects on both phosphorus and nitrogen concentrations in the water. However, there were no general treatment effects on sediment processes that could explain the treatment effects on water chemistry in the enclosures. 4. Hence, overall treatment effects attenuated along the chain of interactions. We conclude that the observed effect of benthic fish on water chemistry was probably because of direct effects on nutrient excretion or resuspension of sediment. The similarity between bream and tench treatments suggests large niche complementarity despite their different habitat preferences. 相似文献
1000.
太湖典型菜地土壤氮磷向水体径流输出与生态草带拦截控制 总被引:20,自引:2,他引:18
农业面源氮磷输出是导致太湖流域地表水富营养化主要原因之一,查明该地区农田土壤地表径流氮磷向水体迁移形态与通量,并实施径流控制,对水体富营养化治理具有重要现实意义。蔬菜地是太湖流域重要的农业种植方式。通过设置野外径流小区,观测了春夏季蔬菜地土壤氮磷径流输出,并探讨了生态拦截草带对径流中不同形态氮磷拦截效果。结果表明,2004年10月25日至2005年8月17日,菜地土壤氮磷径流输出总量分别为3 010.9和695.0 g.hm-2;其中颗粒态为主,分别占64%和75%。可溶态氮中,NH4 -N为主,占50%,可溶态磷中H2PO4-为主,占87%。生态拦截草带对径流氮和磷拦截效率分别为42%~91%,30%~92%。生态草带对颗粒态氮磷拦截效率大于可溶态。拦截草带可有效地控制蔬菜地土壤氮、磷通过径流向水体迁移。 相似文献