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1.
External phosphorus requirements of five tropical grain legumes grown in flowing-solution culture 总被引:4,自引:0,他引:4
Summary Five tropical grain legume species were grown for periods from 4 to 20 days in flowing-solution culture at 7 maintained phosphorus
(P) concentrations, ranging from 0.25 μM to 16 μM. Critical external P requirements were 0.8 μM for cowpea cv. Vita 4 and soybean cv. Fitzroy, 1.0 μM for pigeon pea cv. Royes, 2.0 μM for mungbean cv. Regur and 3.0 μM for guar cv. Brooks. Plant responses to P deficiency included reduced growth rate, increased root percentage, and increased
P uptake potential. The long-term P uptake rates of guar plants were lower than those of the other species at each external
P concentration. Guar plants had a low P uptake potential as indicated by short-term32CP-labelled uptake rate studies from 15 μM P solutions. Cowpea by contrast had high short-term uptake rates indicating a high P uptake potential. 相似文献
2.
Effects of temperature, and availability of nitrogen and phosphorus on the abundance of Anabaena and Microcystis in Lake Biwa, Japan: an experimental approach 总被引:23,自引:0,他引:23
Under optimal nutrient conditions, both Microcystis sp. and Anabaena sp. isolated from Lake Biwa grew optimally at 28–32°C but differed in maximal growth rates, phosphate uptake kinetics, maximal
phosphorus quotas, and growth responses to nitrogen and phosphorus limitation. The maximal growth rates of Microcystis and Anabaena were 1.6 and 1.25 divisions day−1, respectively. With phosphate and nitrate in the growth-limiting range, the growth of Microcystis was optimal at an N : P ratio of 100 : 1 (by weight) and declined at lower (nitrogen limitation) and higher (phosphorus limitation)
ratios. In contrast, Anabaena growth rates did not change at N : P ratios from 1000 : 1 to 10 : 1. Starting with cells containing the maximal phosphorus
quota, Microcystis growth in minus-phosphorus medium ceased in 7–9 days, compared with 12–13 days for Anabaena. The phosphate turnover time in cultures starved to their minimum cell quotas was 7.9 min for Microcystis and 0.6 min for Anabaena. Microcystis had a higher K
s (0.12 μg P l−1 10−6 cells) and lower V
max (9.63 μg P l−1 h−1 10−6 cells), than Anabaena (K
s 0.02 μg P l−1 h−1 10−6 cells; V
max 46.25 63 μg P l−1 h−1 10−6 cells), suggesting that Microcystis would not be able to grow well in phosphorus-limited waters. We conclude that in spite of the higher growth rate under ideal
conditions, Microcystis does not usually bloom in the North Basin because of low availability of phosphorus and nitrogen. Although Anabaena has an efficient phosphorus-uptake system, its main strategy for growth in low-phosphorus environments may depend on storage
of phosphorus during periods of abundant phosphorus supply, which are rare in the North Basin.
Received: July 31, 2000 / Accepted: October 18, 2000 相似文献
3.
Summary Preliminary investigations were carried out on calcareous silty loam (clay content 25%, pH 8.0) at the Cotton Research Institute,
Multan to determine the solubility and desorption rates of phosphorus at various soil depths throughout the cotton growing
season using the EUF technique. The treatments included two applications of single superphosphate, equivalent to 0, 75, 150,
250 and 350 kg P2O5/ha. There was no significant difference in seed cotton yield between the five treatments.
EUF-extracted phosphorus decreased with depth in all samples. There was an increase in phosphorus concentration during the
growing season, but most of the increase was noted in the slowly available phosphorus fraction (10–30 minutes EUF aliquots).
This was attributed to continuous transformation of phosphorus into less soluble calcium phosphate forms. The available phosphorus
fraction (0–10 minute EUF aliquots) remained small throughout the growing season. It was concluded that this fraction was
in equilibrium with the slowly available phosphorus fraction and was continually being replenished as crop uptake continued.
A high level of effectively available phosphorus (0–30 minute EUF aliquots) was recovered in all five treatments and was above
the sufficiency level of 12 ppm phosphorus reported by Nemeth and Makhdam7. There was therefore no difference between treatments in phosporus concentration nor in phosphorus uptake by plants.
This work was carried out under UNDP/FAO Project-PAK 73/026 相似文献
4.
The uptake of soluble phosphate by the green sulfur bacterium Chlorobium limicola UdG6040 was studied in batch culture and in continuous cultures operating at dilution rates of 0.042 or 0.064 h–1. At higher dilution rates, washout occurred at phosphate concentrations below 7.1 μM. This concentration was reduced to 5.1
μM when lower dilution rates were used. The saturation constant for growth on phosphate (K
μ) was between 2.8 and 3.7 μM. The specific rates of phosphate uptake in continuous culture were fitted to a hyperbolic saturation
model and yielded a maximum rate (Va
max) of 66 nmol P (mg protein)–1 h–1 and a saturation constant for transport (K
t) of 1.6 μM. In batch cultures specific rates of phosphate uptake up to 144 nmol P (mg protein)–1 h–1 were measured. This indicates a difference between the potential transport of cells and the utilization of soluble phosphate
for growth, which results in a significant change in the specific phosphorus content. The phosphorus accumulated within the
cells ranged from 0.4 to 1.1 μmol P (mg protein)–1 depending on the growth conditions and the availability of external phosphate. Transport rates of phosphate increased in
response to sudden increases in soluble phosphate, even in exponentially growing cultures. This is interpreted as an advantage
that enables Chl. limicola to thrive in changing environments.
Received: 9 February 1998 / Accepted: June 1998 相似文献
5.
The root surface phosphatases ofEriophorum vaginatum: Effects of temperature,pH, substrate concentration and inorganic phosphorus 总被引:1,自引:1,他引:0
Eriophorum vaginatum L. subsp.spissum (Fern.) Hult., a dominant plant in arctic tundra ecosystems, has acid phosphatase activity evenly distributed along its root
surface from the root tip to a distance at least 16 cm from the tip. These root surface phosphatases have optimal activity
from pH 3.5 to 4.0; mean soil pH for soil samples collected with roots was 3.69. Apparent energy of activation and Q10 values (14.0 kcal mol−1 and 2.2, respectively) do not provide evidence for temperature acclimation, but substantial phosphatase activity was measured
at 1°C. Kinetic parameters determined for this root surface phosphatase were as follows: Km=9.23 mM, Vmax=1.61×10−3 μmoles mm−2h−1. The presence of inorganic phosphorus in the assay medium did not inhibit root surface phosphatase activity except at very
high concentrations (100 mM); even then, only slight inhibition was detected (7 to 19%). A comparison of hydrolysis rates with inorganic phosphate assimilation
rates measured forE. vaginatum indicates that organic phosphate hydrolysis may occur at approximately one third the rate of inorganic phosphate absorption.
Calculations show that inorganic phosphate produced by root surface phosphatase activity may satisfy 65% of the annual phosphate
demand ofE. vaginatum. Since arctic tundra soils are typically higher in dissolved organic phosphorus compounds than in inorganic phosphate, root
surface phosphatase activity may make a considerable contribution to the phosphate nutrition of this widespread and abundant
arctic plant. 相似文献
6.
Increased levels of rhizospheric dissolved inorganic carbon have repeatedly been demonstrated to enhance plant growth by up
to 80%, although carbon from dark fixation accounts for only 1–3% of total plant carbon gain. This study, therefore, aimed
at investigating the effects of bicarbonate on nitrate uptake, assimilation and translocation to shoots. Clonal saplings of
poplar (Populus canescens(Ait.) Sm.) and elder (Sambucus nigraL.) were grown hydroponically for 35 days in a nutrient solution containing 0, 0.5 and 1 mM bicarbonate and 2 mM nitrate as the sole nitrogen source at pH 7.0. Net nitrate uptake, root nitrate accumulation and reduction, and export of
nitrogenous solutes to shoots were measured after incubating plants with 15N-labelled nitrate for 24 h. Net nitrate uptake increased non-significantly in plant species (19–61% compared to control plants)
in response to 1 mM bicarbonate. Root nitrate reduction and nitrogen export to shoots increased by 80 and 95% and 15 and 44% in poplar and elder,
respectively. With enhanced root zone bicarbonate, both species also exhibited a marked shift between the main nitrate utilising
processes. Poplar plants increasingly utilised nitrate via nitrate reduction (73–88% of net nitrate uptake), whereas the proportions
of export (20–9%) and storage in roots (7–3%) declined as plants were exposed to 1 mM external bicarbonate. On the other hand, elder plants exhibited a significant increase of root nitrate reduction (44–66%)
and root nitrate accumulation (6–25%). Nitrate translocation to elder shoots decreased from 50 to 8% of net nitrate uptake.
The improved supply of nitrogen to shoots did not translate into a significant stimulation of growth, relative growth rates
increased by only 16% in poplar saplings and by 7% in elder plants.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
7.
One rape (Brassica napus cv. Wesroona) plant and four cotton (Gossypium hirsutum cv. Sicot 3) plants were grown in plastic cells containing soil labelled with 407 kBq of33P g−1 soil. After 5–8 days of growth, the33P depletion zones of all plants were autoradiographed and33P uptake by plants was measured. The autoradiographs were scanned with a microdensitometer and the optical densities at several
places within the33P depletion zones of roots were obtained. The volume of soil explored by root hairs was estimated from measurements of root
diameters and lengths of roots and root hairs. About half of the total33P depleted by cotion roots came from outside the root hair cylinder whereas most of33P taken up by rape was from within the root hair cylinder. Plants grown in a macrostructured soil may have roots growing in
voids, within aggregates or on the surfaces of aggregates. The results of this study demonstrate that root hairs have a strong
influence on the accessibility of phosphorus to roots in such a soil, and thus on the phosphorus nutrition of plants. 相似文献
8.
Generally, the foliar sheaths of seagrass contribute a large biomass to the dry weight of plants, and are found to be above-sediment
biomass or, sometimes, below-sediment biomass. However, the role of foliar sheaths of seagrass in nutrient uptake has not
yet been established. Thus, this study was performed to test whether the growth form of foliar sheaths affects the nutrient
uptake properties of the seagrass. Two separate sets of morphotypes of the seagrass Thalassia hemprichii were collected from two different tropical meadows in coastal Hainan Island, China in the South China Sea. Ammonium (NH4
+) and phosphate (Pi) uptake by solely blades and roots (experiment I), and above and below-sediment tissues (experiment II) of the two sets of
specimens were examined in partitioned chambers using laboratory incubations. Curve profiles of the blade and root saturation
uptake kinetics were shown to be similar for the two morphotypes of T. hemprichii. However, the above and below-sediment tissues uptake kinetics had different characteristics between the two morphotypes.
For plants with above-sediment foliar sheaths, uptake by the above-sediment tissues contributed an important part of the whole
plants’ nutrient acquisition. In contrast, for plants with below-sediment foliar sheaths, the contribution of nutrient uptake
by above-sediment foliar blade tissues seemed almost negligible. Therefore, the results demonstrated that foliar sheaths of
the tropical seagrass T. hemprichii were able to absorb NH4
+ and Pi. Especially interesting is that the capacity for uptake by robust foliar sheaths growing beneath the sediment was remarkable
(we termed this the Zhang–Huang–Thorhaug effect). The role of sheaths in nutrient acquisition found in this study is critical
in elucidating seagrass nutrient uptake strategies. 相似文献
9.
One-year-old apple cuttings (Malus pumila var.domestica cv. M26) were grown for 6 months in pot culture with and without inoculum of the VA-mycorrhizal fungus (VAMF)Glomus macrocarpum in soil from a long-term fertilizer field experiment with different P availability (20, 210, and 280 mg CAL-extractable P
kg−1). The indigenous VAMF propagule density was reduced by 0.5 Mrad X-irradiation. At harvest, non-inoculated and inoculated
plants had similar proportions of root length bearing vesicles. Net dry weight of tree cuttings was significantly increased
by inoculation only at 20 mg P kg−1 (+62%). Increasing P availability from 210 to 280 mg P kg−1 led to a 4-week depression of shoot elongation rate only in the inoculated plants. Uptake of P was significantly enhanced
by inoculation at 20 and 210 mg P kg−1 (+64 and +12%, respectively). On average, inoculated plants had significantly higher concentrations of Zn in leaves and in
roots (+16 and +14%, respectively) and of copper in stems and in roots (+13 and +126%, respectively). Proportion of vesicle
bearing root length was significantly correlated with root caloric content. A lipid content of 0.9–4.5% in the root dry matter
was attributed to the presence of vesicles corresponding to 1.6–8.2% of total root caloric content.
As the control plants were also infected, the beneficial effect of VA-mycorrhiza on nutrient uptake and growth of apple cuttings
was underestimated at all P levels. Furthermore, VAM-potential at the lowest P level was not fully exploited as onset of infection
was most certainly delayed because of a decreased photosynthetic rate due to P deficiency. Energy drain by VAMF-infection
was most probably underestimated considerably, due to, among others, loss of infected root cortex during root growth, sampling
and staining.
It is concluded that apple cuttings rely on VA-mycorrhizal P-uptake at least in low P soils. In high P soils, apple cuttings
may profit predominantly from the uptake of Zn and Cu by the fungal symbionts. 相似文献
10.
In some plant species, various arsenic (As) species have been reported to efflux from the roots. However, the details of As
efflux by the As hyperaccumulator Pteris vittata remain unknown. In this study, root As efflux was investigated for different phosphorus (P) supply conditions during or after
a 24-h arsenate uptake experiment under hydroponic growth conditions. During an 8-h arsenate uptake experiment, P-supplied
(P+) P. vittata exhibited much greater arsenite efflux relative to arsenate uptake when compared with P-deprived (P–) P. vittata, indicating that arsenite efflux was not proportional to arsenate uptake. In the As efflux experiment following 24 h of arsenate
uptake, arsenate efflux was also observed with arsenite efflux in the external solution. All the results showed relatively
low rates of arsenate efflux, ranging from 5.4 to 16.1% of the previously absorbed As, indicating that a low rate of arsenate
efflux to the external solution is also a characteristic of P. vittata, as was reported with arsenite efflux. In conclusion, after 24 h of arsenate uptake, both P+ and P– P. vittata loaded/effluxed similar amounts of arsenite to the fronds and the external solution, indicating a similar process of xylem
loading and efflux for arsenite, with the order of the arsenite concentrations being solution ≪ roots ≪ fronds. 相似文献
11.
Germund Tyler 《Plant and Soil》1996,184(2):281-289
Veronica officinalis and Carex pilulifera, widespread plants of acid soils in Europe, were grown in 50 soils of natural and seminatural ecosystems representing a wide
range of soil chemical properties. The experiment was performed in a greenhouse at a soil moisture content of 55–65% WHC,
ca. 60% R.H. of the air, temperature 14–16°C at night and 19–21°C by day; additional light 70 W m-2 12 h d-1. Properties closely related to soil acidity precluded growth of V. officinalis and limited the growth rate of C. pilulifera at soil pH-KCl < ca. 3.4. In slightly-moderately alkaline (calcareous) soils, growth was primarily limited by insufficient
phosphate uptake. A low growth rate of C. pilulifera. in such soils was related to low concentrations of exchangeable soil phosphate and low tissue concentrations of phosphorus.
However, in high-pH soils, secondary effects due to suboptimum trace element (probably Fe) conditions, giving rise to symptoms
of chlorosis, were also indicated. The highest growth rates of both species were invariably measured in soils of intermediate
acidity having very high concentrations of exchangeable phosphate. Multiple regression tests on the entire material indicated
that 65–75% of the variability in several growth functions could be accounted for, when two or more soil characters were included
in the equation. Besides phosphate, exchangeable Zn (in C. pilulifera) and nitrate (in V. officinalis) were of considerable importance in accounting for growth rates. 相似文献
12.
Brandon K. Swan James M. Watts Kristen M. Reifel Stuart H. Hurlbert 《Hydrobiologia》2007,576(1):111-125
The Salton Sea currently suffers from several well-documented water quality problems associated with high nutrient loading.
However, the importance of phosphorus regeneration from sediments has not been established. Sediment phosphorus regeneration
rates may be affected by benthic macroinvertebrate activity (e.g. bioturbation and excretion). The polychaete Neanthes
succinea (Frey and Leuckart) is the dominant benthic macroinvertebrate in the Salton Sea. It is widely distributed during periods
of mixing (winter and spring), and inhabits only shallow water areas following development of anoxia in summer. The contribution
of N. succinea to sediment phosphorus regeneration was investigated using laboratory incubations of cores under lake temperatures and dissolved
oxygen concentrations typical of the Salton Sea. Regeneration rates of soluble reactive phosphorus (SRP) were lowest (−0.23–1.03
mg P m−2 day−1) under saturated oxygen conditions, and highest (1.23–4.67 mg P m−2 day−1) under reduced oxygen levels. N. succinea most likely stimulated phosphorus regeneration under reduced oxygen levels via increased burrow ventilation rates. Phosphorus
excretion rates by N. succinea were 60–70% more rapid under reduced oxygen levels than under saturated or hypoxic conditions. SRP accounted for 71–80% of
the dissolved phosphorus excreted under all conditions. Whole-lake SRP regeneration rates predicted from N. succinea biomass densities are highest in early spring, when the lake is mixing frequently and mid-lake phytoplankton populations
are maximal. Thus, any additional phosphorus regenerated from the sediments at that time has potential for contributing to
the overall production of the lake.
Guest Editor: John M. Melack
Saline Water and their Biota 相似文献
13.
Traits associated with improved P-uptake efficiency in CIMMYT's semidwarf spring bread wheat grown on an acid Andisol in Mexico 总被引:2,自引:1,他引:1
Manske G.G.B. Ortiz-Monasterio J.I. Van Ginkel M. González R.M. Rajaram S. Molina E. Vlek P.L.G. 《Plant and Soil》2000,221(2):189-204
Phosphorus deficiency is a major yield limiting constraint in wheat cultivation on acid soils. The plant factors that influence
P uptake efficiency (PUPE) are mainly associated with root characteristics. This study was conducted to analyze the genotypic
differences and relationships between PUPE, root length density (RLD), colonization by vesicular arbuscular and arbuscular
mycorrhizal (V)AM fungi and root excretion of phosphatases in a P-deficient Andisol in the Central Mexican Highlands. Forty-two
semidwarf spring-bread-wheat (Triticum aestivumL.) genotypes from CIMMYT were grown without (−P) and with P fertilization (+P), and subsequently in subsets of 30 and 22
genotypes in replicated field trials over 2 and 3 years, respectively. Acid phosphatase activity at the root surface (APASE)
was analyzed in accompanying greenhouse experiments in nutrient solution. In this environment, PUPE contributed more than
P utilization efficiency, in one experiment almost completely, to the variation of grain yield among genotypes. Late-flowering
genotypes were higher yielding, because the postanthesis period of wheat was extended due to the cold weather at the end of
the crop cycles, and postanthesis P uptake accounted for 40–45% of total P uptake. PUPE was positively correlated with the
numbers of days to anthesis (at −P r=0.57 and at +P r=0.73). The RLD in the upper soil layer (0–20 cm) of the wheat germplasm
tested ranged from 0.5 to 2.4 cm cm-3 at –P and 0.7 to 7.7 at +P. RLD was the most important root trait for improved P absorption, and it was positively genetically
correlated with PUPE (at –P r=0.42 and at +P r=0.63) and the number of spikes m-2 (at –P r=0.58 and at +P r=0.36). RLD in the upper soil layer was more important with P fertilizer application. Without P
fertilization, root proliferation in the deeper soil profile secured access to residual, native P in the deeper soil layer.
(V)AM-colonisation and APASE were to a lesser degree correlated with PUPE. Among genoptypes, the level of (V)AM-colonisation
ranged from 14 to 32% of the RLD in the upper soil layer, and APASE from 0.5 to 1.1 nmol s-1 plant-1 10-2.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
A study was conducted to assess the dynamics of vesicular-arbuscular mycorrhizal (VAM) fungi associated with Acacia farnesiana and A. planifrons in moderately fertile alkaline soils. The intensity of root colonization by VAM fungi and the distribution of VAM fungal
structures varied with host species over a period of time. The occurrence of vesicles with varied morphology in the mycorrhizal
roots indicates infection by different VAM fungal species. This was further confirmed from the presence of spores belonging
to different VAM fungal species in the rhizosphere soils. Root colonization and spore number ranged from 56% – 72% and 5 – 14
g –
1soil in A. farnesiana and from 60% – 73% and 5 – 15 g –
1 soil in A. planifrons. Per cent root colonization and VAM spore number in the rhizosphere soil were inversely related to each other in both the
Acacia species. However, patterns of the occurrence of VAM fungal structures were erratic. Spores of Acaulospora foveata, Gigaspora albida, Glomus fasciculatum, G. geosporum and Sclerocystis sinuosa were isolated from the rhizosphere of A. farnesiana whereas A. scrobiculata,
G. pustulatum, G. fasciculatum,
G. geosporum and G. microcarpum were isolated from that of A. planifrons. The response of VAM status to fluctuating edaphic factors varied with host species. In A. farnesiana though soil nitrogen (N) was positively correlated with root colonization, soil moisture, potassium and air temperature were
negatively correlated to both root colonization and spore number. Per cent root colonization and spore number in A. planifrons were negatively related to each other. Further, in A. planifrons as the soil phosphorus and N were negatively correlated with the density of VAM fungal spores, the same edaphic factors along
with soil moisture negatively influenced root colonization.
Received: 16 May 1995 / Accepted: 7 February 1996 相似文献
15.
Oxygen and CO2 fluxes were measured in hydroponically grown mycorrhizal and non-mycorrhizal Triticum aestivum L. cv. Hano roots. The NO3
– uptake of the plants was used to estimate the amount of root respiration attributable to ion uptake. Plants were grown at
4 mM N and 10 μM P, where a total and viable mycorrhizal root colonisation of 48% and 18%, respectively, by Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) was observed. The O2 consumption and NO3
– uptake rates were similar and the CO2 release was higher in mycorrhizal than in non-mycorrhizal wheat. This resulted in a significantly higher respiratory quotient
(RQ, mol CO2 mol–1 O2) in mycorrhizal (1.27±0.13) than in non-mycorrhizal (0.79±0.05) wheat. As the biomass and N and P concentrations in mycorrhizal
and non-mycorrhizal wheat were the same, the higher RQ resulted from the mycorrhizal colonisation and not differences in nutrition
per se.
Accepted: 26 March 1999 相似文献
16.
Root growth,macro-nutrient uptake dynamics and soil fertility requirements of a high-yielding winter oilseed rape crop 总被引:2,自引:0,他引:2
P. B. Barraclough 《Plant and Soil》1989,119(1):59-70
Shoot growth, root growth and macro-nutrient uptake by a high-yielding (5t/ha grain) winter oilseed rape crop have been measured.
Maximum rooting density in the top 20cm of soil was 9.4 cm cm−3 and roots reached a depth of at least 1.8 m. Maximum nutrient uptakes were 364 kg ha−1 for N, 43 kg ha−1 for P, 308 kg ha−1 for K, 287 kg ha−1 for Ca and 16 kg ha−1 for Mg. A 30-day drought coincided with the flowering period and root and shoot growth, as well as nutrient uptake rates,
were reduced. Nutrient concentrations in the soil solution necessary to sustain the nutrient fluxes into the root system by
diffusive supply have been calculated. Peak values were in the range 10 μM for P to 87 μM for N, lower than the observed concentrations, and it was concluded that nutrient transport to roots was not a limitation
to uptake by this rape crop. 相似文献
17.
We investigated the effect of suspended bentonite and kaolinite clays on phosphorus uptake and turnover by lotic periphyton
in laboratory microcosms. Clays were characterized for their phosphorus affinity using laboratory batch experiments. Periphyton
cultivated on glass microscope slides was subjected to a 0.02 mg L−1 radiolabeled soluble reactive phosphorus solution in which a 200-mg L−1 clay load was suspended. A 1-h uptake experiment was followed by a 10-day turnover experiment. Biomass normalized phosphorus
uptake, and turnover rates were described by mean rate constants ranging from 0.14 to 0.17 min−1 for uptake and 0.04–0.07 days−1 for turnover. Mean phosphorus concentrations were compared among treatments using repeated measures analysis of variance
(ANOVA). Mean phosphorus concentrations among treatments were compared using one-way ANOVA. No significant differences were
found among treatments for either analysis. Under laboratory conditions, these clays appear to have little or no short-term
influence upon phosphorus uptake or turnover by periphyton. 相似文献
18.
Parameters of ecosystem structure and functioning were analyzed in three hypereutrophic lagoons of Ca’Pisani during the season
of 2001. Lagoons are situated at wetlands of the NW Adriatic in the vicinity of the Porto Viro, Po River delta. They are associated
with intensive fish culture enterprise and accept its wastewater. In June, the lagoons were found overloaded with the biomass
of nitrophylic algae. At the end of July, a bloom of potentially toxic dinoflagellate Alexandrium tamarense occurred. Soon, it was supplanted by the picocyanobacterial assemblage, which arrived into the lagoons from the coastal Adriatic
via the Marine channel. Wet biomass of this new picocyanobacterial bloom arrived in September attained 30–60 g m−3. Decrease of white disk water transparency down to 30–40 cm resulted in a gross mortality of macrophytes accompanied by spreading
of floating saprobic alga Enteromorpha. Phytoplankton was dominated in June to July by small mixotrophic phytoflagellates with a wet biomass of 200–1300 mg m−3. Number of bacterioplankton ranged between 4 and 7 × 106 ml−1 and its wet biomass between 1.4 and 2.1 g m−1. Its maximum of 18 × 106 ml−1 was observed in late August, when the mortality of macrophytes had occurred. Zooplankton and zoobenthos were found depleted
in the lagoons especially during the blooms. Diel fluctuations of dissolved oxygen in the lagoons in June to July reached
150–200% of saturation. Photosynthetic oxygen production ranged between 15 and 30 g O2 m−2 d−1. Water column deoxygenation rate was 1–1.5 mg O2 l−1 h−1. Total photosynthesis production reached 3–8 g C m−2 d−1 by the share of phytoplankton 5–15%. Hyper-accumulation of total phosphorus in the water column and of toxic labile sulfides
in the bottom sediments was documented. Content of inorganic phosphorus in water remained unusually high even by its intensive
uptake by microplankton. The PO4P uptake rate measured with 32P-label ranged during the bloom of picocyanobacteria between 10 and 50 nM l−1 min−1, and the residence time of PO4P between 15 and 50 min. The data were generalized via the calculation of energy balance and the deduction of the energy flow
scheme in the ecosystem. Their analysis demonstrates the invalidation of ecosystems in hypereutrophic lagoons due to their
overload with organic matter, with nutrients and with labile sulfides. After having depleted their animal food web, they are
unable to decompose local plus external organic loading.
Electronic supplementary material Electronic supplementary material is available for this article at
and accessible for authorised users. 相似文献
19.
In the present study, we examined the effects of long- and short-term hypoxia on net uptake and transport of phosphorus to shoots of pond pine (Pinus serotina Michx.), a moderately flood-tolerant southern pine, and the influence aerenchyma formation might have in maintenance of P uptake and transport. Seedlings were grown under aerobic (250 μM O2) or hypoxic (≤50 μM O2) solution conditions for 5.3 weeks in continuously flowing solution culture containing 100 μM P. Intact seedlings were then labeled with 32P for up to 24 h to determine how short- and long-term hypoxic solution conditions affected rates of unidirectional influx and the accumulation of 32P in roots and shoots. Seedlings in the long-term hypoxic treatment were grown for 5.3 weeks in hypoxic solution and also labeled in hypoxic uptake solution. The short-term hypoxic treatments included a 24-h hypoxic pretreatment followed by time in labeled hypoxic uptake solution for seedlings grown under aerobic or hypoxic conditions; in the latter case, diffusion of atmospheric O2 entry into stem and root collar lenticels was blocked, thus removing any influence that aerenchyma formation might have had on enhancing O2 concentrations of root tissue. Although unidirectional influx rates of 32P in roots of seedlings grown under long-term hypoxic conditions were 1.4 times those of aerobically grown seedlings, accumulation of 32P in roots was similar after 24 h in labeled uptake solution. These results suggest that 32P efflux was also higher under hypoxic conditions. Higher shoot/root fresh weight ratios and lower shoot P concentrations in seedlings grown under hypoxic solution conditions suggest that the “shoot P demand” per unit root should be high. Yet accumulation of 32P in shoots was reduced by 50% after 24 h in hypoxic uptake solution. Both short-term hypoxic treatments decreased accumulation of 32P in roots by more than 50%. Short-term hypoxia decreased shoot accumulation in seedlings grown under aerobic and hypoxic conditions by 84 and 50%. respectively. Short- and long-term hypoxic conditions increased the percentage of root 32P in the nucleic acid and chelated-P pools, resulting in a significantly smaller percentage of 32P in the soluble inorganic phosphate (pi) pool, the pool available for transport to the shoot. However, a reduction in pool size or in labeling of the pool available for transport cannot fully account for the large reduction in accumulation of 32P in shoots, particularly in the short-term hypoxic treatment of aerobically grown seedlings. Our results suggest that both influx and transport of 32P to shoots of pond pine seedlings are O2-dependent processes, and that the transport of 32P to shoots may be more sensitive to hypoxic solution conditions than influx at the cortical and epidermal plasmalemma, with aerenchyma formation supporting a substantial amount of both 32P uptake and transport. 相似文献
20.
Correlations between foliar δ15N and nitrogen concentrations may indicate plant-mycorrhizal interactions 总被引:1,自引:0,他引:1
Nitrogen isotope measurements may provide insights into changing interactions among plants, mycorrhizal fungi, and soil processes
across environmental gradients. Here, we report changes in δ15N signatures due to shifts in species composition and nitrogen (N) dynamics. These changes were assessed by measuring fine
root biomass, net N mineralization, and N concentrations and δ15N of foliage, fine roots, soil, and mineral N across six sites representing different post-deglaciation ages at Glacier Bay,
Alaska. Foliar δ15N varied widely, between 0 and –2‰ for nitrogen-fixing species, between 0 and –7‰ for deciduous non-fixing species, and between
0 and –11‰ for coniferous species. Relatively constant δ15N values for ammonium and generally low levels of soil nitrate suggested that differences in ammonium or nitrate use were
not important influences on plant δ15N differences among species at individual sites. In fact, the largest variation among plant δ15N values were observed at the youngest and oldest sites, where soil nitrate concentrations were low. Low mineral N concentrations
and low N mineralization at these sites indicated low N availability. The most plausible mechanism to explain low δ15N values in plant foliage was a large isotopic fractionation during transfer of nitrogen from mycorrhizal fungi to plants.
Except for N-fixing plants, the foliar δ15N signatures of individual species were generally lower at sites of low N availability, suggesting either an increased fraction
of N obtained from mycorrhizal uptake (f), or a reduced proportion of mycorrhizal N transferred to vegetation (T
r). Foliar and fine root nitrogen concentrations were also lower at these sites. Foliar N concentrations were significantly
correlated with δ15N in foliage of Populus, Salix, Picea, and Tsuga heterophylla, and also in fine roots. The correlation between δ15N and N concentration may reflect strong underlying relationships among N availability, the relative allocation of carbon
to mycorrhizal fungi, and shifts in either f or T
r.
Received: 14 December 1998 / Accepted: 16 August 1999 相似文献