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1.
The competition between peat mosses ( Sphagnum ) and vascular plants as affected by raised CO2 and increased N deposition was studied in a glasshouse experiment by exposing peat monoliths with monocultures and mixtures of Sphagnum magellanicum and Eriophorum angustifolium to ambient (350 ppmv) or raised (560 ppmv) atmospheric CO2 concentrations, combined with low (no N addition) or high (5 g m−2 yr−1 added) N deposition. Growth of the two species was monitored for three growing seasons.
The presence of Eriophorum did not affect Sphagnum biomass, because Eriophorum density did not become high enough to severely shade the moss surface. In contrast, Sphagnum had a negative effect on Eriophorum biomass, particularly on the number of flowering stems. Possibly, the presence of a living Sphagnum layer decreased nutrient availability to Eriophorum by immobilising nutrients mineralised from the peat.
Raised CO2 and/or increased N deposition did not change these competitive relationships between Sphagnum and Eriophorum , but had independent effects. Raised CO2 had a positive effect both on Sphagnum and Eriophorum biomass, though on Eriophorum the effect was transient, probably because of P limitation. Nitrogen addition had a direct negative effect on Sphagnum height growth in the first growing season, but by the third year an increased shoot density had cancelled this out, so no N effect on Sphagnum biomass was present at the end of the experiment. The response of Eriophorum to N addition was small; N availability appeared not to limit its growth. 相似文献
The presence of Eriophorum did not affect Sphagnum biomass, because Eriophorum density did not become high enough to severely shade the moss surface. In contrast, Sphagnum had a negative effect on Eriophorum biomass, particularly on the number of flowering stems. Possibly, the presence of a living Sphagnum layer decreased nutrient availability to Eriophorum by immobilising nutrients mineralised from the peat.
Raised CO
2.
Element concentrations in mosses and surface waters of western Canadian mires relative to precipitation chemistry and hydrology 总被引:2,自引:0,他引:2
Concentrations of N, P, S, Na, K, Mg, Ca, Mn, Fe, Cu, Cd, Zn, Pb, Al, and AIA (acid insoluble ash) m mosses (three Sphagnum species and Tomenthypnum nitens, all hummock species) from a variety of mires, both ombrotrophic and minerotrophic, in the coastal western and central parts of Canada are considered in relation to surface water pH and concentrations of Na+ , K+ , Mg2+ , Ca2+ , Cl− , and SO4 2- Distinct west-east concentration gradients were present for most elements in both mosses and water, but there were correlations between surface water and moss concentrations only for Ca and Mg
On ombrotrophic sites and sites characterized by poor fen vegetation, wet deposition is the main source of elements in the surface water On rich fen sites, additional Ca and Mg from surrounding soils change the elemental proportions We conclude that hydrochemically the limit between poor and rich fen sites is more decisive than between bog and fen The increase in Ca may give brown mosses a competitive advantage over Sphagnum
Moss concentrations of Na and Mg are the only ones decreasing inland The constancy or inland increase of moss elemental concentrations may depend on either an increasing atmospheric supply (e g Pb), differences in moss growth rates (especially N, P, and K) or site conditions related to the water regime (e g Fe and Al) 相似文献
On ombrotrophic sites and sites characterized by poor fen vegetation, wet deposition is the main source of elements in the surface water On rich fen sites, additional Ca and Mg from surrounding soils change the elemental proportions We conclude that hydrochemically the limit between poor and rich fen sites is more decisive than between bog and fen The increase in Ca may give brown mosses a competitive advantage over Sphagnum
Moss concentrations of Na and Mg are the only ones decreasing inland The constancy or inland increase of moss elemental concentrations may depend on either an increasing atmospheric supply (e g Pb), differences in moss growth rates (especially N, P, and K) or site conditions related to the water regime (e g Fe and Al) 相似文献
3.
Juul Limpens Jeffrey T. A. G. Raymakers Jacqueline Baar Frank Berendse Jantineke D. Zijlstra 《Oikos》2003,103(1):59-68
We report the effects of fertilisation with N and P on the infection of Sphagnum by its fungal parasite Lyophyllum palustre, the expansion of epiphytic algae and the interaction between the latter two from 1998 to 2001. We added 40 kg N ha−1 yr−1 or 3 kg P ha−1 yr−1 in a full factorial design at 4 field sites. In a greenhouse experiment we reinoculated Sphagnum to verify the identity of the fungus and its necrotic effect on Sphagnum .
Lyophyllum palustre was responsible for the necrosis of Sphagnum in our experiments. Adding N induced complete necrosis of Sphagnum cuspidatum by L. palustre , whereas adding P decreased the area of necrotic tissue. Disease severity was related to the N concentration in the Sphagnum capitula. In Sphagnum magellanicum and S. papillosum , infection with L. palustre resulted in defoliation of stem sections. Adding N stimulated the expansion of algae at all sites, reducing the volume of photosynthetic tissue in Sphagnum. The density of the film of algae in the treatments receiving N was a function of the frequency of defoliated Sphagnum stems.
We conclude that infection with parasitic fungi and, in humid environments, the expansion of epiphytic algae, may aggravate the impact of increased N deposition or of other ecosystem disturbances that affect nutrient availability. 相似文献
Lyophyllum palustre was responsible for the necrosis of Sphagnum in our experiments. Adding N induced complete necrosis of Sphagnum cuspidatum by L. palustre , whereas adding P decreased the area of necrotic tissue. Disease severity was related to the N concentration in the Sphagnum capitula. In Sphagnum magellanicum and S. papillosum , infection with L. palustre resulted in defoliation of stem sections. Adding N stimulated the expansion of algae at all sites, reducing the volume of photosynthetic tissue in Sphagnum. The density of the film of algae in the treatments receiving N was a function of the frequency of defoliated Sphagnum stems.
We conclude that infection with parasitic fungi and, in humid environments, the expansion of epiphytic algae, may aggravate the impact of increased N deposition or of other ecosystem disturbances that affect nutrient availability. 相似文献
4.
Six cultivars of spring barley ( Hordeum vulgare L. cvs Salve, Nümberg II, Bomi, Risø 1508, Mona and Sv 73 608) were grown in water culture for three weeks with various combinations of mineral supply and differential roots/shoot temperatures during the growth period. Most important for growth and accumulation of N, K+ , Ca2+ and Mg2+ was the mineral supply, followed by the root temperature and the choice of cultivar. Treatments with low mineral supply or low root temperature induced a uniform reduction in growth and accumulation of the ions studied. The effects of low mineral supply and low root temperature on growth and N accumulation was additive, which indicates that these factors exert their influence independently of each other.
Roots grown at 10°C were smaller and Rb+ (86 Rb) influx was higher than in roots grown at 20°C. It is suggested that the control of Rb+ (86 Rb) influx is affected by the root temperature and the age of the plants. The higher 86 Rb+ (86 Rb) influx into the low temperature roots could not compensate for the smaller root size. However, the lower total mineral accumulation made up for the needs of the smaller plants and cannot explain the reduction in growth. 相似文献
Roots grown at 10°C were smaller and Rb
5.
Magdalena M. Wiedermann Urban Gunnarsson Mats B. Nilsson Annika Nordin Lars Ericson 《Oikos》2009,118(3):449-456
Oligotrophic, Sphagnum -dominated peatlands have been regarded as long-term stable ecosystems that function as carbon sinks. As a result of environmental perturbations, particularly anthropogenic N deposition, this view is now increasingly questioned. We examined whether small-scale field experiments can predict the direction and magnitude of ecosystem responses to increased N supply. We, therefore, compared data from a 10-year field experiment (involving deposition of 2, 15 and 30 kg N ha−1 year−1 ) with data from a gradient associated with increased N deposition (2, 8 and 12 kg N ha−1 year−1 ). We chose to compare: (1) the physiological response of Sphagnum balticum , measured in the form of N accumulation as free amino acids (NAA ); and (2) changes in the total Sphagnum cover, the cover of S. balticum , and vascular plant cover. In all cases we found a highly significant correlation between the two data sets. We attribute the high correspondence between the two data sets to the key function of the dominant group of organisms, the Sphagna, that monopolize N availability and control the water balance, creating an environment hostile to vascular plants. Thus the key role of Sphagna as ecosystem engineers seems to supersede the role of other, scale-dependent processes. We also conclude that NAA is a sensitive indicator that can be used to signal the slow and gradual shift from Sphagnum to vascular plant dominance. 相似文献
6.
Some classes of marine phytoplankton are believed to be more tolerant of high concentrations of trace metals than others, but the results of experimental tests of this hypothesis are ambiguous. Eleven species of phytoplankton representing five classes were grown in Aquil medium containing Cd concentrations between 10−8 and 10−5 M ([Cd2+ ]= 10−9.85 to 10−6.84 M), and growth rates and intracellular concentrations of Cd, C, N, and S were measured. The mean Cd2+ concentration (pCd50 ) that reduced the growth rate of each species to 50% of its maximum varied by 2.5 orders of magnitude, from 10−6.23 for Emiliania huxleyi to 10−8.79 for Synechococcus sp. Taxonomic trends in Cd resistance were not apparent in these data. Cadmium quotas (mol Cd·L−1 cell volume) were lowest in species of Bacillariophyceae (ANOVA, P < 0.001), suggesting that they might regulate Cd transport differently than other taxa. Cellular S:C molar ratios increased in four of seven phytoplankton grown at high pCd (7.37–6.84) compared to low Cd ion concentrations (no added Cd), a result of increases in S·L−1 cell volume. Nitrogen:carbon molar ratios were also higher in Cd-exposed phytoplankton, as changes in N and S were highly correlated ( r = 0.98, P < 0.0001). In two species that were examined, S:C ratios increased as a linear function of increasing Cd concentration. The results demonstrate large variability in Cd resistance among phytoplankton that is primarily a function of interspecific differences in Cd detoxification. 相似文献
7.
Larger capsules enhance short‐range spore dispersal in Sphagnum,but what happens further away? 总被引:1,自引:0,他引:1
Sebastian Sundberg 《Oikos》2005,108(1):115-124
I made a dispersal experiment with six Sphagnum (peat moss) species, representing a wide range of spore and capsule sizes. Spore deposition was recorded at nine distances up to 3.2 m during two four-day periods with sunny conditions in July and August.
Deposition patterns in all species fitted well to the inverse power law (deposition per unit area proportional to distanceb ), with rates of decline b ranging from −1.84 to −2.35 among species (R2 >0.99). However, even when these curves are extended to infinity for the four species with b<−2, they fail to explain all spores being dispersed (e.g. only 11% in S. squarrosum ). Difference in rates of decline b between the periods, despite similar horizontal wind speeds and directions, indicates the importance of thermal updrafts. Spore capsule diameter negatively correlated with the proportions of spores remaining in dehisced capsules (range 5–16%), being deposited within the colony (range 2–14%), and being deposited between the colony edge and the outer sampled perimeter (range 7–22%), probably because a larger capsule shoots the spores higher into the air, in effect meaning an increased initial release height. Spore diameter positively affected deposition outside the colony edge. The deposition curves together with observed long-distance colonisations, omnipresence in mires of many Sphagnum species and genetic evidence, suggest that Sphagnum spores regularly travel far.
Spatial extension of the empirical deposition curves at a regional scale indicate that with increasing isolation of target sites, the higher the proportion of spores would originate from sources farther away than the nearest sources. Given spatial patterns in the source populations, this would result in higher genetic (and species) diversity per coloniser with increasing isolation, thus counteracting differentiation. 相似文献
Deposition patterns in all species fitted well to the inverse power law (deposition per unit area proportional to distance
Spatial extension of the empirical deposition curves at a regional scale indicate that with increasing isolation of target sites, the higher the proportion of spores would originate from sources farther away than the nearest sources. Given spatial patterns in the source populations, this would result in higher genetic (and species) diversity per coloniser with increasing isolation, thus counteracting differentiation. 相似文献
8.
Interferences between Sphagnum and vascular plants: effects on plant community structure and peat formation 总被引:1,自引:0,他引:1
The interference between vascular plants and peat mosses with respect to nitrogen and phosphorus was studied in a fertilization experiment and with respect to competition for light in a removal experiment in poor fens with either soligenous or topogenous hydrology using Narthecium ossifragum (L.) Huds. and three species of Sphagnum sect. Sphagnum as targets. Adding fertilizer either on the moss surface or below it confirmed the hypotheses of an asymmetric competition for nutrients, viz. that the Sphagnum mosses relied on the atmospheric supply while Narthecium depended on mineralization in the peat. The results of the removal experiments and the negatively correlated growth of Narthecium and Sphagnum mosses demonstrated a symmetric competition for light. The intensity of the competition for light increased as the availability of N and P increased. The nutrient resources in the total biomass decreased with decreasing standing crop of Narthecium . Only with a considerable amount of mineral nutrients in the biomass has Narthecium the capacity to grow ahead of Sphagnum, because the asymmetric competition for N and P gives Sphagnum the capacity to reduce the performance of vascular plants. The mosses are more efficient in their use of nutrients and produce a decay-resistant litter inducing low mineralization and increasing the peat accumulation rate, and that withdraws N and P from the rhizosphere. The Sphagnum mosses thus act as ecological engineers structuring the plant community and determining the carbon balance of the system. The development of ombrotrophic conditions through peat accumulation seems less probable on soligenous than on topogenous mires owing to the higher mineralization rate there supporting the growth of the vascular plants. Correspondingly, disturbances of the Sphagnum cover, such as through airborne pollutants, increase the productivity of the vascular plants and decrease the capacity for carbon accumulation. 相似文献
9.
Abstract: The growth cone is responsible for axonal elongation and pathfinding by responding to various modulators for neurite growth, including neurotransmitters, although the sensor mechanisms are not fully understood. Among neurotransmitters, GABA is most likely to demonstrate activity in vivo because GABA and the GABAA receptor appear even in early stages of CNS development. We investigated the GABAA receptor-mediated signaling pathway in the growth cone using isolated growth cones (IGCs). Both the GABAA binding site and the benzodiazepine modulatory site were enriched in the growth cone membrane. In the intact IGC, GABA induced picrotoxin-sensitive Cl− flux (not influx but efflux) and increased the intracellular Ca2+ concentration in a picrotoxin- and verapamil-sensitive manner. Protein kinase C (PKC)-dependent phosphorylation of two proteins identified as GAP-43 and MARCKS protein was enhanced in the intact IGC stimulated by GABA, resulting in the release of MARCKS protein and GAP-43 from the membrane. Collectively, our results suggest the following scheme: activation of the functional GABAA receptor localized in the growth cone membrane → Cl− efflux induction through the GABAA -associated Cl− channel → Ca2+ influx through an L-type voltage-sensitive Ca2+ channel → Ca2+ -dependent phosphorylation of GAP-43 and MARCKS protein by PKC. 相似文献
10.
SAXITOXIN TETRODOTOXIN AND THE METABOLISM AND CATION FLUXES IN ISOLATED CEREBRAL TISSUES 总被引:2,自引:0,他引:2
Abstract— Saxitoxin and tetrodotoxin at low concentrations (10−7 -10−8 M) exerted similar inhibitory effects on the increase in lactate production and the redistrjbution of Na+ and K+ that normally accompany electrical stimulation of rat cerebral cortical slices. In contrast, the toxins exerted dissimilar effects on the production of lactate in response to low concentrations of Ca2+ in the medium. Inhibition by tetrodotoxin occurred at a higher concentration of Ca2+ and was significantly greater than that produced by saxitoxin at concentrations of Ca2+ below 0.75 mM. These differences were not related to differential effects on the redistribution of Na+ and K+ under such conditions. The toxins had different effects on Ca2+ influx. Tetrodotoxin, but not saxitoxin, inhibited the influx of Ca2+ in the absence of electrical stimulation. The influx of Ca2+ increased when electrical pulses were applied and tetrodotoxin inhibited this increase, whereas saxitoxin potentiated influx of Ca2+ during stimulation. Our results suggest that metabolic responses to conditions that increase excitability are not governed solely by changes in the distribution of Na+ and K+ . The differential effects of the toxins on Ca2+ fluxes suggest that one site of Ca2+ entry during electrical stimulation may be functionally independent of Na+ entry. 相似文献
11.
KAY-MAY MIYAGI TOSHIHIKO KINUGASA KOUKI HIKOSAKA TADAKI HIROSE 《Global Change Biology》2007,13(10):2161-2170
Elevated atmospheric CO2 concentration ([CO2 ]) stimulates seed mass production in many species, but the extent of stimulation shows large variation among species. We examined (1) whether seed production is enhanced more in species with lower seed nitrogen concentrations, and (2) whether seed production is enhanced by elevated [CO2 ] when the plant uses more N for seed production. We grew 11 annuals in open top chambers that have different [CO2 ] conditions (ambient: 370 μmol mol−1 , elevated: 700 μmol mol−1 ). Elevated [CO2 ] significantly increased seed production in six out of 11 species with a large interspecific variation (0.84–2.12, elevated/ambient [CO2 ]). Seed nitrogen concentration was not correlated with the enhancement of seed production by elevated [CO2 ]. The enhancement of seed production was strongly correlated with the enhancement of seed nitrogen per plant caused by increased N acquisition during the reproductive period. In particular, legume species tended to acquire more N and produced more seeds at elevated [CO2 ] than non-nitrogen fixing species. Elevated [CO2 ] little affected seed [N] in all species. We conclude that seed production is limited primarily by nitrogen availability and will be enhanced by elevated [CO2 ] only when the plant is able to increase nitrogen acquisition. 相似文献
12.
Important winter and spring varieties of hexaploid rye-wheat (triticale cvs. 6048 and 5004) were selected for study of heterotic effects on growth and ion transport in the hybrids compared to the parental species rye ( Secale cereale L. cvs. MT 77 and Sv 6970) and wheat (Triticum aestivum L. cvs. Starke II and Sonett). After 3 days germination, seedlings were grown 11 days in water culture on a complete nutrient solution diluted to 1, 25 and 50%. Intracellular influx and transport to shoots of K+ , Ca2+ , sulphur and phosphate were determined by using radioactive tracers (86 Rb (for K+ ), 45 Ca, 35 S and 32 P). Varietal differences in the parameters studied were generally small compared to differences between species. The heterotic effect on growth of rye-wheat was mainly localized to the shoots at high ionic strengths (25% and 50%). There were no heterotic effects on ion influx or transport to the shoots. Ion influx and transport characteristics in rye-wheat appear to be inherited mainly from wheat. Growth of all species on 1% medium was severely reduced. At the low ionic strength ion influx was inhibited similarly for all species, except influx of K+ (86 Rb) which was higher in rye-wheat and wheat than in rye. Ion influx and transport in rye-wheat and wheat and in rye differed especially for 25% and 50% media. Rye had the highest ion influx and transport and the highest shoot/root fresh weight ratio at the high ionic strengths. To feed a comparatively large shoot, rye may compensate for a relatively small root system by efficient ion transport mechanisms. 相似文献
13.
Sarah Grimwood Elizabeth Gilbert C. Ian Ragan Peter H. Hutson 《Journal of neurochemistry》1996,66(6):2589-2595
Abstract: A 45 Ca2+ influx assay has been used to investigate the pharmacology of stably expressed recombinant human NR1a/NR2A and NR1a/NR2B N -methyl- d -aspartate (NMDA) receptors. Inhibition of glutamate-stimulated 45 Ca2+ influx by six glycine-site antagonists and inhibition of glycine-stimulated 45 Ca2+ influx by five glutamate-site antagonists revealed no significant differences between affinity values obtained for NR1a/NR2A and NR1a/NR2B receptors. The polyamine site agonist spermine showed differential modulation of glutamate- and glycine-stimulated 45 Ca2+ influx for recombinant NMDA receptors, inhibiting and stimulating 45 Ca2+ influx into cells expressing NR1a/NR2A receptors (IC50 = 408 µ M ) and NR1a/NR2B receptors (EC50 = 37.3 µ M ), respectively. The antagonist ifenprodil was selective for NR1a/NR2B receptors (IC50 = 0.099 µ M ) compared with NR1a/NR2A receptors (IC50 = 164 µ M ). The effects of putative polyamine site antagonists, redox agents, ethanol, and Mg2+ and Zn2+ ions were also compared between NR1a/NR2A and NR1a/NR2B receptors. This study demonstrates the use of 45 Ca2+ influx as a method for investigating the pharmacology of the numerous modulatory sites that regulate the function of recombinant human NMDA receptors stably expressed in L(tk-) cells. 相似文献
14.
Sune Pettersson 《Physiologia plantarum》1986,66(1):122-128
Plants of barley ( Hordeum vulgare L. cv. Salve) were grown with 6.5–35% relative increase of K+ supply per day (RKR) using a special computer-controlled culture unit. After a few days on the culture solution the plants adapted their relative growth rate (RGR) to the rate of nutrient supply. The roots of the plants remained in a low salt status irrespective of the rate of nutrient supply, whereas the concentration of K+ in shoots increased with RKR. Both Vmax and Km for K+ (86 Rb) influx increased with RKR. It is concluded that with a continuous and stable K+ stress, the K+ uptake system is adjusted to provide an effective K+ uptake at each given RKR. Allosteric regulation of K+ influx does not occur and efflux of K+ is very small. 相似文献
15.
The effects of copper (CuCl2 ) on active and passive Rb+ (86 Rb+ ) influx in roots of winter wheat grown in water culture for 1 week were studied. External copper concentrations in the range of 10–500 μ M in the uptake nutrient solution reduced active Rb+ influx by 20–70%, while passive influx was unaffected (ca 10% of the Rb+ influx in the Cu-free solution). At external Rb+ concentrations of up to 1 m M , Cu exposure (50 μ M decreased Vmax to less than half and increased Km to twice the value of the control. Short Cu exposure reduced the K+ concentration in roots of low K+ status. Pretreatment for 5 min in 50 μ M CuCl2 prior to uptake experiments reduced Rb+ influx by 26%. After 60 min pretreatment with Cu, the corresponding reduction was 63%. Cu in the cultivation solution impeded growth, especially of the roots. The Cu concentration in the roots increased linearly with external Cu concentration (0–100 μ M ) while Cu concentration in the shoots was relatively unchanged. The K+ concentration in both roots and shoots decreased significantly with increased Cu in the cultivation solutions. Possible effects of Cu on membranes and ion transport mechanisms are discussed. 相似文献
16.
Two cultivars of wheat (Triticum aestivum L. cvs Kadett and WW 20299) were grown for 9 days with 20% relative increase in nutrient supply per day at pH 4.1. Aluminium at 50 μ M retarded the growth of roots more than that of shoots in both cultivars, thus decreasing the root/shoot ratio. The inhibition was largest in WW 20299. With long term Al treatment (9 days), Km for K+ (86 Rb) influx increased five times in both cultivars and Vmax decreased in WW 20299. Efflux of K+ (86 Rb) was little affected. When the roots were treated with aluminium for two days, only relative growth rate of roots was retarded, while growth of shoots was unaffected and influx of K+ (86 Rb) adjusted to the actual K+ demand of the plants. It is concluded that the effects of aluminium on K+ uptake in these wheat cultivars are not primary factors contributing to aluminium sensitivity. However, in soil with Al the demand for a comparatively high concentration of K+ to maintain an adequate K+ uptake rate, in combination with a slow growth rate of the roots, may secondarily lead to K+ deficiency in the plants. 相似文献
17.
The effects of pH on the growth and the K+ (86 Rb) uptake and K+ content of excised rice ( Oryza sativa L. cv. Dunghan Shali) and wheat ( Triticum aestivum L. cv. GK Szeged) roots were investigated. Rice roots responded to H+ stress with an increased K+ (86 Rb) influx and a decreased K+ content, suggesting an increased exchange between the cytoplasmic K+ pool and the external medium. Under the same experimental conditions wheat did not show any anomalous K+ (86 Rb) influx. Growth of both rice and wheat was relatively insensitive to pH between 4 to 10. 相似文献
18.
1. Root competition can be an important determinant of the performance of neighbours within plant populations and communities. Because plants often maintain larger root systems and allocate more of their carbon to root systems under elevated atmospheric CO2 than they do at lower CO2 concentrations, root–root interactions could play an increasingly important role in determining competitive outcomes among individuals and plant species as global CO2 concentration continues to rise.
2. We established 12 pure stands of Linum usitatissimum (flax) and 12 mixed stands of Linum and its naturally co-occurring weed species Silene cretica in opaque plastic trays each filled with the same amount of nutrient-rich soil mix. In half of the trays from each of these stand types, vertical waterproof partitions separated the root systems of individual plants from each other to prevent root competition, while in the other half no partitions were present. Half of the trays from all treatments were allowed to grow under low atmospheric CO2 concentration (320μll–1 ) and the other half under elevated CO2 (600μll–1 ), in daylight growth chambers for 30 days from seedling emergence until harvest in mid-June. All trays received equal amounts of water so that soils in the low CO2 treatment were maintained at field capacity.
3. Our results indicate that under high soil fertilities: (1) intra-specific root–root interactions alone play a relatively insignificant role in determining plant biomass production within pure Linum populations and (2) the impact of an aggressive species ( Silene ) on co-occurring less aggressive species ( Linum ) becomes more severe under elevated CO2 as a result of amplified interspecific root competition. 相似文献
2. We established 12 pure stands of Linum usitatissimum (flax) and 12 mixed stands of Linum and its naturally co-occurring weed species Silene cretica in opaque plastic trays each filled with the same amount of nutrient-rich soil mix. In half of the trays from each of these stand types, vertical waterproof partitions separated the root systems of individual plants from each other to prevent root competition, while in the other half no partitions were present. Half of the trays from all treatments were allowed to grow under low atmospheric CO
3. Our results indicate that under high soil fertilities: (1) intra-specific root–root interactions alone play a relatively insignificant role in determining plant biomass production within pure Linum populations and (2) the impact of an aggressive species ( Silene ) on co-occurring less aggressive species ( Linum ) becomes more severe under elevated CO
19.
Ken-ichi Ohtani Hiroaki Sakurai Esther Oh Emi Iwata Tomofusa Tsuchiya Masaaki Tsuda 《Journal of neurochemistry》1995,65(2):605-614
Abstract: Stimulation of cultured cerebellar granule cells with N -methyl- d -aspartate (NMDA) or kainic acid (KA) leads to activation of activator protein-1 (AP-1) DNA-binding activity, which can be monitored by an increase in 12- O -tetradecanoylphorbol 13-acetate (TPA)-responsive element (TRE)-binding activity, in concert with c- fos induction. For this increase in TRE-binding activity, Ca2+ influx across the plasma membrane is essential. Treatment of cells with an intracellular Ca2+ chelator, BAPTA-AM, abolished this increase. Close correspondence between the dose-response curves of 45 Ca2+ uptake and TRE-binding activity by NMDA or KA suggested that Ca2+ influx not only triggered sequential activation of Ca2+ -signaling processes leading to the increase in TRE-binding activity, but also controlled its increased level. Stimulation of non-NMDA receptors by KA mainly caused Ca2+ influx through voltage-gated Ca2+ channels, whereas stimulation of NMDA receptors caused Ca2+ influx through NMDA-gated ion channels. The protein kinase C (PKC) inhibitors staurosporine and calphostin C inhibited the increase in TRE-binding activity caused by NMDA and KA at the same concentration at which they inhibited that caused by TPA. Furthermore, down-regulation of PKC inhibited the increase in TRE-binding activity by NMDA and KA. Thus, a common pathway that includes PKC could, at least in part, be involved in the Ca2+ -signaling pathways for the increase in TRE-binding activity coupled with the activation of NMDA- and non-NMDA receptors. 相似文献
20.
Changes in the K, Na and P content of solution-grown and soil-grown winter wheat ( Triticum aestivum L. cv. Martonvásári 8) were followed during the life cycle. In parallel experiments the influx of K+ (86 Rb) and H2 32 PO-4 and the translocation of these ions to the shoot were also measured. The K content increased during the seedling and tillering stages (autumn and winter period), but then decreased rapidly as the temperature rose. The influx and translocation of K+ increased during vegetative growth and declined in the generative phase. Na+ replaced K+ when K+ uptake was limited. The P content changed less than the K content, but influx was maximal during elongation. Both influx and translocation slowed greatly in the grain-filling period. For both minerals the ratio of influx to net uptake was estimated for the life cycle. This ratio was high for the soil-grown plants but low for the solution-grown plants, suggesting that the supply of K and P was limiting the growth of the former but not of the latter plants. It is suggested that the transport of K and P during the life cycle is regulated by metabolism-dependent direct routes (i.e. negative feedback mechanisms) during vegetative growth and by passive, indirect routes in the generative stage. The possibility of hormone-directed transport processes is also discussed. 相似文献