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1.
Bromus tectorum L. (cheatgrass) is an invasive winter
annual whose seeds lose dormancy through dry after-ripening. In this paper
a thermal after-ripening time model for simulating seed dormancy loss of
B. tectorum in the field is presented. The model
employs the hydrothermal time parameter mean base water potential
(b(50)) as an index of dormancy status. Other parameters of the
hydrothermal time equation (the hydrothermal time constant HT,
the standard deviation of base water potentials b, and
the base temperature Tb) are held constant, while
b(50) is allowed to vary and accounts for changes in germination
time-course curves due to stage of after-ripening or incubation
temperature. To obtain hydrothermal time parameters for each of four
collections, seeds were stored dry at 20C
for different intervals, then incubated in water (O MPA) or polyethylene
glycol (PEG) solutions (-0.5, -1.0, -1.5 MPa) at 15 and 25C. Germination data for the thermal after-ripening
time model were obtained from seeds stored dry in the laboratory at 10, 15,
20, 30, 40, and 50°C for 0 to 42 weeks, then incubated at two
alternating temperatures in water. Change in b(50) was
characterized for each collection and incubation temperature as a linear
function of thermal time in storage. Measurements of seed zone temperature
at a field site were combined with equations describing changes in
b(50) during after-ripening to make predictions of seed dormancy
loss in the field. Model predictions were compared with values derived from
incubation of seeds retrieved weekly from the field site. Predictions of
changes in b(50) were generally close to observed values,
suggesting the model is useful for simulating seed dormancy loss during
after-ripening in the field. 相似文献
2.
Hydrothermal time analysis of tomato seed germination responses to priming treatments 总被引:5,自引:1,他引:4
Controlled hydration of seeds followed by drying (seed priming) is used to
break dormancy, speed germination, and improve uniformity of radicle
emergence. To date, empirical trials are used to predict optimal priming
conditions for a given seed lot. Since priming is based upon seed water
relations, it was hypothesized that the sensitivity of germination to
reduced water potential before priming might be mechanistically related to,
and therefore predictive of, priming responsiveness. Analyses of
germination of 13 tomato (Lycopersicon esculentum
Mill.) seed lots at two temperatures (15C
and 20C) and three water potentials (0,
-0.28 and -0.43 MPa) showed that seed lot germination responses could be
quantitatively characterized by parameters derived from thermal time,
hydrotime, and hydrothermal time models
(R20.73-0.99). Six of the seed
lots were primed at two temperatures (15°C and 20°C) and
three water potentials (-1.0, -1.5 and -2.0 MPa) for various durations,
dried, and their subsequent germination rates analysed according to
hydropriming time and hydrothermal priming time models. The responses of
germination rates to priming were characterized by hydropriming time
(HP) and hydrothermal priming time (HTP) constants and
the minimum water potential (min) and temperature
(Tmin) for achieving a priming effect. The values of
min and Tmin varied relatively little among
tomato seed lots, and the generalized values of min=2.39 MPa and
Tmin=9.10°C accounted for 74% (15°C),
57% (20°C), and 62% (across both temperatures) of the increase in
germination rates following priming. Nonetheless, while the hydrothermal
time models described germination patterns both before and after priming,
there was relatively little predictive relationship between
them. 相似文献
3.
The effects of storage conditions on the germination of developingmuskmelon (Cucumis melo L.) seeds were tested to determine whetherafter-ripening is required to obtain maximum seed vigour. Seedswere harvested at 5 d intervals from 35 (immature) to 60 (fullymature) days after anthesis (DAA), washed, dried, and storedat water contents of 3·3 to 19% (dry weight basis) at6, 20, or 30°C for up to one year. Germination was testedin water and in polyethylene glycol 8000 solutions ( 0·2to 1·2 MPa osmotic potential) at 15, 20, 25 or30°C. Germination percentages and rates (inverse of meantimes to radicle emergence) were compared to those of newlyharvested, washed and dried seeds. For 40 and 60 DAA seeds,one year of storage at 20°C and water contents <6·5%significantly increased germination percentages and rates at20°C, but had little effect on germination at 25 and 30°C.Storage reduced the estimated base temperature (Tb) and meanbase water potential (b) for germination of both 40 and 60 DAAseeds by approximately 5°C and 0·3 MPa, respectively.Immature 35 DAA seeds showed the greatest benefit from storageat 3 to 5% water content and 30°C, as germination percentagesand rates increased at all water potentials (). Storage underthese same conditions had little effect on the germination ofmature seeds in water, but increased germination percentagesand rates at reduced 's. Accelerated ageing for one month at30°C and water contents from 15 to 19° increased germinationrates and percentages of mature seeds at reduced 's, but longerdurations resulted in sharp declines in both parameters. Immatureseeds lost viability within one month under accelerated ageingconditions. An after-ripening period is required at all stagesof muskmelon seed development to expand the temperature andwater potential ranges allowing germination and to achieve maximumgerminability and vigour. Post-harvest dormancy is deepest atthe point of maximum seed dry weight accumulation and declinesthereafter, both in situ within the ripening fruit and duringdry storage. Key words: Muskmelon, Cucumis melo L., seed, development, dormancy, germination, vigour, after-ripening 相似文献
4.
Modelling the effects of water stress and temperature on germination rate of Orobanche aegyptiaca seeds 总被引:2,自引:0,他引:2
Orobanche aegyptiaca seeds were germinated at a range
of water potentials and temperatures and the progress of germination within
the seed population was modelled. Base water potentials (at which the rate
of progress towards germination is zero) varied between individual seeds
according to a normal distribution with a mean of -1.96 MPa and standard
deviation of 0.33 MPa at 20C. Contrary to
the underlying assumption of the hydrothermal time model in the literature,
the median base water potential varied significantly with temperature,
being c. -2 MPa at 14-23C and increasing at both higher and lower
temperatures. Thermal times to germination also varied according to a
normal distribution between individual seeds with a mean of 49°Cd
and standard deviation of 18°Cd in water. The median thermal time
to germination varied with water potential. Again, however, an assumption
of the hydrothermal time model was found to be invalid since the base
temperature for rate of germination also varied significantly with water
potential. The relationship of both base temperature and thermal time to
water potential were linear such that germination progress curves in 33
different hydrothermal environments (8-26°C and 0 to -1.2 MPa)
could be described according to a new modified thermal time model which
accounted for 78% of the variation in the data.Keywords:
Water stress, temperature, Orobanche
aegyptiaca, germination rate, hydrothermal time models.
相似文献
5.
Seed priming (imbibition in water or osmotic solutions followedby redrying) generally accelerates germination rates upon subsequentre-imbibition, but the response to priming treatments can varyboth within and among seed lots. Seed maturity could influenceresponsiveness to priming, perhaps explaining variable primingeffects among developmentally heterogeneous seed lots. In thecurrent study, muskmelon (Cucumis melo L.) seeds at two stagesof development, maturing (40 d after anthesis (DAA)) and fullymature (60 DAA), were primed in 0?3 M KNO3 for 48 h at 30 ?C,dried, and imbibed in polyethylene glycol 8000 solutions of0 to 1?2 MPa at 15, 20, 25, and 30 ?C. Germination sensitivitiesto temperature and water potential () were quantified as indicatorsof the influence of seed maturity and priming on seed vigour.Germination percentages of 40 and 60 DAA control seeds weresimilar in water at 30 ?C, but the mean germination rate (inverseof time to germination) of 40 DAA seeds was 50% less than thatof 60 DAA seeds. Germination percentages and rates of both 40and 60 DAA seeds decreased at temperatures below 25 ?C. Reductionsin also delayed and inhibited germination, with the 40 DAAseeds being more sensitive to low than the 60 DAA seeds. Primingsignificantly improved the performance of 40 DAA seeds at lowtemperatures and reduced , but had less effect on 60 DAA seeds.Priming lowered both the minimum temperature (Tb) and the minimum (b) at which germination occurred. Overall, priming of 40 DAAseeds improved their germination performance under stress conditionsto equal or exceed that of control 60 DAA seeds, while 60 DAAseeds exhibited only modest improvements due to priming. Asthe osmotic environment inside mature fruits approximates thatof a priming solution, muskmelon seeds may be primedin situ during the late stage of development after maximum dryweight accumulation. Key words: Cucumis melo L., seed priming, germination, vigour, development, temperature 相似文献
6.
A quantitative model for loss of primary dormancy and induction of secondary dormancy in imbibed seeds of Orobanche spp 总被引:1,自引:0,他引:1
Seeds of three species of Orobanche were conditioned
(e.e. stored fully imbibed in darkness) for periods up to 210 d in order to
model relief of primary dormancy and induction of secondary dormancy. The
data were consistent with the hypothesis that periods for loss and
induction of formancy and loss of viability are normally distributed in
populations of imbibed sees and that these three processes are independent.
There was a positive, linear relationship between the rate of loss of
primary dormancy and temperature from 10-30C
in O. aegyptiaca and O. cernua
and 10-25C in O.
crenata. In all three species, the rate of induction of
secondary dormancy was highest at 10°C and decreased with increase
of temperature up to about 20°C, above which there was little
further change in the rate with temperature. The resulting model explained
over 90% of the variation in germination after conditioning in both
O. aegyptiaca and O. cernua. In
O. crenata, however, this model was only satisfactory
at 10 and 15°C. At higher temperatures, dormancy was relatively
stable for periods of conditioning from 70 to about 154 d. Possible
explanations for this are discussed. Applications of these models for
estimating the time required to reduce Orobanche
infestations in the field are also briefly discussed.Key words:
Orobanche spp., broomrape, seed dormancy, temperature, dormancy
model
相似文献
7.
Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes: I. GERMINATION AT SUBOPTIMAL TEMPERATURE 总被引:2,自引:0,他引:2
DAHAL PEETAMBAR; BRADFORD KENT J.; JONES RICHARD A. 《Journal of experimental botany》1990,41(11):1431-1439
The bases of differences in germination rates (GRg = inverseof time to germination [tg] of percentage g) among three cold/salt-toleranttomato (Lycopersicon esculentum Mill.) accessions (PI 341988,PI 120256, and PI 174263) and one cold/salt-sensitive tomatocultivar (T5) were investigated. The effects of seed priming(6 d imbibition in aerated 1.2 MPa polyethylene glycolsolution at 20 ?C followed by redrying) and of removing theendosperm/testa cap covering the radicle on the temperaturesensitivity of GRg, and the interaction of these treatmentswith genotypes, were also examined. GRg decreased linearly withdecreasing temperature for all genotypes and seed treatments.The minimum or base temperatures for germination (Tb) variedby 1 ?C among the tomato lines, so genotypic differences inGRg were due to differing thermal time requirements for germination.The mean thermal time requirement for germination of T5 seeds was 22% and 19% greater than that of PI 341988 andPI 120256 seeds, respectively, but only 9% greater than thatof PI 174263 seeds. Seed priming did not lower Tb of any genotype,but significantly reduced by 24, 49, 41, and 49% in T5, PI 341988, PI 120256, and PI 174263, respectively,indicating that priming increased the rate at which the seedsprogressed towards germination when T>Tb, but did not lowerthe minimum temperature at which germination could occur. Primingincreased the GRg of T5 seeds to equal or exceed those of control(non-primed) seeds of the cold/salt-tolerant genotypes at anyT>Tb, but the PI lines exhibited an even greater responseto priming. Times to germination within each seed lot were normallydistributed on a logarithmic scale. Priming increased the variancein tg within a seed lot when compared to control seeds. However,the variation in thermal time for germination between the 10thand 90th percentiles of the seed population (T(1090))was relatively unaffected by priming due to the reduction in in primed seeds. Removing the endosperm cap and testa opposite the radicle tip decreased almost 6-fold and and reduced Tb by 5 ?C in T5 and PI 341988,implicating processes in the endosperm/testa as the limitingfactors in germination at suboptimal temperatures. Key words: Lycopersicon esculentum Mill., tomato, genetic variation, seed priming, thermal time, germination rate 相似文献
8.
The temperature dependence of the stimulation of photosynthesis by elevated carbon dioxide in wheat and barley 总被引:9,自引:3,他引:6
The temperature dependencies of the solubility of carbon dioxide and oxygen
in water and the temperature dependency of the kinetic characteristics of
the ribulose-1,5 bisphosphate carboxylase/oxygenase (Rubisco) enzyme result
in the short-term stimulation of photosynthesis with a doubling of carbon
dioxide from 350 to 700 mol
mol-1 usually decreasing from about 90% at 30C to about 25% at 10C
at high photon flux. In field-grown wheat and barley, the expected values
at 30°C were observed, but also values as high as 60% at
10°C. The much larger than expected stimulation at cool
temperatures in these species also occurred in plants grown at
15°C, but not at 23°C in controlled environment chambers.
Gas exchange analysis indicated that an unusually high diffusive limitation
was not an explanation for the large response. Assessment of the apparent
in vivo specificity of Rubisco by determining the
carbon dioxide concentration at which carboxylation equalled carbon dioxide
release from oxygenation, indicated that growth at low temperatures altered
the apparent enzyme specificity in these species compared to these species
grown at the warmer temperature. Inserting the observed specificities into
a biochemical model of photosynthesis indicated that altered Rubisco
specificity was consistent with the observed rates of assimilation. Whether
altered apparent Rubisco specificity is caused by altered stoichiometry of
photorespiration or an actual change in enzyme specificity, the results
indicate that the temperature dependence of the stimulation of
photosynthesis by elevated carbon dioxide may vary greatly with species and
with prior exposure to low temperature.Keywords:
Barley, carbon dioxide, photosynthesis, temperature, wheat.
相似文献
9.
Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes: II. GERMINATION AT REDUCED WATER POTENTIAL 总被引:3,自引:0,他引:3
Seed germination rates (GR =inverse of time to germination)are sensitive to genetic, environmental, and physiological factors.We have compared the GR of tomato (Lycopersicon esculentum Mill.)seeds of cultivar T5 to those of rapidly germinating L. esculentumgenotypes PI 341988 and PI 120256 over a range of water potential(). The influence of seed priming treatments and removal ofthe endosperm/testa cap enclosing the radicle tip on germinationat reduced were also assessed. Germination time-courses atdifferent 's were analysed according to a model that identifieda base, or minimum, allowing germination of a specific percentage(g) of the seed population (b(g)), and a hydrotime constant(H) indicating the rate of progress toward germination per MPa.h.The distribution of b(g) determined by probit analysis was characterizedby a mean base (b) and the standard deviation in b among seeds(b). The three derived parameters, b, b) and H, were sufficientto predict the time-courses of germination of intact seeds atany . A normalized time-scale for comparing germination responsesto reduced is introduced. The time to germination at any (tg())can be normalized to be equivalent to that observed in water(tg(0)) according to the equation tg(0)=[l(/b(g))]tg().PI 341988 seeds were more tolerant of reduced and had a morerapid GR than T5 seeds due to both a lower b and a smaller H.The rapid germination of PI 120256, on the other hand, couldbe attributed entirely to a smaller H. Seed priming (6 d in1.2 MPa polyethylene glycol 8000 solution at 20 ?C followedby drying) increased GR at all >b(g), but did not lower theminimum allowing germination; i.e. priming reduced H withoutlowering b. Removing the endosperm/testa cap (cut seeds) markedlyincreased GR and lowered the mean required to inhibit germinationby 0.7 to 0.9 MPa. However, this resulted primarily from downwardadjustment in b during the incubation of cut seeds at low inthe test solutions. The difference in b between intact and cutseeds incubated at high was much less (0.l MPa), indicatingthat at the time of radicle protrusion, the endosperm had weakenedto the point where it constituted only a small mechanical barrier.In the intact seed, endosperm weakening and the downward adjustmentin embryo b ceased at < 0.6 MPa, while the reductionin H associated with priming proceeded down to at least 1.2MPa. Based on these data and on the pressure required to pushthe embryos from the seeds at various times after imbibition,it appears that the primary effect of priming was to shortenthe time required for final endosperm weakening to occur. However,as priming increased GR even in cut seeds, priming effects onthe embryo may control the rate of endosperm weakening. Key words: tomato, Lycopersicon esculentum Mill., water potential, germination rate, seed priming, genetic variation 相似文献
10.
Yellow cedar (Chamaecyparis nootkatensis) seeds
exhibit prolonged dormancy following their dispersal from the parent plant.
Embryos excised fully from their enclosing seed tissues exhibit 100%
germination, indicating that the seed tissues enclosing the embryo (the
testa, remnants of the nucellus and the megagametophyte) play an inhibitory
role and prevent radicle emergence. As part of an assessment of the role of
seed tissues in the dormancy mechanism of yellow cedar seeds, light
microscopy was used to examine changes within the major structures of the
seed following a 90 d war (26C)/cold
(4C) moist treatment ('stratification') and
during germination. In the micropylar tip of the seed, the nucellus forms a
hard nucellar cap covering the radicle. The nucellar cap is composed
primarily of degenerated cells; histological staining with ruthenium red
revealed a predominance of pectins. There were no obvious cellular or
morphological differences (detected by light microscopy) between mature
seeds subjected to a 3 d soak and seeds subjected to a 3 d soak and the 90
d dormancy-breaking treatment. However, just prior to germination there was
an outward projection of the nucellar cap through the micropyle, which
appeared to be caused by the extension of highly folded proteinaceous
strands lying immediately in front of the radicle. When the testa was
removed, the embryo enclosed within the intact megagametophyte was
incapable of germination. If, however, the megagametophyte surrounding the
embryo was slit or the embryo surrounded by an intact megagametophyte was
subjected to a 3d rinse in water, some germination occurred, perhaps as a
result of an enhanced release of inhibitors from the megagametophyte. After
stratification, dormancy of yellow cedar seeds is broken; concurrent with
dormancy breakage, there was a mechanical weakening of the megagametophyte.
The embryo also underwent changes that included an increase in turgor and a
reduced sensitivity to highly negative osmotic potential. It is concluded
that coat-imposed dormancy of yellow cedar seeds is enforced by mechanical
restraint of the megagametophyte as well as a leachable chemical inhibitor
(most probably ABA). 相似文献
11.
Even moderate chilling temperatures may cause important modifications in
assimilate movement in maize seedlings from the shoot to the roots, but
there is no information on long-distance transport of assimilates in plants
subjected to vertical gradients of moderately low temperatures in the root
zone. Seedlings of a chilling-tolerant (KW1074) and a chilling-sensitive
inbred line (CM109) of maize were grown in a system that allowed the
maintenance of temperature gradients between the topsoil (0-10 cm) and the
subsoil (10-50 cm). After pregrowth at 24C
until the third-leaf stage, plants were subjected to chilling-stress
regimes for 6 d (17/17/17C,
17/17/12°C, 12/12/12°C, 12/12/17°C,
air/topsoil/subsoil). The time taken for the assimilates to enter the
phloem from the second leaf increased at low temperatures for both lines,
but to a much greater extent in CM109. Although mainly influenced by air
and topsoil temperature, low temperature in the subsoil also affected this
trait in CM109. The speed of assimilate transport between the second leaf
and the mesocotyl in KW1074 was strongly reduced by cool temperatures in
the shoot and topsoil as well as by 12°C in the subsoil in CM109,
because the latter line had a larger portion of its root system in the
subsoil as compared to KW1074. The portion of assimilates allocated to the
root decreased at low temperatures in both lines, but to a greater extent
in CM109, and was controlled mostly by the subsoil temperature. After
rewarming, values of all measured parameters of assimilate transport
returned to near pregrowth levels within a few days.Keywords:
Assimilate transport, low temperature stress, root growth,
vertical soil temperature gradients, Zea mays L.
相似文献
12.
Leaf diffusion resistance interpreted as stomatal resistance,leaf water potential (w), solute potential (s) and leaf turgorpotential (p) of the chilling sensitive species Phaseolus vulgariswere determined during chilling at 4 °C in the light. Bothchill-hardened and non-hardened plants were used. For comparison,the chilling resistant species Pisum sativum was also used. The results for chilled P. sativum were similar to those obtainedfor chill-hardened P. vulgaris plants receiving a chilling treatment.In both cases a reduction in stomatal aperture and the maintenanceof a positive leaf turgor were the responses to chilling. Leavesof chilled but non-hardened P. vulgaris plants were found tomaintain open stomata throughout the chilling treatment despitea severe wilt developing after 7 h at 4 °C. This was incontrast to the chill-resistant P. sativum. which showed a rapidclosing and subsequent re-opening of the stomata to a new reducedaperture. During the first 12 h of chilling wof P. vulgaris leaves changedfrom 0.47 MPa to 1.24 MPa. On more prolonged chillingw tended to return to pre-chilling values. In addition. p decreasedfrom 0.42 MPa to zero after only 9 h of chilling, and remainedat this value for the remainder of the chilling period, s, changedrapidly from 0.89 MPa to 1.35 MPa in the first7.5 h, and after 9 h. w and s, were equal, i.e. zero p. In contrast,the chilling resistant plant P. sativum maintained a positivep throughout the chilling period, and there was little differencebetween values of w, and s in control and chilled leaves. Key words: Chilling, Stomata, ater relations, Phaseolus vulgaris, Pisum sativum 相似文献
13.
An improved strain-gauge device for continuous field measurement of stem and fruit diameter 总被引:7,自引:2,他引:5
An improved strain-gauge dendrometer was tested on apple (Pyrus
malus L.) tree trunks and fruit to measure thickness dynamics.
The sensor is similar to previous devices, but is more flexible allowing
for a greater range of thickness change before it has to be physically
reset. The practical resolution of the measurement system is given as one
standard deviation about the mean of 51 observations taken on an Invar
metal alloy in the field when temperatures ranged between 16C and 17C. The mean
of these observations was 3.68356 mm with one standard deviation of 0.00947
mm. There is a positive correlation between temperature and sensor output
having a slope of 2.96 m°C-1. For a typical
daily temperature change of 21°C, this causes an apparent change of
62 m. Stem thickness varied 0.7 mm diurnally
with maximum values at night and minimum values during the day. Apple fruit
diameter increased 3.3 mm over the 15 d period.Keywords:
Strain gauge dendrometer, plant stem and fruit thickness sensor,
plant water status, growth.
相似文献
14.
J. W. Bradbeer 《Planta》1968,78(3):266-276
Summary The dormancy of freshly harvested hazel seeds appears to be induced by inhibitors occuring mainly in the testa and pericarp. Although d abscisic acid may not be one of the natural inhibitors involved, d,l abscisic acid has been shown to strongly inhibit the germination of hazel seeds, probably through its antagonism towards the action of gibberellin. Dry storage of hazel nuts causes a deeper state of dormancy (secondary dormancy) to be superimposed on the primary dormancy. It is suggested that secondary dormancy consists of a block to gibberellin synthesis. The essential effect of chilling intact hazel seeds, which is the natural means of breaking their dormancy, may be to activate the mechanism for gibberellin synthesis, the subsequent synthesis of gibberellin being thought to occur at the germination temperature (20°C) and not at the chilling temperature (5°C). 相似文献
15.
Suboptimal temperature (T) affects germination rates (reciprocalof time to radicle emergence) on a thermal time basis; thatis, the T in excess of a base or minimum temperature multipliedby the time to a given per cent germination [tg) is a constant.Respiration rates are also sensitive to T, and proportionalrelationships are often found between respiration rates andgermination rates. Reduced water potential () delays seed germinationon a hydrotime basis (i.e. the in excess of a base water potentialmultiplied by tg is a constant). It was tested whether respirationrates prior to radicle emergence vary in proportion to T and as expected from the thermal and hydrotime models. Respirationrates (C02 evolution) of cold-tolerant, rapidly germinating(PI 341988) and cold-sensitive, more slowly germinating (T5)tomato [Lycopersicon esculentum Mill.) seeds were evaluatedover a range of T and conditions. For both genotypes, respirationrates until the beginning of radicle emergence were relatedto T on a thermal time basis and increased approximately linearlywith above -2.0 MPa, consistent with the hydrotime model. Respirationrates were uniquely related to germination rates, regardlessof whether germination timing was affected by T, , or genotype.However, germination timing was unaffected when respirationrates were manipulated by varying 02 partial pressure. Thus,while both germination and respiration rates vary with T and consistent with thermal and hydrotime models of biologicaltime, respiration rates per se were not the limiting factorin germination timing of tomato seeds. Key words: Lycopersicon esculentum Mill., tomato, germination, respiration, temperature, water potential 相似文献
16.
In a companion paper several methods of calculating the marginal unit water
cost of plant carbon gain (E/A) were tested to determine
whether stomata were behaving optimally in relation to regulating leaf gas
exchange. In this paper one method is applied to several tropical tree
species when leaf-to-air vapour pressure difference (D), photosynthetic
photon flux density, leaf temperature, and atmospheric soil water
availability were manipulated. The response of leaves that had expanded
during the dry season were also compared to that of leaves that had
expanded in the wet season. Few differences in absolute value of
E/A, or the form of the relationship, were observed
between species or between seasons. In the majority of species,
E/A increased significantly as either leaf-to-air vapour
pressure difference increased, at a leaf temperature of either 33C or 38C, or as in
photosynthetic photon flux density increased. In contrast, as leaf
temperature increased at constant D, E/A was generally
constant. As pre-dawn water potential declined, E/A
declined. The relationship between E/A and D did not
differ whether internal or ambient carbon dioxide concentration were kept
constant. It is concluded that stomata are only behaving optimally over a
very small range of D. If a larger range of D is used, to incorporate
values that more closely reflect those experienced by tropical trees in a
savanna environment optimization is incomplete.Key
words: Stomatal optimization theory, marginal unit water cost.
相似文献
17.
Rapid acclimation of root hydraulic conductivity to low temperature 总被引:14,自引:5,他引:9
Root hydraulic conductance of many species is substantially reduced by
exposure to low temperatures. The objective of this research was to
investigate the decrease and recovery of root hydraulic conductivity in
spinach (Spinacia oleracea L.) root systems upon
exposure to low temperature. Root hydraulic conductivity
(Lp) was determined for detached whole root systems as
the slope of the flux and an applied pressure gradient. Water flux
(Jv), of root systems grown at 20C, decreased immediately upon exposure to 5C. After 2-5 h Jv recovered and
reached a stable value after 12 h exposure to 5°C. In separate
experiments, the root Lp of plants acclimated for 7 d
at 5°C was 125% greater than that of isolated root systems
acclimated for 12 h at 5°C. Lp of plants grown
and measured at 5°C was about 50% of the Lp of
plants grown and measured at 20°C. The rapid acclimation to low
temperatures observed in detopped root systems was also indicated in intact
plants at 20/5°C (shoot/root temperatures) using mass flow
porometry. Acclimation of the root system after exposure to 5°C was
apparent by recovery of stomatal opening. These results indicate that
spinach root systems have the ability to acclimate rapidly to changes in
temperature and to continue acclimating during prolonged exposure to low
temperature. 相似文献
18.
A controlled environment chamber for whole plants is described in which
vapour pressure deficit (VPD) and temperature can be controlled
independently. Plant responses to changes in VPD at constant temperature
were measured in terms of leaf extension and plant transpiration rates.
Manipulation of VPD independently of temperature was shown to be capable of
altering the leaf extension rates of the C4 grass Miscanthus x
giganteus grown in hydroponics. The effects of VPD on leaf
extension are attributed to changes in transpiration rate and hence leaf
water status. It was found that, at a temperature of 20C, the influence of a fixed change in VPD was
proportionally less than those observed at temperatures which are close to
the threshold for growth (between 6 and 10C). These responses are discussed in relation to our
current understanding of the mechanisms of cell growth. The fact that the
VPD effects on leaf expansion rates were largely transient suggest that
simple models driven by temperature alone are adequate to predict leaf
expansion within the temperature range 6-20°C, for this genotype of
Miscanthus, in the field.Key
words: Leaf growth, Miscanthus x giganteus,
temperature, vapour pressure deficit, C4 plants.
相似文献
19.
The effect of rhizosphere dissolved inorganic carbon on gas exchange characteristics and growth rates of tomato seedlings 总被引:2,自引:0,他引:2
The possibility that an enhanced supply of dissolved inorganic carbon
(DIC=CO2+HCO3-) to the root solution could increase
the growth of Lycopersicon esculentum (L.) Mill. cv.
F144 was investigated under both saline and non-saline root medium
conditions. Tomato seedlings were grown in hydroponic culture with and
without NaCl and the root solution was aerated with CO2 concentrations in
the range between 0 and 5000 mol
mol-1. The biomass of both control and
salinity-stressed plants grown at high temperatures (daily maximum of
37C) and an irradiance of 1500 mol m-2
s-1 was increased by up to 200% by enriched
rhizosphere DIC. The growth rates of plants grown with irradiances of less
than 100 mol m-2 s-1
were increased by elevated rhizosphere DIC concentrations only when grown
at high shoot temperatures (35C) or with
salinity 28°C). At high light intensities, the photosynthetic rate,
the CO2 and light-saturated photosynthetic rate (jmax)
and the stomatal conductance of plants grown at high light intensity were
lower in plants supplied with enriched compared to ambient DIC. This was
interpreted as 'down-regulation' of the photosynthetic system in plants
supplied with elevated DIC. Labelled organic carbon in the xylem sap
derived from root DI14C incorporation was found to
be sufficient to deliver carbon to the shoot at rates equivalent to 1% and
10% of the photosynthetic rate of the plants supplied with ambient- and
enriched-DIC, respectively. It was concluded that organic carbon derived
from DIC incorporation and translocated in the xylem from the root to the
shoot may provide a source of carbon for the shoots, especially under
conditions where low stomatal conductance may be advantageous, such as
salinity stress, high shoot temperatures and high light
intensities. 相似文献
20.
Dead seeds that expand to nearly twice their normal volume whenfully hydrated are called osmotically distended (OD). Theseseeds swell osmotically in response to a water potential ()gradient created by solutes trapped in the free space betweenthe embryo and the surrounding endosperm or perisperm tissues.The formation of OD seeds in planta is poorly understood, althoughthey often occur in newly harvested muskmelon (Cucumis meloL. Reticulatus group) seed lots. Muskmelon fruit senescenceand seed germinability were contrasted with Armenian cucumber(Cucumis melo L. Flexuosus group) from 50 d after anthesis (DAA)to when seeds were released from the fruit. Fifty DAA muskmelonseeds were incubated in the laboratory for 30 d at 15, 25, and35 °C in factorial combinations of ethanol, acetic acid,and to simulate conditions in decaying fruits. Seed releasefrom Armenian cucumber occurred 20 d earlier than muskmelon.In both years of the study, less than 25% of the muskmelon seedsreleased from the fruit were viable, and 52% and 24% of thedead seeds were OD in year one and two, respectively. All Armeniancucumber seeds were viable or had germinated precociously atseed release. From 50 to 60 DAA, soluble solids in muskmelonfruit pericarp tissue declined from 11·4 to 7·8° Brix, pH declined from 6·2 to 5·1, increasedfrom 1·76 to 1·36 MPa, acetic acidincreased to 61 mol m3;, and ethanol content rose from0·1% to 0·3%. O2 and CO2 partial pressures inthe seed cavities of 40 to 55 DAA fruits were generally 12 and8 kPa, respectively, at midday. All 50 DAA muskmelon seeds incubatedin acetic acid and ethanol germinated, because these chemicalscould not penetrate the perisperm tissue. Incubating 50 DAAmuskmelon seeds in the laboratory for 30 d at 15 or 25 °Chad little effect on germinability, regardless of . Germinationpercentages of muskmelon seeds incubated at 35 °C and 's<1·28MPa were less than 50%. Muskmelon seeds died and became OD insidedecaying fruits in the field because of the combined effectsof low , high temperature, and low O2 partial pressures. Fruitsof muskmelon cultivars bred to resist decomposition and to havehigh sugar content showed decreased reproductive capacity comparedto Armenian cucumber which decomposed more rapidly. Key words: Muskmelon, seed, fruit, germination, senescence, water potential, temperature, oxygen, carbon dioxide 相似文献