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1.
The rate of photosynthesis of leaves of perennial ryegrass (Loliumperenne L.) and white clover (Trifollum pratense L.) grown atdifferent temperatures was measured at a range of temperatures.There was a small effect of the temperature at which a leafhad grown on its photosynthetic rate, but a large effect ofmeasurement temperature, especially in bright light, where photosyntheticrates at 15°C were about twice those at 5°C. It appearsthat temperature could affect sward photosynthesis in the field.Ryegrass and clover had similar photosynthetic rates which respondedsimilarly to temperature. Lolium perenne L., ryegrass, Trifolium pratense L., white clover, photosynthesis, temperature, irradiance  相似文献   

2.
NORRIS  I. B. 《Annals of botany》1985,56(3):317-322
Effects of temperature on floral initiation of ten white clovervarieties growing in controlled environments are described.Plants grown under long days (16 h) were subjected to constanttemperatures of 26, 18 and 10 °C. Relationships betweenmorphological and physiological traits and flowering were examined. Most plants flowered at the two higher temperatures but only10 per cent of plants flowered at 10 °C. Larger leaved typestended to produce more reproductive buds per stolon at the highertemperatures than did smaller leaved varieties. Of the floral characters studied, floret number was least affectedby temperature. Ovule number and peduncle length were greatestat 18 °C. Variation in, and absolute level of nectar secretionwas greatest at the highest temperature. Trifolium repens, white clover, flowering, temperature  相似文献   

3.
Single, clonal plants of white clover were grown without inorganicnitrogen in four contrasting day/night temperature regimes,with a 12 h photoperiod, in controlled environments. Root andnodule respiration and acetylene reduction activity were measuredin a flow-through system during both day and night for plantsacclimated to day/night regimes of 23/18, 15/10 and 10/5 ?C.Similar measurements were made on plants acclimated to 20/15?C and stepwise at temperatures from 4 to 33 ?C. Peak rate of ethylene production, nitrogenase-linked respirationand basal root + nodule respiration increased approximatelylinearly from 5 to 23 ?C both in temperature-acclimated plantsand in plants exposed to varying measurement temperatures. Themeasured attributes did not vary significantly between day andnight. Temperatures above 23–25 ?C did not further enhancethe rate of ethylene production, which remained essentiallythe same up to the maximum measured temperature of 33 ?C. The measurements of nitrogenase-linked respiration between 5and 23 ?C, during both day and night, demonstrated a constant‘energetic cost’ of acetylene reduction of 2.9 µmolCO2 µmol C2H4–1,. Over the same temperature range,the approximate activation energy of acetylene reduction was60 kJ mol–1. The integrated day plus night nitrogenase-linkedrespiration accounted for 13.4–16% of the plant‘snet shoot photosynthesis in a single diurnal period: there wasno significant effect of temperature between 5 and 23 ?C. Key words: Trifolium repens, white clover, temperature, N2 fixation, respiration  相似文献   

4.
In three experiments measurements of photosynthesis were madeon single leaves of white clover (Trifolium repens L.) on threecultivars grown in a controlled environment. Plants which had grown under an irradiance of 30 J m–2s–1, or in shade within a simulated mixed sward, producedleaves with photosynthetic capacities some 30 per cent lowerthan did plants grown at 120 J m–2 s–1 without shade.There were no differences between treatments either in photosynthesismeasured at 30 J m–2 s–1, or in respiration ratesper unit leaf dry weight. Respiration per unit leaf area washigher in the plants grown at 120 J m–2 s–1, reflectingthe lower specific leaf area of these leaves. There were nodifferences between the three cultivars examined. Leaves which were removed from the shade of a simulated swardshortly after becoming half expanded achieved photosyntheticcapacities as high as those which were in full light throughouttheir development. It is suggested that it is this characteristicwhich enables clover plants growing in an increasingly densemixed sward to produce a succession of leaves of high photosyntheticcapacity, even though each lamina only reaches the top of thesward at a relatively late stage in its development. Trifolium repens L., white clover, photosynthesis, leaf expansion, shade, specific leaf area, stomatal conductance  相似文献   

5.
Microswards of white clover (Trifolium repens L.) were grownin controlled environments at 10/7, 18/13 and 26/21 °C day/nighttemperatures. The vertical distribution of leaves of differentages and their rates of 14CO2-uptake in situ were studied. Extending petioles carried the laminae of young leaves throughthe existing foliage. A final position was reached within 1/4to 1/3 of the time between unfolding and death. Newly unfoldedleaves had higher rates of 14CO2-uptake per leaf area than olderones at the same height in the canopy. At higher temperatures,the decrease with age was faster. However, the light-photosynthesisresponse of leaves which were removed from different heightsin the canopy varied much less with leaf age than did the ratesof 14CO2-uptake in situ. The comparison of the rates of 14CO2-uptake in situ with thelight-photosynthesis response curves suggests that young leavesreceive more light than older ones at the same height in thecanopy. This would imply that young white clover leaves havethe ability to reach canopy positions having a favourable lightenvironment. This ability may improve the chances of survivalof white clover in competition with other species. Trifolium repens L., white clover, photosynthesis, canopy, leaf age, 14CO2-uptake, ecotypes, temperature  相似文献   

6.
A period of growth under shade netting in the glasshouse allowedthe cultivation of white clover stolons with an accumulationof undeveloped axillary buds similar to that often found onstolons from grass/clover swards. The subsequent capacity ofthese nodes to develop branches under different circumstanceswas investigated in three experiments. Removal of the laminaeand petioles subtending sets of four buds along a stolon reducedthe rate at which branches were initiated from the buds. Treatmentsin which petioles, or petioles plus laminae, were retained initiatedbranches more quickly. Shading the stolons reduced both therate of initiation and the percentage of buds which developed,unless both petioles and laminae were retained. There was someevidence that conditions applied to individual buds may actin the same way as the same conditions applied to sets of fourbuds and that illuminated nodes may depress the performanceof neighbouring shaded notes. Fewer buds developed at older nodes than at younger nodes duringthe summer, but during the autumn younger buds initially developedmore slowly than older buds. This suggests that buds can developat a younger nodal age in summer than in winter. When leafless stolons were cut up into component internodesbuds developed faster than on intact stolons, provided the budwas located at the end of the internode nearest the main stolongrowing point. If the bud was at the other end, branch developmentwas slower than on intact stolons. The results are discussedin relation to clover growth in sward conditions. White clover, Trifolium repens, axillary bud development, branching, growing points, defoliation, shading  相似文献   

7.
Gordon, A. J., Mitchell, D. F., Ryle, G. J. A. and Powell, C.E. 1987. Diurnal production and utilization of photosynthatein nodulated white clover.—J. exp. Bot. 38: 84–98. A steady-state 14C-labelling technique was used to examine thediurnal carbon fixation, storage and export characteristicsof white clover leaves. Approximately 70% of fixed carbon wasexported to other organs during the photoperiod. The remainingcarbon was stored mainly as starch (80% at the end of the photoperiod)with smaller amounts of sucrose, hexoses and charged compounds.Carbon export from the leaf at night was provided by remobilizationof starch. During the photoperiod it was estimated that c.60% of carbonexported from the leaf was directed towards the nodulated root;45% to nodules and 15% to roots. The 40% directed towards theshoot was supplemented by a further 11% of carbon (in the formof amides) re-exported from the nodules. During the photoperiod, all organs of the plant accumulatedcarbohydrate which was available for use during darkness, inconjunction with a diminished supply of exported carbon fromleaves. Nodules exhibited a striking pattern of carbohydratestorage and depletion. The levels of sucrose and starch in thenodules at the end of the photoperiod were sufficient to maintainN2 fixation for 8–9 h of the 12 h dark period. We proposethat continued import from leaves provided the additional sucrosenecessary to support undiminished nodule function throughoutthe entire dark period. Key words: White clover, photosynthate, starch, carbohydrate, nodules, N2 fixation  相似文献   

8.
Miniswards of white clover (Trifolium repensL.) varieties Menna,Huia, AberCrest and AberHerald, with contrasting winter hardiness,were established from cloned material in flat boxes. The miniswardswere placed in an unheated glasshouse with natural lightingfor the winter of 1995/96. During this time there were severalperiods of cold weather. The plants experienced temperaturesat least as severe as those experienced by unprotected plantsduring preceding mild winters. Growth measurements carried outmonthly suggested the cloned genotypes were representative ofthe varieties from which they were derived. Growth continuedthroughout the experiment, particularly when expressed as appearanceof new internodes. During the coldest weather these internodeswere short, and the amount of tissue produced was small. Starchconcentration showed a complex pattern of changes during thewinter. Older internodes were the major site of starch storagein the autumn; starch was lost from these internodes duringthe winter and early spring. Starch synthesis also occurred,even during the coldest periods. Starch accumulated in all newstolon tissue. There were significant differences between varieties.AberCrest and AberHerald retained higher concentrations of starchin older stolon tissue, synthesized higher concentrations ofstarch in young tissue and retained these for longer. Therewere few differences in soluble sugar concentrations betweenvarieties, but there were significant changes during the winter.In mid-winter, sucrose and pinitol were at their highest concentrations,whereas reducing sugars were at their lowest concentrations.This study further supports the important role of starch reservesin supporting winter survival.Copyright 1998 Annals of BotanyCompany Trifolium repens; white clover; winter hardiness; starch; sugar; pinitol.  相似文献   

9.
The growth of white clover (Trifolium repens L.) in conditionstypical of April in Southern England (8 °C day/4 °Cnight, 12 h photoperiod of 90 J m–2 s–1 visibleradiation) was extremely slow, whether the plants were dependentfor nitrogen on fixation by their root nodules or were suppliedwith abundant nitrate; although growth was slower in the nodulatedplants. The reasons for slow growth were a large root: shootratio and a small leaf area, particularly in the nodulated plants,and a low photosynthetic rate in all plants. The probable effectsof these characteristics on the growth of white clover withgrasses in mixed pastures are discussed. Trifolium repens L, white clover, low temperature, leaf area, photosynthetic rate, nitrogen supply, growth  相似文献   

10.
White clover (Trifolium repens L.) was grown in controlled environmentsto determine the distinct effects of root and shoot temperatureon the accumulation of total and fixed (15 N dilution) nitrogenat two levels of nitrate (10 and 75 mM). Nitrogen fixation(BNF) showed a positive response to higher shoot temperature(23 vs. 13 C day temperature), irrespective of whether or notroot temperature was increased in parallel. Low root temperature(5 C) caused a marked reduction in the accumulation of totalnitrogen at both nitrate levels, and led to a lower proportionof N derived from BNF. The temperature response of BNF was attributedfor the major part to an adaptation to the demand for fixedN. It is therefore concluded that BNF is not primarily responsiblefor the reduced clover growth at low temperatures. White clover, Trifolium repens L., temperature, nitrogen fixation, nitrate, root, shoot  相似文献   

11.
SHEPHERD  W. 《Annals of botany》1964,28(2):207-220
The experiments described were concerned with losses of moisturefrom laminae and petioles of leaves of white clover (Trifoliumrepens L.) detached from parent plants, and with the resistancesin the two pathways of loss of petiole moisture-via laminaeand direct from petiole surfaces. Methods involving determination of moisture losses from separatedlaminae and petioles were unsatisfactory and transpiration chamberswere therefore used to permit determinations with intact leaves. Up to 24 per cent of the total petiole moisture was lost viathe laminae, the amount frequently exceeding that initiallyresiding in the xylem of the petioles. Stomatal, cuticular, and external resistances were calculatedat several stages of wilting. Rates of loss of petiole moistureby both pathways were controlled by stomatal and external resistancesin the early stages and by cuticular and internal resistancesin the later stages. Under certain conditions, transpirationof petiole moisture via the lamina ceased earlier than mighthave been expected; estimates were made of the resistances involved.  相似文献   

12.
NORRIS  I. B. 《Annals of botany》1987,59(2):197-202
The response to different combinations of daylength (14, 15and 16 h) and day/night temperature (20/10°C, 30/15°C)of four white clover (Trifolium repens) varieties in terms offloral initiation and development was studied. More plants flowered under long days (16 h) at 30°C thanin any other combination. Varietal differences in response todaylength were large but temperature was the factor controllinginitiation. Daylength was more important in regulating peduncle length,floret and ovule numbers than was temperature. The amount ofnectar produced was lowest at the higher temperature althoughnectar concentration was unaffected by temperature. Nectar concentrationwas lowest in the shortest daylength (14 h). White clover, floral initiation, temperature, daylength  相似文献   

13.
Red clover mottle virus isolated in Czechoslovakia was studied in relation to its reaction to varying temperature on primary French bean leaves (Phaseolus vulgaris L.) on which it forms local necrotic lesions. The plants were kept 24 or 48 h before, or 24 or 48 h after inoculation at the temperatures 23, 25, 27, 30, 33 and 36°C. After such exposures the French beans were kept at a constant temperature of 25°C. The lesions were counted at various intervals. In the experiment the optimal temperature for the maximum number of lesions seems to be 36°C 48 h before inoculation. The temperature above 25°C applied 24 h after inoculation seems to have a decreasing effect upon the number of lesions formed by RCMV on primary leaves of French beans and the lesions appeared several hours later, especially at 30, 33 and 36°C. The temperatures 27, 30 and 33°C applied 48 h after inoculation have a further decreasing effect on the number of lesions. The temperature of 36°C applied 48 h after inoculation has an inactivating effect upon RCMV inoculated on French bean leaves and no lesions appeared 5 days after inoculation.  相似文献   

14.
Precipitation and temperature are important drivers of soil respiration. The role of moisture and temperature are generally explored at seasonal or inter-annual timescales; however, significant variability also occurs on hourly to daily time-scales. We used small (1.54 m2), throughfall exclusion shelters to evaluate the role soil moisture and temperature as temporal controls on soil CO2 efflux from a humid tropical forest in Puerto Rico. We measured hourly soil CO2 efflux, temperature and moisture in control and exclusion plots (n = 6) for 6-months. The variance of each time series was analyzed using orthonormal wavelet transformation and Haar-wavelet coherence. We found strong negative coherence between soil moisture and soil respiration in control plots corresponding to a two-day periodicity. Across all plots, there was a significant parabolic relationship between soil moisture and soil CO2 efflux with peak soil respiration occurring at volumetric soil moisture of approximately 0.375 m3/m3. We additionally found a weak positive coherence between CO2 and temperature at longer time-scales and a significant positive relationship between soil temperature and CO2 efflux when the analysis was limited to the control plots. The coherence between CO2 and both temperature and soil moisture were reduced in exclusion plots. The reduced CO2 response to temperature in exclusion plots suggests that the positive effect of temperature on CO2 is constrained by soil moisture availability.  相似文献   

15.
Understanding the response of ecosystem respiration (ER) to major environmental drivers is critical for estimating carbon sequestration and large-scale modeling research. Temperature effect on ER is modified by other environmental factors, mainly soil moisture, and such information is lacking for switchgrass (Panicum virgatum L.) ecosystems. The objective of this study was to examine seasonal variation in ER and its relationship with soil temperature (T s) and moisture in a switchgrass field. ER from the nighttime net ecosystem CO2 exchange measurements by eddy covariance system during the 2011 and 2012 growing seasons was analyzed. Nighttime ER ranged from about 2 (early growing season) to as high as 13 μmol m?2 s?1 (peak growing period) and showed a clear seasonality, with low rates during warm (>30 °C) and dry periods (<0.20 m3 m?3 of soil water content). No single temperature or moisture function described variability in ER on the seasonal scale. However, an exponential temperature–respiration function explained over 50 % of seasonal variation in ER at adequate soil moisture (>0.20 m3 m?3), indicating that soil moisture <0.20 m3 m?3 started to limit ER. Due to the limitation of soil–atmosphere gas exchange, ER rates declined markedly in wet soil conditions (>0.35 m3 m?3) as well. Consequently, both dry and wet conditions lowered temperature sensitivity of respiration (Q 10). Stronger ER–T s relationships were observed at higher soil moisture levels. These results demonstrate that soil moisture greatly influences the dynamics of ER and its relationship with T s in drought prone switchgrass ecosystems.  相似文献   

16.
Root-infecting nematodes are a major cause of white clover, Trifolium repens, not reaching its potential in New Zealand pastures. Resistance and/or tolerance are the preferred control options. Greenhouse-based, recurrent selection programs have developed resistance to Meloidogyne trifoliophila and Heterodera trifolii, and a field-based program has developed tolerance. Lines from these programs were compared with commercial cultivars as controls in a series of field trials at four sites over 4 years. Resistant lines from the CCN program performed better than susceptible lines and as well as most cultivars, reflecting the high level of resistance developed in this greenhouse-based program. In stained root from Cambridge, numbers of CCN were lower in resistant lines than in cultivars; numbers in susceptible lines were intermediate. CCN resistance was also reflected to a lesser extent in the number of cysts counted in soil under resistant lines in Palmerston North. The root-knot nematode-resistant material performed better than the susceptible and as well as most cultivars. In one trial of CRKN-resistant lines, resistant and susceptible lines had similar numbers of CRKN which were both lower than the numbers in the cultivars; in the second trial, there were fewer CRKN in resistant than in susceptible lines or cultivars. The tolerant selections, developed under field conditions, performed as well as or better than the cultivars. The selections from the breeding programmes have exhibited strong agronomic potential across locations and years, and the best material has been crossed; progeny are being assessed in current field trials.  相似文献   

17.
Detached leaves of white clover (Trifolium repens L.) were keptfor 1 h under various conditions of temperature, oxygen concentrationand light intensity. Rates of photosynthesis were measured whereappropriate and then ribulosebisphosphate carboxylase oxygenase(RuBPCO) was extracted rapidly and its initial activity measuredimmediately. The extracted activity increased with increased intensity ofillumination of the leaves. Where leaves were pretreated atlow light intensity, the lower the temperature of the leavesthe higher the extracted activity of RuBPCO. At high light intensitytemperature did not affect the activity of subsequently extractedRuBPCO but the light intensity which was necessary for maximumactivity increased with temperature. Activity of RuBPCO fromleaves pretreated in the dark was least when CO2 was low andtemperature high. Leaves, pretreated at low temperatures andhigh light intensity in 20% O2, yielded higher activity in extractsthan leaves pretreated under similar conditions but in 2% O2.A relatively weak temperature response of photosynthesis atlow irradiances was associated with a decrease in extractableRuBPCO activity with increasing temperature. A strong temperaturedependence of the oxygen inhibition of photosynthesis was associatedwith lower extractable RuBPCO activity in leaves pretreatedat low oxygen concentration at low temperatures. With leavesfrom plants grown at low temperatures prior to treatment ofleaves, oxygen inhibition of photosynthesis was less temperaturedependent and activity of RuBPCO in extracts was not decreasedby low O2 at low temperatures. Differences in the activationof RuBPCO appear to influence photosynthesis and account foran absence of oxygen inhibition of photosynthesis at low temperaturesin plants grown in warm conditions. Key words: Ribulosebisphosphate carboxylase oxygenase activation, Photosynthesis, Temperature, O2 effect, White clover  相似文献   

18.
Ewing EE 《Plant physiology》1978,62(3):348-353
The intensity of “tuberization stimulus” in potato shoots (Solanum tuberosum L.) can be assessed from cuttings containing one or more leaves. Cuttings maintained in a mist chamber under long days will form tubers from underground buds if prior to taking the cutting the leaves received sufficient exposure to photoperiods less than the critical photoperiod. The greatest tendency to tuberize was found in cuttings that consisted of a single, fully expanded leaf and its subtended bud. Grafts showed that genetical differences in critical photoperiod resided in properties of the leaf. Short days before cutting tended to shift growth from above ground buds of two-node cuttings to below ground buds, even if the number of short days was insufficient for tuber induction. As few as 6 short days reduced growth of shoots at the upper bud and increased underground growth of shoots and stolons.  相似文献   

19.
Successful inoculation of peanuts and cowpeas depends on the survival of rhizobia in soils which fluctuate between wide temperature and moisture extremes. Survival of two cowpea rhizobial strains (TAL309 and 3281) and two peanut rhizobial strains (T-1 and 201) was measured in two soils under three moisture conditions (air-dry, moist (−0.33 bar), and saturated soil) and at two temperatures (25 and 35°C) when soil was not sterilized and at 40°C when soil was sterilized. Populations of rhizobia were measured periodically for 45 days. The results in nonsterilized soil indicated that strain 201 survived relatively well under all environmental conditions. The 35°C temperature in conjunction with the air-dry or saturated soil was the most detrimental to survival. At this temperature, the numbers of strains T-1, TAL309, and 3281 decreased about 2 logs in dry soil and 2.5 logs in saturated soil during 45 days of incubation. In sterilized soil, the populations of all strains in moist soil increased during the first 2 weeks, but decreased rapidly when incubated under dry conditions. The populations did not decline under saturated soil conditions. From these results it appears that rhizobial strains to be used for inoculant production should be screened under simulated field conditions for enhanced survival before their selection for commercial inoculant production.  相似文献   

20.
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