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1.
Starting in 1996, individual trees of Scots pine (Pinus sylvestrisL.) aged 30 years, were grown in closed-top chambers and exposedto either normal ambient conditions (CON), elevated CO2(approx.700 µmol mol-1; Elev. C), elevated temperature (approx.2 °C and approx. 6 °C above the outside ambient temperatureduring the ‘growing season’ and ‘off season’,respectively; Elev. T) or a combination of elevated CO2and warmertemperature (Elev. CT). Sap flow was monitored simultaneouslyby the constant-power heat balance method in a total of 16 trees,four for each treatment, over a 32 d period in summer 1998 (afterthe completion of needle expansion and branch elongation). Toquantify the contributions of crown and physical environmentalvariables to total crown transpiration, a ‘sun/shade model’was developed and used to partition the changes in transpirationto different sources. The results of the sap flow measurementsindicate that (1) total daily sap flow (Etree.d) varied from0.15–3.41 kg per tree; (2) the treatment effect on Etree.ddependedgreatly on the weather conditions; (3) the cumulative Etree.dforthe 32 d dropped significantly by 22% relative to CON (P =0.038)under Elev. C and increased significantly by 21% (P =0.043)and 16% (P =0.048) under Elev. T and Elev. CT, respectively.In general, the modelled transpiration gave good agreement withthe sap flow results. The model computations showed that, ona typical sunny day in summer, the effect of treatment on crownstomatal conductance was responsible for approx. 80% of thechange inEtree.d , while the increase in needle area and theeffect on total radiation absorption contributed only a smallpercentage. Furthermore, sunlit needles were responsible forover 60% of change in transpiration. The effect of the treatmentson Etree.dwas larger at high temperature and vapour pressuredeficit but was not sensitive to incident daily radiation. Copyright2000 Annals of Botany Company Transpiration model, sap flow, CO2and temperature elevation, environment-controlled chamber, Pinus sylvestris L.  相似文献   

2.
REY  ANA; JARVIS  PAUL G. 《Annals of botany》1997,80(6):809-816
A field experiment consisting of 18 birch trees grown in opentop chambers in ambient and elevated CO2concentrations was setup with the aim of testing whether the positive growth responseobserved in many short-term studies is maintained after severalgrowing seasons. We present the results of growth and biomassafter 4.5 years of CO2exposure, one of the longest studies sofar on deciduous tree species. We found that elevated CO2ledto a 58% increase in biomass at the end of the experiment. However,estimation of stem mass during the growing season showed thatelevated CO2did not affect relative growth rate during the fourthgrowing season, and therefore, that the large accumulation ofbiomass was the result of an early effect on relative growthrate in previous years. Trees grown in elevated CO2investedmore carbon into fine roots and had relatively less leaf areathan trees grown in ambient CO2. In contrast with previous studies,acceleration of growth did not involve a significant declinein nutrient concentrations of any plant tissue. It is likelythat increased fine root density assisted the trees in meetingtheir nutrient demands. Changes in the species composition ofthe ectomycorrhizal fungi associated with the trees grown inelevated CO2in favour of late successional species supportsthe hypothesis of an acceleration of the ontogeny of the treesin elevated CO2.Copyright 1997 Annals of Botany Company Betula pendula; silver birch; elevated CO2; growth; biomass allocation; ectomycorrhizas; tissue composition; nutrients; leaf morphology; specific leaf area; stomatal density; shoot structure  相似文献   

3.
The effects of increased atmospheric carbon dioxide (CO2) of700 µmol mol–1 and increased air temperature of+ 4C were examined in Lolium perenne L. cv. Vigor, growingin semi-controlled greenhouses. Leaf growth, segmental elongationrates (SER), water relations, cell wall (tensiometric) extensibility(%P) and epidermal cell lengths (ECL) were measured in expandingleaves in spring and summer. In elevated CO2, shoot dry weight (SDW) increased in mid-summer.In both seasons, SDW decreased in elevated air temperatureswith this reduction being greater in summer as compared to spring.Specific leaf area (SLA) decreased in elevated CO2 and in CO2 temperature in both seasons. In spring, increased leaf extensionand SER in elevated CO2 were linked with increased ECL, %P andfinal leaf size whilst in summer all were reduced. In high temperature,leaf extension, SER, %P and final leaf size were reduced inboth seasons. In elevated CO2 temperature, leaf extension,SER, %P, and ECL increased in spring, but final leaf size remainedunaltered, whilst in summer all decreased. Mid-morning waterpotential did not differ with CO2 or temperature treatments.Leaf turgor pressure increased in elevated CO2 in spring andremained similar to the control in summer whilst solute potentialdecreased in spring and increased in summer. Contrasting seasonalgrowth responses of L. perenne in response to elevated CO2 andtemperature suggests pasture management may change in the future.The grazing season may be prolonged, but whole season productivitymay become more variable than today. Key words: Lolium perenne, ryegrass, CO2 and temperature, leaf extension, cell wall rheology  相似文献   

4.
The effect of elevated atmospheric CO2 and temperature on resource allocation and secondary chemistry of white birch (Betula pendula Roth) under a non-limiting nutrient and water supply was investigated. Birch seedlings were grown in closed-top chambers exposed to ambient CO2 and temperature, elevated atmospheric CO2 (700 ppm), elevated temperature (2°C above ambient) and a combination of elevated CO2 and temperature for one growing season. Elevated CO2 significantly increased the total biomass of the seedlings. The combined effect of the elevated CO2 and temperature treatments further increased the total biomass, but not significantly. The content of nitrogen and water decreased, while some secondary compounds (such as condensed tannins and flavonol glycosides) increased in leaves subjected to CO2 enrichment. Elevated temperature increased the concentration of total flavone aglycones and decreased that of total HPLC-phenolics in the leaves, due to the decrease in individual flavonol glycosides, cinnamoylquinic acids and (+)-catechin. There were no significant interactive effects between CO2 and temperature in the phenolic concentrations of the leaves and in the stems, while the number of resin droplets in the top part of the stems showed significant interaction. This clearly implies that carbon allocation into secondary metabolites in the leaves and stems differ under enhanced CO2 and temperature, and the combined effect of CO2 and temperature on the herbivore resistance of birches, is lower than that of CO2 and temperature alone.  相似文献   

5.
To test the hypothesis that elevated atmospheric CO2and elevatedtemperature, simulating current and predicted future growingseason conditions, act antagonistically on phosphorus acquisitionof ponderosa pine, seedlings were grown in controlled-environmentchambers in a two temperature (25/10 °C and 30/15 °C)xtwoCO2(350 and 700 µl-1) experimental design. Mycorrhizalseedlings were watered daily with a nutrient solution with Padded in organic form as inositol hexaphosphate (64 ppm P).Thus seedlings were challenged to use active forms of P acquisition.Elevated CO2increased the relative growth rate by approx. 5%which resulted in an approx. 33% increase in biomass after 4months. There was no main effect of temperature on growth. Increasedgrowth under elevated CO2and temperature was supported by increasesin specific absorption rate and the specific utilization rateof P. The contribution of mycorrhizae to P uptake may have beengreater under simulated future conditions, as elevated CO2increasedthe number of mycorrhizal roots. There was no main effect oftemperature on root phosphatase activity, but elevated CO2causeda decrease in activity. The inverse pattern of root phosphataseactivity and mycorrhizal infection across treatments suggestsa physiological coordination between these avenues of P acquisition.The concentration of oxalate in the soil increased under elevatedCO2and decreased under elevated temperature. This small molecularweight acid solubilizes inorganic P making it available foruptake. Increased mycorrhizal infection and exudation of oxalateincreased P uptake in ponderosa pine seedlings under elevatedCO2, and there was no net negative effect of increased temperature.The increased carbon status of pine under elevated CO2may facilitateuptake of limiting P in native ecosystems. Atmospheric CO2; climate change; growth analysis; oxalate; Pinus ponderosa ; ponderosa pine; phosphorus uptake; rhizosphere; root phosphatase; temperature  相似文献   

6.
Large turves from a ryegrass/white clover based pasture wereexposed to 350 or 700 µl l-1 CO2 for a period of 217 din controlled environment rooms. The temperature was increasedduring the experiment from 10/4 °C day/night to 16/10 °Cand finally to 22/16 °C. The turves were cut to a heightof 2 cm at intervals and growth rates calculated from the regrowth. Growth rates over the duration of the experiment were 8% higherat elevated CO2; the difference between CO2 treatments beingstatistically significant only at the highest temperature. Speciescomposition of the turves at 350 µl l-1 CO2 showed seasonalchanges similar to those measured in the field. The effect ofCO2 was to exaggerate the normal decline of ryegrass at warmertemperatures and increase the proportion of white clover. About30% of the total growth rate was from other species (notablyBromus hordeaceus L. and Poa trivialis L.) and this fractionwas similar between CO2 levels. Root mass was measured at theend of the experiment and was 50% higher at elevated CO2. The modest above-ground response to CO2 was a result of CO2stimulation occurring only at the higher temperature. Becauseof the CO2 x temperature interaction, the effect of CO2 in temperateregions will be seasonal. When this is matched with seasonalgrowth patterns of herbage species, a complex response of pasturecommunities to CO2 is possible. In our case, white clover wasgrowing most strongly during the period of greatest CO2 stimulationand consequently its growth was enhanced more than that of ryegrass;however, the cooler season growth of ryegrass gives it a temporalniche which is little affected by CO2 and this may be importantfor ryegrass stability if it is an inherently poor responderto CO2. The results indicate that for temperate species theeffects of competition at elevated CO2 cannot be easily determinedfrom experiments conducted at a single temperature.Copyright1994, 1999 Academic Press CO2 enrichment, seasonal growth, species composition, turves, Trifolium repens L., Lolium perenne L., climate change  相似文献   

7.
Effects of ozone on the leaf anatomy and ultrastructure of fivebirch (Betula pendula Roth.) clones were studied during onegrowing season in open-field conditions. Cumulative ozone exposurewas 1·5 times higher than ambient. Ozone exposure decreasedtotal leaf thickness in one, ozone sensitive, clone. The effecton palisade spongy mesophyll thickness was clone-specific, whilethe amount of palisade intercellular space was reduced in allclones. A second effect was a change in the relative amountsof adaxial and abaxial epidermis. In palisade and spongy parenchymacells of all clones, ozone increased the number of irregularand spherical shaped chloroplasts, the electron density of chloroplaststroma, swelling and curling of thylakoids, translucency ofthe mitochondrial matrix and also the amount of cytoplasmiclipids. In the sensitive clone shorter chloroplasts and reducedamount of starch were observed in ozone-exposed plants, whilst,in the tolerant clone, the size of chloroplasts and the amountof starch were unaffected. Ozone effects on number, size andelectron density of plastoglobuli and vacuolar tannin were clone-dependent.At the ultrastructural level, the normal leaf ageing processprogressed at different rates in the birch clones. Ozone acceleratedsenescence-related structural changes, in accordance with earlierobservations of deciduous species.Copyright 1995, 1999 AcademicPress Betula pendula Roth., birch, clones, ageing, ozone, leaf anatomy, ultrastructure  相似文献   

8.
The effects of elevated atmospheric CO2 concentrations on theecophysiological responses (gas exchange, chlorophyll a fluorescence,Rubisco activity, leaf area development) as well as on the growthand biomass production of two poplar clones (i.e. Populus trichocarpax P. deltoides clone Beaupré and P. x euramericana cloneRobusta) were examined under open top chamber conditions. Theelevated CO2 treatment (ambient + 350 µmol mol-1) stimulatedabove-ground biomass of clones Robusta and Beaupré afterthe first growing season by 55 and 38%, respectively. This increasedbiomass production under elevated CO2 was associated with asignificant increase in plant height, the latter being the resultof enhanced internode elongation rather than an increased productionof leaves or internodes. Both an increased leaf area index (LAI)and a stimulated net photosynthesis per unit leaf contributedto a significantly higher stem biomass per unit leaf area, andthus to the increased above-ground biomass production underthe elevated CO2 concentrations in both clones. The larger LAIwas caused by a larger individual leaf size and leaf growthrate; the number of leaves was not altered by the elevated CO2treatment. The higher net leaf photosynthesis was the resultof an increase in the photochemical (maximal chlorophyll fluorescenceFm and photochemical efficiency Fv/Fm) as well as in the biochemical(increased Rubisco activity) process capacities. No significantdifferences were found in dark respiration rate, neither betweenclones nor between treatments, but specific leaf area significantlydecreased under elevated CO2 conditions.Copyright 1995, 1999Academic Press Biomass, chlorophyll a fluorescence, elevated CO2, growth, Populus, poplar, photosynthesis, respiration, Rubisco  相似文献   

9.
Abstract 1 The effect of elevated CO2 and temperature on the foliar chemistry Betula pendula Roth and the feeding performance of polyphagous weevils Phyllobius maculicornis Germ. was studied. Birch seedlings were grown during one growing season in chamber‐less field conditions and in closed‐top chambers exposed to four different treatments: ambient CO2 (350 p.p.m) and temperature, elevated atmospheric CO2 (700 p.p.m) and ambient temperature, elevated temperature +3 °C above ambient) and ambient CO2, and a combination of elevated CO2 and temperature. 2 In leaves under CO2 enrichment, the concentration of nitrogen and some flavonol glycosides significantly decreased, whereas the concentration of total phenolics, condensed tannins and (+)‐catechin significantly increased. The total concentration of cinnamoylquinic acids was significantly increased by CO2 and decreased by temperature. The concentration of salidroside increased under elevated temperature. 3 Weevil‐feeding experiments were carried out in a five‐choice arrangement, one leaf from each of the five treatments (chamber‐less field controls and four different treatments in chambers) being placed in random order in a plastic box. The weevils preferred the leaves grown under elevated CO2, which had low nitrogen, high phenolics and the highest condensed tannin concentrations. Whether the reason for this trend is due to the stimulating effect of condensed tannins and/or a change in other secondary compounds, remains unknown. The weevils did not show any obviously different response in feeding performance to temperature and the combination of elevated CO2 and temperature.  相似文献   

10.
Two common tallgrass prairie species, Andropogon gerardii, thedominant C4 grass in this North American grassland, and Salviapitcheri, a C3 forb, were exposed to ambient and elevated (twiceambient) CO2 within open-top chambers throughout the 1993 growingseason. After full canopy development, stomatal density on abaxialand adaxial surfaces, guard cell length and specific leaf mass(SLM; mg cm-2) were determined for plants in the chambers aswell as in adjacent unchambered plots. Record high rainfallamounts during the 1993 growing season minimized water stressin these plants (leaf xylem pressure potential was usually >-1·5 MPa in A. gerardii) and also minimized differencesin water status among treatments. In A. gerardii, stomatal densitywas significantly higher (190 ± 7 mm-2; mean ±s.e.) in plants grown outside of the chambers compared to plantsthat developed inside the ambient CO2 chambers (161 ±5 mm-2). Thus, there was a significant 'chamber effect' on stomataldensity. At elevated levels of CO2, stomatal density was evenlower (P < 0·05; 121 ± 5 mm-2). Most stomatawere on abaxial leaf surfaces in this grass, but the ratio ofadaxial to abaxial stomatal density was greater at elevatedlevels of CO2. In S. pitcheri, stomatal density was also significantlylower when plants were grown in the open-top chambers (235 ±10 mm-2 outside vs. 140 ± 6 mm-2 in the ambient CO2 chamber).However, stomatal density was greater at elevated CO2 (218 ±12 mm-2) compared to plants from the ambient CO2 chamber. Theratio of stomata on adaxial vs. abaxial surfaces did not varysignificantly in this herb. Guard cell lengths were not significantlyaffected by growth in the chambers or by elevated CO2 for eitherspecies. Growth within the chambers resulted in lower SLM inS. pitcheri, but CO2 concentration had no effect. In A. gerardii,SLM was lower at elevated CO2. These results indicate that stomataland leaf responses to elevated CO2 are species specific, andreinforce the need to assess chamber effects along with treatmenteffects (CO2) when using open-top chambers.Copyright 1994, 1999Academic Press Andropogon gerardii, elevated CO2, Salvia pitcheri, stomatal density, tallgrass prairie  相似文献   

11.
Pascopyrum smithii (C3) andBouteloua gracilis (C4) are importantforage grasses native to the Colorado shortgrass steppe. Thisstudy investigated photosynthetic responses of these grassesto long-term CO2enrichment and temperature in relation to leafnonstructural carbohydrate (TNC) and [N]. Glasshouse-grown seedlingswere transferred to growth chambers and grown for 49 d at twoCO2concentrations (380 and 750 µmol mol-1) at 20 and 35°C, and two additional temperatures (25 and 30 °C) at750 µmol mol-1CO2. Leaf CO2exchange rate (CER) was measuredat a plant's respective growth temperature and at two CO2concentrationsof approx. 380 and 700 µmol mol-1. Long-term CO2enrichmentstimulated CER in both species, although the response was greaterin the C3,P. smithii . Doubling the [CO2] from 380 to 750 µmolmol-1stimulated CER ofP. smithii slightly more in plants grownand measured at 30 °C compared to plants grown at 20, 25or 35 °C. CO2-enriched plants sometimes exhibited lowerCER when compared to ambient-grown controls measured at thesame [CO2], indicating photosynthetic acclimation to CO2growthregime. InP. smithii , such reductions in CER were associatedwith increases in TNC and specific leaf mass, reductions inleaf [N] and, in one instance, a reduction in leaf conductancecompared to controls. InB. gracilis , photosynthetic acclimationwas observed more often, but significant changes in leaf metabolitelevels from growth at different [CO2] were generally less evident.Temperatures considered optimal for growth (C3: 20 °C; C4:35 °C) sometimes led to CO2-induced accumulations of TNCin both species, with starch accumulating in the leaves of bothspecies, and fructans accumulating only inP. smithii. Photosynthesisof both species is likely to be enhanced in future CO2-enrichedand warmer environments, although responses will sometimes beattenuated by acclimation. Acclimation; blue grama (Bouteloua gracilis (H.B.K.) Lag ex Steud.); leaf nitrogen concentration; nonstructural carbohydrates; photosynthesis; western wheatgrass (Pascopyrum smithii (Rydb.) Love)  相似文献   

12.
The variations of leaf carbohydrate concentration, carbon isotopediscrimination () of leaf soluble carbohydrate, gas-exchangeand growth during a soil drying cycle under 350 and 700 µmolmol-1 CO2 concentrations ([CO2]) inQuercus robur seedlings wereanalysed. In well-watered conditions, a doubling of [CO2] causedan increase of CO2 assimilation rate (A) ( +47%) and a decreaseof stomatal conductance for water vapour (g) (–25%),anddoubled the intrinsic water-use efficiency (A/g). The valuesof A were not affected by elevated [CO2] which was consistentwith the 2-fold increase of A/g. Elevated [CO2 also significantlyincreased sucrose and starch leaf concentrations as well asaerial growth and plant dry weight. The stimulating effect ofCO2 enrichment on A and A/g was maintained in moderate droughtconditions, but disappeared in the most severe drought conditions.Drought induced an increase of hexose concentrations in both[CO2], but this effect was more pronounced under elevated [CO2],which may contribute to increase osmoregulation. From the onsetof drought, starch was depleted in both [CO2]. Carbon isotopediscrimination decreased in response to drought, which correspondedto an increase in A/g according to the two-step model of isotopicdiscrimination. In contrast, the A/g values derived from instantaneousleaf gas-exchange measurements decreased along the drying cycle.The discrepancy observed between the two independent estimatesof water-use efficiency is discussed in terms of time-scaleintegration. The results obtained with the isotopic approachusing soluble carbohydrate suggest a predominant stomatal limitationof CO2 assimilation in response to drought. Soil drying cycle,elevated CO2, leaf gas-exchange, leaf carbohydrate concentrations,carbon isotope discrimination, growth, Quercus robur. Key words: soil drying cycle, elevated CO2, leaf gas-exchange, leaf carbohydrate concentrations, carbon isotope discrimination, growth, Quercus robur  相似文献   

13.
Photosynthetic rates of outdoor-grown soybean (Glycine max L.Merr. cv. Bragg) canopies increased with increasing CO2 concentrationduring growth, before and after canopy closure (complete lightinterception), when measured over a wide range of solar irradiancevalues. Total canopy leaf area was greater as the CO2 concentrationduring growth was increased from 160 to 990 mm3 dm–3.Photosynthetic rates of canopies grown at 330 and 660 mm3 CO2dm–3 were similar when measured at the same CO2 concentrationsand high irradiance. There was no difference in ribulose bisphosphatecarboxylase/oxygenase (rubisco) activity or ribulose 1,5-bisphosphate(RuBP) concentration between plants grown at the two CO2 concentrations.However, photosynthetic rates averaged 87% greater for the canopiesgrown and measured at 660 mm3 CO2 dm–3. A 10°C differencein air temperature during growth resulted in only a 4°Cleaf temperature difference, which was insufficient to changethe photosynthetic rate or rubisco activity in canopies grownand measured at either 330 or 660 mm3 CO2 dm–3. RuBP concentrationsdecreased as air temperature during growth was increased atboth CO2 concentrations. These data indicate that the increasedphotosynthetic rates of soybean canopies at elevated CO2 aredue to several factors, including: more rapid development ofthe leaf area index; a reduction in substrate CO2 limitation;and no downward acclimation in photosynthetic capacity, as occurin some other species. Key words: CO2 concentration, soybean, canopy photosynthesis  相似文献   

14.
Rumex obtusifolius plants were grown for several months in daylitenvironment chambers (Solardomes) force-ventilated with aircontaining 350 or 600 µ;mol mol–1 C02. ElevatedCO2 was found to accelerate the natural ontogenic decline inphotosynthesis, but did not reduce leaf duration. In both CO2treatments photosynthetic rates declined progressively withincreasing leaf age, the decline being greater for plants grownin elevated C02 such that rates became lower than in ambientCO2. The degree of CO2-induced photosynthetic down-regulationas determined by A/C1 analysis was found to be dependent onleaf age. The major contribution to the decline in photosynthesiswas likely to be a reduction in Rubisco activity as changesin stomataland mesophyll limitations were small. Instantaneouswater use efficiency (WUE1) was greater for plants in elevatedCO2, but these values declined rapidly with leaf age, whereasin ambient CO2 values were always lower, but were maintainedfor longer. Growth analysis indicated an increased root:-shootratio for plants grown in elevated CO2, this occurring almostentirely as a result of increased root growth. Greater rootproliferation and increased WUE1, are characteristics whichshould give this persistent and troublesome weed an increasedcompetitive advantage under projected conditions of climatechange Key words: tusifoliu, elevated CO2, gas exchange, leaf age, senescence  相似文献   

15.
Agrostis capillaris L.5, Festuca vivipara L. and Poaalpina L.were grown in outdoor open-top chambers at either ambient (340 3µmol mol–1) or elevated (6804µmol mol–1)concentrations of atmospheric carbon dioxide (CO2) for periodsfrom 79–189 d. Photosynthetic capacity of source leaves of plants grown atboth ambient and elevated CO2 concentrations was measured atsaturating light and 5% CO2. Dark respiration of leaves wasmeasured using a liquid phase oxygen electrode with the buffersolution in equilibrium with air (21% O2, 0.034% CO2). Photo-syntheticcapacity of P. alpina was reduced by growth at 680 µmolmol–1 CO2 by 105 d, and that of F. vivipara was reducedat 65 d and 189 d after CO2 enrichment began, suggesting down-regulationor acclimation. Dark respiration of successive leaf blades ofall three species was unaltered by growth at 680 relative to340 µmol mol–1 CO2. In F. vivipara, leaf respirationrate was markedly lower at 189 d than at either 0 d or 65 d,irrespective of growth CO2 concentration. There was a significantlylower total non-structural carbohydrate (TNC) concentrationin the leaf blades and leaf sheaths of A. capillaris grown at680µmol mol–1 CO2. TNC of roots of A. capillariswas unaltered by CO2 treatment. TNC concentration was increasedin both leaves and sheaths of P. alpina and F. vivipara after105 d and 65 d growth, respectively. A 4-fold increase in thewater-soluble fraction (fructan) in P. alpina and in all carbohydratefractions in F. vivipara accounted for the increased TNC content. In F. vivipara the relationship between leaf photosyn-theticcapacity and leaf carbohydrate concentration was such that therewas a strong positive correlation between photosynthetic capacityand total leaf N concentration (expressed on a per unit structuraldry weight basis), and total nitrogen concentration of successivemature leaves reduced with time. Multiple regression of leafphotosynthetic capacity upon leaf nitrogen and carbohydrateconcentrations further confirmed that leaf photosynthetic capacitywas mainly determined by leaf N concentration. In P. alpina,leaf photosynthetic capacity was mainly determined by leaf CHOconcentration. Thus there is evidence for down-regulation ofphotosynthetic capacity in P. alpina resulting from increasedcarbohydrate accumulation in source leaves. Leaf dark respiration and total N concentration were positivelycorrelated in P. alpina and F. vivipara. Leaf dark respirationand soluble carbohydrate concentration of source leaves werepositively correlated in A. capillaris. Changes in source leafphotosynthetic capacity and carbohydrate concentration of plantsgrown at ambient or elevated CO2 are discussed in relation toplant growth, nutrient relations and availability of sinks forcarbon. Key words: Elevated CO2, Climate change, grasses, carbohydrate partitioning, photosynthesis, respiration  相似文献   

16.
Clonal plants of white clover (Trifolium repens L ), whollydependent on N2 fixation, were grown for 6 weeks in controlledenvironments providing either (C680 regime) 23/18 °C day/nighttemperatures and a CO2, concentration of 680 µmol mol–1,or (C340 regime) 20/15 °C day/night temperatures and a CO2,concentration of 340 µmol mol–1 During the firsthalf of the experimental period the C680 plants grew fasterthan their C340 counterparts so that by week 3 they were twicethe weight this 2 1 superiority in weight persisted until theend of the experiment The faster initial growth of the C680plants was based on an approx 70 % increase in leaf numbersand an approx 30 % increase in their individual area Initially,specific leaf area (cm2 g–1 leaf) was lower in C680 thanin C340 leaves but became similar in the latter half of theexperiment Shoot organ weights, including petioles and stolons,reflected the C680 plant's better growth in terms of photosyntheticsurface Throughout, C680 plants invested less of their weightin root than C340 plants and this disparity increased with timeAcetylene reduction assays showed that nitrogenase activityper unit nodule weight was the same in both C680 and C340 plantsBoth groups of plants invested about the same fraction of totalweight in nodules Nitrogen contents of plant tissues were similarirrespective of growth regime, but C680 expanded leaves containedslightly less nitrogen and their stolons slightly more nitrogenthan their C340 counterparts However, C680 leaves containedmore non-structural carbohydrate Young, unshaded C680 leavespossessed larger palisade cells, packed more tightly withinthe leaf, than equivalent C340 leaves The reason for the C680regime's loss of superiority in relative growth rate duringthe second half of the experiment was not clear, but more accumulationof non-structural carbohydrate, constriction of root growthand increased self-shading appear to be the most likely causes Trifolium repens, white clover, elevated CO2, elevated temperature, growth, N2 fixation, leaf structure  相似文献   

17.
The objectives of this study were to quantify changes in leaffreezing resistance and carbohydrate concentrations caused bylong-term (6 years) exposure to elevated CO2(ambient: 360 µll-1, elevated: 600 µl l-1) in five dominant plant speciesgrowing in situ in a native temperate grassland. Across allfive species tested from three functional groups, the mean temperatureat which all leaves were damaged (T100) significantly (P = 0.016)increased from -9.6 to -8.5 °C under elevated CO2 , anda similar marginally significant (P = 0.079) reduction was observedfor the mean temperature that caused 50% leaf damage (T50),from -6.7 to -6.0 °C. The mean temperature at which initialleaf damage was observed (T0) was not significantly influencedby elevated CO2 . Although concentrations of soluble sugars(+25%,P = 0.042), starch (+53%, P < 0.001), and total non-structuralcarbohydrates (TNC, +40%, P < 0.001) were significantly higherunder elevated CO2 , leaf freezing resistance actually decreasedunder elevated CO2 . Concentrations of soluble sugars were positivelycorrelated with freezing resistance when viewed across all fivecommunity dominants, but within any individual species, no suchrelationships were found. We also found no evidence for ouroriginal hypothesis that increased concentrations of solublesugars increase freezing resistance. Thus, future atmosphericCO2levels may instead increase the risk of late spring freezingdamage. Furthermore, the strong differences in freezing resistanceobserved among the species, along with decreased freezing resistance,may increase the risk of losing species that have inherentlyweak freezing resistances from the plant community. Copyright2001 Annals of Botany Company CO2enrichment, frost hardiness, sugar, starch, total non-structural carbohydrates (TNC)  相似文献   

18.
Mature second leaves of Lolium perenne L. cv. Vigor, were sampledin a spring and summer regrowth period. Effects of CO2enrichmentand increased air temperature on stomatal density, stomatalindex, guard cell length, epidermal cell density, epidermalcell length and mesophyll cell area were examined for differentpositions on the leaf and seasons of growth. Leaf stomatal density was smaller in spring but greater in summerin elevated CO2and higher in both seasons in elevated temperatureand in elevated CO2xtemperature relative to the respective controls.In spring, leaf stomatal index was reduced in elevated CO2butin summer it varied with position on the leaf. In elevated temperature,stomatal index in both seasons was lower at the tip/middle ofthe leaf but slightly higher at the base. In elevated CO2xtemperature,stomatal index varied with position on the leaf and betweenseasons. Leaf epidermal cell density was higher in all treatmentsrelative to controls except in elevated CO2(spring) and elevatedCO2xtemperature (summer), it was reduced at the leaf base. Inall treatments, stomatal density and epidermal cell densitydeclined from leaf tip to base, whilst guard cell length showedan inverse relationship, increasing towards the base. Leaf epidermalcell length and mesophyll cell area increased in elevated CO2inspring and decreased in summer. In elevated CO2xtemperatureleaf epidermal cell length remained unaltered in spring comparedto the control but decreased in summer. Stomatal conductancewas lower in all treatments except in summer in elevated CO2itwas higher than in the ambient CO2. These contrasting responses in anatomy to elevated CO2and temperatureprovide information that might account for differences in seasonalleaf area development observed in L. perenne under the sameconditions. Lolium perenne ; perennial ryegrass; elevated CO2and temperature; stomatal density; stomatal index; cell size  相似文献   

19.
Single clonal plants of white clover (Trifolium repens L) grownfrom explants in a Perlite rooting medium, and dependent fornitrogen on N2 fixation in root nodules, were grown for severalweeks in controlled environments which provided two regimesof CO2, and temperature 23/18 °C day/night temperaturesat 680 µmol mol–1 CO2, (C680), and 20/15 °Cday/night temperatures at 340 µmol mol–1 CO2 (C340)After 3–4 weeks of growth, when the plants were acclimatedto the environmental regimes, leaf and whole-plant photosynthesisand respiration were measured using conventional infra-red gasanalysis techniques Elevated CO2 and temperature increased ratesof photosynthesis of young, fully expanded leaves at the growthirradiance by 17–29%, despite decreased stomatal conductancesand transpiration rates Water use efficiency (mol CO2 mol H2O–1)was also significantly increased Plants acclimated to elevatedCO2, and temperature exhibited rates of leaf photosynthesisvery similar to those of C340 leaves ‘instantaneously’exposed to the C680 regime However, leaves developed in theC680 regime photosynthesised less rapidly than C340 leaves whenboth were exposed to a normal CO2, and temperature environmentIn measurements where irradiance was varied, the enhancementof photosynthesis in elevated CO2 at 23 °C increased graduallyfrom approx 10 % at 100 µmol m–1 s–1 to >27 % at 1170 µmol m–2 s–1 In parallel, wateruse efficiency increased by 20–40 % at 315 µmolm–2 s–1 In parallel, water use efficiency increasedby 20–40 % at 315 µmol m–2 s–1 In parallel,water use efficiency increased by 20–40 % at 315 µmolm–2 s–1 In parallel, water use efficiency increasedby 20–40 % at 315 µmol m–2 s–1 to approx100 % at the highest irradiance Elevated CO2, and temperatureincreased whole-plant photosynthesis by > 40 %, when expressedin terms of shoot surface area or shoot weight No effects ofelevated CO2 and temperature on rate of tissue respiration,either during growth or measurement, were established for singleleaves or for whole plants Dependence on N2, fixation in rootnodules appeared to have no detrimental effect on photosyntheticperformance in elevated CO2, and temperature Trifolium repens, white clover, photosynthesis, respiration, elevated CO2, elevated temperature, water use efficiency, N2 fixation  相似文献   

20.
Long-term effects of atmospheric carbon dioxide concentration(ambient or 700 µmol mol–1) and air temperature(simulation of field conditions or + 4 C) on leaf photosyntheticrate were examined in Lolium perenne L. cv. Vigor, exposed tonatural illumination during winter. Photosynthetic capacitywas compared over a range of air temperatures and photon fluxdensities of photosynthetically active radiation which wererepresentative of winter climate (5–15 C and 0–500µmol m–2s–1), with CO2 level during measurementsimilar to that during the experimental period. Long-term exposureto increased air temperature reduced leaf CO2 fixation capacityby 23% (averaged over all measurement conditions), resultingfrom a decline in lightsaturated uptake rate, but not in incident-lightquantum efficiency. CO2- stimulation was largely absent in plantsgrown in ambient temperature, but pronounced in plants grownunder +4 C, where it compensated for two-thirds of the 23%drop. This enhancing effect of elevated CO2 level on leaf CO2uptake rate observed in the warmer treatment, was strongly dependenton measurement temperature, increasing from 5% at 5 C, to upto 32% at 15 C. Measurements of chlorophyll fluorescence anddry matter corresponded with the observed changes in assimilationcapacity, which could not be attributed to a deteriorated nitrogenstatus of the leaves as there was a similar N content on anarea basis. Several hypotheses are considered to explain theobserved CO2-temperature interactions. Key words: Acclimation, chlorophyll fluorescence, elevated CO2 level, global warming, low temperature  相似文献   

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