Interaction of gibberellic acid and photoperiod on leaf sheath elongation in normal and gibberellin-insensitive genotype of wheat

Effect of gibberellic acid (GA₃) on leaf sheath elongation in a normal (cv. Møystad) and a gibberellin(GA)-insensitive (cv. Siete Cerros) genotype of wheat ( Triticum aestivum L.) were studied at 18 and 12°C under short (SD, 12 h) or long (LD, 24 h) photoperiod. Leaf sheath length in cv. Møystad was signficantly increased by exogenous GA₃ both under SD and LD. LD alone stimulated leaf sheath elongation and the combined effect of LD and GA₃ was additive, and there was no statistically signficant interaction between photoperiod and GA₃ concentrations. Leaf sheath length in cv. Siete Cerros was not significantly affected by GA₃ under any conditions. However, there was a highly significant stimulation of leaf sheath elongation by LD in cv. Siete Cerros as well. These results indicate that stimulation of elongation growth in wheat leaves by LD is not mediated by gibberellin.     

Effects of exogenously applied growth regulators on shoot growth of inbred lines of Plantago major differing in relative growth rate: differential response to gibberellic acid and (2-chloroethyl)-trimethyl-ammonium chloride

The possibility of modulating shoot growth charaeteristics of seedlings of two inbred lines of Plantago major L., differing in relative growth rate (RGR), by exogenously applied 6-benzylaminopurine (BA), α-naphthalene acetic acid (NAA), (gibberellic acid (GA₃) and (2-chloroethyl)-trimethyl-ammonium chloride (CCC) was investigated. BA completely inhibited growth of the shoot at a concentration of 1 m M , while lower concentrations had no effect. NAA reduced growth of the shoot at 10 ü M , while 1 m M completely inhibited growth. Addition of 10 μ M GA₃ or higher stimulated shoot fresh weight up to 20% and leaf area up to 30% for the slow growing inbred line (W9), but less for the fast growing line (A4). Application of 1 m M CCC, an inhibitor of gibberellin metabolism, reduced growth of both inbred lines, but to a larger extent in the fast growing seedlings.
The lower shoot growth of W9 was associated with a lower specific leaf area (SLA) and a higher dry matter percentage of the shoot, as compared with A4. NAA reduced growth by reducing SLA and increasing leaf thickness, but the percentage dry matter of the leaves was unaffected. Stimulation of the shoot growth by GA₃ application was associated with higher SLA and lower dry matter percentage. Application of CCC had opposite effects on SLA and dry matter percentage as compared with GA₃. GA seems to be involved in the regulation of at least part of the genetic difference in RGR in Plantago major .     

Internode length in Lathyrus odoratus. The involvement of gibberellins

Evidence was obtained by gas chromatography-mass spectrometry and gas chromatography-selected ion monitoring for the presence of gibberellin A₂₀), GA₁, GA₂₉, GA₈ and 2-epiGA₂₉ in vegetative shoots of tall sweet pea, Lathyrus odoratus L. Both tall (genotype L –) and dwarf (genotype II ) sweet peas elongated markedly in response to exogenous GA₁ attaining similar internode lengths at the highest dose levels. Likewise internode length in both genotypes was reduced by application of the GA biosynthesis inhibitor, PP333. The ratio of leaflet length to width was reduced by application of PP333 to tall plants and this effect was reversed by GA₁. When applied to plants previously treated with PP333, GA₂₀ promoted internode elongation of L – plants as effectively as GA₁, but GA₂₉ was not as effective as GA₁ when applied to II plants. In contrast, GA₂₀ and GA₁ were equally effective when applied to the semidwarf lb mutant but GA-treated lblb plants did not attain the same internode length as comparable GA-treated Lb – plants. The difference in stature between the tall and dwarf types persisted in dark-grown plants. It is concluded that GA₁ may be important for internode elongation and leaf growth in sweet pea. Mutant l may influence GA₁ synthesis by reducing 3β-hydroxylation of GA₂₀ whereas mutant lb appears to affect GA sensitivity.     

Effects of prohexadione (BX-112) and gibberellins on shoot growth in seedlings of Salix pentandra

Effects of gibberellins A₁, A_4/7, A₉, A₁₉ and A₂₀ and growth retardants were studied on shoot elongation in seedlings of Salix pentandra L. The growth-retarding effects of CCC and ancymidol were antagonized by all the gibberellins tested. The novel plant growth regulator prohexadione (free acid of BX-112), which is suggested to block 3β-hydroxylation of gibberellins, effectively prevented shoot elongation in seedlings grown under long photoperiod. Initiation of new leaves was only slightly reduced. GA₁, but not GA₁₉ and GA₂₀, was active in overcoming the inhibition of stem elongation of seedlings, treated with prohexadione, GA₁₉, GA₂₀ and GA₁ are native in S. pentandra , and the results are compatible with the hypothesis that GA₁ is active per se in shoot elongation, and that the effect of GA₁₉ and GA₂₀ is dependent on their conversion to GA₁.
A mixture of GA₄ and GA₇ was as active as GA₁ in promoting shoot elongation in seedlings treated with prohexadione, while GA₉ showed slight activity only when applied at high doses.     

Interaction of potassium ions and gibberellin in the control of hypocotyl growth in Amaranthus caudatus

Potassium promotes growth in several plant tissues. Elongation growth of the hypocotyls of Amaranthus caudatus L. ev. Lalsag is mainly controlled by gibberellins, but K⁺ also promotes growth. In the present study the interaction of K⁺ with gibberellin (GA₃) and chlorocholine chloride (CCC) has been investigated. When K⁺ was applied externally in the dark, hypocotyl growth was promoted in the seedlings. External application of GA₃ did not promote growth in the dark. GA₃ was effective in the light and K⁺ was synergistic with GA₃ in promoting elongation. Application of CCC in the dark makes the seedlings sensitive to GA₃. The inhibition of growth by CCC was also reversed by K⁺. The results indicate a possible role of K⁺ in GA₃ induced elongation of hypocotyls.     

Inhibitory and promotive effects of gibberellic acid on floral initiation and development in Poa pratensis and Bromus inermis

Flowering in Poa pratensis L. cv. Holt and Bromus inermis Leyss. cv. Manchar requires exposure to short days (SD) for primary induction to occur, followed by long days (LD) to allow the inflorescence to develop. Weekly sprays with gibberellic acid (GA₃) during primary induction inhibited flower initiation in both P. pratensis and B. inermis . With 10⁻⁴ M GA₃ flowering of P. pratensis was suppressed even after an induction period of 10 weeks. Since both GA₃ and non-inductive LD conditions greatly stimulate leaf elongation, the degree of primary induction was closely negatively correlated with plant height (leaf sheath and blade length) at the end of the induction period. GA₃ application or the interpolation of LD during SD induction were most inhibitory during the later middle part of the SD period, whereas they were stimulatory near the beginning or immediately before the SD period. We suggest that changes in the portfolio or levels of endogenous gibberellins mediate photoperiodic control of growth and floral initiation in these plants. However, GA₃ sprays could not substitute for LD in causing heading and culm elongation in SD induced plants of the two species. The results are discussed in the light of results with other plants with dual floral induction requirements.     

Gibberellin status and responsiveness in shoots of tall and dwarf genotypes of diploid rye (Secale cereale)

The recessive dwarfing alleles of rye ( Secale cereale L.), ct1 and ct2 , caused a 35–55% reduction in the length of leaf 2 compared with corresponding tall lines grown at both 10°C and 20°C. The dwarf lines were 45–50% as responsive to applied GA₃ as the tall lines at 20°C but the absolute GA-responsiveness of the dwarfs was greater at 10°C than at 20°C. There was no significant difference in the contents of GA₁₉, GA₂₀, GA₂₉, GA₁, GA₃ and GA₈ in the leaf extension zone of tall and dwarf seedlings grown at 20°C. It was concluded that the mechanism whereby GA homeostasis is maintained is functional in both tall and dwarf lines despite marked differences in leaf extension rate. The recessive rye mutations may cause loss of function late in the GA-cell elongation pathway or, alternatively, indirectly affect GA-responsiveness in vegetative tissues. The genetic and physiological evidence indicates that ct1 and ct2 are unrelated to the GA-insensitive Rht genes in hexaploid bread wheat.     

Photoperiodic control of endogenous gibberellins in seedlings of Salix pentandra

In the temperate-zone woody species Salix pentandra elongation growth is regulated by the photoperiod. Long days sustain active growth, whereas short days induce cessation of apical growth, which is a prerequisite for winter hardening. It is shown that this is correlated to quantitative changes in levels of endogenous GA₁₉ GA₂₀, and GA₁. Within two short days the amount of the active GA₁ and its immediate precursor GA₂₀, decreased markedly in young leaves us well as in stem tissue. Also, the amount of GA¹⁹, declined, but the decrease was delayed relative to that of GA₁ and GA₂₀. The ability of S. pentandra seedlings to respond to exogenous GA₁₉, decreased with increasing numbers of short days. Observations that support the hypothesis that the level of GA₁ in S. pentandra is regulated by the photoperiod in a quantitative mode with conversion of GA₁₉, to GA₂₀, being one target for control.
Different distribution of GAs in various plant parts was observed. The level of GA was higher in young leaves than in other plant parts, and the amount of GA₁₉ was 5–10 times higher in stem tissue than in leaves and roots. The ratios of GA₈ to GA¹ and GA₂₀, were higher in roots as compared with other parts, as rods contained very low levels of GA₁ and GA₂₀, but amounts of GA₂₀ comparable with other parts.     

CO2 enrichment, drought stress and growth of Alaska pea plants (Pisum sativum)

The interaction of CO₂ enrichment and drought on water status and growth of pea plants was investigated. Pisum sativum L. (cv. Alaska) plants were grown from seeds in growth chambers using 350 and 675 μl I1 CO₂, a photon flux density of 600 μmol M-2 S-1, a 16 h photoperiod and a temperature regime of 20/14°C. The drought treatment was started at the beginning of branch initiation and lasted for 9 or 11 days. The water status of the plants was monitored daily by measuring total leaf water potential and stomatal conductance. The total leaf water potential of well-watered plants was not affected by the CO₂ level. Under draughting conditions total leaf water potential decreased, with a slower decrease under the high CO₂ regime, due, at least in part, to reduced stomatal conductance. Upon rewatering, total leaf water potential and stomatal conductance recovered within one day. High CO₂ counteracted the reduction in height and, to some extent, leaf area that developed in low CO₂ unwatered plants. Additional CO₂ had no effect on branch number and did not prevent the complete inhibition of branch development that resulted from drought stress. Removing the drought conditions resulted in a rapid recovery of the internal water status and also a rapid recovery of most, but not all, plant growth parameters.     

Stimulation of shoot elongation in Salix pentandra by gibberellin A9; activity appears to be dependent upon hydroxylation to GAl via GA20

Cessation of shoot elongation in seedlings of Salix pentandra L. is induced by short photoperiod. Gibbereliin A₉ (GA₉) applied either to the apical bud or injected into a mature leaf, induced shoot elongation under a short photoperiod of 12 h, and GA₉ could completely substitute for a transfer to a long photoperiod. When [³H]GA₉ or [²H₂]GA₉ was injected into a leaf, no [³H]GA₉ was detected in the elongating apex and only traces of [³H]GA₉ were found in the shoot above the treated leaf. By the use of gas chromatography-mass spectrometry (GC-MS), [²H₂]GA₂₀ was identified as the main metabolite of [²H₂]GA₉ in both the shoot and the treated leaf. In addition, [²H₂]GA₁ and [²H₂]GA₂₉ were also identified as metabolites of [²H₂]GA₉. These results are consistent with the hypothesis that exogenous GA, promotes shoot elongation in Salix through its metabolism to GA₂₀ and GA,.     

Biological activity, identification and quantification of gibberellins in seedlings of Norway spruce (Picea abies) grown under different photoperiods

Short photoperiod induces growth cessation in seedlings of Norway spruce ( Picea abies (L.] Karst.). Application of different gibberellins (GAS) to seedlings growing under a short photoperiod show that GA₉ and GA₂₀ can not induce growth. In contrast application of GA, and GA₄ induced shoot elongation. The results indicate that 3β-hydroxylation of GA₉ to GA₄ and of GA₂₀ to GA₁ is under photoperiodic control. To confirm that conclusion, both qualitative and quantitative analyses of endogenous GAs were performed. GA₁, GA₃, GA₄, GA₇, GA₉, GA₁₂, GA₁₅, GA₁₅, GA₂₀, GA₂₉, GA₃₄ and GA₅₁ were identified by combined gas chromatography-mass spectrometry in shoots of Norway spruce seedlings. The effect of photoperiod on GA levels was determined by using deuterated and ¹⁴C-labelled GAs as intermal standards. In short days, the amounts of GA₉, GA₄ and GA₁ are less than in plants grown in continuous light. There is no significant difference in the amounts of GA₃, GA₁₂, and GA₂₀ between the different photoperiods. The lack of accumulation of GA₉ and GA₂₀ under short days is discussed.     

Effects of di-n-butyl phthalate on growth and photosynthesis in algae and on isolated organelles from higher plants

Di- n -butyl phthalate (DBF) is widely used as a plasticizer and has been found in all types of ecosystems. It inhibits growth and photosynthesis of green algae ( Chlorella emersonii CCAP strain 211/8 h and Selenastrum capricornutum CCAP strain 278/4) at concentrations higher than 10-⁵ M . The IC₅₀ value for CO₂-dependent oxygen evolution in algae was 3 × 10^-4M. The CO₂-reduction in isolated protoplasts prepared from barley ( Hordeum vulgare L. cv. Simba) was also inhibited by phthalate. The IC₅₀ value was 2 × 10^-4 M . The electron transport in isolated thylakoids prepared from spinach was inhibited with an IC₅₀ value of 3 × 10^-4 M . The IC₅₀ value for uncoupled electron transport extrapolated to zero chlorophyll concentration was 2.5 × 10^-5 M . The effect of di-n-butyl phthalate was localized to reactions in photosystem II. Di-n-butyl phthalate could thus be a pollutant which affects growth and photosynthesis of plants. The reported IC₅₀ values may be underestimated since di- n -butyl phthalate can attach to surfaces. The results are discussed in relation to observed effects of di- n -butyl phthalate on other organisms.     

Photosynthesis, growth and nutrient changes in non-nodulated Phaseolus vulgaris grown under atmospheric and elevated carbon dioxide conditions

The response of Phaseolus vulgaris L. cv. Contender grown under controlled environment at either ambient or elevated (360 and 700 μmol mol^-1, respectively) CO₂ concentrations ([CO₂]), was monitored from 10 days after germination (DAG) until the onset of senescence. Elevated CO₂ had a pronounced effect on total plant height (TPH), leaf area (LA), leaf dry weight (LD), total plant biomass (TB) accumulation and specific leaf area (SLA). All of these were significantly increased under elevated carbon dioxide with the exception of SLA which was significantly reduced. Other than high initial growth rates in CO₂-enriched plants, relative growth rates remained relatively unchanged throughout the growth period. While the trends in growth parameters were clearly different between [CO₂], some physiological processes were largely transient, in particular, net assimilation rate (NAR) and foliar nutrient concentrations of N, Mg and Cu. CO₂ enrichment significantly increased NAR, but from 20 DAG, a steady decline to almost similar levels to those measured in plants grown under ambient CO₂ occurred. A similar trend was observed for leaf N content where the loss of leaf nitrogen in CO₂-enriched plants after 20 DAG, was significantly greater than that observed for ambient-CO₂ plants. Under enhanced CO₂, the foliar concentrations of K and Mn were increased significantly whilst P, Ca, Fe and Zn were reduced significantly. Changes in Mg and Cu concentrations were insignificant. In addition. high CO₂ grown plants exhibited a pronounced leaf discoloration or chlorosis, coupled with a significant reduction in leaf longevity.     

The role of temperature in determining the stimulation of CO2 assimilation at elevated carbon dioxide concentration in soybean seedlings

Soybean ( Glycine max cv. Clark) was grown at both ambient (ca 350 μmol mol⁻¹) and elevated (ca 700 μmol mol⁻¹) CO₂ concentration at 5 growth temperatures (constant day/night temperatures of 20, 25, 30, 35 and 40°C) for 17–22 days after sowing to determine the interaction between temperature and CO₂ concentration on photosynthesis (measured as A, the rate of CO₂ assimilation per unit leaf area) at both the single leaf and whole plant level. Single leaves of soybean demonstrated increasingly greater stimulation of A at elevated CO₂ as temperature increased from 25 to 35°C (i.e. optimal growth rates). At 40°C, primary leaves failed to develop and plants eventually died. In contrast, for both whole plant A and total biomass production, increasing temperature resulted in less stimulation by elevated CO₂ concentration. For whole plants, increased CO₂ stimulated leaf area more as growth temperature increased. Differences between the response of A to elevated CO₂ for single leaves and whole plants may be related to increased self-shading experienced by whole plants at elevated CO₂ as temperature increased. Results from the present study suggest that self-shading could limit the response of CO₂ assimilation rate and the growth response of soybean plants if temperature and CO₂ increase concurrently, and illustrate that light may be an important consideration in predicting the relative stimulation of photosynthesis by elevated CO₂ at the whole plant level.     

Relation between relative growth rate, endogenous gibberellins, and the response to applied gibberellic acid for Plantago major

Relationships between relative growth rate (RGR), endogenous gibberellin (GA) concentration and the response to application of gibberellic acid (GA₃) were studied for two inbred lines of Plantago major L., which differed in RGR. A4, the fast-growing inbred line, had a higher free GA concentration than the slow-growing W9, as analyzed by enzyme immunoassay. GA₃ application increased total plant weight and RGR₃ particularly for the slow-growing line. Chlorophyll a content and photosynthetic activity per unit leaf area were decreased, while transpiration rate was unaffected by GA₃ application. The increase in RGR by GA₃ application was associated with an increased leaf weight ratio; specific leaf area and percentage of dry matter in the leaves were only temporarily affected. Root respiration rate per unit dry weight was unaffected.
The correlation between low RGR, low GA concentration and high responsiveness to applied GA₃ supports the contention that gibberellins are involved in the regulation of RGR. However, the transient influence of GA₃ application on some growth components suggests the involvement of other regulatory factors in addition to GA.     

Growth and photosynthetic response of three soybean cultivars to simultaneous increases in growth temperature and CO2

Three soybean ( Glycine max L. Merr.) cultivars (Maple Glen, Clark and CNS) were exposed to three CO₂ concentrations (370, 555 and 740 μmol mol⁻¹) and three growth temperatures (20/15°, 25/20° and 31/26°C, day/night) to determine intraspecific differences in single leaf/whole plant photosynthesis, growth and partitioning, phenology and final biomass. Based on known carboxylation kinetics, a synergistic effect between temperature and CO₂ on growth and photosynthesis was predicted since elevated CO₂ increases photosynthesis by reducing photorespiration and photorespiration increases with temperature. Increasing CO₂ concentrations resulted in a stimulation of single leaf photosynthesis for 40–60 days after emergence (DAE) at 20/15°C in all cultivars and for Maple Glen and CNS at all temperatures. For Clark, however, the onset of flowering at warmer temperatures coincided with the loss of stimulation in single leaf photosynthesis at elevated CO₂ concentrations. Despite the season-long stimulation of single leaf photosynthesis, elevated CO₂ concentrations did not increase whole plant photosynthesis except at the highest growth temperature in Maple Glen and CNS, and there was no synergistic effect on final biomass. Instead, the stimulatory effect of CO₂ on growth was delayed by higher temperatures. Data from this experiment suggest that: (1) intraspecific variation could be used to select for optimum soybean cultivars with future climate change; and (2) the relationship between temperature and CO₂ concentration may be expressed differently at the leaf and whole plant levels and may not solely reflect known changes in carboxylation kinetics.     

Flooding, gas exchange and hydraulic root conductivity of highbush blueberry

Highbush blueberry plants ( Vaccinium corymbosum L. cv. Bluecrop) growing in containers were flooded in the laboratory for various durations to determine the effect of flooding on carbon assimilation, photosynthetic response to varying CO₂ and O₂ concentrations and apparent quantum yield as measured in an open flow gas analysis system. Hydraulic conductivity of the root was also measured using a pressure chamber. Root conductivity was lower and the effect of increasing CO₂ levels on carbon assimilation less for flooded than unflooded plants after short-(i-2 days), intermediate-(10–14 days) and long-term (35–40 days) flooding. A reduction in O₂ levels surrounding the leaves from 21 to 2% for unflooded plants increased carbon assimilation by 33% and carboxylation efficiency from 0.012 to 0.021 mol CO₂ fixed (mol CO₂)⁻¹. Carboxylation efficiency of flooded plants, however, was unaffected by a decrease in percentage O₂, averaging 0.005 mol CO₂ fixed (mol CO₂)⁻¹. Apparent quantum yield decreased from 2.2 × 10⁻¹ mol of CO₂ fixed (mol light)⁻¹ for unflooded plants to 2.0 × 10⁻³ and 9.0 × 10⁻⁴ for intermediate- and long-term flooding durations, respectively. Shortterm flooding reduced carbon assimilation via a decrease in stomatal conductance, while longer flooding durations also decreased the carboxylation efficiency of the leaf.     

Elevated CO2 enhances stomatal responses to osmotic stress and abscisic acid in Arabidopsis thaliana

A , carbon assimilation rate
ABA, abscisic acid
Ci , intercellular space CO₂ concentration
g , leaf conductance
WUE, water use efficiency

Carbon dioxide and abscisic acid (ABA) are two major signals triggering stomatal closure. Their putative interaction in stomatal regulation was investigated in well-watered air-grown or double CO₂-grown Arabidopsis thaliana plants, using gas exchange and epidermal strip experiments. With plants grown in normal air, a doubling of the CO₂ concentration resulted in a rapid and transient drop in leaf conductance followed by recovery to the pre-treatment level after about two photoperiods. Despite the fact that plants placed in air or in double CO₂ for 2 d exhibited similar levels of leaf conductance, their stomatal responses to an osmotic stress (0·16–0·24 MPa) were different. The decrease in leaf conductance in response to the osmotic stress was strongly enhanced at elevated CO₂. Similarly, the drop in leaf conductance triggered by 1 μ M ABA applied at the root level was stronger at double CO₂. Identical experiments were performed with plants fully grown at double CO₂. Levels of leaf conductance and carbon assimilation rate measured at double CO₂ were similar for air-grown and elevated CO₂-grown plants. An enhanced response to ABA was still observed at high CO₂ in pre-conditioned plants. It is concluded that: (i) in the absence of stress, elevated CO₂ slightly affects leaf conductance in A. thaliana ; (ii) there is a strong interaction in stomatal responses to CO₂ and ABA which is not modified by growth at elevated CO₂.     

Adjustments of net photosynthesis in Solanum tuberosum in response to reciprocal changes in ambient and elevated growth CO2 partial pressures

Single leaf photosynthetic rates and various leaf components of potato ( Solanum tuberosum L.) were studied 1–3 days after reciprocally transferring plants between the ambient and elevated growth CO₂ treatments. Plants were raised from individual tuber sections in controlled environment chambers at either ambient (36 Pa) or elevated (72 Pa) CO₂. One half of the plants in each growth CO₂ treatment were transferred to the opposite CO₂ treatment 34 days after sowing (DAS). Net photosynthesis (P_n) rates and various leaf components were then measured 34, 35 and 37 DAS at both 36 and 72 Pa CO₂. Three-day means of single leaf P_n rates, leaf starch, glucose, initial and total Rubisco activity, Rubisco protein, chlorophyll ( a + b ), chlorophyll ( a/b ), α -amino N, and nitrate levels differed significantly in the continuous ambient and elevated CO₂ treatments. Acclimation of single leaf P_n rates was partially to completely reversed 3 days after elevated CO₂-grown plants were shifted to ambient CO₂, whereas there was little evidence of photosynthetic acclimation 3 days after ambient CO₂-grown plants were shifted to elevated CO₂. In a four-way comparison of the 36, 72, 36 to 72 (shifted up) and 72 to 36 (shifted down) Pa CO₂ treatments 37 DAS, leaf starch, soluble carbohydrates, Rubisco protein and nitrate were the only photosynthetic factors that differed significantly. Simple and multiple regression analyses suggested that negative changes of P_n in response to growth CO₂ treatment were most closely correlated with increased leaf starch levels.     

Effects of elevated CO2 concentration on photosynthesis, respiration and carbohydrate status of coppice Populus hybrids

To determine how increased atmospheric CO₂ will affect the physiology of coppiced plants, sprouts originating from two hybrid poplar clones ( Populus trichocarpa × P. deltoides - Beaupre and P. deltoides × P. nigra - Robusta) were grown in open-top chambers containing ambient or elevated (ambient + 360 μmol mol⁻¹) CO₂ concentration. The effects of elevated CO₂ concentration on leaf photosynthesis, stomatal conductance, dark respiration, carbohydrate concentration and nitrogen concentration were measured. Furthermore, dark respiration of leaves was partitioned into growth and maintenance components by regressing specific respiration rate vs specific growth rate. Sprouts of both clones exposed to CO₂ enrichment showed no indication of photosynthetic down-regulation. During reciprocal gas exchange measurements, CO₂ enrichment significantly increased photosynthesis of all sprouts by approximately 60% ( P < 0.01) on both an early and late season sampling date, decreased stomatal conductance of all sprouts by 10% ( P < 0.04) on the early sampling date and nonsignificantly decreased dark respiration by an average of 11%. Growth under elevated CO₂ had no consistent effect on foliar sugar concentration but significantly increased foliar starch by 80%. Respiration rate was highly correlated with both specific growth rate and percent nitrogen. Long-term CO₂ enrichment did not significantly affect the maintenance respiration coefficient or the growth respiration coefficient. Carbon dioxide enrichment affected the physiology of the sprouts the same way it affected these plants before they were coppiced.