Leaf senescence and late-season net photosynthesis of sun and shade leaves of overstory sweetgum (Liquidambar styraciflua) grown in elevated and ambient carbon dioxide concentrations

We examined the effects of elevated CO2 concentration ([CO2]) on leaf demography, late-season photosynthesis and leaf N resorption of overstory sweetgum (Liquidambar styraciflua L.) trees in the Duke Forest Free Air CO2 Enrichment (FACE) experiment. Sun and shade leaves were subdivided into early leaves (formed in the overwintering bud) and late leaves (formed during the growing season). Overall, we found that leaf-level net photosynthetic rates were enhanced by atmospheric CO2 enrichment throughout the season until early November; however, sun leaves showed a greater response to atmospheric CO2 enrichment than shade leaves. Elevated [CO2] did not affect leaf longevity, emergence date or abscission date of sun leaves or shade leaves. Leaf number and leaf area per shoot were unaffected by CO2 treatment. A simple shoot photosynthesis model indicated that elevated [CO2] stimulated photosynthesis by 60% in sun shoots, but by only 3% in shade shoots. Whole-shoot photosynthetic rate was more than 12 times greater in sun shoots than in shade shoots. In senescent leaves, elevated [CO2] did not affect residual leaf nitrogen, and nitrogen resorption was largely unaffected by atmospheric CO2 enrichment, except for a small decrease in shade leaves. Overall, elevated [CO2] had little effect on the number of leaves per shoot at any time during the season and, therefore, did not change seasonal carbon gain by extending or shortening the growing season. Stimulation of carbon gain by atmospheric CO2 enrichment in sweetgum trees growing in the Duke Forest FACE experiment was the result of a strong stimulation of photosynthesis throughout the growing season.     

Effects of CO2 enrichment on the photosynthetic light response of sun and shade leaves of canopy sweetgum (Liquidambar styraciflua) in a forest ecosystem

To investigate whether sun and shade leaves respond differently to CO2 enrichment, we examined photosynthetic light response of sun and shade leaves in canopy sweetgum (Liquidambar styraciflua L.) trees growing at ambient and elevated (ambient + 200 microliters per liter) atmospheric CO2 in the Brookhaven National Laboratory/Duke University Free Air CO2 Enrichment (FACE) experiment. The sweetgum trees were naturally established in a 15-year-old forest dominated by loblolly pine (Pinus taeda L.). Measurements were made in early June and late August 1997 during the first full year of CO2 fumigation in the Duke Forest FACE experiment. Sun leaves had a 68% greater leaf mass per unit area, 63% more leaf N per unit leaf area, 27% more chlorophyll per unit leaf area and 77% greater light-saturated photosynthetic rates than shade leaves. Elevated CO2 strongly stimulated light-saturated photosynthetic rates of sun and shade leaves in June and August; however, the relative photosynthetic enhancement by elevated CO2 for sun leaves was more than double the relative enhancement of shade leaves. Elevated CO2 stimulated apparent quantum yield by 30%, but there was no interaction between CO2 and leaf position. Daytime leaf-level carbon gain extrapolated from photosynthetic light response curves indicated that sun leaves were enhanced 98% by elevated CO2, whereas shade leaves were enhanced 41%. Elevated CO2 did not significantly affect leaf N per unit area in sun or shade leaves during either measurement period. Thus, the greater CO2 enhancement of light-saturated photosynthesis in sun leaves than in shade leaves was probably a result of a greater amount of nitrogen per unit leaf area in sun leaves. A full understanding of the effects of increasing atmospheric CO2 concentrations on forest ecosystems must take account of the complex nature of the light environment through the canopy and how light interacts with CO2 to affect photosynthesis.     

Sapwood development in Pinus radiata trees grown for three years at ambient and elevated carbon dioxide partial pressures

Clonal trees of Pinus radiata D. Don were grown in open-top chambers at a field site in New Zealand for 3 years at ambient (37 Pa) or elevated (65 Pa) carbon dioxide (CO2) partial pressure. Nitrogen (N) was supplied to half of the trees in each CO2 treatment, at 15 g N m-2 in the first year and 60 g N m-2 in the subsequent 2 years (high-N treatment). Trees in the low-N treatment were not supplied with N but received the same amount of other nutrients as trees in the high-N treatment. In the first year, stem basal area increased more in trees growing at elevated CO2 partial pressure and high-N supply than in control trees, suggesting a positive interaction between these resources. However, the relative rate of growth became the same across trees in all treatments after 450 days, resulting in trees growing at elevated CO2 partial pressure and high-N supply having larger basal areas than trees in the other treatments. Sapwood N content per unit dry mass was consistently about 0.09% in all treatments, indicating that N status was not suppressed by elevated CO2 partial pressure. Thus, during the first year of growth, an elevated CO2 partial pressure enhanced carbon (C) and N storage in woody stems, but there was no further stimulus to C and N deposition after the first year. The chemical composition of sapwood was unaffected by elevated CO2 partial pressure, indicating that no additional C was sequestered through lignification. However, independent of the treatments, early wood was 13% richer in lignin than late wood. Elevated CO2 partial pressure decreased the proportion of sapwood occupied by the lumina of tracheids by up to 12%, indicating increased sapwood density in response to CO2 enrichment. This effect was probably a result of thicker tracheid walls rather than narrower lumina.     

Isoprene emission, photosynthesis, and growth in sweetgum (Liquidambar styraciflua) seedlings exposed to short- and long-term drying cycles

Isoprene emissions were studied in one-year old sweetgum (Liquidambar styraciflua L.) seedlings during nine drying-rewatering cycles extending over five months. Each drying cycle lasted to the point of leaf wilting. Growth was essentially stopped in response to the first drying cycle, though seedling survival and capacity to recover turgor on rewatering remained high throughout the entire nine cycles. Photosynthetic rates of leaves were inhibited by the drying treatments. Under severe drought, isoprene emission rates of leaves were also inhibited, though isoprene emission was generally less sensitive to drought than photosynthesis. The lower drought sensitivity of isoprene emission compared with photosynthesis resulted in a higher percentage of fixed carbon lost as isoprene as seedlings became more stressed. During the recovery phase of the drying-rewatering cycles, isoprene emission rates in several seedlings were higher than in well-watered control seedlings. Following the ninth drying-rewatering cycle, sustained daily watering resulted in recovery of isoprene emission rates to control values within four days. Photosynthetic rates only recovered to 50% of control values after seven days. We conclude that the mechanisms regulating photosynthetic rate and isoprene emission rate are differentially influenced by limited water supplies. The results are consistent with past studies that predict a protective role for isoprene emission during stress, particularly protection from excessive leaf temperatures during drought.     

Wood properties of Scots pines (Pinus sylvestris) grown at elevated temperature and carbon dioxide concentration

Impacts of elevated temperature and carbon dioxide concentration ([CO2]) on wood properties of 15-year-old Scots pines (Pinus sylvestris L.) grown under conditions of low nitrogen supply were investigated in open-top chambers. The treatments consisted of (i) ambient temperature and ambient [CO2] (AT+AC), (ii) ambient temperature and elevated [CO2] (AT+EC), (iii) elevated temperature and ambient [CO2] (ET+AC) and (iv) elevated temperature and elevated [CO2] (ET+EC). Wood properties analyzed for the years 1992-1994 included ring width, early- and latewood width and their proportions, intra-ring wood density (minimum, maximum and mean, as well as early- and latewood densities), mean fiber length and chemical composition of the wood (cellulose, hemicellulose, lignin and acetone extractive concentration). Absolute radial growth over the 3-year period was 54% greater in AT+EC trees and 30 and 25% greater in ET+AC and ET+EC trees, respectively, than in AT+AC trees. Neither elevated temperature nor elevated [CO2] had a statistically significant effect on ring width, early- and latewood widths or their proportions. Both latewood density and maximum intra-ring density were increased by elevated [CO2], whereas fiber length was increased by elevated temperature. Hemicellulose concentration decreased and lignin concentration increased significantly in response to elevated temperature. There were no statistically significant interaction effects of elevated temperature and elevated [CO2] on the wood properties, except on earlywood density.     

Direct inhibition of maintenance respiration in western hemlock roots exposed to ambient soil carbon dioxide concentrations

Root respiration often exhibits a direct and immediate decline with increasing concentrations of ambient soil carbon dioxide concentration ([CO(2)]), and recent evidence suggests this decline may be attributable to a decline in maintenance respiration within the root. If true, this concept could provide a clue to the biochemical process underlying respiratory inhibition as well as improve our knowledge of the timing and degree to which this inhibition occurs in nature. To test the hypothesis that maintenance respiration exhibits a direct, negative response to increasing [CO(2)], we measured total respiration in intact root systems of western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedlings grown at different relative growth rates and exposed to soil [CO(2)]s ranging from 91 to 7008 &mgr;mol mol(-1). Analysis of covariance was used to separate maintenance from total respiration. Total respiration declined exponentially with increasing [CO(2)]. Maintenance respiration, which comprised 85% of total respiration over all treatments, also declined exponentially with increasing [CO(2)]. Growth respiration was not inhibited at any [CO(2)]. These findings may explain why roots of some fast-growing species do not show [CO(2)] inhibition.     

Growth and annual ring structure of Larix sibirica grown at different carbon dioxide concentrations and nutrient supply rates

We compared effects of ambient (360 vpm) and elevated (720 vpm) carbon dioxide concentration ([CO2]) and high and low nutrient supply rates on stem growth, annual ring structure and tracheid anatomy of Siberian larch (Larix sibirica Ledeb.) seedlings over two growing seasons. Elevated [CO2] had no significant effect on either stem height or diameter growth; however, both stem height and diameter growth were enhanced by the high nutrient supply rate, and these increases were stimulated by elevated [CO2]. Elevated [CO2] tended to increase the width of the annual xylem ring, the number of cells in a radial file spanning the ring, and tracheid lumen diameter, whereas it tended to reduce cell wall thickness, although there were no statistically significant CO2 effects on tracheid anatomy. Changes in tracheid cell morphology seemed to be dependent on changes in shoot elongation rates.     

Diameter growth of Scots pine (Pinus sylvestris) trees grown at elevated temperature and carbon dioxide concentration under boreal conditions

We investigated the impacts of elevated temperature and carbon dioxide concentration ([CO2]) on diameter growth of Scots pine (Pinus sylvestris L.), aged about 20 years, grown with a low nitrogen supply in closed chambers at (i) ambient temperature and [CO2] (AT+AC), (ii) ambient temperature and elevated [CO2] (AT+EC), (iii) elevated temperature and ambient [CO2] (ET+AC), and (iv). elevated temperature and [CO2] (ET+EC). Each treatment was replicated four times. Diameter growth was monitored with a band dendrograph at 15-min intervals throughout the growing seasons of 1997, 1998 and 1999. Over the monitoring period, diameter growth began 2-3 weeks earlier in trees in the ET+EC and ET+AC chambers than in trees in the AT+AC and AT+EC chambers. However, the cessation of growth occurred about a week later in trees in the ET+EC, ET+AC and AT+EC chambers compared with the AT+AC chambers. The duration of the growing season was 115 and 108 days in the ET+EC and ET+AC chambers, respectively, and 95 and 84 days in the AT+EC and AT+AC chambers, respectively. The ET+AC and ET+EC treatments enhanced diameter growth most early in the growing season, whereas in trees in the AT+AC and AT+EC treatments diameter growth rate was highest in the middle of the growing season. Diameter growth rate leveled off more slowly in trees in the ET+EC and AT+EC treatments than in the other treatments. The growth response to elevated T, elevated [CO2] or both decreased with time and it was less than the maximum observed in other studies for small seedlings and under optimal growth conditions. Nevertheless, cumulative diameter growth for the 3-year period was 67% greater in trees in the ET+EC treatment, and 57 and 26% greater in trees in the AT+EC and ET+AC treatments, respectively, compared with trees in the AT+AC treatment. Over the 3 years, [CO2] had a statistically significant (P < 0.10) effect on both absolute and relative diameter growth, but the interaction between [CO2] and temperature was not significant.     

Temperature responses of growth and wood anatomy in European beech saplings grown in different carbon dioxide concentrations

Effects of temperature on growth and wood anatomy were studied in young European beech (Fagus sylvatica L.) grown in 7-l pots for 2.5 years in field-phytotron chambers supplied with an ambient (approximately 400 micromol mol-1) or elevated (approximately 700 micromol mol-1) carbon dioxide concentration ([CO2]). Temperatures in the chambers ranged in increments of 2 degrees C from -4 degrees C to +4 degrees C relative to the long-term mean monthly (day and night) air temperature in Berlin-Dahlem. Soil was not fertilized and soil water and air humidity were kept constant. Data were evaluated by regression analysis. At final harvest, stem diameter was significantly greater at increased temperature (Delta1 degrees C: 2.4%), stems were taller (Delta1 degrees C: 8.5%) and stem mass tree-1 (Delta1 degrees C: 10.9%) and leaf area tree-1(Delta1 degrees C: 6.5%) were greater. Allocation pattern was slightly influenced by temperature: leaf mass ratio and leaf area ratio decreased with increasing temperature (Delta1 degrees C: 2.3% and 2.2% respectively), whereas stem mass/total mass increased (Delta1 degrees C: 2.1%). Elevated [CO2] enhanced height growth by 8.8% and decreased coarse root mass/total mass by 10.3% and root/shoot ratio by 11.7%. Additional carbon was mainly invested in aboveground growth. At final harvest a synergistic interaction between elevated [CO2] and temperature yielded trees that were 3.2% taller at -4 degrees C and 12.7% taller at +4 degrees C than trees in ambient [CO2]. After 2.5 seasons, cross-sectional area of the oldest stem part was approximately 32% greater in the +4 degrees C treatment than in the -4 degrees C treatment, and in the last year approximately 67% more leaf area/unit tree ring area was produced in the highest temperature regime compared with the lowest. Elevated [CO2] decreased mean vessel area of the 120 largest vessels per mm2 by 5.8%, causing a decrease in water conducting capacity. There was a positive interaction between temperature and elevated [CO2] for relative vessel area, which was approximately 38% higher at +4 degrees C than at -4 degrees C in elevated [CO2] compared with ambient [CO2]. Overall, temperature had a greater effect on growth than [CO2], but elevated [CO2] caused quantitative changes in wood anatomy.     

Relationships between net photosynthesis and foliar nitrogen concentrations in a loblolly pine forest ecosystem grown in elevated atmospheric carbon dioxide

We examined the effects of elevated carbon dioxide concentration ([CO2]) on the relationship between light-saturated net photosynthesis (A(sat)) and area-based foliar nitrogen (N) concentration (N(a)) in the canopy of the Duke Forest FACE experiment. Measurements of A(sat) and N(a) were made on two tree species growing in the forest overstory and four tree species growing in the forest understory, in ambient and elevated [CO2] FACE rings, during early and late summer of 1999, 2001 and 2002, corresponding to years three, five and six of CO2 treatment. When measured at the growth [CO2], net photosynthetic rates of each species examined in the forest overstory and understory were stimulated by elevated [CO2] at each measurement date. We found no effect of elevated [CO2] on N(a) in any of the species. The slope of the A(sat)-N relationship was 81% greater in elevated [CO2] than in ambient [CO2] when averaged across all sample dates, reflecting a differential CO2 effect on photosynthesis at the top and bottom of the canopy. We compared A(sat)-N relationships in trees grown in ambient and elevated [CO2] at two common CO2 concentrations, during late summer 2001 and both early and late 2002, to determine if the stimulatory effect of elevated [CO2] on photosynthesis diminishes over time. At all three sample times, neither the slopes nor the y-intercepts of the A(sat)-N relationships of trees grown in ambient or elevated [CO2] differed when measured at common CO2 concentrations, indicating that the responses of photosynthesis to long-term elevated [CO2] did not differ from the responses to a short-term increase in [CO2]. This finding, together with the observation that N(a) was unaffected by growth in elevated [CO2], indicates that these overstory and understory trees growing at the Duke Forest FACE experiment continue to show a strong stimulation of photosynthesis by elevated [CO2].     

Phosphorus supply affects the photosynthetic capacity of loblolly pine grown in elevated carbon dioxide

Effects of phosphorus supply and mycorrhizal status on the response of photosynthetic capacity to elevated CO(2) were investigated in loblolly pine (Pinus taeda L.) seedlings. Seedlings were grown in greenhouses maintained at either 35.5 or 71.0 Pa CO(2) in a full factorial experiment with or without mycorrhizal inoculum (Pisolithus tinctorius (Pers.) Coker & Couch) and with an adequate or a limiting supply of phosphorus. Assimilation versus internal CO(2) partial pressure (C(i)) curves were used to estimate maximum Rubisco activity (V(c,max)), electron transport mediated ribulose 1,5-bisphosphate regeneration capacity (J(max)), phosphate regeneration capacity (PiRC) and daytime respiration rates (R(d)). Nonmycorrhizal seedlings grown with limiting phosphorus had significantly reduced V(c,max) and PiRC compared to seedlings in other treatments. Elevated CO(2) increased photosynthetic capacity in nonmycorrhizal seedlings in the low phosphorus treatment by increasing PiRC, whereas it induced phosphorus limitation in mycorrhizal seedlings in the low phosphorus treatment and did not affect the photosynthetic capacity of seedlings in the high phosphorus treatment. Despite the variety of effects on photosynthetic capacity, seedlings in the elevated CO(2) treatments had higher net assimilation rates than seedlings in the ambient CO(2) treatments. We conclude that phosphorus supply affects photosynthetic capacity during long-term exposure to elevated CO(2) through effects on Rubisco activity and ribulose 1,5-bisphosphate regeneration rates.     

Influence of elevated CO2 and mycorrhizae on nitrogen acquisition: contrasting responses in Pinus taeda and Liquidambar styraciflua

An understanding of root system capacity to acquire nitrogen (N) is critical in assessing the long-term growth impact of rising atmospheric CO2 concentration ([CO2]) on trees and forest ecosystems. We examined the effects of mycorrhizal inoculation and elevated [CO2] on root ammonium (NH4+) and nitrate (NO3-) uptake capacity in sweetgum (Liquidambar styraciflua L.) and loblolly pine (Pinus taeda L.). Mycorrhizal treatments included inoculation of seedlings with the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck & Smith in sweetgum and the ectomycorrhizal (EM) fungus Laccaria bicolor (Maire) Orton in loblolly pine. These plants were then equally divided between ambient and elevated [CO2] treatments. After 6 months of treatment, root systems of both species exhibited a greater uptake capacity for NH4+ than for NO3-. In both species, mycorrhizal inoculation significantly increased uptake capacity for NO3-, but not for NH4+. In sweetgum, the mycorrhizal effect on NO3- and NH4+ uptake capacity depended on growth [C02]. Similarly, in loblolly pine, the mycorrhizal effect on NO3- uptake capacity depended on growth [CO2], but the effect on NH4+ uptake capacity did not. Mycorrhizal inoculation significantly enhanced root nitrate reductase activity (NRA) in both species, but elevated [CO2] increased root NRA only in sweetgum. Leaf NRA in sweetgum did not change significantly with mycorrhizal inoculation, but increased in response to [CO2]. Leaf NRA in loblolly pine was unaffected by either treatment. The results indicate that the mycorrhizal effect on specific root N uptake in these species depends on both the form of inorganic N and the mycorrhizal type. However, our data show that in addressing N status of plants under high [CO2], reliable prediction is possible only when information about other root system adjustments (e.g., biomass allocation to fine roots) is simultaneously considered.     

Long-term elevation of atmospheric CO(2) concentration and the carbon exchange rates of saplings of Pinus taeda L. and Liquidambar styraciflua L

The relationship between carbon exchange rate (CER) and internal CO(2) concentration was measured in leaves of saplings of Liquidambar styraciflua L. (sweetgum) and Pinus taeda L. (loblolly pine) grown from seed for more than 14 months at atmospheric CO(2) concentrations of either 350 or 500 microl l(-1). An elevated concentration of CO(2) during growth reduced CER at any given internal CO(2) concentration in sweetgum, but not in loblolly pine. Stomatal limitation of CER showed little response to concentration of CO(2) during measurement, but was higher in both species when grown at 500 than at 350 microl l(-1) CO(2). The net effect of a long-term increase in CO(2) concentration from 350 to 500 microl l(-1) was an increase in CER of loblolly pine, but a slight decrease in CER of sweetgum. It is suggested that the depression of CER in sweetgum resulted from a reduction in the activity of ribulose-1,5-bisphosphate carboxylase-oxygenase.     

Exposure to elevated carbon dioxide concentration in the dark lowers the respiration quotient of Vitis cane wood

Cane cuttings of the grapevine rootstock Vitis rupestris Scheele x V. riparia Michx. cv. 3309 Couderc were brought out of endodormancy by warming at 30 degrees C. Cane pieces (12 to 13 cm long) with nodes containing a primary bud were placed in a gas exchange system and monitored for net respiratory fluxes of CO2 and O2. Grapevine respiration rates expressed on a wood volume basis were 1.4 to 3.4 mmol CO2 or O2 m-3s-1, which is higher than stem respiration rates reported for many other woody taxa but similar to rates measured for ecodormant buds of other Vitis species. Passive water loss from canes was 0.7 to 1.2 mmol H2O m-3s-1. During a 7-day period, nonstructural carbohydrate concentrations in cane wood declined only slightly, whereas sucrose was nearly completely consumed. When ambient CO2 concentration ([CO2]) was raised from 300 to 750 micro molmol-1 and then 2000 micromol mol-1, net CO2 exchange rates declined by 5.9 +/- 0.6 and then 11.0 +/- 0.6%, whereas net O2 consumption rates remained about constant. The mean respiration quotient (net CO2/O2 flux) for canes with intact ecodormant buds was 0.99 +/- 0.03 when the [CO2] was 300 micromol mol-1, and decreased to 0.87 +/- 0.03 and 0.088 +/- 0.02 when the [CO2] was increased to 750 and 2000 micromol mol-1, respectively. The results support the hypothesis that, in Vitis canes, inhibition of respiratory CO2 efflux in response to high [CO2] is an indirect consequence of non-photosynthetic carboxylation reactions, and not a result of inhibition of respiratory metabolism.     

Interaction of spittlebug and forage grass under different carbon dioxide concentrations

This study evaluated the impact of different CO₂ levels on the biological characteristics of Mahanarva spectabilis (Distant) and on the performance of forage grasses. The signal grasses Brachiaria decumbens Stapf (susceptible) and Brachiaria brizantha (A. Rich.) (resistant), the elephant grass Pennisetum purpureum (Schum.), including the Roxo de Botucatu cultivar (susceptible) and the Pioneiro cultivar (resistant) and the insects were kept in climate-controlled chambers with constant low (250 ppm) CO₂ levels, constant high (500 ppm) CO₂ levels, or fluctuating CO₂ levels (mean, 368 ppm). Among these three CO₂ treatments, no significant differences were found in the nymphal survival of M. spectabilis when the nymphs were fed on two signal grass species. On the other hand, under a constant low CO₂ level (250 ppm), nymphal survival rates were significantly lower when the insects were kept in Roxo de Botucatu and Pioneiro cultivars. The mean adult longevity values for M. spectabilis were not significantly different among the three levels of CO₂ evaluated. We observed that increased CO₂ levels improved the performance of M. spectabilis and elephant grass cultivars in accumulating dry mass, which was not evident in signal grass. We further conclude that the levels of susceptibility and resistance of the forages tested will be maintained in future scenarios under which atmospheric CO₂ levels are expected to increase.     

Variations in dark respiration and mitochondrial numbers within needles of Pinus radiata grown in ambient or elevated CO2 partial pressure

Within-leaf variations in cell size, mitochondrial numbers and dark respiration rates were compared in the most recently expanded tip, the mid-section and base of needles of Pinus radiata D. Don trees grown for 4 years in open-top chambers at ambient (36 Pa) or elevated (65 Pa) carbon dioxide partial pressure (p(CO2)a). Mitochondrial numbers and respiratory activity varied along the length of the needle, with the highest number of mitochondria per unit cytoplasm and the highest rate of respiration per unit leaf area at the base of the needle. Regardless of the location of the cells (tip, middle or basal sections), needles collected from trees grown in elevated p(CO2)a had nearly twice the number of mitochondria per unit cytoplasm as those grown in ambient p(CO2)a. This stimulation of mitochondrial density by growth at elevated p(CO2)a was greater at the tip of the needle (2.7 times more mitochondria than in needles grown in ambient CO2) than at the base of the needle (1.7 times). The mean size of individual mitochondria was unaffected either by growth at elevated p(CO2)a or by position along the needle. Tree growth at elevated p(CO2)a had a variable effect on respiration per unit leaf area, significantly increasing respiration in the tip of the needles (+25%) and decreasing respiration at the mid-section and base of the needles (-14% and -25%, respectively). Although a simple relationship between respiration per unit leaf area and mitochondrial number per unit cytoplasm was found within each CO2 treatment, the variable effect of growth at elevated p(CO2)a on respiration along the length of the needles indicates that a more complex relationship must determine the association between structure and function in these needles.     

Effects of elevated concentrations of ozone and carbon dioxide on the electrical impedance of leaves of silver birch (Betula pendula) clones

Effects of elevated concentrations of tropospheric ozone ([O3]) and carbon dioxide ([CO2]) on leaves of two silver birch (Betula pendula Roth) clones were monitored for three growing seasons (1998, 1999, 2000) by means of electrical impedance spectroscopy (EIS). The field trial with open-top chambers (OTCs) was conducted on two clones (Clone 4 and Clone 80) with five treatments and four independent replicates. Treatments were: (1) outside control, (2) chamber control, (3) 2x ambient [O3], (4) 2x ambient [CO2] and (5) 2x ambient [CO2] + 2x ambient [O3]. Fumigations started in 1999 and continued in 2000. Measurements were made in 1998 before the fumigations and thereafter EIS was carried out four times in each season. The impedance spectra of about 10 leaves from each tree at each time were measured at 42 frequencies between 80 and 1 MHz. Leaf spectra were modeled by a distributed circuit element model (DCE) (one DCE in series with a resistor), which yields the extracellular and intracellular resistances, the relaxation time and the distribution coefficient of the relaxation time. The EIS properties of the leaves changed significantly during the growing season when new leaves were expanding. The clones differed in their EIS properties. Clone 4 had a significantly higher extracellular resistance and distribution coefficient than Clone 80. The clones responded similarly to the fumigation treatments. Differences between treatments emerged especially during the second fumigation season in 2000. Elevated [O3] reduced both the relaxation time and the extracellular resistance, indicating cell membrane damage. Elevated [CO2] increased the intracellular resistance, indicating changes in symplastic composition. The biological interpretation of the EIS parameters in birch leaves is discussed.     

Lignification in beech (Fagus sylvatica) grown at elevated CO2 concentrations: interaction with nutrient availability and leaf maturation

Beech (Fagus sylvatica L.) seedlings were grown in an ambient or elevated CO2 concentration ([CO2]) either in small stands in microcosms for three to four seasons or individually in pots fertilized at different nutrient supply rates. Leaves at different stages of development, as well as stems and roots at the end of the growing season, were used for analysis of structural biomass and lignin. In elevated [CO2], lignification of leaves was slightly retarded compared with structural biomass production and showed a strong correlation with the activities of ionically, cell-wall-bound peroxidases but not with total soluble peroxidases or covalently wall-bound peroxidases. The effect of elevated [CO2] on lignin concentration of mature tissues was dependent on nutrient supply rate. In leaves and roots, elevated [CO2] increased the lignin concentration in dry mass in N-limited plants. In seedlings grown with high nutrient supply, the lignin concentration in dry mass was unaffected or diminished by elevated [CO2]. Because elevated [CO2] enhanced seedling growth in the high nutrient supply treatments, the total amount of lignin produced per seedling was higher in these treatments. We predict that long-term sequestration of carbon will increase as long as biomass production is stimulated by elevated [CO2] and that tissue quality will change depending on developmental stage and nutrient availability.     

Biochemical acclimation patterns of Betula pendula and Pinus sylvestris seedlings to elevated carbon dioxide concentrations

Acclimation of photosynthesis to increasing atmospheric carbon dioxide concentration ([CO2]; 350 to 2,000 micromol mol-1) was followed in silver birch (Betula pendula Roth.) and Scots pine (Pinus sylvestris L.) seedlings for two years. Chlorophyll fluorescence and concentrations of Rubisco, chlorophyll, total soluble protein and nitrogen were monitored together with steady-state gas exchange at three CO2 concentrations (ambient [CO2] (345 +/- 20 micromol mol-1), the growth [CO2] and 1950 +/- 55 micromol mol-1). Rubisco and chlorophyll concentrations decreased in birch and Scots pine with increasing growth [CO2]. A nonlinear response was recorded for Rubisco and chlorophyll concentrations in birch, which was correlated with a significant decrease in specific leaf area. Nitrogen concentration decreased in birch leaves, but was unchanged in Scots pine needles. The species differed substantially in their steady-state CO2 exchange response to increasing growth [CO2]. The principal effect in birch was a significant nonlinear decrease in the steady-state gas exchange rate at the ambient [CO2], whereas in Scots pine the main effect was a significant increase in the steady-state gas exchange rate at the growth [CO2].     

Chlorophyll and carotenoid concentrations in two varieties of Pinus ponderosa seedlings subjected to long-term elevated carbon dioxide

Two varieties of ponderosa pine (Pinus ponderosa Dougl. var. scopulorum (Rocky Mountain variety) and P. ponderosa var. ponderosa (Sierran variety)) seedlings were subjected to elevated atmospheric CO(2) for two and a half years. The CO(2) concentrations were ambient, ambient + 75 microl l(-1), ambient + 150 microl l(-1) and ambient + 300 microl l(-1), or approximately 350, 425, 500 and 650 microl l(-1) CO(2). After one and a half years of exposure to elevated CO(2) and until the end of the study, seedlings of both varieties showed symptoms of stress including mottling, mid-needle abscission and early senescence. In both varieties, exposure to CO(2) concentrations greater than ambient + 75 microl l(-1) resulted in lower chlorophyll a, chlorophyll b and carotenoid concentrations. At elevated CO(2) concentrations, the concentrations of pigments in needles of the Sierran variety were lower than those in the Rocky Mountain variety. Also, at elevated CO(2) concentrations, the pigment concentrations in the 1-year-old needles of both P. ponderosa varieties were lower than those in current-season needles.