秋枫和木棉对大气臭氧浓度升高的生理响应

以秋枫Bischofi a javanica Bl.和木棉Bombax malabaricum DC.苗木为试验材料,采用自行设计的开顶式熏气室装置,研究在4种体积分数的臭氧(O3)[E200,Φ(O3)=200×10-9;E100,Φ(O3)=100×10-9;E50,Φ(O3)=50×10-9;环境大气NF,Φ(O3)=10×10-9~20×10-9]下2种植物叶片可溶性糖含量、可溶性蛋白质含量、保护酶活性和膜脂过氧化程度的变化情况,旨在探究在地表臭氧浓度升高的条件下2种植物的生理生化指标的变化情况及其响应机理。结果显示:随臭氧浓度的增加,2种植物膜透性和丙二醛含量均逐渐上升,且与臭氧浓度呈显著正相关关系,说明2种植物膜脂过氧化程度加剧;秋枫可溶性蛋白含量均逐渐下降,木棉先降低后大幅上升;二者可溶性糖含量均是先上升后小幅度下降;POD活性均是先降低后升高;秋枫CAT活性呈先升高再降低的趋势,木棉则是逐渐降低。对2种植物各生理指标进行主成分分析表明,2种植物耐臭氧能力顺序为秋枫木棉。     

Radiation-use efficiency of a forest exposed to elevated concentrations of atmospheric carbon dioxide

We compared radiation-use efficiency of growth (epsilon;), defined as rate of biomass accumulation per unit of absorbed photosynthetically active radiation, of forest plots exposed to ambient (approximately 360 micro l l-1) or elevated (approximately 560 micro l l-1) atmospheric CO2 concentration ([CO2]). Large plots (30-m diameter) in a loblolly pine (Pinus taeda L.) plantation, which contained several hardwood species in the understory, were fumigated with a free-air CO2 enrichment system. Biomass accumulation of the dominant loblolly pines was calculated from monthly measurements of tree growth and site-specific allometric equations. Depending on the species, leaf area index (L*) was estimated by three methods: optical, allometric and litterfall. Based on the relationship between tree height and diameter during the first 3 years of exposure, we conclude that elevated [CO2] did not alter the pattern of aboveground biomass allocation in loblolly pine. There was considerable variation in L* estimates by the different methods; total L* was 18-42% lower when estimated by the optical method compared with estimates from allometric calculations, and this discrepancy was reduced when optical measurements were corrected for the non-random distribution of loblolly pine foliage. The allometric + litterfall approach revealed a seasonal maximum total L* of 6.2-7.1 with about 1/3 of the total from hardwood foliage. Elevated [CO2] had only a slight effect on L* in the first 3 years of this study. Mean epsilon; (+/- SD), calculated for loblolly pine only, was 0.49 +/- 0.05 and 0.62 +/- 0.04 g MJ-1 for trees in the ambient and elevated [CO2] plots, respectively. The 27% increase in epsilon; in response to CO2 enrichment was caused primarily by the stimulation of biomass increment, as there was only a small effect of elevated [CO2] on L* during the initial years of fumigation. Long-term increases in atmospheric [CO2] can increase epsilon; in closed-canopy forests but the absolute magnitude and duration of this increase remain uncertain.     

Carbon content variation in boles of mature sugar maple and giant sequoia

At present, a carbon (C) content of 50% (w/w) in dry wood is widely accepted as a generic value; however, few wood C measurements have been reported. We used elemental analysis to investigate C content per unit of dry matter and observed that it varied both radially and vertically in boles of two old-growth tree species: sugar maple (Acer saccharum Marsh.) and giant sequoia (Sequoiadendron giganteum (Lindl.) Bucholz). In sugar maple there was considerable variation in tree ring widths among four radii for particular annual layers of xylem, revealing that the annual rate of C assimilation differs around the circumference and from the base of each tree to its top, but the observed variation in C content was unrelated to diameter growth rate and strongly related to the calendar year when the wood was formed. Carbon content in sugar maple wood increased in an approximately linear fashion, from < 50 to 51% from pith to cambium, at both the base and top of the boles. In giant sequoia, C was essentially constant at > 55% across many hundreds of years of heartwood, but it declined abruptly at the sapwood-heartwood boundary and remained lower in all sapwood samples, an indication that heartwood formation involves anabolic metabolism. Factors that may be responsible for the different C contents and trends with age between sugar maple and sequoia trees are considered. Tree-ring data from this study do not support some of the key assumptions made by dendrochronology.     

Sap flux in pure aspen and mixed aspen-birch forests exposed to elevated concentrations of carbon dioxide and ozone

Elevated concentrations of atmospheric carbon dioxide ([CO2]) and tropospheric ozone ([O3]) have the potential to affect tree physiology and structure and hence forest water use, which has implications for climate feedbacks. We investigated how a 40% increase above ambient values in [CO2] and [O3], alone and in combination, affect tree water use of pure aspen and mixed aspen-birch forests in the free air CO2-O3 enrichment experiment near Rhinelander, Wisconsin (Aspen FACE). Measurements of sap flux and canopy leaf area index (L) were made during two growing seasons, when steady-state L had been reached after more than 6 years of exposure to elevated [CO2] and [O3]. Maximum stand-level sap flux was not significantly affected by elevated [O3], but was increased by 18% by elevated [CO2] averaged across years, communities and O(3) regimes. Treatment effects were similar in pure aspen and mixed aspen-birch communities. Increased tree water use in response to elevated [CO2] was related to positive CO2 treatment effects on tree size and L (+40%). Tree water use was not reduced by elevated [O3] despite strong negative O3 treatment effects on tree size and L (-22%). Elevated [O3] predisposed pure aspen stands to drought-induced sap flux reductions, whereas increased tree water use in response to elevated [CO2] did not result in lower soil water content in the upper soil or decreasing sap flux relative to control values during dry periods. Maintenance of soil water content in the upper soil in the elevated [CO2] treatment was at least partly a function of enhanced soil water-holding capacity, probably a result of increased organic matter content from increased litter inputs. Our findings that larger trees growing in elevated [CO2] used more water and that tree size, but not maximal water use, was negatively affected by elevated [O3] suggest that the long-term cumulative effects on stand structure may be more important than the expected primary stomatal closure responses to elevated [CO2] and [O3] in determining stand-level water use under possible future atmospheric conditions.     

Effect of pruning severity and timing of treatment on epicormic sprout development in giant sequoia

Giant sequoia (Sequoiadendron giganteum (Lindl.) Buchh.) treeswere pruned monthly over a 12-month period to assess the effectsof timing of pruning operations on epicormic sprout development.Trees were pruned to three pruning heights in each month. Periodiccounts of total sprouts and measurement of the length of thelongest sprout were used to assess sprout development followingpruning. Sprouting was initially delayed following pruning duringgrowing season months as compared with non-growing season months.Six years after study initiation, greater numbers of sproutsand larger maximum branch lengths were found from pruning outsidethe May through September growing season. These differenceswere most pronounced in the first years following treatmentbut differences diminished markedly after 6 years. However,a logistic model to predict the probability of sprouting indicatesthat pruning severity was a much more significant explanatoryvariable than season of pruning. Seasonal differences in epicormicsprout development may be temporary and are of less importancein affecting sprout development than pruning severity. Epicormicsprouts also occurred with greater frequency on the south orexposed side of pruned tree boles.     

Silver birch and climate change: variable growth and carbon allocation responses to elevated concentrations of carbon dioxide and ozone

We studied the effects of elevated concentrations of carbon dioxide ([CO2]) and ozone ([O3]) on growth, biomass allocation and leaf area of field-grown O3-tolerant (Clone 4) and O3-sensitive clones (Clone 80) of European silver birch (Betula pendula Roth) trees during 1999-2001. Seven-year-old trees of Clones 4 and 80 growing outside in open-top chambers were exposed for 3 years to the following treatments: outside control (OC); chamber control (CC); 2 x ambient [CO2] (EC); 2 x ambient [O3] (EO); and 2 x ambient [CO2] + 2 x ambient [O3] (EC+EO). When the results for the two clones were analyzed together, elevated [CO2] increased tree growth and biomass, but had no effect on biomass allocation. Total leaf area increased and leaf abscission was delayed in response to elevated [CO2]. Elevated [O3] decreased dry mass of roots and branches and mean leaf size and induced earlier leaf abscission in the autumn; otherwise, the effects of elevated [O3] were small across the clones. However, there were significant interactions between elevated [CO2] and elevated [O3]. When results for the clones were analyzed separately, stem diameter, volume growth and total biomass of Clone 80 were increased by elevated [CO2] and the stimulatory effects of elevated [CO2] on stem volume growth and total leaf area increased during the 3-year study. Clone 80 was unaffected by elevated [O3]. In Clone 4, elevated [O3] decreased root and branch biomass by 38 and 29%, respectively, whereas this clone showed few responses to elevated [CO2]. Elevated [CO2] significantly increased total leaf area in Clone 80 only, which may partly explain the smaller growth responses to elevated [CO2] of Clone 4 compared with Clone 80. Although we observed responses to elevated [O3], the responses to the EC+EO and EC treatments were similar, indicating that the trees only responded to elevated [O3] under ambient [CO2] conditions, perhaps reflecting a greater quantity of carbohydrates available for detoxification and repair in elevated [CO2].     

Effects of elevated concentrations of atmospheric CO2 and tropospheric O3 on decomposition of fine roots

Rising atmospheric carbon dioxide (CO2) concentration ([CO2]) could alter terrestrial carbon (C) cycling by affecting plant growth, litter chemistry and decomposition. How the concurrent increase in tropospheric ozone (O3) concentration ([O3]) will interact with rising atmospheric [CO2] to affect C cycling is unknown. A major component of carbon cycling in forests is fine root production, mortality and decomposition. To better understand the effects of elevated [CO2] and [O3] on the dynamics of fine root C, we conducted a combined field and laboratory incubation experiment to monitor decomposition dynamics and changes in fine root litter chemistry. Free-air CO2 enrichment (FACE) technology at the FACTS-II Aspen FACE project in Rhinelander, Wisconsin, elevated [CO2] (535 microl 1-1) and [O3] (53 nl 1-1) in intact stands of pure trembling aspen (Populus tremuloides Michx.) and in mixed stands of trembling aspen plus paper birch (Betula papyrifera Marsh.) and trembling aspen plus sugar maple (Acer saccharum Marsh.). We hypothesized that the trees would react to increased C availability (elevated [CO2]) by increasing allocation to C-based secondary compounds (CBSCs), thereby decreasing rates of decomposition. Because of its lower growth potential, we reasoned this effect would be greatest in the aspen-maple community relative to the aspen and aspen-birch communities. As a result of decreased C availability, we expected elevated [O3] to counteract shifts in C allocation induced by elevated [CO2]. Concentrations of CBSCs were rarely significantly affected by the CO2 and O3 treatments in decomposing fine roots. Rates of microbial respiration and mass loss from fine roots were unaffected by the treatments, although the production of dissolved organic C differed among communities. We conclude that elevated [CO2] and [O3] induce only small changes in fine root chemistry that are insufficient to significantly influence fine root decomposition. If changes in soil C cycling occur in the future, they will most likely be brought about by changes in litter production.     

城市蒙古栎对近地层臭氧浓度升高的光合生理响应

近地层O3浓度的增加已经成为当今环境科学研究的热点问题之一,该文主要模拟沈阳城市森林的常用绿化树种蒙古栎对近地层O3浓度升高的光合生理响应,为沈阳市城市采林树种的选育提供理论依据.本试验利用开顶式气室研究蒙古栎叶片对臭氧浓度升高的光合生理响应.结果表明,蒙古栎叶片在高浓度O3熏蒸下,净光合速率、光合色素、光合产物、光合电子传递和光合磷酸化指标随着熏蒸时间的延长而呈现出先上升后下降的趋势,相对电导率呈上升趋势.在通气30d时,净光合速率、类胡萝卜紊含量、ATP酶及淀粉含量均与对照达到差异极显著(p＜0.01),而叶绿素含量与对照差异显著(p＜0.05);在通气90d时,净光合速率和类胡萝卜素含量与对照差异显著(p＜0.05),而叶绿素含量和Mg2+-ATP酶活性与对照差异极显著(p＜0.01).在臭氧浓度升高条件下,蒙古栎叶片光合作用能力下降.     

A comparison of latewood pits,fibril orientation,and shrinkage of normal and compression wood of giant sequoia

Summary Giant sequoia latewood compression wood (CW) tracheids had pit canals that flared toward the lumen with extended poorly defined inner apertures that paralleled the fibrils in the S2 walls. Boiling and drying of CW and normal wood (NW) blocks induced split extensions at the CW pit aperture grooves but not at the NW pit apertures. These split extensions of the CW pit apertures were present also in longitudinal microsections. The mean fibril angle of 21 to 25 degrees of this well-defined CW was appreciably below the 45 degrees frequently reported. The CW tangential/radial shrinkage ratio of about 1 was distinetly lower than NW (1.6 and 2.1), and appeared to be the result of much lower tangential shrinkage. Both NW and CW specimens when dried quickly in an oven at 100° C had higher shrinkage (long., tang. and rad.) than when air-dried first at lower temperature and higher relative humidity.The SEM photographs were made in the Electronics Research Laboratory which is under the direction of Dr. T. E. Everhart who has a Cambridge Stereoscan Mark II SEM operated under NIH Grant No. G. M. 17523.     

Response of canopy stomatal conductance of Acacia mangium forest to environmental driving factors

Granier’s probes were applied to measure the sap flow of 14 sample trees in an Acacia mangium forest on the hilly lands in Heshan City, Guangdong, during the time period of October, 2003. The photosynthetically active radiation (PAR), air relative humidity (RH) and temperature of air (T) above the forest canopy were recorded. The sap flow measurement was used in combination with morphological characteristics of tree and forest structure to calculate the whole-tree transpiration (E), stand transpiration (E _t), and mean canopy stomatal conductance (g _c). Analyses on the relationships between tree morphological characters and whole-tree water use, and on the responses of g _c to PAR and vapor pressure deficit (D) were conducted. The results showed that whole-tree transpiration correlated significantly and positively with tree diameter at breast height (DBH) (p<0.0001), with sapwood area (p<0.0001), and with canopy size (p = 0.0007) logarithmically, but exponentially with tree height (p = 0.014). The analyses on the responses of canopy stomatal conductance showed that the maximum g _c (g _cmax) changed with PAR in a hyperbolic curve (p<0.0001) and with D in a logarithmic one (p<0.0001). The results obtained with sap flow technique indicate its reliability and accuracy of the methods of estimation of whole-tree and stand transpirations and canopy stomatal conductance. __________ Translated from Chinese Journal of Applied Ecology, 2006, 17(7): 1149–1156 [译自: 应用生态学报]     

A comparison of static bending,compression and tension parallel to grain and toughness properties of compression wood and normal wood of a giant sequoia

Summary Compression wood (CW) of the giant sequoia studied had higher values than normal wood (NW) in crushing strength and ultimate stress in tension parallel to grain, in toughness, in modulus of rupture, and in work to maximum load and total work in static bending. In the green condition CW had higher values than NW in stress at the proportional limit and work to the proportional limit, and about the same modulus of elasticity in static bending. In the dry condition CW was about equivalent to NW in work to the proportional limit, but was slightly weaker in stress at proportional limit and modulus of elasticity in static bending. The compression wood of this giant sequoia, even though formed when the tree was suppressed and having relatively narrow rings, can therefore be said to be essentially equivalent to normal wood so far as the mechanical properties tested in this study are concerned.Given at FPRS meeting in Dallas, Texas, June 1972     

Mild ozone exposure alters (14)C dynamics in foliage of Pinus taeda L

To explore the physiological mechanisms underlying ozone-induced growth reductions in loblolly pine (Pinus taeda L.), seedlings were exposed to sub-ambient (charcoal-filtered), ambient or twice-ambient ozone in open-top chambers for three growing seasons. In the final year of exposure, current-year needle fascicles were labeled with (14)CO(2) and the incorporation of (14)C into biochemical fractions was followed for 48 hours. Irrespective of ozone treatment, losses of (14)C-assimilates from foliage to respiration and translocation were minimal during the first 3 hours, whereas more than 60% of the label was lost during the next 45 hours. Radiolabel in sugar decreased rapidly after a lag period, roughly paralleling the pattern of total (14)C loss. The amount of (14)C label in starch and lipids plus pigments remained constant throughout the 48-hour chase period, whereas the amount of (14)C label in other fractions showed a net decrease over the 48-hour chase period. Ozone treatments altered foliar carbon dynamics in two ways: (1) ozone exposure increased foliar (14)C retention up to 21% for the first 5 hours after labeling, but not thereafter, and (2) ozone exposure decreased partitioning of (14)C into starch and increased partitioning of (14)C into organic acids, residue, and lipids plus pigments, indicating an intensified partitioning of carbon to injury and repair processes. Both short-term carbon retention and diversion of carbon from storage compounds to repair processes are foliar mechanisms by which ozone exposure could decrease growth in loblolly pine seedlings.     

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].     

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.     

Response of oriental beech (Fagus orientalis Lipsky) seedlings to canopy gap size

The response of nursery seedlings and wildings of oriental beech(Fagus orientalis Lipsky) to canopy gap size was studied ina climax beech forest in northern Iran with respect to seedlingsurvival, shoot growth and vitality. These parameters were followedfor 2 years after planting in gaps of 50, 200 and 600 m², aswell as in the open field. Foliage coloration was used as acriterion for vitality. The survival rate of nursery seedlingsand wildings dropped rapidly with increasing gap size from 84per cent in 50-m² canopy openings to     

Leaf respiration at different canopy positions in sweetgum (Liquidambar styraciflua) grown in ambient and elevated concentrations of carbon dioxide in the field

Trees exposed to elevated CO2 partial pressure ([CO2]) generally show increased rates of photosynthesis and growth, but effects on leaf respiration are more variable. The causes of this variable response are unresolved. We grew 12-year-old sweetgum trees (Liquidambar styraciflua L.) in a Free-Air CO2 Enrichment (FACE) facility in ambient [CO2] (37/44 Pa daytime/nighttime) and elevated [CO2] (57/65 Pa daytime/nighttime) in native soil at Oak Ridge National Environmental Research Park. Nighttime respiration (R(N)) was measured on leaves in the upper and lower canopy in the second (1999) and third (2000) growing seasons of CO2 fumigation. Leaf respiration in the light (R(L)) was estimated by the technique of Brooks and Farquhar (1985) in the upper canopy during the third growing season. There were no significant short-term effects of elevated [CO2] on R(N) or long-term effects on R(N) or R(L), when expressed on an area, mass or nitrogen (N) basis. Upper-canopy leaves had 54% higher R(N) (area basis) than lower-canopy leaves, but this relationship was unaffected by CO2 growth treatment. In August 2000, R(L) was about 40% of R(N) in the upper canopy. Elevated [CO(2)] significantly increased the number of leaf mitochondria (62%), leaf mass per unit area (LMA; 9%), and leaf starch (31%) compared with leaves in ambient [CO(2)]. Upper-canopy leaves had a significantly higher number of mitochondria (73%), N (53%), LMA (38%), sugar (117%) and starch (23%) than lower-canopy leaves. Growth in elevated [CO2] did not affect the relationships (i.e., intercept and slope) between R(N) and the measured leaf characteristics. Although no factor explained more than 45% of the variation in R(N), leaf N and LMA were the best predictors for R(N). Therefore, the response of RN to CO2 treatment and canopy position was largely dependent on the magnitude of the effect of elevated [CO2] or canopy position on these characteristics. Because elevated [CO2] had little or no effect on N or LMA, there was no effect on R(N). Canopy position had large effects on these leaf characteristics, however, such that upper-canopy leaves exhibited higher R(N) than lower-canopy leaves. We conclude that elevated [CO2] does not directly impact leaf respiration in sweetgum and that barring changes in leaf nitrogen or leaf chemical composition, long-term effects of elevated [CO2] on respiration in this species will be minimal.     

Seasonal patterns of light-saturated photosynthesis and leaf conductance for mature and seedling Quercus rubra L. foliage: differential sensitivity to ozone exposure

Extrapolation of the effects of ozone on seedlings to large trees and forest stands is a common objective of current assessment activities, but few studies have examined whether seedlings are useful surrogates for understanding how mature trees respond to ozone. This two-year study utilized a replicated open-top chamber facility to test the effects of subambient, ambient and twice ambient ozone concentrations on light-saturated net photosynthesis (P(max)) and leaf conductance (g(l)) of leaves from mature trees and genetically related seedlings of northern red oak (Quercus rubra L.). Gas exchange measurements were collected four times during the 1992 and 1993 growing seasons. Both P(max) and g(l) of all foliage followed normal seasonal patterns of ontogeny, but mature tree foliage had greater P(max) and g(l) than seedling foliage at physiological maturity. At the end of the growing season, P(max) and g(l) of the mature tree foliage exposed to ambient ( approximately 80-100 ppm-h) and twice ambient ( approximately 150-190 ppm-h) exposures of ozone were reduced 25 and 50%, respectively, compared with the values for foliage in the subambient ozone treatment ( approximately 35 ppm-h). In seedling leaves, P(max) and g(l) were less affected by ozone exposure than in mature leaves. Extrapolations of the results of seedling exposure studies to foliar responses of mature forests without considering differences in foliar anatomy and stomatal response between juvenile and mature foliage may introduce large errors into projections of the response of mature trees to ozone.     

Genotypic variation in physiological and growth responses of Populus tremuloides to elevated atmospheric CO2 concentration

Physiological and biomass responses of six genotypes of Populus tremuloides Michx., grown in ambient t (357 micromol mol(-1)) or twice ambient (707 micromol mol(-1)) CO2 concentration ([CO2]) and in low-N or high-N soils, were studied in 1995 and 1996 in northern Lower Michigan, USA. There was a significant CO2 x genotype interaction in photosynthetic responses. Net CO2 assimilation (A) was significantly enhanced by elevated [CO2] for five genotypes in high-N soil and for four genotypes in low-N soil. Enhancement of A by elevated [CO2] ranged from 14 to 68%. Genotypes also differed in their biomass responses to elevated [CO2], but biomass responses were poorly correlated with A responses. There was a correlation between magnitude of A enhancement by elevated [CO2] and stomatal sensitivity to CO2. Genotypes with low stomatal sensitivity to CO2 had a significantly higher A at elevated [CO2] than at ambient [CO2], but elevated [CO2] did not affect the ratio of intercellular [CO2] to leaf surface [CO2]. Stomatal conductance and A of different genotypes responded differentially to recovery from drought stress. Photosynthetic quantum yield and light compensation point were unaffected by elevated [CO2]. We conclude that P. tremuloides genotypes will respond differentially to rising atmospheric [CO2], with the degree of response dependent on other abiotic factors, such as soil N and water availability. The observed genotypic variation in growth could result in altered genotypic representation within natural populations and could affect the composition and structure of plant communities in a higher [CO2] environment in the future.     

Response of seedlings of different tree species to elevated C02 in Changbai Mountain

Eco-physiological responses of seedlings of eight species,Pinus koraiensis, Picea koraiensis, Larix olgensis, Populus ussuriensis, Betula platyphylla, Tilia amurensis, Traxinus mandshurica andAcer mono from broadleaved/Korean pine forest, to elevated CO₂ were studied by using open-top chambers under natural sunlight in Changbai Mountain, China in two growing seasons (1998–1999). Two concentrations of CO₂ were designed: elevated CO₂ (700 μmol·mol⁻¹) and ambient CO₂ (400 μmol·mol⁻¹). The study results showed that the height growth of the tree seedlings grown at elevated CO₂ increased by about 10%–40% compared to those grown at ambient CO₂. And the water using efficiency of seedlings also followed the same tendency. However, the responses of seedlings in transpiration and chlorophyll content to elevated CO₂ varied with tree species. The broad-leaf tree species were more sensitive to the elevated CO₂ than conifer tree species. All seedlings showed a photosynthetic acclimation to long-term elevated CO₂. Foundation item: The project was supported by National Key Basic Development of China (G1999043400) and the grant KZCX 406-4, KZCX1 SW-01 of the Chinese Academy of Sciences Biography: WANG Miao (1964-), maie, associate professor in Institute of applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P. R. China. Responsible editor: Song Funan     

大气CO2倍增对长白山不同树种的苗木的影响

组成长白山阔叶红松林的主要树种红松、云杉、落叶松、大青杨、白桦、椴树、水曲柳和色木的幼树,盆栽于模拟自然光照和人工调节CO2浓度为700祄olmol-1、400祄olmol-1的气室内两个生长季(1998-1999),以生长在400祄olmol-1下的幼树为对照组。研究结果表明:高CO2浓度下生长的红松、云杉、落叶松、大青杨、白桦、椴树、水曲柳和色木的高生长比对照组的幼树提高10%~40%。水分利用效率均有不同程度的提高,但不同树种叶绿素含量和蒸腾速率对高CO2浓度反应不一。长期高CO2浓度环境下生长的阔叶树对大气CO2浓度升高反应较针叶树敏感,供试8个树种对CO2浓度的升高均发生光合驯化现象。图2表2参24。