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1.
Many plants emit isoprene, a hydrocarbon that has important influences on atmospheric chemistry. Pathogens may affect isoprene fluxes, both through damage to plant tissue and by changing the abundance of isoprene-emitting species. Live oaks (Quercus fusiformis (Small) Sarg. and Q. virginiana Mill) are major emitters of isoprene in the southern United States, and oak populations in Texas are being dramatically reduced by oak wilt, a widespread fungal vascular disease. We investigated the effects of oak wilt on isoprene emissions from live oak leaves (Q. fusiformis) in the field, as a first step in exploring the physiological effects of oak wilt on isoprene production and the implications of these effects for larger-scale isoprene fluxes. Isoprene emission rates per unit dry leaf mass were 44% lower for actively symptomatic leaves than for leaves on healthy trees (P = 0.033). Isoprene fluxes were significantly negatively correlated with rankings of disease activity in the host tree (fluxes in leaves on healthy trees > healthy leaves on survivor trees > healthy leaves on the same branch as symptomatic leaves > symptomatic leaves; isoprene per unit dry mass: Spearman's rho = -0.781, P = 0.001; isoprene per unit leaf area: Spearman's rho = -0.652, P = 0.008). Photosynthesis and stomatal conductance were reduced by 57 and 63%, respectively, in symptomatic relative to healthy leaves (P < 0.05); these reductions were proportionally greater than the reductions in isoprene emissions. Low isoprene emission rates in symptomatic leaves are most simply explained by physiological constraints on isoprene production, such as water stress as a result of xylem blockage, rather than direct effects of the oak wilt fungus on isoprene synthesis. The effects of oak wilt on leaf-level isoprene emission rates are probably less important for regional isoprene fluxes than the reduction in oak leaf area across landscapes. 相似文献
2.
The atmospheric hydrocarbon budget is important for predicting ozone episodes and the effects of pollution mitigation strategies. Isoprene emission from plants is an important part of the atmospheric hydrocarbon budget. We measured isoprene emission capacity at the bottom, middle, and top of the canopies of a white oak (Quercus alba L.) tree and a red oak (Quercus rubra L.) tree growing adjacent to a tower in the Duke University Forest. Leaves at the top of the white oak tree canopy had a three- to fivefold greater capacity for emitting isoprene than leaves at the bottom of the tree canopy. Isoprene emission rate increased with increasing temperature up to about 42 degrees C. We conclude that leaves at the top of the white oak tree canopy had higher isoprene emission rates because they were exposed to more sunlight, reduced water availability, and higher temperature than leaves at the bottom of the canopy. Between 35 and 40 degrees C, white oak photosynthesis and stomatal conductance declined, whereas red oak (Quercus rubra) photosynthesis and stomatal conductance increased over this range. Red oak had lower rates of isoprene emission than white oak, perhaps reflecting the higher stomatal conductance that would keep leaves cool. The concentration of isoprene inside the leaf was estimated with a simplified form of the equation used to estimate CO(2) inside leaves. 相似文献
3.
S Welter A Bracho-Nuñez C Mir I Zimmer J Kesselmeier R Lumaret JP Schnitzler M Staudt 《Tree physiology》2012,32(9):1082-1091
Interspecific gene flow is common in oaks. In the Mediterranean, this process produced geographical differentiations and new species, which may have contributed to the diversification of the production of volatile terpenes in the oak species of this region. The endemic North African deciduous oak Quercus afares (Pomel) is considered to be a stabilized hybrid between the evergreen Quercus suber (L.) and the deciduous Quercus canariensis (Willd.), presumably being monoterpene and isoprene emitters, respectively. In a common garden experiment, we examined the terpene emission capacities, terpene synthase (TPS) activities and nuclear genetic markers in 52 trees of these three oak species. All but one of the Q. suber and Q. canariensis trees were found to be genetically pure, whereas most Q. afares trees possessed a mixed genotype with a predominance of Q. suber alleles. Analysis of the foliar terpene emissions and TPS activities revealed that all the Q. canariensis trees strongly produced isoprene while all the Q. suber trees were strong monoterpene producers. Quercus afares trees produced monoterpenes as well but at more variable and significantly lower rates, and with a monoterpene pattern different than that observed in Q. suber. Among 17 individuals tested, one Q. afares tree emitted only an insignificant amount of terpenes. No mixed isoprene/monoterpene emitter was detected. Our results suggest that the capacity and pattern of volatile terpene production in Algerian Q. afares populations have strongly diverged from those of its parental species and became quantitatively and qualitatively reduced, including the complete suppression of isoprene production. 相似文献
4.
Variation in cold hardiness and carbohydrate concentration from dormancy induction to bud burst among provenances of three European oak species 总被引：1，自引：0，他引：1
Morin X Améglio T Ahas R Kurz-Besson C Lanta V Lebourgeois F Miglietta F Chuine I 《Tree physiology》2007,27(6):817-825
Although cold hardiness is known to be a major determinant of tree species distribution, its dynamics and the factors that regulate it remain poorly understood. Variation in cold hardiness and carbohydrate concentration, from dormancy induction until bud burst, were investigated in populations of two deciduous (Quercus robur L. and Quercus pubescens Willd.) and one evergreen (Quercus ilex L.) European oak. Mean cold hardiness values in January were -56, -45 and -27 degrees C for Q. robur, Q. pubescens and Q. ilex, respectively. Soluble carbohydrate concentrations were closely related to instantaneous cold hardiness, estimated by the electrolyte leakage method, whereas total carbohydrate concentration was related to maximum cold hardiness. Both cold hardiness and carbohydrate concentration showed a close linear relationship with temperatures at the location of the sampled population. Our results show that temporal variation in both the inter- and intraspecific cold hardiness in European oaks can be related to variations in the concentrations of soluble carbohydrates and that these relationships appear to be driven by temperature. 相似文献
5.
Flooding is assumed to cause an energy crisis in plants because-due to a lack of O(2)-mitochondrial respiration is replaced by alcoholic fermentation which yields considerably less energy equivalents. In the present study, the effect of flooding on the carbon metabolism of flooding-tolerant pedunculate oak (Quercus robur L.) and flooding-sensitive European beech (Fagus sylvatica L.) seedlings was characterized. Whereas soluble carbohydrate concentrations dropped in roots of F. sylvatica, they were constant in Q. robur during flooding. At the same time, root alcohol dehydrogenase activities were decreased in beech but not in oak, suggesting substrate limitation of alcoholic fermentation in beech roots. Surprisingly, leaf and phloem sap sugar concentrations increased in both species but to a much higher degree in beech. This finding suggests that the phloem unloading process in flooding-sensitive beech was strongly impaired. It is assumed that root-derived ethanol is transported to the leaves via the transpiration stream. This mechanism is considered an adaptation to flooding because it helps avoid the accumulation of toxic ethanol in the roots and supports the whole plant's carbon metabolism by channelling ethanol into the oxidative metabolism of the leaves. A labelling experiment demonstrated that in the leaves of flooded trees, ethanol metabolism does not differ between flooded beech and oak, indicating that processes in the roots are crucial for the trees' flooding tolerance. 相似文献
6.
In summer 1992, isoprene emission was measured on intact leaves and branches of Quercus alba (L.) at two heights in a forest canopy. Isoprene emission capacity (measured at 30 degrees C and a photosynthetic photon flux density of 1000 micro mol m(-2) s(-1)) was significantly higher in sun leaves than in shade leaves when expressed on a leaf area basis (51 versus 31 nmol m(-2) s(-1); P < 0.01). Because leaf mass per unit area (LMA, g m(-2)) was higher in sun leaves than in shade leaves, emissions of sun and shade leaves expressed on a dry mass basis did not differ significantly (99 versus 89 micro g C g(DW) (-1) h(-1); P = 0.05). Similar measurements in 1995 were consistent with the 1992 data, but data from leaves in more shaded locations demonstrated that isoprene emission capacity decreased with decreasing growth irradiance, irrespective of units of expression. Isoprene emission capacity in leaves of Q. coccinea Muenchh. and Q. velutina Lam. also declined steeply with canopy depth. Emission capacity, on a dry mass basis, showed no obvious pattern with canopy position in Q. prinus L. There was no difference in the temperature response of sun versus shade leaves of Q. alba, but shade leaves exhibited a greater quantum efficiency and saturated at lower irradiance than sun leaves. Rates of isoprene emission measured on branches of Q. alba were approximately 60% of those measured on individual leaves, as a result of self-shading within branch enclosures. It is recommended that within-canopy variation in isoprene emission capacity be incorporated into regional emission models. 相似文献
7.
Evaluation of potential techniques for rejuvenating oak shoots requires robust quantitative markers for juvenile and mature plants. To identify suitable in vitro markers, shoot cultures of Quercus species of juvenile, adolescent and mature origin were screened for a range of morphological and physiological markers of juvenility and maturity. Criteria examined included angle of the shoot to the horizontal, stem length, stem diameter (tip, mid, base), leaf number, scale leaf number and shoot number. Image analysis was also carried out to determine leaf area, size, perimeter and breadth and length of leaves. Mature Q. robur L. clones had a larger mid-stem and tip diameter than juvenile clones, whereas mature Q. petraea ex Liebl. clones were characterized by plagiotropic growth and larger mid-stem and tip diameters compared with juvenile clones. Based on discriminant analysis of the data, we propose the following formulae for discrimination of juvenile and mature shoots, where a negative value for the discriminant score (D) indicates juvenility. For Q. petraea: D = -1.308 - 0.0351 SA + 2.206 TD + 1.435 MSD, where SA is stem angle ( degrees ), TD is tip diameter (mm) and MSD is mid-stem diameter (mm). For Q. robur: D = -3.546 + 2.418 TD + 2.202 MSD. Quercus robur clones derived from stump sprouts and designated as juvenile had a negative D value suggesting a juvenile status for these clones. Clones sourced from a hedged, grafted Q. robur tree of mature origin had a positive D value indicating a mature status. Clones initiated from a 20-25-year-old Q. petraea tree displayed morphology in vitro consistent with a mature status and had a positive D value; however, these clones displayed other traits such as vigor suggesting that vestiges of juvenility remain. Multiplication rate and leaf size and shape were variable among clones and did not provide suitable markers for juvenility or maturity for these Quercus species. 相似文献
8.
Quercus robur L. and Quercus petraea (Matt.) Liebl. are sympatric oak species with different ecological requirements. Quercus robur is more tolerant to waterlogging than Q. petraea. This ecological divergence may play a role in the maintenance of the two species despite the absence of an insurmountable reproductive barrier between them. We predicted that the genetic architecture of traits related to waterlogging tolerance differs between the species. To gain insight into this architecture in the absence of genetic markers for waterlogging tolerance, we compared populations of seedlings of each species for diversity in the expression of quantitative phenotypic traits induced by severe hypoxia. To determine the capacity for hypertrophied lenticel formation, we applied gas-impermeable mastic to stems of seedlings. Two months after application, the mastic treatment had induced the formation of 3 (+/- 2) cm(-2) hypertrophied lenticels in the absence of root hypoxia. Leaf epinasty during root hypoxia was an early predictor of seedling mortality. Four weeks of waterlogging resulted in greater epinasty in Q. petraea than in Q. robur, but fewer hypertrophied lenticels (16 +/- 6 versus 21 +/- 9 cm(-2)) and adventitious roots (2.7 +/- 4.7 versus 5.2 +/- 5.9). Differences between species in these traits were associated with differences in the frequencies of extreme phenotypes rather than with a generally higher tolerance to waterlogging in Q. robur seedlings. 相似文献
9.
The susceptibility of oak seedlings (Quercus palustris, Quercus robur, Quercus rubra) and chestnut seedlings (Castanea sativa) to Phytophthora cinnamomi was tested. The dynamics of infection was examined in plant material raised in a rhizotron. In the oak species, primary root tissues were susceptible whereas secondary cortical tissues showed some resistance to P. cinnamomi. Secondary cortical tissues of the tap root in C. sativa were susceptible. Inoculations with P. cinnamomi were performed both in situ and on excised roots of mature Q. rubra. In both cases, the resistance of Q. rubra roots and shoots was negatively correlated with diameter at the inoculation point. Small roots (l–5-cm diameter) were resistant, whereas collar and trunk were susceptible. In contrast to oak, small excised roots of mature C. sativa (0.7–2-cm diameter) were susceptible to P. cinnamomi. This may explain why P. cinnamomi does not induce a decline of the attacked oaks, but rather a trunk canker. 相似文献
10.
Photosynthetic capacity in relation to nitrogen in the canopy of a Quercus robur, Fraxinus angustifolia and Tilia cordata flood plain forest 总被引：1，自引：0，他引：1
We measured gas exchange and various leaf parameters of ash (Fraxinus angustifolia Vahl.) and oak (Quercus robur L.) in the high canopy and of lime (Tilia cordata Mill.) in the lower canopy of a planted, 120-year-old floodplain forest in southern Moravia, Czech Republic. The high-canopy leaves of F. angustifolia and Q. robur had nitrogen concentrations on a leaf area basis (N(area)) that were twice those of low-canopy leaves of T. cordata. Upper-canopy leaves of F. angustifolia had a photosynthetic rate at light saturation (A(max)) of about 16 micromol CO2 m(-2) s(-1), whereas A(max) of the upper-canopy foliage of Q. robur achieved only about two thirds of this value. Contrary to previous investigations of photosynthetic performance in monospecific stands, leaves of the uppermost branches of T. cordata at 15-m height had the highest A(max) and transpiration rate among the species studied. Water-use efficiency (WUE) was low in T. cordata at 15-m canopy height, whereas WUE was significantly higher for Q. robur leaves at 27-m height than for the other species. Leaves of T. cordata at 15-m height showed the strongest relationship between A(max) and N(area) (R2 = 0.90) followed by F. angustifolia (R2 = 0.69). The strong correlation between photosynthesis and nitrogen concentration in T. cordata at 15 m, together with the steep regression slope for the A(max):N(area) relationship, indicated that nitrogen allocation to the photosynthetic apparatus resulted in high nitrogen-use efficiency of light-saturated photosynthesis (PNUE). Despite differences in PNUE among species, PNUE was fairly constant for leaves sampled from the same canopy position, suggesting that single-leaf parameters are matched to optimize PNUE for prevailing light conditions. High PNUE in T. cordata at 15 m partially compensated for the species' subordinate position in the canopy, and may be an important mechanism for its coexistence in highly structured vegetation. 相似文献
11.
Seedlings of two sympatric oak species, Quercus robur L. and Quercus petraea (Matt.) Liebl., were grown in common garden conditions to test for potential interspecific differences in intrinsic water-use efficiency (WUE). Intrinsic water-use efficiency was estimated based on carbon isotope composition of shoots (delta13C) and on gas exchange measurements (ratio of net CO2 assimilation rate to stomatal conductance (A/g(sw))). In addition, genotype x environment interactions were tested by subjecting the seedlings to four irradiance treatments (8, 18, 48 and 100% of incident solar irradiance) imposed by neutral shading nets, and, in the 100% irradiance treatment, two watering regimes. In all treatments, initial growth of Q. robur was faster than that of Q. petraea. In both species, there was a tight correlation between delta13C and A/g(sw). Intrinsic water-use efficiency increased with increasing irradiance (almost doubling from 8 to 100% irradiance), and this effect paralleled the increase in A with increasing irradiance. In full sun, WUE of Q. petraea seedlings was 10-15% higher than in Q. robur seedlings, with the difference attributable to a difference between the species in g(sw). The interspecific difference in WUE was maintained during drought, despite the appreciable increase in WUE and decrease in growth imposed by drought. No interspecific differences in WUE were observed at low irradiances, suggesting a strong genotype x environment interaction for WUE. These findings confirm the existence of interspecific genetic differences in WUE, but also show that there is large intraspecific variability and plasticity in WUE. The initially greater height and biomass increments in Q. robur seedlings illustrate the ability of this species to out-compete Q. petraea in the early stages of forest regeneration. For adult trees growing in closed canopies, the high WUE of Q. petraea may contribute significantly to its survival during dry years, whereas the low WUE of Q. robur may account for the frequently observed declines in adult trees of this species following drought. 相似文献
12.
《Scandinavian Journal of Forest Research》2012,27(3):297-308
A study of 33 provenances in Danish field trials with Quercus robur and Q. petraea was made between 1993 and 1998. The trials include Danish, Dutch, German, Norwegian and Swedish provenances, and were established between 1900 and 1988. Growth, flushing, stem form and epicormic shoot formation were studied. There were strong geographical clines for growth; however, the variation within regions was considerable. Time of flushing followed a more complex clinal pattern and was related to both latitude and distance from the ocean. Stem form was highly variable within different geographical regions and it is suggested that this could be caused by different management regimes in the past. Oaks from some locations in Sweden and Norway seemed especially straight. Stem form is one of the most important parameters for commercial oak management and could be seriously improved through breeding, as it was under considerable genetic control. Epicormic shoot production was in part under genetic control, but no geographical patterns were found. Danish provenances of Q. petraea were growing more rapidly than similar Q. robur on sandy locations. Quercus petraea produced fewer epicormic branches and stem form was equal to or better than Q. robur. Quercus petraea should be recommended for landscape use on windy locations in Denmark. 相似文献
13.
Takafumi Miyama Motonori Okumura Yuji Kominami Kennichi Yoshimura Mioko Ataka Akira Tani 《Journal of Forest Research》2013,18(1):4-12
Quercus serrata Thunb. ex Murray is a widespread deciduous oak in China, the Korean Peninsula, and Japan, and a strong isoprene emitter. Establishing accurate inventories of this species and estimating net carbon budgets, including biogenic volatile organic compounds (BVOC), necessitates detailed evaluation of BVOC emission and oxidation characteristics. Emissions of isoprene, the most abundant BVOC, presumably contribute to atmospheric chemistry through the formation of photochemical oxidants and secondary organic aerosols. We built an isoprene flux monitoring system to simultaneously reveal characteristics of the flux and fate of isoprene at multiple locations in Q. serrata forests. We used proton transfer reaction mass spectrometry (PTR-MS) and an automated closed chamber to measure isoprene emissions from soil and leaves in a warm-temperate Q. serrata forest. We used a relaxed eddy accumulation system with PTR-MS to simultaneously measure the canopy flux. In continuous foliage chamber measurements, we observed daily variations of isoprene emissions and continuous nocturnal emissions from leaves. Nocturnal emissions exceeded 25 % of total daily leaf emissions and were relatively high at sunset and low at sunrise. These results suggest that nocturnal emissions from mature trees may not be negligible. When leaf emissions were high in the daytime, the canopy isoprene flux tended to plateau at an upper limit. Observations of isoprene concentrations and gradients suggest that the plateau was caused by acceleration of isoprene oxidation, and sequential formation of secondary organic aerosols may occur near the leaf just after emission. Elucidation of these linkages may require continuous field measurements with a simultaneous multi-flux monitoring system. 相似文献
14.
15.
The composition of the endophytic fungal assemblages in Quercus cerris, Q. pubescens and Q. robur, three oak species most susceptible to decline, was investigated in Fagarè (Padova), Ulignano (Pisa), and Radda in Chianti (Firenze). The endophytic assemblages were studied as a function of health status of the whole tree and of twigs and leaves. The effect of station altitude was tested on Q. cerris. Samples were gathered from healthy and declining trees. In April (bud opening time) 20 twigs and 10 leaves were collected from each tree. Fungi were isolated from twig segments and leaf portions. A total of 23 fungal genera with 27 different species were isolated, in addition to a few sterile mycelia. Eleven species were found to be common to all three oak species, while other species were found only on one oak species, suggesting host specificity. Among the fungal species isolated, some were known to be pathogenic (Apiognomonia quercina, Colpoma quercinum, Diplodia mutila, Phomopsis quercina). The colonization frequency (CF) of pathogenic species varied between 0.9% for A. quercina in Q. cerris and 60.2% for P. quercina in Q. robur. Analysis of variance showed a statistically significant difference among the oak species tested. The CF was higher in declining trees in comparison with healthy trees, and also in twigs vs. leaves. The CF was found to be higher for Q. cerris trees growing at sea level as compared with those situated at an elevation of 350–400 m. In stands where, on account of particular ecological conditions, pathogenic behaviour is displayed simultaneously by more than one endophytic fungal species, trees accentuate their decline. 相似文献
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17.
The Wessex Silvicultural Group spent three years studying themanagement and silviculture of the oaks (Quercus robur L andQ petraea (Matt) Leibl) in the Wessex area. Low input methodsof establishment including the use of tree shelters and thetending and thinning of younger oak stands together with controlof timber quality were examined in twenty-one forests and estates.Environmental values were acknowledged. While Q robur has previouslypredominated, Q petraea is now generally preferred. 相似文献
18.
Quercus robur (L.) and Q. petraea (Matt.) Liebl. are European oak species that often grow in forest soils with high soluble manganese (Mn2+) concentrations. We tested the effects of Mn2+ at concentrations of 0.0024 mM (control), 0.24 mM (typical of acidic forest soils) and 1.2 mM (typical of forest soils under strongly reducing conditions) on the growth, tissue anatomy, foliar element concentrations, subcellular element distribution and gas exchange of solution-cultured seedlings. At the highest Mn2+ concentration, seedlings were grown with and without an elevated concentration (1.2 mM) of magnesium (Mg2+). At 0.24 mM Mn2+, foliar Mn concentrations were higher than observed in the field. Vacuoles of the leaf epidermis and mesophyll were the main sites of manganese accumulation. High nutrient solution Mn2+ concentration significantly lowered foliar iron (Fe) and Mg concentrations. Elevated Mg2+ concentration raised the foliar Mg concentrations to control values, but Fe concentrations and gas exchange remained depressed. In seedlings grown in the 1.2 mM Mn2+ treatment without elevated Mg2+ damage to the phloem of the petioles and a reduction in root mass were observed in both species. The effects on shoot and root growth were greatest in Q. petraea. Alleviation of manganese toxicity symptoms by Mg2+ in Q. petraea was less effective than in Q. robur. Our results suggest that the soil solution Mn2+ concentrations that occur in European oak forests are unlikely to affect the distribution and performance of Q. robur and Q. petraea in the field. 相似文献
19.
We used a localized ozone (O3) fumigation (LOF) system to study acute and short-term O(3) effects on physiological leaf traits. The LOF system enabled investigation of primary and secondary metabolic responses of similarly and differently aged leaves on the same plant to three different O3 concentrations ([O3]), unconfounded by other influences on O3 sensitivity, such as genetic, meteorological and soil factors. To simulate the diurnal cycle of O3 formation, current-year and 1-year-old Quercus ilex (L.) and Quercus pubescens (L.) leaves were fumigated with O3 at different positions (and hence, different leaf ages) on the same branch over three consecutive days. The LOF system supplied a high [O3] (300+/-50 ppb) on leaves appressed to the vents, and an intermediate, super-ambient [O3] (varying between 120 and 280 ppb) on leaves less than 30 cm from the vent. Leaves more than 60 cm from the O3 vent were exposed to an [O3] comparable with the ambient concentration, with a 100 ppb peak during the hottest hours of the day. Only leaves exposed to the high [O3] were affected by the 3-day treatment, confirming that Mediterranean oak are tolerant to ambient and super-ambient [O3], but may be damaged by acute exposure to high [O3]. Stomatal and mesophyll conductance and photosynthesis were all reduced immediately after fumigation with high [O3], but recovered to control values within 72 h. Both the intercellular and chloroplast CO2 concentrations ([CO2]) remained constant throughout the experiment. Thus, although treatment with a high [O3] may have induced stomatal closure and consequent down-regulation of photosynthesis, we found no evidence that photosynthesis was limited by low [CO2] at the site of fixation. One-year-old leaves of Q. ilex were much less sensitive to O3 than current-year leaves, suggesting that the low stomatal conductance observed in aging leaves limited O3 uptake. No similar effect of leaf age was found in Q. pubescens. Dark respiration decreased during the treatment period, but a similar decrease was observed in leaves exposed to low [O3], and therefore may not be an effect of O3 treatment. Light respiration, on the other hand, was mostly constant in ozone-treated leaves and increased only in leaves in which photosynthesis was temporarily inhibited by high [O3], preventing them from acting as strong sinks that recycle respiratory CO2 in the leaves. There was no evidence of photochemical damage in Q. ilex leaves, whereas Q. pubescens leaves exposed to a high [O3] showed limited photochemical damage, but recovered rapidly. Biochemical markers were affected by the high [O3], indicating accumulation of reactive oxygen species (ROS) and increased denaturation of lipid membranes, followed by activation of isoprene biosynthesis in Q. pubescens leaves. We speculate that the high isoprene emissions helped quench ROS and normalize membrane stability in leaves recovering from O3 stress. 相似文献
20.
Bur oak (Quercus macrocarpa Michx.) and chinquapin oak (Q. muehlenbergii Engl.) leaves were exposed to high temperatures at various photosynthetic photon flux densities under laboratory conditions to determine if species-specific responses to these factors were consistent with the distribution of these oaks in gallery forests in the tallgrass prairies of northeastern Kansas, USA. Measurements of the ratio of chlorophyll fluorescence decrease, R(fd), indicated that chinquapin oak maintained greater photosynthetic capacity than bur oak across all tested combinations of irradiance (100, 400, 700 and 1000 micro mol m(-2) s(-1)) and temperature (40, 42, 44, 46 and 48 degrees C). In both oak species, manipulation of leaf temperature to about 47 degrees C for 45 min in the field led to a 45% decrease in carbon assimilation up to one week after the heat treatment, and to sharp reductions in stomatal conductance. Photosynthetic recovery patterns indicated that bur oak took longer to recover from heat stress than chinquapin oak, suggesting that heat stress may be important in determining distribution patterns of these oak species. Based on a comparison of the results with data from other forest species, we conclude that the photosynthetic temperature tolerances of bur oak and chinquapin oaks facilitate their dominance at the western limit of the eastern deciduous forest. 相似文献