共查询到20条相似文献，搜索用时 46 毫秒
1.
The light screen hypothesis states that foliar anthocyanins shade the photosynthetic apparatus from excess light. In this paper we extend the light screen hypothesis, postulating that plant species at risk of photoinhibitory conditions during autumnal leaf senescence often utilize anthocyanins to protect the photosynthetic apparatus during the period of nutrient resorption. When senescence-related photosynthetic instabilities are compounded by other environmental stresses, particularly low temperature, severe photoinhibition may result in reduced resorption of critical foliar nutrients, which can significantly affect plant fitness. There is evidence that environments where low and often freezing temperatures are common in autumn selectively favor the production of anthocyanins in senescing foliage. The stimuli for, and the timing and location of, autumnal anthocyanin production are all consistent with a photoprotective role for these pigments in senescing leaves. Furthermore, differences in nitrogen allocation strategies between early and late successional species appear to affect photosynthetic stability during leaf senescence, resulting in a reduced need for foliar autumnal anthocyanins in many early successional plants. The ecological and physiological evidence presented in this paper suggest that, for many deciduous species, the production of anthocyanins provides effective photoprotection during the critical period of foliar nutrient resorption. 相似文献
2.
《Forest Ecology and Management》2006,221(1-3):42-51
We studied two pairs of congeneric species (Dipterocarpus hispidus, Dipterocarpus zeylanicus, Mesua ferrea, and Mesua nagassarium). These species are canopy trees of rain forest in south-west Sri Lanka that exhibit differing topographic affinities. We hypothesized that topographic affinity is related to successional status and species ability to endure drought. We tested for these changes by measuring morphology of seedlings growing with each other in differing combinations of light and water. We constructed shade houses with a range of photosynthetic photon flux densities (PFD) and red:far red (R:FR) ratios. Two watering regimes within shade treatments created soil conditions that were either evermoist or periodically dry. Seedlings of the four species were inter-planted at equal spacing within large flats. They were allowed to grow amongst each other for a 2-year period. The more shade-intolerant Dipterocarpus spp. exhibited greater morphological responsiveness to increases in irradiance than the more shade-tolerant Mesua spp. We also demonstrate that all four species differ substantially from each other when morphological attributes (height, dry mass, leaf area) are compared together. Differences among these four species can be logically explained by their sequential competitive exclusion in relation to increasingly limited resources of light and soil water. In high light and evermoist soil conditions D. zeylanicus performs best. Under deep shade Mesua spp. have greater height than Dipterocarpus spp. When soil water is limiting, and the level of shade intermittent, M. nagassarium has greater height than the other three species. These results conform to species observed topographic distribution in the forest. Further studies are needed of wild populations growing across a range of forest sites to confirm whether these four species differ when grown under natural field conditions. 相似文献
3.
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. 相似文献
4.
Alyne Oliveira Lavinsky Cristiano De Souza Sant&#;Ana Marcelo Schramm Mielke Alex-Alan Furtado De Almeida Fábio Pinto Gomes Solange Fran?a Delmira Da Costa Silva 《New Forests》2007,34(1):41-50
Genipa americana L. (Rubiaceae) is a late successional neotropical fruit tree used in riparian forest restoration programs. We analyze the
effects of light availability and soil flooding on the growth and photosynthetic characteristics of G. americana seedlings under nursery and natural light conditions. Two light levels (full sunlight and shade), and two levels of soil
water (flooded and control) were used in the experiment. Flooding induced significant changes in the total seedling biomass
(P < 0.01). The differences among water treatments were 70 and 10% at full sunlight and shade, respectively. These changes were
explained by alterations in the maximum quantum efficiency of the photosystem 2 (Fv/Fm), light-saturated net photosynthetic rates (A
sat) and intrinsic water use efficiency (WUE). G. americana has high physiological plasticity in relation to the light availability and flooding, although significant interactive effects
between high light exposure and soil flooding were observed in several photosynthetic and growth variables. The results highlight
the importance of the synergistic effects between physical environmental variables on the establishment and growth of G. americana seedlings. In the practical point of view we can indicate that, in degraded riparian forests subjected to soil flooding,
seedlings of this species should be planted under partially shaded environments. 相似文献
5.
Leaf optical properties in Venezuelan cloud forest trees 总被引：1，自引：0，他引：1
Leaf optical properties and related leaf characteristics were compared for thirteen cloud forest tree species differing in successional status. Sun leaves were sampled for the eight pioneer species and sun and shade leaves were sampled for the five climax species. Sun leaves had a slightly higher absorptance than shade leaves, although differences were small. Sun leaves had a higher leaf mass per unit area (LMA) and a lower chlorophyll concentration per unit leaf mass, resulting in similar chlorophyll concentrations per unit leaf area and hence similar light harvesting capacities as shade leaves. However, shade leaves realized a higher efficiency of absorptance per unit leaf biomass than sun leaves. There were few differences in leaf characteristics of sun leaves between the climax and pioneer species. Absorptance values of cloud forest species were comparable with values reported for rain forest and more seasonal forest species. Intraspecific variation in leaf absorptance was largely the result of variation in LMA, whereas interspecific variation in leaf absorptance was largely a result of variation in chlorophyll concentration per unit leaf area. 相似文献
6.
南亚热带4个不同演替阶段树种苗木环境适应性研究 总被引：6，自引：0，他引：6
本文用净光合作用速率为指标从生态位宽度、重叠和理论生态位中心与现实生态位中心的偏离程度等方面来探讨不同演替阶段森林群落的优势树种苗木对环境适应性的问题 ,并采用同位素技术研究了光环境与苗木光合产物的输出和分配的关系。研究结果表明 ,森林演替先锋树种马尾松的苗木对土壤含水量变化 (变旱 )和全日照的光环境的适应性最强 ;演替后期种黄果厚壳桂对土壤含水量的变化的适应性最差 ;演替过渡种藜蒴对pH值的变化适应性最强 ,演替后期种黄果厚壳桂的适应性最差 ;生态位宽度与生态位中心偏离值都表现出演替过渡种藜蒴和荷木对矿物质浓度梯度变化适应性最强 ,这与它们苗木有较发达的根系相关密切 ,从而反映了森林演替过渡种比先锋树种和演替后期种有较强的对矿物质营养浓度等条件变化适应性。 4个树种苗木的生态位重叠度都较高 ,说明在森林演替过程中 ,各阶段的树种对资源的竞争是比较激烈的。同时光合产物输出与分配规律的研究结果还表明了 ,弱光对森林演替先锋树种马尾松的光合产物的输出与分配是不利的 ,而全日照的光环境却不利于森林演替过渡种和演替后期种苗木的光合产物的输出与分配 相似文献
7.
Growth and physiological response of six Australian rainforest tree species to a light gradient 总被引：1，自引：0，他引：1
An understanding of growth and photosynthetic potential of subtropical rainforest species to variations in light environment can be useful for determining the sequence of species introductions in rainforest restoration projects and mixed species plantations. We examined the growth and physiology of six Australian subtropical rainforest tree species in a greenhouse consisting of three artificial light environments (10%, 30%, and 60% full sunlight). Morphological responses followed the typical sun-shade dichotomy, with early and late secondary species (Elaeocarpus grandis, Flindersia brayleyana, Flindersia schottiana, and Gmelina leichhardtii) displaying higher relative growth rate (RGR) compared to mature stage species (Cryptocarya erythroxylon and Heritiera trifoliolatum). Growth and photosynthetic performance of most species reached a maximum in 30–60% full sunlight. Physiological responses provided limited evidence of a distinct dichotomy between early and late successional species. E. grandis and F. brayleyana, provided a clear representation of early successional species, with marked increase in Amax in high light and an ability to down regulate photosynthetic machinery in low light conditions. The remaining species (F. schottiana, G. leichhardtii, and H. trifoliolatum) were better represented as falling along a shade-tolerant continuum, with limited ability to adjust physiologically to an increase or decrease in light, maintaining similar Amax across all light environments. Results show that most species belong to a shade-tolerant constituency, with an ability to grow and persist across a wide range of light environments. The species offer a wide range of potential planting scenarios and silvicultural options, with ample potential to achieve rapid canopy closure and rainforest restoration goals. 相似文献
8.
《Journal of Sustainable Forestry》2013,32(1-2):73-84
Abstract Growth characteristics of ash (Fraxinus mandshuricavar. japonicd)and kalopanax (Kalopanax pictus), two mid-succcs-sional species, were monitored in relation to seasonal light in a deciduous broadleaf forest. During the growing, relative light intensity of the gap was 4 to 6 times higher than that under the closed canopy. Seedlings could be found on the mixed hardwood forest floor where relative light intensity was around greater than 7% of full sunlight. When saplings gap openings which had relative light intensities above 20%, they quickly developed lateral branches and increased their foliage volume. The light-photosynthesis curve of seedlings of both species showed a curve typical of the “shade leaf” type even though they grew under sunlight. In contrast, saplings of both species showed the “sun leaf” type of light-photosynthesis curve. This seedling to sapling shift from shade to sun adaptation was also found in other foliage characteristics. This study shows that species can efficiently adjust their leaf and branch characteristics to changing light environments from shade to openings in a forest. 相似文献
9.
Seasonal ecophysiology, leaf structure and nitrogen were measured in saplings of early (Populus grandidentata Michx. and Prunus serotina J.F. Ehrh.), middle (Fraxinus americana L. and Carya tomentosa Nutt.) and late (Acer rubrum L. and Cornus florida L.) successional tree species during severe drought on adjacent open and understory sites in central Pennsylvania, USA. Area-based net photosynthesis (A) and leaf conductance to water vapor diffusion (g(wv)) varied by site and species and were highest in open growing plants and early successional species at both the open and understory sites. In response to the period of maximum drought, both sunfleck and sun leaves of the early successional species exhibited smaller decreases in A than leaves of the other species. Shaded understory leaves of all species were more susceptible to drought than sun leaves and had negative midday A values during the middle and later growing season. Shaded understory leaves also displayed a reduced photosynthetic light response during the peak drought period. Sun leaves were thicker and had a greater mass per area (LMA) and nitrogen (N) content than shaded leaves, and early and middle successional species had higher N contents and concentrations than late successional species. In both sunfleck and sun leaves, seasonal A was positively related to predawn leaf Psi, g(wv), LMA and N, and was negatively related to vapor pressure deficit, midday leaf Psi and internal CO(2). Although a significant amount of plasticity occurred in all species for most gas exchange and leaf structural parameters, middle successional species exhibited the largest degree of phenotypic plasticity between open and understory plants. 相似文献
10.
Jaime Puértolas Marta Pardos María Dolores Jiménez Ismael Aranda José Alberto Pardos 《Annals of Forest Science》2008,65(6):611-611
11.
Vázquez-Yanes C Rojas-Aréchiga M Sánchez-Coronado ME Orozco-Segovia A 《Tree physiology》1996,16(10):871-875
The major components of annual seed deposition in the rain forest at Los Tuxtlas, Veracruz, México are seeds of the pioneer tree species Cecropia obtusifolia and those of some species of Ficus. Cecropia obtusifolia Bertol. forms a relatively persistent viable soil seed bank, whereas seeds of Ficus are seldom found in the soil. Both genera require light for seed germination; however, the species differ in their germination responses to far red (FR) light under laboratory and field conditions. Seeds of C. obtusifolia did not germinate in low red/far red (R/FR) or pure FR, whereas seeds of the Ficus species did. This suggests that Ficus seeds do not become dormant under the light conditions (low R/FR ratio) beneath the leaf canopy of the rain forest. This difference may explain why the species differ in their presence in the soil seed bank. 相似文献
12.
Growth,photosynthetic performance and shade adaptation of rubber (Hevea brasiliensis) grown in natural shade 总被引：3，自引：0，他引：3
We compared growth, photosynthetic performance and shade adaptation of rubber (Hevea brasiliensis Muell. Arg.) plants growing in natural shade (33, 55 and 77% reduction in incoming radiation) to control plants growing in full sunlight. Stem diameter and plant height, measured over a 15-month period, were greatest in plants grown in full sunlight, and both parameters decreased with increasing shade. At 7 and 14 months after planting (MAP), total plant dry mass was highest in control plants and lowest in plants in 77% shade. Expansion of the fourth leaf whorl, monitored at 5-6 MAP, was slowest in plants in 77% shade and fastest in unshaded plants, which had more leaves and higher leaf areas and inter-whorl shoot lengths. In response to increasing shade, specific leaf area increased, whereas leaf weight ratio and relative growth rate decreased. Chlorophyll a/b ratio decreased with increasing shade, indicating shade-induced partitioning of chlorophyll into light-harvesting complexes. Compared to the response in unshaded plants, CO2 assimilation saturated at lower photosynthetic photon flux densities in plants in 77% shade, with a lower upper-asymptote to the light response curve. Chlorophyll fluorescence revealed no evidence of sustained photoinhibitory damage in unshaded plants. Dynamic photoinhibition decreased with increasing shade, with the greatest depression in the ratio of variable to maximal fluorescence around midday. We conclude that shade adaptation and shade-induced reductions in dynamic photoinhibition account for the enhanced early growth of rubber in light shade. 相似文献
13.
Amy L. ClarkSamuel B. St. Clair 《Forest Ecology and Management》2011,262(2):203-207
Plant succession and mycorrhizal fungi both play crucial roles in shaping the development of forest ecosystems. However, despite the strong potential for interactions between them, few studies have examined how patterns of forest succession affect mycorrhizal associations that a majority of plant species depend on to alleviate soil resource constraints. Fire suppression in subalpine forests over the last century has changed successional patterns in ways that may have important implications for mycorrhizal associations of forest tree species. To better understand these relationships we conducted a field and greenhouse study in which we examined mycorrhizal infection along gradients of light intensity and soil nutrient availability that develop as aspen becomes seral to conifers under longer fire return intervals. We examined whether ectomycorrhizal associations of quaking aspen (Populus tremuloides), a shade intolerant, early succession species, were more sensitive to light and soil resource limitations than subalpine fir (Abies lasiocarpa), a shade tolerant, late succession species. In the field study, ectomycorrhizal infection of aspen roots was reduced by 50% in conifer dominated stands relative to aspen stands. In contrast, subalpine fir maintained its EM associations regardless of the successional status of the stand. The greenhouse results were consistent with field results and indicated that light limitation was the driving force behind reductions in EM infection of aspen roots in later stages of succession. These results suggest that nutrient limitations constraining early successional species may be exacerbated by losses in EM associations via light limitations created by late successional species. This is one potential mechanism by which climax forest species create a competitive advantage over early successional species and these results suggest that it is likely exacerbated by longer fire return intervals. 相似文献
14.
To determine the effects of shade on biomass, carbon allocation patterns and photosynthetic response, seedlings of loblolly pine (Pinus taeda L.), white pine (Pinus strobus L.), red maple (Acer rubrum L.), and yellow-poplar (Liriodendron tulipifera L.) were grown without shade or in shade treatments providing a 79 or 89% reduction of full sunlight for two growing seasons. The shade treatments resulted in less total biomass for all species, with loblolly pine showing the greatest shade-induced growth reduction. Yellow-poplar was the only species to show increased stem height growth in the 89% shade treatment. The shade treatments increased specific leaf area of all species. Quantum efficiency, dark respiration and light compensation point were generally not affected by the shade treatments. Quantum efficiency, dark respiration, maximum photosynthesis and light compensation point did not change consistently between the first and second growing seasons. We conclude that differences in shade tolerance among these species are not the result of changes in the photosynthetic mechanism in response to shade. 相似文献
15.
Valladares F Arrieta S Aranda I Lorenzo D Sánchez-Gómez D Tena D Suárez F Alberto Pardos J 《Tree physiology》2005,25(8):1041-1052
Shade tolerance, plastic phenotypic response to light and sensitivity to photoinhibition were studied in holly (Ilex aquifolium L.) seedlings transported from the field to a greenhouse and in adult trees in the field. All plants were growing in, or originated from, continental Mediterranean sites in central Spain. Seedlings tolerated moderate but not deep shade. Mortality was high and growth reduced in 1% sunlight. Survival was maximal in 12% sunlight and minimal in full sunlight, although the relative growth rate of the seedlings surviving in high light was similar to that of plants in moderate shade. Maximum photochemical efficiency at predawn was significantly lower in sun plants than in shade plants in the field, revealing chronic photoinhibition that was most pronounced in winter. Plasticity in response to available light varied according to the variable studied, being low for photosynthetic capacity and stomatal conductance, and high for specific leaf area, root:shoot ratio and leaf area ratio, particularly in seedlings. Differences in water relations and hydraulic features between sun and shade plants in the field were marginal. High water potential at the turgor loss point of field-grown plants suggested that holly is sensitive to drought during both the seedling and the adult stage. Low relative growth rates in both high and low light with low physiological plasticity in response to light indicate the existence of a stress-tolerance mechanism. We conclude that holly is a facultative understory plant in areas of oceanic and relatively mild climate, but an obligate understory plant in dry continental areas such as the study site. The impact of abandonment of traditional management practices and climate change on these Mediterranean populations is discussed. 相似文献
16.
Interspecific variation of photosynthesis and leaf characteristics in canopy trees of five species of Dipterocarpaceae in a tropical rain forest 总被引：1，自引：0，他引：1
Kenzo T Ichie T Yoneda R Kitahashi Y Watanabe Y Ninomiya I Koike T 《Tree physiology》2004,24(10):1187-1192
Photosynthetic rate, nitrogen concentration and morphological properties of canopy leaves were studied in 18 trees, comprising five dipterocarp species, in a tropical rain forest in Sarawak, Malaysia. Photosynthetic rate at light saturation (Pmax) differed significantly across species, varying from 7 to 18 micro mol m(-2) s(-1). Leaf nitrogen concentration and morphological properties, such as leaf blade and palisade layer thickness, leaf mass per area (LMA) and surface area of mesophyll cells per unit leaf area (Ames/A), also varied significantly across species. Among the relationships with leaf characteristics, Pmax had the strongest correlation with leaf mesophyll parameters, such as palisade cell layer thickness (r2 = 0.76, P < 0.001) and Ames/A (r2 = 0.73, P < 0.001). Leaf nitrogen concentration and Pmax per unit area also had a significant but weaker correlation (r2 = 0.46, P < 0.01), whereas Pmax had no correlation, or only weakly significant correlations, with leaf blade thickness and LMA. Shorea beccariana Burck, which had the highest P(max) of the species studied, also had the thickest palisade layer, with up to five or more layers. We conclude that interspecific variation in photosynthetic capacity in tropical rain forest canopies is influenced more by leaf mesophyll structure than by leaf thickness, LMA or leaf nitrogen concentration. 相似文献
17.
The leaf dynamics of two early (Alnus nepalensis and Schima khasiana) and three late (Machilus kingii, Quercus dealbata and Q. griffithii) successional tree species of a subtropical humid, evergreen, montane forest at Upper Shillong (1900 m) in north-eastern India has been studied using demographic techniques. The open-grown early successional species show greater leaf production and higher turnover rate than the open-grown late successional species. The latter, under forest situations, have still slower turnover rates but with leaves of several age groups. It is suggested that the early successional species are attuned to environments of temporary resource availability while the late successional species are adapted to the relatively predictable but highly competitive environments of closed forests. 相似文献
18.
Lianas differ from trees in many life history characteristics, and we predicted that they are phenotypically more responsive to environmental variation than trees. We analyzed responsiveness to light and nutrient availability of five Bauhinia species (three lianas and two trees). Seedlings were grown in a shade house in two light regimes (5 and 25% of full sunlight) and two nutrient supply regimes (field soil and N fertilization equivalent to 100 kg ha(-1)), and important growth-related physiological and morphological plant parameters were measured. Light availability affected most of the measured variables, whereas N addition had only weak effects. In the four light-demanding species (two lianas and two trees), relative plant biomass growth rate increased and specific leaf area (SLA) decreased with increased light availability, whereas a shade-tolerant liana did not respond. Leaf N concentration and light-saturated photosynthetic rate per unit leaf area increased in response to increased irradiance or soil N in the light-demanding tree species and the shade-tolerant liana, but not in the two light-demanding lianas. The light-demanding lianas also had higher SLA and leaf mass ratio, resulting in a higher leaf area ratio (LAR) in high light, whereas the light-demanding trees did not. Across all treatments, mean plasticity indices of physiological and morphological traits, and all traits combined were similar among the studied species. Plasticity was higher in response to light than to N, indicating that light is the main factor controlling seedling responses of the studied species. Although lianas and trees did not differ in mean plasticity in response to light and N, the light-demanding lianas were phenotypically less plastic in LAR and in photosynthetic rates and biomass allocation than the trees. Light and N interacted in their effects on most physiological variables, but the consequences for relative growth rate differed little among species. We conclude that, contrary to our predictions, lianas were no more responsive to variation in light and N availability than trees. 相似文献
19.
Claudia González-Salvatierra Ernesto Iván Badano Joel Flores Juan Pablo Rodas 《林业研究》2013,24(1):23-28
Forest restorations conducted in semiarid, seasonally dry climates must deal with the intense drought stress that affects tree seedlings during the dry season. Although this water deficit is the most commonly invoked source of mortality for seedlings, several other environmental factors may also preclude survival of transplants. For instance, it has been widely reported that excessive light reduces the efficiency of the photosynthetic apparatus, hence decreasing plant survival, but most seedling transplants in deforested areas are conducted under these light conditions. This study is focused in determining whether excessive light affects the photosynthetic performance and survival of Quercus coccolobifolia, a Mexican oak species, when their seedlings are transplanted in semiarid deforested areas. Further, this study tests the possibility of using artificial shade shelters to improve the ecophysiological performance and survival of seedlings. Oak seedlings were transplanted under full sunlight conditions and beneath artificial shade shelters of two different colors: white and black. To reduce water stress, and hence isolate the effects of light treatments, a drip irrigation system was implemented at each experimental plot. Seedling survival was monitored weekly for 128 days and photosynthetic performance was assessed by measuring chlorophyll fluorescence at three opportunities during the experiment. Sun-exposed seedlings showed lower photosynthetic performance and survival rates than those beneath shelters of both colors. These results suggest that sunlight damage can reduce seedling survival when they are transplanted in exposed sites, and that shade shelters can improve the success of forest restoration programs in semiarid climates. 相似文献
20.
Photosynthetic acclimation of deciduous broad-leaved tree species was studied along a vertical gradient within the canopy of a multi-species deciduous forest in northern Japan. We investigated variations in (1) local light regime and CO2 concentration ([CO2]), and (2) morphological (area, thickness and area per mass), biochemical (nitrogen and chlorophyll concentrations) and physiological (light-saturated photosynthetic rate) attributes of leaves of seven major species on three occasions (June, August and October). We studied early successional species, alder (Alnus hirsuta (Spach) Rupr.) and birch (Betula platyphylla var. japonica (Miq.) Hara); gap phase species, walnut (Juglans ailanthifolia Carrière) and ash (Fraxinus mandshurica var. japonica Rupr.); mid-successional species, basswood (Tilia japonica (Miq.) Simonk.) and elm (Ulmus davidiana var. japonica (Rehd.) Nakai); and the late-successional species, maple (Acer mono Bunge). All but maple initiated leaf unfolding from the lower part of the crown. The [CO2] within the vertical profile ranged from 320-350 ppm in the upper canopy to 405-560 ppm near the ground. The lowest and highest ambient [CO2] occurred during the day and during the night, respectively. This trend was observed consistently during the summer, but not when trees were leafless. Chlorophyll concentration was positively related to maximum photosynthetic rate within, but not among, species. Leaf senescence started from the inner part of the crown in alder and birch, but started either in the outer or top portion of the canopy of ash, basswood and maple. Chlorophyll (Chl) to nitrogen ratio in leaves increased with decreasing photon flux density. However, Chl b concentration in all species remained stable until the beginning of leaf senescence. Maximum photosynthetic rates observed in sun leaves of early successional species, gap phase or mid-successional species, and late successional species were 12.5-14.8 micromol m(-2) s(-1), 4.1-7.8 micromol m(-2) s(-1) and 3.1 micromol m(-2) s(-1), respectively. 相似文献