Do fossil plants signal palaeoatmospheric carbon dioxide concentration in the geological past?

Fossil, subfossil, and herbarium leaves have been shown to provide a morphological signal of the atmospheric carbon dioxide environment in which they developed by means of their stomatal density and index. An inverse relationship between stomatal density/index and atmospheric carbon dioxide concentration has been documented for all the studies to date concerning fossil and subfossil material. Furthermore, this relationship has been demonstrated experimentally by growing plants under elevated and reducedcarbon dioxide concentrations. To date, the mechanism that controls the stomatal density response to atmospheric carbon dioxide concentration remains unknown. However, stomatal parameters of fossil plants have been successfully used as a proxy indicator of palaeo-carbon dioxide levels. This paper presents new estimates of palaeo-atmospheric carbon dioxide concentrations for the Middle Eocene (Lutetian), based on the stomatal ratios of fossil Lauraceae species from Bournemouth in England. Estimates of atmospheric carbon dioxide concentrations derived from stomatal data from plants of the Early Devonian, Late Carboniferous, Early Permian and Middle Jurassic ages are reviewed in the light of new data. Semi-quantitative palaeo-carbon dioxide estimates based on the stomatal ratio (a ratio of the stomatal index of a fossil plant to that of a selected nearest living equivalent) have in the past relied on the use of a Carboniferous standard. The application of a new standard based on the present-day carbon dioxide level is reported here for comparison. The resultant ranges of palaeo-carbon dioxide estimates made from standardized fossil stomatal ratio data are in good agreement with both carbon isotopic data from terrestrial and marine sources and long-term carbon cycle modelling estimates for all the time periods studied. These data indicate elevated atmospheric carbon dioxide concentrations during the Early Devonian, Middle Jurassic and Middle Eocene, and reduced concentrations during the Late Carboniferous and Early Permian. Such data are important in demonstrating the long-term responses of plants to changing carbon dioxide concentrations and in contributing to the database needed for general circulation model climatic analogues.     

Comparison of Palaeobotanical Observations with Experimental Data on the Leaf Anatomy of Durmast Oak [Quercus petraea(Fagaceae)] in Response to Environmental Change

To test whether stomatal density measurements on oak leaf remainsare reliable tools for assessing palaeoatmospheric carbon dioxideconcentration [CO₂], under changing Late Miocene palaeoenvironmentalconditions, young seedings of oak (Quercus petraea,Liebl.) weregrown at elevatedvs.ambient atmospheric [CO₂] and at high humiditycombined with an increased air temperature. The leaf anatomyof the young oaks was compared with that of fossil leaves ofthe same species. In the experiments, stomatal density and stomatalindex were significantly decreased at elevated [CO₂] in comparisonto ambient [CO₂]. Elevated [CO₂] induced leaf cell expansionand reduced the intercellular air space by 35%. Leaf cell sizeor length were also stimulated at high air humidity and temperature.Regardless of a temperate or subtropical palaeoclimate, leafcell size in fossil oak was not enhanced, since neither epidermalcell density nor length of the stomatal apparatus changed. Theabsence of these effects may be attributed to the phenologicalresponse of trees to climatic changes that balanced temporalchanges in environmental variables to maintain leaf growth underoptimal and stable conditions.Quercus petraea,which evolvedunder recurring depletions in the palaeoatmospheric [CO₂], maypossess sufficient phenotypic plasticity to alter stomatal frequencyin hypostomatous leaves allowing high maximum stomatal conductanceand high assimilation rates during these phases of low [CO₂].Copyright1998 Annals of Botany Company Atmospheric CO₂, high humidity, elevated temperature,Quercus petraea,durmast oak, Late Miocene, palaeoclimates, leaf anatomy, stomatal density, stomatal index     

Leaf age and salinity influence water relations of pepper leaves

Plant growth is reduced under saline conditions even when turgor in mature leaves is maintained by osmotic adjustment. The objective of this study was to determine if young leaves from salt-affected plants were also osmotically adjusted. Pepper plants (Capsicum annuum L. cv. California Wonder) were grown in several levels of solution osmotic potential and various components of the plants' water relations were measured to determine if young, rapidly growing leaves could accumulate solutes rapidly enough to maintain turgor for normal cell enlargement. Psychrometric measurements indicated that osmotic adjustment is similar for both young and mature leaves although osmotic potential is slightly lower for young leaves. Total water potential is also lower for young leaves, particularly at dawn for the saline treatments. The result is reduced turgor under saline conditions at dawn for young but not mature leaves. This reduced turgor at dawn, and presumably low night value, is possibly a cause of reduced growth under saline conditions. No differences in leaf turgor occur at midday. Porometer measurements indicated that young leaves at a given salinity level have a higher stomatal conductance than mature leaves, regardless of the time of day. The result of stomatal closure is a linear reduction of transpiration.     

Stomatal frequency of Betula pubescens and Pinus sylvestris shows no proportional relationship with atmospheric CO2 concentration

We investigated the relationship between stomatal frequency and a range of atmospheric CO₂ concentrations ([CO₂]_atm) in Betula pubescens and Pinus sylvestris , two important boreal trees in Scandinavia. If strong relationships exist, they can be used to reconstruct past [CO₂]_atm from stomatal frequency of fossil Betula and Pinus leaves. Responses of epidermal characters (stomatal density (SD), epidermal cell density (ED), stomatal index (SI)) to different CO₂ concentrations were investigated utilising (1) the lower partial pressure of CO₂ at increasing altitudes for B. pubescens , and in herbarium specimens of B. pubescens and P. sylvestris collected during the post-industrial rise of [CO₂]_atm from c. 280 ppmv to c. 360 ppmv in 1997 and (2) concentrations (560 ppmv) and temperatures (3° summer) above present day in the CLIMEX greenhouse experiment. All the results show no clear relationship between SD or SI and [CO₂] _atm for either B. pubescens or P. sylvestris. Most likely there are stronger genetically and environmentally induced factors that affect the development of the leaves. Problems with collecting representative samples from herbarium specimens are discussed. Since the effects of changes in [CO₂]_atm cannot be statistically modelled, B. pubescens and P. sylvestris are not suitable for reconstructing past atmospheric CO₂ concentrations from fossil leaves using stomatal density or stomatal index     

Changes in land plant function over the Phanerozoic: reconstructions based on the fossil record

Major fluctuations in the concentrations of atmospheric CO₂ and O₂, are predicted by historical long-term carbon and oxygen cycle models of atmospheric evolution and will have impacted directly on past climates, plant function and evolutionary processes. Here, palaeobotanical evidence is presented from the stomatal density record of fossil leaves spanning the past 400 Myr supporting the predicted changes in atsmopheric CO₂. Evidence from experiments on plants exposed to long-term high CO₂, environments and the newly-assembled fossil data indicate the potential for genetic modification of stomatal characters. The influence of the changes in fossil stomatal characteristics and atmospheric composition on the rates of leaf gas exchange over the course of land plant evolution has been investigated through modelling. Three contrasting eras of plain water economics emerge in the Devonian (high), Carboniferous (low) and from the Upper Jurassic to the present-day (high but declining). These patterns of change result from structural changes of the leaves and the impact of atmospheric CO₂, and O₂, concentrations on RuBisCo function and are consistent with the fossil evidence of sequential appearances of novel plant anatomical changes. The modelling approach is tested by comparing predicted leaf stable carbon isotope ratios with those measured on fossil plant and organic material. Viewed in a geological context, current and future increases in the concentration of atmospheric CO₂, might be considered as restoring plant function to that more typically experienced by plants over the majority of their evolutionary history.     

Stomatal Density and Index of Fossil Plants Track Atmospheric Carbon Dioxide in the Palaeozoic

It has been demonstrated that the leaves of a range of foresttree species have responded to the rising concentration of atmosphericCO₂ over the last 200 years by a decrease in both stomatal densityand stomatal index. This response has also been demonstratedexperimentally by growing plants under elevated CO₂ concentrations.Investigation of Quaternary fossil leaves has shown a correspondingstomatal response to changing CO₂ concentrations through a glacial-interglacialcycle, as revealed by ice core data. Tertiary leaves show asimilar pattern of stomatal density change, using palynologicalevidence of palaeo-temperature as a proxy measure of CO₂ concentration.The present work extends this approach into the Palaeozoic fossilplant record. The stomatal density and index of Early Devonian,Carboniferous and Early Permian plants has been investigated,to test for any relationship that they may show with the changesin atmospheric CO₂ concentration, derived from physical evidence,over that period. Observed changes in the stomatal data givesupport to the suggestion from physical evidence, that atmosphericCO₂ concentrations fell from an Early Devonian high of 10-12times its present value, to one comparable to that of the presentday by the end of the Carboniferous. These results suggest thatstomatal density of fossil leaves has potential value for assessingchanges in atmospheric CO₂ concentration through geologicaltime.Copyright 1995, 1999 Academic Press Aglaophyton major, Sawdonia ornata, Swillingtonia denticulata, Lebachia frondosa, Juncus effusus, Psilotum nudum, Araucaria heterophylla, stomatal density, stomatal index, Palaeozoic CO₂     

Hydroreactivity of stomata in kale leaves of different insertion level as determined by analysis of transpiration curves

Values of the water saturation deficit (WSD) for hydroactive stomatal movements of kale leaves were estimated using the method of transpiration curve analysis. Stomata of young leaves started closing at WSD values of 5 to 6 per cent and were completely closed at 18 to 20 per cent WSD. During maturation and ageing of leaves these WSD values increased to 12.5 and 18 to 23 per cent respectively. Thus the stomatal reaction is more sensitive to changes in WSD in adult leaves than in young ones. After maturation is attained both values decrease. In apparently withering leaves the individual phases of transpiration curves can barely be distinguished, probably for the reason that even under optimal conditions their stomata remain half-closed and at high WSD values an incomplete closing of the aperture occurs. The injured cuticle of withering leaves affects the shape of the transpiration curve as well.     

Stomatal frequency adjustment of four conifer species to historical changes in atmospheric CO2

The species-specific inverse relation between atmospheric CO(2) concentration and stomatal frequency for many woody angiosperm species is being used increasingly with fossil leaves to reconstruct past atmospheric CO(2) levels. To extend our limited knowledge of the responsiveness of conifer needles to CO(2) fluctuations, the stomatal frequency response of four native North American conifer species (Tsuga heterophylla, Picea glauca, Picea mariana, and Larix laricina) to a range of historical CO(2) mixing ratios (290 to 370 ppmV) was analyzed. Because of the specific mode of leaf development and the subsequent stomatal patterning in conifer needles, the stomatal index of these species was not affected by CO(2). In contrast, a new measure of stomatal frequency, based on the number of stomata per millimeter of needle length, decreased significantly with increasing CO(2). For Tsuga heterophylla, the stomatal frequency response to CO(2) changes in the last century is validated through assessment of the influence of other biological and environmental variables. Because of their sensitive response to CO(2), combined with a high preservation capacity, fossil needles of Tsuga heterophylla, Picea glauca, P. mariana, and Larix laricina have great potential for detecting and quantifying past atmospheric CO(2) fluctuations.     

Effect of exogenous 24-epibrassinolide on chlorophyll fluorescence,leaf surface morphology and cellular ultrastructure of grape seedlings (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L.) under water stress

The effects of 24-epibrassinolide (EBR) on chlorophyll fluorescence, leaf surface morphology and cellular ultrastructure of grape seedlings (Vitis vinifera L.) under water stress were investigated. The grape seedlings were subjected to 10 % (w/v) polyethylene glycol (PEG-6000) and treated with 0.05, 0.10 or 0.20 mg L^?1 EBR, respectively. EBR application increased chlorophyll contents, the effective photochemical quantum yield of PSII, maximum photochemical efficiency of PSII, maximal fluorescence and non-photochemical quenching coefficient under water stress in each concentration. Compared with water stress control, higher stomatal density and stomatal length were observed in young leaves under EBR treatments, but not in mature leaves. In-depth analysis of the ultrastructure of leaves indicated that water stress induced disappearance of nucleus, chloroplast swelling, fractured mitochondrial cristae and disorder of thylakoid arrangement both in young leaves and mature leaves. However, EBR application counteracted the detrimental effects of water stress on the structure of the photosynthetic apparatus better in young leaves than in mature leaves. Compared to the other treatments, treatment of 0.10 mg L^?1 EBR had best ameliorative effect against water stress. These results suggested that exogenous EBR could alleviate water stress-induced inhibition of photosynthesis on grape possibly through increasing chlorophyll content, lessening the stomatal and non-stomatal limitation of photosynthesis performance.     

Leaf Age as a Determinant in Stomatal Control of Water Loss from Cotton during Water Stress

The stomatal resistance of individual leaves of young cotton plants (Gossypium hirsutum L. var. Stoneville 213) was measured during a period of soil moisture stress under conditions of constant evaporative demand. When plants were subjected to increasing soil water stress, increases in stomatal resistance occurred first on the lower leaves and the stomata on the upper surfaces were the most sensitive to decreasing leaf-water potential. Stomatal closure proceeded from the oldest leaves to the youngest as the stress became more severe. This apparent effect of leaf age was not due to radiation differences during the stress period. Radiation adjustments on individual leaves during their development altered the stomatal closure potential for all leaves, but did not change the within-plant pattern. Our data indicate that no single value of leaf water potential will adequately represent a threshold for stomatal closure in cotton. Rather, the stomatal resistance of each leaf is uniquely related to its own water potential as modified by age and radiation regime during development. The effect of age on stress-induced stomatal closure was not associated with a loss of potassium from older leaves. Increases in both the free and bound forms of abscisic acid were observed in water-stressed plants, but the largest accumulations occurred in the youngest leaves. Thus, the pattern of abscisic acid accumulation in response to water stress did not parallel the pattern of stomatal closure induced by water stress.     

Stomatal density of cowpea correlates with carbon isotope discrimination in different phosphorus, water and CO2 environments

* Stomatal formation is affected by a plant's external environment, with long-distance signaling from mature to young leaves seemingly involved. However, it is still unclear what is responsible for this signal. To address this question, the relationship between carbon isotope discrimination (Delta) and stomatal density was examined in cowpea (Vigna sinensis). * Plants were grown under various environments that combined different amounts of soil phosphorus (P), soil water, and atmospheric CO(2). At harvest, stomatal density was measured in the youngest fully expanded leaf. The (13)C : (12)C ratio was measured in a young leaf to determine the Delta in mature leaves. * Results indicated that stomatal density is affected by P as well as by amounts of water and CO(2). However, stomatal responses to water and CO(2) were complex because of strong interactions with P. This suggests that the responses are relative, depending on some internal factor being affected by each external variable. Despite such complicated responses, a linear correlation was found between stomatal density and Delta across all environments examined. * It is proposed that the Delta value is a good surrogate for the long-term mean of the intercellular (C(i)) to the atmospheric (C(a)) CO(2) concentration ratio (C(i) : C(a)) and may be useful in understanding stomatal formation beyond complicated interactions.     

Ethylene limits abscisic acid‐ or soil drying‐induced stomatal closure in aged wheat leaves

The mechanism of age‐induced decreased stomatal sensitivity to abscisic acid (ABA) and soil drying has been explored here. Older, fully expanded leaves partly lost their ability to close stomata in response to foliar ABA sprays, and soil drying which stimulated endogenous ABA production, while young fully expanded leaves closed their stomata more fully. However, ABA‐ or soil drying‐induced stomatal closure of older leaves was partly restored by pretreating plants with 1‐methylcyclopropene (1‐MCP), which can antagonize ethylene receptors, or by inoculating soil around the roots with the rhizobacterium Variovorax paradoxus 5C‐2, which contains 1‐aminocyclopropane‐1‐carboxylic acid (ACC)‐deaminase. ACC (the immediate biosynthetic precursor of ethylene) sprays revealed higher sensitivity of stomata to ethylene in older leaves than younger leaves, despite no differences in endogenous ACC concentrations or ethylene emission. Taken together, these results indicate that the relative insensitivity of stomatal closure to ABA and soil drying in older leaves is likely due to altered stomatal sensitivity to ethylene, rather than ethylene production. To our knowledge, this is the first study to mechanistically explain diminished stomatal responses to soil moisture deficit in older leaves, and the associated reduction in leaf water‐use efficiency.     

Short communication. Stomatal responses of the 'living fossil' Ginkgo biloba L. to changes in atmospheric CO2 concentrations

Leaf stomatal density and index of Ginkgo biloba L. were both significantly (P<0.05) reduced after 3 years growth at elevated CO2 (560 ppm), with values comparable to those of cuticles prepared from Triassic and Jurassic fossil Ginkgo leaves thought to have developed in the high CO2 'greenhouse world' of the Mesozoic. A reciprocal transfer experiment indicated that reductions in stomatal density and index irreversibly reduced stomatal conductance, particularly at low leaf-to-air vapour pressure deficits and low internal leaf CO2 concentrations (Ci). These effects probably contributed to the high water-use efficiency of Ginkgo spp. in the Mesozoic relative to those of the present, as determined from carbon isotope measurements of extant and fossil cuticles.Keywords: Stomata, gas exchange, elevated CO2, fossils.      

适应不同光环境小蜡叶片气孔导度、气孔开度和气孔密度的时空变化

对生长在强光环境和弱光环境小蜡叶片的气孔参数测定发现 :气孔导度和气孔开度在 4个取样部位存在异质性分布。气孔导度和气孔开度经回归分析呈线性、指数或多项式分布。统计分析表明 :强光下的叶片气孔导度和气孔开度的相关性明显高于弱光环境叶片的数值。无论强光环境还是弱光环境下的叶片 ,在取样部位编号为1和 3,其气孔导度和气孔开度均存在显著的线性关系。弱光环境下叶片的气孔密度要远低于强光环境下的叶片。强光环境下叶片对变化环境的敏感性要大于弱光环境下的叶片 ,这可能与强光环境叶片具有较高的气孔密度有关。     

Movement of water from old to young leaves in three species of succulents

A hypothetical adaptive response of succulent plants to drought-stress is the redistribution of water from old to young leaves. We examined the effects of possible movement of water from old to young leaves in three succulent species, Carpobrotus edulis (weak CAM-inducible), Kalanchoe tubiflora (CAM) and Sedum spectabile (possibly a CAM-cycler or CAM-inducible). Old leaves were removed from plants, and photosynthesis, transpiration, f. wt : d. wt ratios, diurnal acid fluctuations, stomatal conductance and internal CO2 concentrations of the remaining young leaves were measured during drought-stress. Comparison was made with plants retaining old leaves. There was no evidence that water moved from old to young leaves during drought-stress as previously hypothesized. Only in drought-stressed plants of K. tubiflora, were photosynthetic and transpiration rates of young leaves greater on shoots with old leaves removed compared with attached. There was a trend in all species for greater fluctuations in acidity in young leaves on shoots that lacked older leaves. For two of the three species studied, the f. wt : d. wt ratios of young leaves were greater under drought-stress, on shoots with old leaves removed than with them attached. Absence of old leaves may reduce competition for water with young leaves, which consequently have higher water content and greater photosynthetic rates.     

Loss of Stomatal Function in Ageing Hybrid Poplar Leaves

Under a variety of conditions old, non-senescent hybrid poplar(Populus sp.) leaves exhibited less stomatal control than young,mature leaves. Stomata of older leaves displayed oscillatorybehaviour more frequently, and oscillations were more random,than in younger leaves. Also, diffusive conductance of olderleaves changed less following sudden shifts from either darkto light, or vice versa, than in younger leaves, and temporalpatterns of diffusive conductance in older leaves appeared tobe relatively independent of microenvironmental conditions.Levels of conductance of older leaves were higher both in thedark and following excision than in younger leaves, while inthe light the situation was reversed. Total range of responseand stability of diffusive conductance were also lower in olderrather than in younger leaves. All of the observed age-relateddifferences suggest a loss of stomatal control with increasingleaf age. Leaf age, Populus sp., stomatal cycling, stomatal function, hybrid poplar     

Circadian Rhythms of Leaf and Stomatal Movements in Gymnosperm Species

It is generally accepted that various physiological, morphological and gene expression phenomena are under the control of a circadian clock, and that this time keeping mechanism is universally present. Although such endogenously regulated phenomena have first been documented in plants more than 250 years ago and much work has been accumulated particularly in the past 70 years, it was not obvious from the literature whether such time keeping mechanisms exist in gymnosperms. Two prominent parameters were investigated in several gymnosperm species which have been demonstrated to be under the control of a circadian clock in many plants: (i) leaf movement and (ii) stomata movement. In young plants of Pinus sylvestris, Picea abies, Taxus baccata, Araucaria angustifolia, Araucaria heterophylla and Ginkgo biloba leaf oscillations could be recorded for about 5 days. However, compared to angiosperm plants, the amplitude was small. The period length under free running conditions (constant temperature and continuous light) was characteristic for the species. Stomatal movement was observed in Ginkgo biloba leaves by electron microscopy. Stomata were open at noon and closed at midnight under normal day/night conditions (LD) as well as under constant light conditions (LL), indicating that stomatal aperture is under circadian control in the gymnosperm Ginkgo biloba. Online recordings of stomata conductance however, exhibited diurnal but not circadian oscillations of net CO₂-exchange in G. biloba leaves. Our results show that a circadian clock controls leaf and stomatal movements in gymnosperm species indicating that endogenous time keeping mechanisms are present.     

Systemic regulation of leaf anatomical structure, photosynthetic performance, and high-light tolerance in sorghum

Leaf anatomy of C3 plants is mainly regulated by a systemic irradiance signal. Since the anatomical features of C4 plants are different from that of C3 plants, we investigated whether the systemic irradiance signal regulates leaf anatomical structure and photosynthetic performance in sorghum (Sorghum bicolor), a C4 plant. Compared with growth under ambient conditions (A), no significant changes in anatomical structure were observed in newly developed leaves by shading young leaves alone (YS). Shading mature leaves (MS) or whole plants (S), on the other hand, caused shade-leaf anatomy in newly developed leaves. By contrast, chloroplast ultrastructure in developing leaves depended only on their local light conditions. Functionally, shading young leaves alone had little effect on their net photosynthetic capacity and stomatal conductance, but shading mature leaves or whole plants significantly decreased these two parameters in newly developed leaves. Specifically, the net photosynthetic rate in newly developed leaves exhibited a positive linear correlation with that of mature leaves, as did stomatal conductance. In MS and S treatments, newly developed leaves exhibited severe photoinhibition under high light. By contrast, newly developed leaves in A and YS treatments were more resistant to high light relative to those in MS- and S-treated seedlings. We suggest that (1) leaf anatomical structure, photosynthetic capacity, and high-light tolerance in newly developed sorghum leaves were regulated by a systemic irradiance signal from mature leaves; and (2) chloroplast ultrastructure only weakly influenced the development of photosynthetic capacity and high-light tolerance. The potential significance of the regulation by a systemic irradiance signal is discussed.     

热带雨林冠层树种绒毛番龙眼两种发育阶段叶片的光抑制

 通过测定西双版纳热带雨林冠层树种绒毛番龙眼(Pometia tomentosa)完全伸展嫩叶和成熟叶的叶片解剖、生理特征和雨季晴天自然条件下叶绿素a荧光以及午间强光对部分保护酶活性和膜脂过氧化作用的影响,探讨了两种不同发育阶段叶片光合作用的光抑制与强光和温度的关系。结果表明：绒毛番龙眼全展嫩叶和成熟叶表现出明显的解剖和生理特征差异。与全展嫩叶相比,成熟叶的叶片较厚、叶绿素含量高、气孔导度大、羧化效率高、最大净光合速率和光饱和点高,而气孔密度和保卫细胞长度没有显著差别。在雨季晴天自然条件下,午间最高光强可达2 200 μmol·m-2·s-1以上,最高叶温比气温高7～8 ℃,而成熟叶片的最高温度比全展嫩叶高1.5～2 ℃。上午随光强的增大,两种叶片的非光化学猝灭系数（NPQ）增大,PSⅡ原初光化学效率(Fv/Fm)、实际光化学效率［(Fm′_Fs)/Fm′］逐渐减小,在15∶30左右达最小。下午随着光强的减弱,Fv/Fm逐渐恢复,在傍晚基本恢复到清晨值。初始荧光(F0)在一天中变化很小。这表明绒毛番龙眼叶片光抑制是非辐射能量耗散增加引起的保护光合机构免受光破坏的保护性反应,而非光破坏。全展嫩叶比成熟叶有较低的光化学效率和非辐射耗散能力,对强光和高温处理的敏感性也较强,但在自然条件下一天中的光抑制程度与成熟叶没有显著差别。田间午间强光导致两种叶片的保护酶活性(超氧化物歧化酶,SOD;抗坏血酸过氧化物酶,APX)升高,而H2O2含量变化较小。其中,全展嫩叶的保护酶活性高,丙二醛(MDA)含量低。这表明自然条件下,与成熟叶相比,绒毛番龙眼全展嫩叶通过较低的光能利用效率、较低的叶温和高的保护酶活性减轻了强光高温的光抑制程度。     

中国辽宁省始新世水杉的研究

以辽宁省抚顺早始新世古城子组和计军屯组的水杉（Ｍｅｔａｓｅｑｕｏｉａ Ｍｉｋｉ）为研究对象,对其雌球果、雄球花枝和营养枝叶的形态、叶表皮和雄球花苞片表皮的结构进行了研究分析,并与Ｍ．ｇｌｙｐｔｏｓｔｒｏｂｏｉｄｅｓ,Ｍ．ｏｃｃｉｄｅｎｔａｌｉｓ,Ｍ．ｍｉｌｌｅｒｉ的性状进行比较,认定其属于Ｍ．ｏｃｃｉｄｅｎｔａｌｉｓ。并没得Ｍ．ｇｌｙｐｔｏｓｔｒｏｂｏｉｄｅｓ和抚顺水杉叶下表皮气孔分布区内的平均气