Leaf morphology of 40 evergreen and deciduous broadleaved subtropical tree species and relationships to functional ecophysiological traits

We explored potential of morphological and anatomical leaf traits for predicting ecophysiological key functions in subtropical trees. We asked whether the ecophysiological parameters stomatal conductance and xylem cavitation vulnerability could be predicted from microscopy leaf traits. We investigated 21 deciduous and 19 evergreen subtropical tree species, using individuals of the same age and from the same environment in the Biodiversity‐Ecosystem Functioning experiment at Jiangxi (BEF‐China). Information‐theoretic linear model selection was used to identify the best combination of morphological and anatomical predictors for ecophysiological functions. Leaf anatomy and morphology strongly depended on leaf habit. Evergreen species tended to have thicker leaves, thicker spongy and palisade mesophyll, more palisade mesophyll layers and a thicker subepidermis. Over 50% of all evergreen species had leaves with multi‐layered palisade parenchyma, while only one deciduous species (Koelreuteria bipinnata) had this. Interactions with leaf habit were also included in best multi‐predictor models for stomatal conductance (g_s) and xylem cavitation vulnerability. In addition, maximum g_s was positively related to log ratio of palisade to spongy mesophyll thickness. Vapour pressure deficit (vpd) for maximum g_s increased with the log ratio of palisade to spongy mesophyll thickness in species having leaves with papillae. In contrast, maximum specific hydraulic conductivity and xylem pressure at which 50% loss of maximum specific xylem hydraulic conductivity occurred (Ψ₅₀) were best predicted by leaf habit and density of spongy parenchyma. Evergreen species had lower Ψ₅₀ values and lower maximum xylem hydraulic conductivities. As hydraulic leaf and wood characteristics were reflected in structural leaf traits, there is high potential for identifying further linkages between morphological and anatomical leaf traits and ecophysiological responses.     

Variation in leaf traits at different altitudes reflects the adaptive strategy of plants to environmental changes

Leaf anatomical traits play key roles in plant functions and display evolutionary adaptive changes to suit the surrounding environment. To reveal the adaptive mode and mechanisms of plants in response to global warming, we analyzed leaf morphology and anatomical structures in three different species, Epilobium amurense Hausskn., Pedicularis densispica Franch., and Potentilla fulgens Wall. ex Hook., growing along an elevational gradient (3,000–4,600 m) in the Yulong Mountains. The results showed leaf length and width decreased, whereas leaf thickness increased with increasing altitude in all three species. Thickness of leaf upper epidermis, lower epidermis, palisade and spongy mesophyll, and main vein increased with rising altitude. Stomatal density in each species increased with rising elevation. These results illustrate that plants can adapt to the environmental changes that accompany high altitudes by decreasing leaf area and increasing leaf thickness, mesophyll tissue thickness, and stomatal density. Such morphological and anatomical plasticity would lead to lower transpiration rates, enhanced internal temperature and water status, and improved photosynthetic capability.     

Leaf and stem anatomical responses to periodical waterlogging in simulated tidal floods in mangrove Avicennia marina seedlings

This study was aimed to evaluate anatomical responses to waterlogging of mangrove seedlings (Avicennia marina (Forsk.) Vierh.) grown in experimentally simulated semidiurnal tides. The following treatments were used: 0, 2, 4, 6, 8, 10 and 12 h submergence period with two daily tidal cycles. With increasing waterlogging duration, the leaf thickness, mesophyll thickness, palisade parenchyma thickness, palisade–spongy ratio and hypodermis thickness decreased, but the mesophyll to leaf thickness ratio, stem and pith diameter, and cortex thickness increased. The tangential vessel diameter, vessel wall thickness in stem and leaf and fiber wall thickness in stem showed a similar tendency in response to waterlogging, remaining constant between 0 and 4 h waterlogging duration, but decreasing with more prolonged waterlogging. When the waterlogging duration exceeded 4 h, no sclerenchyma cells in leaves or gelatinous fibers in stems were observed. The response of these leaf and stem features indicated that water transport and mechanical support could remain relatively stable in the 0–4 h waterlogging duration, but they would be negatively influenced by longer flooding. Tissues for gas exchange were stimulated by waterlogging, while the functions of water storage, photosynthesis, mesophyll conductance were weakened with increasing waterlogging.     

Response of leaf anatomy of <Emphasis Type="Italic">Chenopodium acuminatum</Emphasis> to soil resource availability in a semi-arid grassland

Soil water (W), nitrogen (N), and phosphorus (P) availability were manipulated for 2 years in a factorial experiment in a semi-arid grassland in the southeastern Keerqin Sandy Lands, China, to determine what soil resource(s) limits plant growth. We quantified the responses of leaf chemical and anatomical traits for the dominant annual herb Chenopodium acuminatum in this ecosystem to test hypotheses about leaf form and function in relation to soil resource limitation. Nitrogen was the principal limiting factor, and N treatments (alone and in combination with W and P) elicited consistent increases in leaf size and decreases in leaf thickness and water content. Differentiation in the leaf mesophyll between palisade and spongy parenchyma was lacking in N deficient plants and stimulated in all +N treatments. The greater tissue density and cell packing may promote more efficient light capture with improved N nutrition. Mixed additions of W, N, and P were generally more advantageous to leaf expansion and nutrient balance than their isolated additions, therefore water and nutrients synchronous management would be a better approach to promote plant growth at the semi-arid region.     

Structural Adaptation of the Leaf Mesophyll to Shading

Structural characteristics of the mesophyll were studied in five boreal grass species experiencing a wide range of light and water supply conditions. Quantitative indices of the palisade and spongy mesophyll tissues (cell and chloroplast sizes, the number of chloroplasts per cell, the total cell and chloroplast surface area per unit leaf surface area) were determined in leaves of each of the species. The cell surface area and the cell volume in spongy mesophyll were determined with a novel method based on stereological analysis of cell projections. An important role of spongy parenchyma in the photosynthetic apparatus was demonstrated. In leaves of the species studied, the spongy parenchyma constituted about 50% of the total volume and 40% of the total surface area of mesophyll cells. The proportion of the palisade to spongy mesophyll tissues varied with plant species and growth conditions. In a xerophyte Genista tinctoria, the total cell volume, cell abundance, and the total surface area of cells and chloroplasts were 30–40% larger in the palisade than in the spongy mesophyll. In contrast, in a shade-loving species Veronica chamaedris, the spongy mesophyll was 1.5–2 times more developed than the palisade mesophyll. In mesophyte species grown under high light conditions, the cell abundance and the total cell surface area were 10–20% greater in the palisade mesophyll than in the spongy parenchyma. In shaded habitats, these indices were similar in the palisade and spongy mesophyll or were 10–20% lower in the palisade mesophyll. In mesophytes, CO₂ conductance of the spongy mesophyll accounted for about 50% of the total mesophyll conductance, as calculated from the structural characteristics, with the mesophyll CO₂ conductance increasing with leaf shading.     

Albinism in plants – far beyond the loss of chlorophyll: Structural and physiological aspects of wild‐type and albino royal poinciana (Delonix regia) seedlings

• The partial or complete loss of chlorophylls, or albinism, is a rare phenomenon in plants. In the present study, we provide the first report of the occurrence in albino Delonix regia seedlings and describe the morpho‐physiological changes associated with albinism.
• Wild‐type (WT) and albino seedlings were characterized. Leaflets samples were processed following common procedures for analysis with light, scanning and transmission electron microscopy. The chlorophyll a fluorescence parameters and the carbohydrate, lipid and soluble protein content were also determined in leaf and cotyledon samples of both albino and WT seedlings.
• Albino seedlings showed reduced growth. They also had lower chlorophyll and protein content in foliar tissues than WT seedlings, in addition to lower concentrations of lipids and carbohydrates stored in cotyledons. The chloroplasts of albino seedlings were poorly developed, with an undefined internal membrane system and the presence of plastoglobules. Wild‐type seedlings had a uniseriate and hypoestomatic epidermis. The mesophyll was dorsiventral, consisting of a layer of palisade parenchyma and two to four layers of spongy parenchyma. In albino seedlings, the spongy parenchyma was compact, with few intercellular spaces, and the thickness of the mesophyll was larger, resulting in increased thickness of the leaf blade. Albino seedlings had higher stomatal density and number of pavement cells, although the stomata had smaller dimensions.
• In addition to the partial loss of chlorophylls, albino D. regia showed changes at physiological and structural levels, demonstrating the crucial nature of photosynthetic pigments during the development and differentiation of plant leaf tissues/cells.

     

Differential leaf traits of a neotropical tree Cariniana legalis (Mart.) Kuntze (Lecythidaceae): comparing saplings and emergent trees

Cariniana legalis is an emergent tree that reaches the upper canopy in Brazilian Semideciduous Forest. Spatial contrasts in microclimatic conditions between the upper canopy and understorey in a forest may affect morpho-physiological leaf traits. In order to test the hypothesis that the upper canopy is more stressful to leaves than a gap environment we compared emergent trees of C. legalis, 28–29 m in height to gap saplings, 6–9 m in height, for the following parameters: leaf area, leaf mass area (LMA the dry weight:leaf area ratio), leaf thickness, leaf anatomical parameters, stomata conductance, and chlorophyll a fluorescence. Leaves from emergent trees had smaller leaf areas but greater LMA compared to saplings. Leaf thickness, palisade layer thickness, and stomatal density were higher for emergent trees than for saplings. The opposite pattern was observed for spongy layer thickness and spongy/palisade ratio. Stomatal conductance was also higher for emergent tree leaves than for sapling leaves, but the magnitude of depression on stomatal conductance near midday was more pronounced in emergent trees. The potential quantum yield of photosystem II, as determined by the F _v/F _m ratio was lower for leaves from saplings. The lower values of stomatal conductance, indicating restriction in CO₂ diffusion into the mesophyll can be related to higher photoinhibition observed in the saplings. Leaves from emergent trees and saplings exhibited similar values for apparent electron transport rates and non-photochemical quenching. Our results suggest that changes in leaf traits could be associated to dry conditions at the upper canopy as well as to the ontogenetic transition between sapling/emergent tree life stages.     

越冬期遮阴条件下3个不同秋眠型紫花苜蓿品种叶片解剖结构与其光生态适应性

在我国南北气候过渡地区, 采用遮阴试验和石蜡切片法, 研究越冬期不同光强对3个不同秋眠型紫花苜蓿(Medicago sativa)品种(‘维多利亚’、 ‘巨人201’和‘游客’)叶片解剖结构的影响。结果表明: 随着光强减弱, 各紫花苜蓿品种表皮结构中上、下表皮角质层厚度, 气孔密度和气孔开度明显下降; 上、下表皮厚度呈上升趋势。随着遮阴强度增加, 叶肉组织中海绵组织细胞宽度显著上升, 栅栏组织厚度、栅栏组织细胞层数、栅栏组织厚度/海绵组织厚度显著下降; 品种间海绵组织厚度和栅栏组织细胞宽度变化趋势不一致。叶片结构整体特征中叶片厚度、叶肉厚度、中脉厚度、组织结构紧密度随光强减弱而显著下降, 组织结构疏松度明显上升, 叶脉突起度变化不明显。品种间各叶片解剖性状变幅及可塑性指数具有明显的差异, 表明其对弱光适应方式不同。Pearson相关分析表明, 各紫花苜蓿品种叶片气孔密度、栅栏组织厚度、叶肉厚度、叶片厚度及栅栏组织厚度/海绵组织厚度与光强呈显著正相关, 可能是紫花苜蓿叶片解剖结构光强敏感特征参数, 其中, ‘维多利亚’叶片敏感特征参数与光强相关程度较低, 与光强相关的性状较少。综合各项分析结果, 初步确定越冬期紫花苜蓿耐阴性与其秋眠性相关, 半秋眠型品种‘维多利亚’ >秋眠型品种‘巨人201’≥非秋眠型品种‘游客’。     

Anatomical adaptations of Astragalus gombiformis Pomel. under drought stress

The present study was designed to study the effect of drought on root, stem and leaf anatomy of Astragalus gombiformis Pomel. Several root, stem and leaf anatomical parameters (cross section diameter, cortex, root cortical cells, pith, leaf lamina and mesophyll thickness) were reduced under moderate to severe water deficit (20–30 days of withheld irrigation). The stele/cross section root ratio increased under moderate water deficit. The root’s and stems vascular systems showed reduced xylem vessel diameter and increased wall thickness under water deficit. In addition, the root xylem vessel density was increased in these drought conditions while it was unchanged in the stems. The stomata density was increased under prolonged drought conditions whereas the stomata size was untouched. The leaf vascular system showed reduced xylem and phloem tissue thickness in the main vein under moderate to severe water deficit. However, in the lamina the vascular tissue and the distance between vascular bundle were unaffected. Our findings suggest a complex network of anatomical adaptations such as a reduced vessel size with increased wall thickness, lesser cortical and mesophyll parenchyma formation and increased stomata density. These proprieties are required for the maintenance of water potential and energy storage under water stress which can improve the resistance of A. gombiformis to survive in arid areas.     

<Emphasis Type="Italic">mesophyll cell defective1</Emphasis>, a mutation that disrupts leaf mesophyll differentiation in sunflower

Mutants with altered leaf morphology are useful as markers for the study of genetic systems and for probing the leaf differentiation process. One such mutant with deficient greening and altered development of the leaf mesophyll appeared in an inbred line of sunflower (Helianthus annuus L.). The objectives of the present study were to determine the inheritance of the mutant leaf trait and its morphological characterisation. The mutation, named mesophyll cell defective1 (mcd1), has pleiotropic effects and it is inherited as a monogenic recessive. The structure and tissue organization of mcd1 leaves are disrupted. In mcd1 leaves, the mesophyll has prominent intercellular spaces, and palisade and spongy tissues are not properly shaped. The mutant palisade cells also appear to be more vacuolated and with a reduced number of chloroplasts than the wild type leaves of equivalent developmental stage. The lamina thickness of mcd1 leaves is greatly variable and in some areas no mesophyll cells are present between the adaxial and abaxial epidermis. The leaf area of the mcd1 mutant is extremely reduced as well as the stem height. A deficient accumulation of photosynthetic pigments characterizes both cotyledons and leaves of the mutant. In mcd1 leaves, chlorophyll (Chl) fluorescence imaging evidences a spatial heterogeneity of leaf photosynthetic performance. Little black points, which correspond to photosystem II (PSII) maximum efficiency (F_v/F_m) values close to zero, characterize the mcd1 leaves. Similarly, the lightadapted quantum efficiency (Φ_PSII) values show a homogeneous distribution over wild type leaf lamina, while the damaged areas in mcd1 leaves, represented by yellow zones, are prominent. In conclusion, the loss of function of the MCD1 gene in Helianthus annuus is correlated with a variegated leaf phenotype characterized by a localized destruction of mesophyll morphogenesis and defeat of PSII activity.     

湖南安息香属植物的叶片比较解剖学研究

利用光学显微镜和扫描电镜对湖南产安息香属10种植物叶表皮微形态和解剖结构进行了观察和测量。结果表明:(1)表皮均由单层细胞构成,细胞形状为多边形和无规则形,垂周壁式样为平直、弓形、波状;(2)气孔器大小及密度在种间的差异明显;(3)气孔外拱盖内缘主要为波状和浅波状,气孔器外围角质纹饰以越南安息香的鸟巢状和栓叶安息香的碗状为显著区别特征;(4)老鸹铃、垂珠花和白花龙的气孔器保卫细胞两极有"T"形加厚;(5)栓叶安息香和大果安息香叶上表皮由大型细胞组成;(6)叶肉分化为栅栏组织和海绵组织,二者的厚度及比值在种间有明显的差异,其中越南安息香栅栏组织分化为2层;(7)大果安息香和芬芳安息香的主脉维管组织构成一圈封闭的环状结构,而其他种则为开放的半圆形结构;(8)叶片及主脉的厚度在种间差异明显。安息香属植物的表皮微形态及解剖结构特征比较稳定,可作为种间鉴定和分类的重要依据。     

Interactive effects of elevated CO2 and temperature on the anatomical characteristics of leaves in eleven species

The anatomical features of leaves in 11 species of plants grown in a temperature gradient and a temperature + CO₂ gradient were studied. The palisade parenchyma thickness, the spongy parenchyma thickness and the total leaf thickness were measured and analyzed to investigate the effects of elevated temperature and CO₂ on the anatomical characteristics of the leaves. Our results show that with the increase of temperature, the leaf thickness of C₄ species increased while the leaf thickness of C₃ species showed no constant changes. With increased CO₂, seven out of nine C₃ species exhibited increased total leaf thickness. In C₄ species, leaf thickness decreased. As for the trend on the multi-grades, the plants exhibited linear or non-linear changes. With the increase of temperature or both temperature and CO₂ for the 11 species investigated, leaf thickness varied greatly in different plants (species) and even in different branches on the same plant. These results demonstrated that the effect of increasing CO₂ and temperature on the anatomical features of the leaves were species-specific. Since plant structures are correlated with plant functions, the changes in leaf anatomical characteristics in elevated temperature and CO₂ may lead to functional differences. Translated from Acta Ecologica Sinica, 2006, 26(2): 326–333 [译自: 生态学报]     

STRUCTURE OF THE LEAF OF PYROSSIA LONGIFOLIA—A FERN EXHIBITING CRASSULACEAN ACID METABOLISM

The leaf of Pyrossia longifolia (Burm.) Morton, an epiphytic fern known to exhibit CAM, was examined by light and electron microscopy. The relatively thick leaf contains a single-layered epidermis, “water-storage” tissue, and a reticulate vascular system embedded in mesophyll tissue not differentiated into palisade and spongy layers. Mesophyll is composed of large, slightly elongate cells each with a thin, parietal layer of cytoplasm and a large central vacuole. The chloroplast-microbody ratio in mesophyll cells indicates that Pyrossia may be a high photorespirer and thus similar in that sense to C₃ plants. Mesophyll is separated from the vascular tissue by a tightly-arranged layer of endodermal cells with Casparian strips. The inner layer of mesophyll cells and the endodermal cells lack suberin lamellae. The collateral veins contain sieve elements, tracheary elements, pericycle and vascular parenchyma cells, the latter conspicuously larger than the sieve elements. The vascular parenchyma is the only cell type in the leaf which contains plastids with a peripheral reticulum. The parenchymatic elements of the leaf are connected by plasmodesmata, all of which lack neck constrictions and sphincters, or sphincter-like structures. The connections between sieve elements and adjacent parenchymatic elements are pore-plasmodesmata characterized by prominent wall thickenings on the parenchymatic-element side of the wall. The distribution and relative frequencies of plasmodesmata between the various cell types of the leaf indicate photoassimilates may move either symplastically or by a combination of symplast and apoplast from the mesophyll to the site of phloem loading in the veins.     

Anatomical changes induced by increasing NaCl salinity in three fodder shrubs, <Emphasis Type="Italic">Nitraria retusa</Emphasis>, <Emphasis Type="Italic">Atriplex halimus</Emphasis> and <Emphasis Type="Italic">Medicago arborea</Emphasis>

Nitraria retusa and Atriplex halimus (xero-halophytes) plants were grown in the range 0–800 mM NaCl while Medicago arborea (glycophyte) in 0–300 mM NaCl. Plants were harvested after 120 days of salt-treatment. The present study was designed to study the effect of salinity on root, stem and leaf anatomy, water relationship, and plant growth in greenhouse conditions. Salinity induced anatomical changes in the roots, stems and leaves. The cuticle and epidermis of N. retusa and A. halimus stems were unaffected by salinity. However, root anatomical parameters (root cross section area, cortex thickness and stele to root area ratio), and stem anatomical parameters (stem cross section area and cortex area) were promoted at 100–200 mM NaCl. Indicating that low to moderate salinity had a stimulating effect on root and stem growth of these xero-halophytic species. At higher salinities, root and stem structures were altered significantly, and their percentages of reduction were higher in A. halimus than in N. retusa whereas, in M. arborea, they were strongly altered as salinity rose. NaCl (100–300 mM) reduced leaf water content by 21.2–56.2% and specific leaf area by 51–88.1%, while increased leaf anatomical parameters in M. arborea (e.g. increased thickness of upper and lower epidermis, palisade and spongy mesophyll, entire lamina, and increased palisade to spongy mesophyll ratio). Similar results were evidenced in A. halimus leaves with salinity exceeding 100 mM NaCl. Leaves of N. retusa were thinner in salt-stressed plants while epidermis thickness and water content was unaffected by salinity. The size of xylem vessel was unchanged under salinity in the leaf’s main vein of the three species while we have increased number in M. arborea leaf main vein in the range of 200–300 mM NaCl. A longer distance between leaf vascular bundle, a reduced size and increased number of xylem vessel especially in stem than in root vascular system was evidenced in M. arborea treated plants and only at (400–800 mM) in the xero-halophytic species. The effects of NaCl toxicity on leaf, stem and root ultrastructure are discussed in relation to the degree of salt resistance of these three species. Our results suggest that both N. retusa and A. halimus show high tolerance to salinity while M. arborea was considered as a salt tolerant species.     

Interactive effects of elevated CO2 and temperature on the anatomical characteristics of leaves in eleven species

The anatomical features of leaves in 11 species of plants grown in a temperature gradient and a temperature + CO₂ gradient were studied. The palisade parenchyma thickness, the spongy parenchyma thickness and the total leaf thickness were measured and analyzed to investigate the effects of elevated temperature and CO₂ on the anatomical characteristics of the leaves. Our results show that with the increase of temperature, the leaf thickness of C₄ species increased while the leaf thickness of C₃ species showed no constant changes. With increased CO₂, seven out of nine C₃ species exhibited increased total leaf thickness. In C₄ species, leaf thickness decreased. As for the trend on the multi-grades, the plants exhibited linear or non-linear changes. With the increase of temperature or both temperature and CO₂ for the 11 species investigated, leaf thickness varied greatly in different plants (species) and even in different branches on the same plant. These results demonstrated that the effect of increasing CO₂ and temperature on the anatomical features of the leaves were species-specific. Since plant structures are correlated with plant functions, the changes in leaf anatomical characteristics in elevated temperature and CO₂ may lead to functional differences.     

Photosystem II efficiency of the palisade and spongy mesophyll in <Emphasis Type="Italic">Quercus coccifera</Emphasis> using adaxial/abaxial illumination and excitation light sources with wavelengths varying in penetration into the leaf tissue

The existence of major vertical gradients within the leaf is often overlooked in studies of photosynthesis. These gradients, which involve light heterogeneity, cell composition, and CO₂ concentration across the mesophyll, can generate differences in the maximum potential PSII efficiency (F _V/F _M or F _V/F _P) of the different cell layers. Evidence is presented for a step gradient of F _V/F _P ratios across the mesophyll, from the adaxial (palisade parenchyma, optimal efficiencies) to the abaxial (spongy parenchyma, sub-optimal efficiencies) side of Quercus coccifera leaves. For this purpose, light sources with different wavelengths that penetrate more or less deep within the leaf were employed, and measurements from the adaxial and abaxial sides were performed. To our knowledge, this is the first report where a low photosynthetic performance in the abaxial side of leaves is accompanied by impaired F _V/F _P ratios. This low photosynthetic efficiency of the abaxial side could be related to the occurrence of bundle sheath extensions, which facilitates the penetration of high light intensities deep within the mesophyll. Also, leaf morphology (twisted in shape) and orientation (with a marked angle from the horizontal plane) imply direct sunlight illumination of the abaxial side. The existence of cell layers within leaves with different photosynthetic efficiencies makes appropriate the evaluation of how light penetrates within the mesophyll when using Chl fluorescence or gas exchange techniques that use different wavelengths for excitation and/or for driving photosynthesis.     

Responses of four succession tree species in low subtropics to enhanced UV-B radiation in the field

The tested tree species included pioneer species Acacia mangium, early succession stage species Schima superba, mesophyte intermediate-succession species Machilus chinensis, and shade-tolerant plant or late-succession species Cryptocarya concinna which occur in the lower subtropical forest community. A comparison with the current ambient level of UV-B radiation (UV-B) showed the leaf net photosynthetic rate (P _N), transpiration rate (E), and stomatal conductance (g _s) of the four species ranged from significantly decreased to no significant change. Additionally, the thickness of palisade and mesophyll in leaves of four tree species were decreased sharply by enhanced UV-B. The thickness of spongy parenchyma in leaves was also decreased except for M. chinensis. UV-B increased the leaf width of A. mangium but its leaf length, leaf thickness, and dry mass per unit area were not affected. Significantly increased stomata width was observed in A. mangium leaf epidermis in response to UV-B. Significantly decreased stomata width and significantly increased stomata density of leaf abaxial epidermis in M. chinensis were also observed. The stomata density of abaxial epidermis of C. concinna was remarkably increased by enhanced UV-B. The height and branch biomass of A. mangium and the height of S. superba were reduced visibly by enhanced UV-B. The four plant species could be classified into three groups of UV-B sensitiveness by hierarchical cluster analysis. A. mangium was sensitive to enhanced UV-B, while C. concinna showed more tolerance.     

山东银莲花叶片形态结构对异质生境和海拔变化的响应

山东银莲花为一分布极其狭域的稀有物种,对海拔600 m以上的针阔混交林和山顶灌丛两种异质的生境都具有较高的适应性。为探索其适应策略,选择两种异质生境中的5个海拔梯度样带,采用常规石蜡切片法和显微观察技术,对叶片进行观察、分析和测量,通过比较叶片外部形态特征参数和内部解剖结构的差异,推测其叶片适应海拔和异质生境的响应策略。结果表明:为适应阴暗、潮湿的针阔混交林和干旱、强光照的山顶灌丛两种不同环境,山东银莲花分别表现出不同的适应策略。针阔混交林下,叶片的背腹表皮毛密度、比叶面积和气孔相对开度较山顶灌丛的大,而气孔密度、叶片厚度、栅栏组织和海绵组织的厚度较山顶灌丛的小;山顶灌丛植株叶片栅栏组织细胞排列较林下更加整齐紧密。两种生境中叶片腹面表皮毛的长度、气孔相对开度都随海拔的升高而减小,且差异明显;而叶片厚度、比叶面积、气孔指数等对600 m以上海拔变化未表现出明显的规律性。本研究将为山东银莲花的保护和利用提供理论基础及依据,为其他植物的相关研究提供参考。     

Photosynthetic and anatomic responses of peanut leaves to cadmium stress

Cadmium (Cd) treatments caused an inhibition in the net photosynthetic rate (P _N) of peanut (Arachis hypogaea) plants, due to the reduction of stomatal conductance (g _s) and photosynthetic pigment contents, as well as the alteration in leaf structure. The decrease of the transpiration rate and g _s might result from the Cd-induced xerophyte anatomic features of leaves (i.e. thick lamina, upper epidermis, palisade mesophyll, high palisade to spongy thickness ratio, as well as abundant and small stomata). The decline of P _N was independent of the impairment in photosystem 2.     

Effect of Mn toxicity on morphological and physiological changes in two <Emphasis Type="Italic">Populus cathayana</Emphasis> populations originating from different habitats

The cuttings of Populus cathayana were exposed to four different manganese (Mn) concentrations (0, 0.1, 0.5 and 1 mM) in a greenhouse to investigate the toxicity of Mn and the detoxifying responses of woody plants. Two contrasting populations of P. cathayana, which were from wet and dry climate regions in western China, respectively, were examined in our study. The results showed that high concentration of Mn caused significant decrease in shoot height, biomass accumulation, and leaf number and leaf areas. Injuries to the anatomical features of leaves were also found as the reduced thickness of palisade and spongy parenchyma, the decreased density in the conducting tissue and the collapse and split in the meristematic tissue in the central vein. Moreover, Mn treatments caused the accumulation of hydrogen peroxide (H₂O₂), and then resulted in oxidative stress indicated by the oxidation of proteins and DNA. Many physiological responses were employed to cope with the toxicity of Mn, including the increase in the contents of non-protein thiol (NP-SH), phytochelatins (PCs) and phenolics compounds and the stimulated activities of guaiacol peroxidase (GPX) and polyphenol oxidase (PPO) for the chelation of Mn and for the antioxidation of reactive oxygen species. The population from dry climate habitat showed a lower leaf concentration of Mn, higher contents of the chelators, and higher activities of GPX and PPO than did the wet climate population at the same Mn treatment, thereby possessing a superior Mn tolerance. In both populations, most of the Mn was accumulated in the shoot, which is favorable regarding phytoremediation.