Carotenoid composition of peridermal twigs does not fully conform to a shade acclimation hypothesis

The photosynthetic pigments of twigs in five tree and shrub species possessing chlorenchyma under a well developed, stomata-less, and highly photon absorptive periderm were analysed and compared to those of the corresponding canopy leaves. We asked whether the unavoidable shade acclimation of corticular chlorenchyma results in photosynthetic pigment complements typically found in shade leaves. As expected, chlorophyll (Chl) a/b ratios in twigs were consistently low. However, carotenoid (Car) analysis did not confirm the initial hypothesis, since twigs generally contained increased Chl-based pool sizes of the xanthophyll cycle components. The contents of photo-selective neoxanthin and lutein were high as well. Yet, β-carotene content was extraordinarily low. In addition, twigs retained high pre-dawn ratios of the deepoxidized antheraxanthin and zeaxanthin, although environmental conditions were not pre-disposing for such a state. The unexpected Car composition allows the conclusion that other micro-environmental conditions within twigs (hypoxia, increased red to blue photon ratios, and extremely high CO₂ concentrations) are more important than shade in shaping the Car profiles.     

Leaf-twig carbon isotope ratio differences in photosynthetic-twig desert shrubs

Summary Carbon isotope ratios were determined for bulk tissues of both leaves and current season twigs of 29 species of Mohave Desert shrubs. Leaf and twig tissues were found to differ in their carbon isotope ratios, only in those species which had photosynthetic twigs. These data suggest that the twigs of these species operate at lower intercellular CO₂ values than leaves, an interpretation which is consistent with available gas-exchange data. An effect of microhabitat was also evident between the mean isotope ratios of leaves from wash versus slope habitats.This research has been supported by NSF Grant BSR-8410943 and by DOE Grant DE-FGO2-86ER60399.     

Carotenoid composition of peridermal twigs does not fully conform to a shade acclimation hypothesis

The photosynthetic pigments of twigs in five tree and shrub species possessing chlorenchyma under a well developed, stomata-less, and highly photon absorptive periderm were analysed and compared to those of the corresponding canopy leaves. We asked whether the unavoidable shade acclimation of corticular chlorenchyma results in photosynthetic pigment complements typically found in shade leaves. As expected, chlorophyll (Chl) a/b ratios in twigs were consistently low. However, carotenoid (Car) analysis did not confirm the initial hypothesis, since twigs generally contained increased Chl-based pool sizes of the xanthophyll cycle components. The contents of photo-selective neoxanthin and lutein were high as well. Yet, -carotene content was extraordinarily low. In addition, twigs retained high pre-dawn ratios of the deepoxidized antheraxanthin and zeaxanthin, although environmental conditions were not pre-disposing for such a state. The unexpected Car composition allows the conclusion that other micro-environmental conditions within twigs (hypoxia, increased red to blue photon ratios, and extremely high CO₂ concentrations) are more important than shade in shaping the Car profiles.This revised version was published online in March 2005 with corrections to the page numbers.     

Evidence for light-independent and steeply decreasing PSII efficiency along twig depth in four tree species

Recent reports have indicated a considerably inactivated PSII in twig cortices, in spite of the low light transmittance of overlying periderms. Corresponding information for more deeply located and less illuminated tissues like xylem rays and pith are lacking. In this investigation we aimed to characterize the efficiency of PSII and its light sensitivity along twig depth, in conjunction with the prevailing light quantity and quality. To that aim, optical methods (spectral reflectance and transmittance, chlorophyll fluorescence imaging, low temperature fluorescence spectra) and photoinhibitory treatments were applied in cut twig sections of four tree species, while corresponding leaves served as controls. Compared to leaves, twig tissues displayed lower chlorophyll (Chl) levels and dark-adapted PSII efficiency, with strong decreasing gradients towards the twig center. The low PSII efficiencies in the inner stem were not an artifact due to an actinic effect of measuring beam or to an enhanced contribution of PSI fluorescence. In fact, the PSII/PSI ratios in cortices were higher and those in the xylem rays similar to that of leaves. Inner twig tissues were quite resistant to photoinhibitory treatments, tolerating irradiation levels several-fold higher than those encountered in their microenvironment. Moreover, the extent of high light tolerance was similar in naturally exposed and shaded twig sides. The results indicate an increasing, inherent and light-independent inactivation of PSII along twig depth. The findings are discussed on the basis of a recently proposed model for photosynthetic electron flow in twigs, taking into account the specific atmospheric and light microenvironment as well as the possible metabolic needs of such bulky organs.     

互花米草与芦苇光合色素含量对淹水措施的响应

以上海崇明东滩入侵植物互花米草与本地种芦苇为研究对象,研究持续淹水胁迫对两种植物光合色素含量的影响.结果表明：互花米草与芦苇叶片的光合色素基本组成与含量不同,对持续淹水的响应也不同.在持续淹水胁迫下,互花米草叶绿素a、叶绿素b及类胡萝卜素含量降低,叶绿素a／b、类胡萝卜素／叶绿素值提高;芦苇各色素含量升高,叶绿素a／b、类胡萝卜素/叶绿素值基本保持稳定.解除持续淹水胁迫后,互花米草各色素含量逐渐升高,叶绿素a／b、类胡萝卜素／叶绿素值降低,并逐渐接近对照水平;而芦苇各色素含量显著高于对照.两种植物均表现出一定的补偿效应,但芦苇比互花米草更能适应同等程度的持续淹水胁迫.应用持续淹水措施治理互花米草时,可采用本地种芦苇作为治理后湿地恢复的替代植物.     

Spectral reflectance indices and pigment functions during leaf ontogenesis in six subtropical landscape plants

Pigment combinations are regulated during leaf ontogenesis. To better understand pigment function, alterations in chlorophyll, carotenoid and anthocyanin concentrations were investigated during different leaf development stages in six subtropical landscape plants, namely Ixora chinensis Lam, Camellia japonica Linn, Eugenia oleina Wight, Mangifera indica L., Osmanthus fragrans Lowr and Saraca dives Pierre. High concentrations of anthocyanin were associated with reduced chlorophyll in juvenile leaves. As leaves developed, the photosynthetic pigments (chlorophyll and carotenoid) of all six species increased while anthocyanin concentration declined. Chlorophyll fluorescence imaging of Φ_PSII (effective quantum yield of PSII) and of NPQ (non-photochemical fluorescence quenching) and determination of electron transport rate-rapid light curve (RLC) showed that maximum ETR (leaf electron transport rate), Φ_PSII and the saturation point in RLC increased during leaf development but declined as they aged. Juvenile leaves displayed higher values of NPQ and Car/Chl ratios than leaves at other developmental stages. Leaf reflectance spectra (400–800 nm) were measured to provide an in vivo non-destructive assessment of pigments in leaves during ontogenesis. Four reflectance indices, related to pigment characters, were compared with data obtained quantitatively from biochemical analysis. The results showed that the ARI (anthocyanin reflectance index) was linearly correlated to anthocyanin concentration in juvenile leaves, while a positive correlation of Chl NDI (chlorophyll normalized difference vegetation index) to chlorophyll a concentration was species dependent. Photosynthetic reflectance index was not closely related to Car/Chl ratio, while a structural-independent pigment index was not greatly altered by leaf development or species. Accordingly, it is suggested that the high concentration of anthocyanin, higher NPQ and Car/Chl ratio in juvenile leaves are important functional responses to cope with high radiation when the photosynthetic apparatus is not fully developed. Another two leaf reflectance indices, ARI and Chl NDI, are valuable for in vivo pigment evaluation during leaf development.     

Probing corticular photosynthesis through in vivo chlorophyll fluorescence measurements: evidence that high internal CO levels suppress electron flow and increase the risk of photoinhibition

Twigs of many woody plants possess chlorenchyma under a well-developed periderm which lacks stomata and impedes both gas diffusion and light penetration. The so-called corticular photosynthesis, occurring in the shade and under extremely high CO(2) concentrations, was probed in this study through in vivo chlorophyll fluorescence measurements. Field comparisons between twigs and corresponding leaves in five species indicated that both the dark- and light-adapted PSII photochemical efficiencies are considerably lower in twigs at all incident photon fluence rates, in spite of the significant attenuation of solar radiation by the periderm. Light saturation curves for linear electron transport rates (corrected according to the actual light intensities reaching twig chlorenchyma) were compatible with a shade-acclimated photosynthetic machinery, showing very low maximum electron transport rates (at approximately 5% of the corresponding leaf values) and threshold irradiances for light saturation. However, removing periderms from twig segments (i.e. relieving the twig interior form the high CO(2) partial pressures) considerably improved the light-adapted (but not the dark-adapted) PSII photochemical efficiency, allowing the assumption that the high internal CO(2) levels may interfere with the smooth functioning of photosynthesis. Indeed, laboratory experiments with twig segments equilibrated under various CO(2) levels (0.036-20%), resulted in a progressive decrease of light-adapted PSII photochemical yield, with the values obtained at 20% CO(2) being similar to those obtained with intact twigs in the field. Further experiments indicated that high CO(2) combined with high light suppressed the development of a photoprotective non-photochemical quenching through a reduction of its fast relaxing component, accompanied by a higher risk of photoinhibition. It is suggested that high internal CO(2) concentrations in twigs impede photosynthesis possibly through acidification of protoplasm and impairment of the pH-dependent high energy state quenching followed by reduction in the efficiency of heat dissipation.     

一个番茄EMS叶色黄化突变体的叶绿素含量及光合作用

本试验以测序番茄品种‘Heinz 1706’的甲基磺酸乙酯(EMS)诱变所获得的叶色黄化突变体(Y55)为试材,分析了突变体的植株生长、叶片叶绿素含量及光合参数.结果表明: Y55的株高、茎粗、鲜质量均显著降低;叶绿素 a、叶绿素 b 、类胡萝卜素、总叶绿素含量以及叶绿素 a/b均显著降低,Y55叶绿素合成的前体物质含量均显著低于野生型,尤其是粪卟啉原Ⅲ及其后前体物质;且Y55叶片净光合速率、蒸腾速率、胞间CO₂浓度、气孔导度均显著低于野生型,最大光合速率、CO₂饱和点与补偿点、光饱和点与补偿点也显著下降;Y55的PSII最大量子效率显著降低,F_o显著升高,PSII与PSI的光合电子产量和电子传递速率显著降低;Y55处于基态的捕光色素分子、捕光色素分子处于最低激发态的平均寿命均显著降低.表明粪卟啉原Ⅲ的合成受阻可能是黄化突变体Y55叶绿素含量下降的主要原因,黄化突变降低了叶片捕光色素分子数量,影响了叶片的光合作用,进而抑制了植株的生长发育.     

Age-dependent bark photosynthesis of aspen twigs

The photosynthetic performance of trembling aspen (Populus tremula L.) twigs and leaves was studied in relation to selected structural features of aspen bark. PFD transmittance of intact periderm was reduced by about 90% in current-year twigs through peridermal thickening. However, because of drastic changes within the bark microstructure, PFD transmittance increased in 1-year-old twig segments up to 26% of the incident PFD. On a unit surface area basis, the chlorophyll content of young twigs (425 mg Chl m^-2) almost reached that of leaves (460 mg Chl m^-2). The chlorophyll content of aspen bark chlorenchyma was clearly age-dependent, even increasing in current-year twigs with advancing internodal age. The low bark chlorophyll a/b ratios (about 2.6 compared with 3.9 in leaves) indicate that bark chloroplasts are shade-adapted. Positive net photosynthesis was not found in aspen twigs, but apparent respiration was distinctly reduced in the light due to light-driven carbon refixation (bark photosynthesis) within the chlorenchymal tissues. Under constant microclimatic conditions, dark respiration rates were strongly correlated with stem-internal CO₂ refixation. In accordance with increasing dark respiration rates, the efficiency of this carbon recycling was generally greater in the metabolically more active, younger twig segments than in older segments; carbon refixation rates reached up to 80% of dark respiration values. At least in young twigs and branches and thus in the light-exposed outer parts of tree crowns, respiratory CO₂ losses by the tree skeleton could efficiently be reduced. Refixation of carbon dioxide may be of great importance for carbon budgets in the environmentally controlled or pathogen-induced leafless states of deciduous aspen trees.     

水分胁迫对牛心朴子叶片光合色素及叶绿素荧光的影响

研究了水分胁迫对牛心朴子叶片光合色素及叶绿素荧光动力学参数的影响。结果表明,在长期的水分胁迫中,牛心朴子叶片的叶绿素a(Chl a)、叶绿素b(Chl b)和类胡萝卜素(Car)含量没有下降或下降不明显。直到处理末期才显著下降;叶片叶绿素荧光动力学参数Fo、Fm、Fv、Fv／Fm变化不大,在处理末期各处理Fo降低,轻度、重度水分胁迫的Fm、Fv、Fv／Fm升高。说明K期水分胁迫后牛心朴子的光合功能受到影响,但牛心朴子仍表现出较强的适应干旱的能力。     

Differences in pigment composition, photosynthetic rates and chlorophyll fluorescence images of sun and shade leaves of four tree species.

The differential pigment composition and photosynthetic activity of sun and shade leaves of deciduous (Acer pseudoplatanus, Fagus sylvatica, Tilia cordata) and coniferous (Abies alba) trees was comparatively determined by studying the photosynthetic rates via CO(2) measurements and also by imaging the Chl fluorescence decrease ratio (R(Fd)), which is an in vivo indicator of the net CO(2) assimilation rates. The thicker sun leaves and needles in all tree species were characterized by a lower specific leaf area, lower water content, higher total chlorophyll (Chl) a+b and total carotenoid (Cars) content per leaf area unit, as well as higher values for the ratio Chl a/b compared to the much thinner shade leaves and needles that possess a higher Chl a+b and Cars content on a dry matter basis and higher values for the weight ratio Chls/Cars. Sun leaves and needles exhibited higher rates of maximum net photosynthetic CO(2) assimilation (P(Nmax)) measured at saturating irradiance associated with higher maximum stomatal conductance for water vapor efflux. The differences in photosynthetic activity between sun and shade leaves and needles could also be sensed via imaging the Chl fluorescence decrease ratio R(Fd), since it linearly correlated to the P(Nmax) rates at saturating irradiance. Chl fluorescence imaging not only provided the possibility to screen the differences in P(N) rates between sun and shade leaves, but in addition permitted detection and quantification of the large gradients in photosynthetic rates across the leaf area existing in sun and shade leaves.     

The effects of leaf size,leaf habit,and leaf form on leaf/stem relationships in plant twigs of temperate woody species

Question: Do thick‐twigged/large‐leaf species have an advantage in leaf display over their counterparts, and what are the effects of leaf habit and leaf form on the leaf‐stem relationship in plant twigs of temperature broadleaf woody species? Location: Gongga Mountain, southwest China. Methods: (1) We investigated stem cross‐sectional area and stem mass, leaf area and leaf/lamina mass of plant twigs (terminal branches of current‐year shoots) of 89 species belonging to 55 genera in 31 families. (2) Data were analyzed to determine leaf‐stem scaling relationships using both the Model type II regression method and the phylogenetically independent comparative (PIC) method. Results: (1) Significant, positive allometric relationships were found between twig cross‐sectional area and total leaf area supported by the twig, and between the cross‐sectional area and individual leaf area, suggesting that species with large leaves and thick twigs could support a disproportionately greater leaf area for a given twig cross‐sectional area. (2) However, the scaling relationships between twig stem mass and total leaf area and between stem mass and total lamina mass were approximately isometric, which indicates that the efficiency of deploying leaf area and lamina mass was independent of leaf size and twig size. The results of PIC were consistent with these correlations. (3) The evergreen species were usually smaller in total leaf area for a given twig stem investment in terms of both cross‐sectional area and stem mass, compared to deciduous species. Leaf mass per area (LMA) was negatively associated with the stem efficiency in deploying leaf area. (4) Compound leaf species could usually support a larger leaf area for a given twig stem mass and were usually larger in both leaf size and twig size than simple leaf species. Conclusions: Generally, thick‐twigged/large‐leaf species do not have an advantage over their counterparts in deploying photosynthetic compartments for a given twig stem investment. Leaf habit and leaf form types can modify leaf‐stem scaling relationships, possibly because of contrasting leaf properties. The leaf size‐twig size spectrum is related to the LMA‐leaf life span dimension of plant life history strategies.     

基于叶绿素荧光参数的小麦叶片叶绿素相对含量估算方法

叶绿素含量是植物学和农业相关研究领域常用的生理指标.叶绿素含量和叶片光合功能密切相关,但是现有的叶绿素含量的测定方法无法实现叶绿素含量和光合功能的同步测定和关联分析.为解决该问题,本研究通过测定35个小麦品种旗叶的SPAD值和叶绿素荧光诱导动力学曲线,分别使用不同时间的快速叶绿素荧光动力学曲线的荧光值,以及33个常用荧...     

The fine structure and photosynthetic cost of structural leaf variegation

The leaves of some plants display an optical patchiness on their upper side, displaying light- and dark-green areas with high and low reflectance, respectively. In this investigation, we studied the fine structure of the corresponding sectors and we asked whether the lost reflected light entails a photosynthetic cost to these leaves. Four species, i.e. Arum italicum, Ranunculus ficaria, Cyclamen hederifolium and Cyclamen persicum were investigated. Scanning electron microscope examination revealed that epidermal cells of light-green sectors of all species are more bulgy than corresponding cells of neighboring dark-green leaf sectors. The comparative anatomical study revealed that (i) epidermis thickness of the light-green areas and the number of mesophyll cell layers does not differ from those of the adjacent dark-green leaf sectors and (ii) palisade cells of light-green sectors are slightly larger and more loosely arranged, allowing a much higher percentage of intercellular air spaces. The latter histological feature seems to provide the structural basis for the different optical properties between the two leaf sectors. Contrary to expectations, net photosynthetic rates (expressed on a leaf area basis) were similar in the light-green and the dark-green areas of the two cyclamen species. Yet, in C. persicum net photosynthesis was higher in the light-green areas, if expressed on a dry mass basis. The small size of the light-green spots in the rest of the test plants precluded CO₂ assimilation measurements, yet maximum linear photosynthetic electron transport rates displayed no differences between the two sectors in all plants. Thus, the assumption of a photosynthetic cost in the light-green areas was not confirmed. On the contrary, a higher construction cost was evident in the dark-green areas of three species, displaying a significantly higher specific leaf mass, without any photosynthetic benefit. The results on net photosynthesis were compatible with leaf optical properties and pigment levels. Thus, in spite of the considerably higher reflectance of the light-green areas and their lower (yet normal for a green leaf) chlorophyll levels, corresponding differences in absorptance were slight. In addition, dry mass-based pigment contents in dark-green areas were higher, while chlorophyll a/b (in two species) and carotenoid/chlorophyll ratios (in three species) were lower, pointing to a shade adaptation in these sectors. We conclude that in variegated leaves of this kind, dark-green areas are more costly to build and probably less photosynthetically active. We argue that the high pigment contents of dark-green areas establish steep light gradients in the corresponding mesophyll, rendering deeper chloroplast layers more shade adapted.     

Response to ozone in two lettuce varieties on chlorophyll a fluorescence, photosynthetic pigments and lipid peroxidation.

The effect of different O3 concentrations on two lettuce (Lactuca sativa L.) varieties (Valladolid and Morella) was investigated through chlorophyll (Chl) a fluorescence parameters, photosynthetic pigments (Chl a, b and total carotenoid), lipid peroxidation and crop yield. Ozone fumigation caused: a decrease in maximum quantum yield of photosystem II (PSII) photochemistry (Fv/Fm) in mature leaves, a reduction in the non-cyclic electron flow (phiPSII) and a lower capacity to reoxidize the QA pool (qP). These reductions were significant in the Valladolid var. but not in the Morella var. A significant decrease in Chl a, b and in the total carotenoids was observed in the Valladolid var. but not in the Morella var. mainly under O3 fumigation conditions. We observed that the NPQ parameter did not increase in parallel to the qP reduction seen in the Valladolid var. O3 fumigation with respect to air charcoal filtered air conditions. This fact could be associated with a lower capacity for dissipation of non-radiative excess energy and it may be closely correlated with significant decreases in photosynthetic pigment concentration. A decrease in NPQ from air ozone-free to ozone fumigation in the Morella var. can be explained by the need to maintain the photochemical quenching under O3 stress. It may also be associated with a slight increase in photosynthetic pigments. The differences between the two varieties may indicate that the Valladolid var. is more susceptible to O3 damage.     

分株比例对异质光环境下美丽箬竹克隆系统光合生理的影响

分株数量或生物量比例差异会明显影响克隆系统对资源异质性环境的生态适应性, 地下茎木质化、连接稳固的竹类植物在生长过程中相连克隆分株通常会生活在异质光环境中, 但其叶片光合生理特性对异质光环境的响应及其分株比例效应则未见报道。该研究以地下茎相连的美丽箬竹(Indocalamus decorus)克隆系统为实验材料, 设置2个遮光率(分别为50% ± 5%和75% ± 5%)和3个分株比例(遮光与未遮光分株比例分别为1:3、2:2、3:1)处理, 分株数量为4株。分别测定了遮光处理后30、90、150天遮光和未遮光分株叶片光响应特征、气体交换参数、光合色素含量, 分析了异质光环境下美丽箬竹光合生理的变化规律。结果显示: 分株比例对美丽箬竹光合生理有显著影响, 且其与遮光、处理时间交互作用显著。美丽箬竹克隆系统遮光分株比例越大, 即遮光相对分株数量越多, 其表观量子效率(AQE)、光饱和点、最大净光合速率(P_{n max})、净光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)、水分利用效率越大, 光补偿点、暗呼吸速率越小, 其光合效率越高, 光能利用能力越强, 而与之相连的未遮光分株则相反; 随遮光分株比例的增大, 遮光分株叶片叶绿素a、叶绿素b含量呈先升高而后下降的变化趋势, 类胡萝卜素(Car)含量则持续下降, 而与之相连的未遮光分株叶片光合色素含量则呈下降趋势; 遮光率提高, 相同分株比例美丽箬竹克隆系统遮光分株叶片AQE、P_{n max}、P_n、G_s、胞间CO₂浓度(C_i)和光合色素含量总体升高, 而与之相连的未遮光分株叶片P_{n max}、C_i以及Car含量则总体下降。研究结果表明异质光环境下, 遮光分株光合效率和弱光利用能力明显增强, 而未遮光分株则相反, 克隆系统内分株间发生了明显的克隆分工, 且2:2、3:1分株比例克隆系统较1:3分株比例对异质光环境具有更好的适应能力。美丽箬竹克隆系统可通过差异性调节分株光合生理特性和光合色素含量, 提高遮光分株光能利用和光合效率来适应异质光环境, 以提高克隆系统的适合度。     

Consequences of chlorophyll deficiency for leaf carotenoid composition in tobacco synthesizing glutamate 1-semialdehyde aminotransferase antisense RNA: dependency on developmental age and growth light

Transgenic tobacco (Nicotiana tabacum), with a reduced chlorophyll content of up to less than 10% of the wild-type level due to a different expression of antisense RNA coding for glutamate 1-semialdehyde aminotransferase, were used to study the relationship between chlorophyll accumulation and changes in carotenoid composition in developing and mature leaves grown either under low (30 mol photons m^-2 s^-1) or high light (300 mol photons m^-2 s^-1). Regardless of the extent to which chlorophyll synthesis was reduced, under low light the ratios of total chlorophyll to carotenoids remained constant. In contrast, under high light the content of carotenoids was elevated relative to chlorophyll and increased further with progressive inhibition in chlorophyll synthesis. The xanthophyll-cycle pigment pool was most strongly increased (up to 18-fold) upon suppression of chlorophyll synthesis. Concurrently to the higher pool sizes a higher extent of violaxanthin was converted into antheraxanthin and zeaxanthin and this was found to be correlated with a decrease in the quantum yield of photosystem II photochemistry. While lutein increased (up to 3-fold) with decreasing chlorophyll contents in high light transformants, neoxanthin remained rather constant in all plants analysed. Based on the present results, two different levels for the regulation of carotenoid synthesis are proposed depending on (I) the chlorophyll synthesizing capacity, and (ii) the photosynthetic light utilization efficiency. The first point suggests a co-regulation between carotenoid and chlorophyll synthesis; the second emphasizes the special role of carotenoids for protection against light stress.     

Within-twig biomass allocation in subtropical evergreen broad-leaved species along an altitudinal gradient: allometric scaling analysis

We studied the effects of twig size and altitude on biomass allocation within plant twigs (terminal branches of current-year shoots), to determine whether species with large twigs/leaves or living at low altitude allocate a higher proportion of biomass to laminas than their counterparts with small twigs/leaves or living at high altitude. Stem mass, lamina mass and area, and petiole mass were measured for terminal branches of current-year shoots in 80 subtropical evergreen broad-leaved species belonging to 38 genera from 24 families along an altitudinal gradient of Mt. Emei, Southwest China. The scaling relationships between the biomass allocations of within-twig components were determined using model type II regression method. Isometric relationships were found between leaf mass and twig mass and between lamina mass and twig mass, suggesting that the biomass allocation to either leaves or laminas was independent of twig mass. Petiole mass disproportionally increased with both lamina mass and twig mass, indicating the importance of leaf petioles to the within-twig biomass allocation. These cross-species correlations were consistent with those among evolutionary divergences. In addition, species at low altitude tended to have a greater leaf and lamina mass but a smaller stem mass at a given twig mass than at middle and high altitudes. This is possibly due to the high requirement in physical support and the low efficiency of eco-physiological transport for the species living at high altitude. In general, within-twig biomass allocation pattern was not significantly affected by twig size but was greatly modulated by altitude.     

Leaf and photosynthetic characteristics of pioneer and forest species in tropical montane habitats

Gas exchange and chlorophyll a fluorescence measurements of expanding and adult leaves of four plant species were compared under field conditions. The pioneer species (PS) tended to have thinner leaves with lower nitrogen content and higher stomatal density compared to forest species (FS). Expanding leaves featured lower photosynthetic pigment contents and gas exchange capacity than adult leaves consistent with an immature photosynthetic apparatus. At the time of maximum irradiance, sun-exposed leaves of both PS and FS showed alteration of initial, variable, and maximum fluorescence as well as their ratios indicating photoinhibition. However, leaves recovered to some extent at predawn, suggesting the activation of photoprotective mechanisms. Sun-exposed leaves had comparable responses to high irradiance.     

外源甜菜碱对盐胁迫下枸杞光合功能的改善

研究了外源甜菜碱对盐胁迫下枸杞扦插苗叶片光合功能的影响。结果表明,外源甜菜碱能使盐胁迫下的枸杞叶片叶绿素荧光动力学参数Fo、Fm、Fv、Fv／Fm、Fm／Fo和Fv／Fo增高,使光合色素叶绿素a(Chla)、叶绿素b(Chlb)和类胡萝卜素(Car)含量明显增加,叶绿素a与b的比值(Chla／Chlb)升高,类胡萝卜素与叶绿素的比值(Car／Chl)降低,说明外源甜菜碱有利于植物对光能的捕获、吸收、传递和转换,提高叶片的光合活性,降低盐胁迫对植物的抑制作用。