松嫩草地全叶马兰夏季与秋季光合及蒸腾作用的比较

在生长季晴天条件下,夏季和秋季松嫩草地全叶马兰的光合,蒸腾作用的日变化均为双峰曲线,但不同季节有所差异,夏季日均净光合速率与蒸腾速率均高于秋季,光合和蒸腾作用与环境因子的植物内部因子之间有密切关系。分析表明,叶片净光合速率与有效光辐射呈极显著相关,与气孔阻力,胞间CO2呈负相关;蒸腾速率与有效光辐射呈极显著相关,与叶温,饱和差呈正相关,与气孔阻力,胞间CO2浓度呈负相关,有效光辐射是影响光合和蒸腾作用诸因子中的主导因子,而气孔阻力变化则在调节光合和蒸腾中起着重要作用,蒸腾速率午降主要由于光辐射强,叶温高,湿度低,植物体缺水,气孔部分关闭所致。     

Functional dynamics of plant growth and photosynthesis--from steady-state to dynamics--from homogeneity to heterogeneity

Plants are much more dynamic than we usually expect them to be. This dynamic behaviour is of paramount importance for their performance under natural conditions, when resources are distributed heterogeneously in space and time. However, plants are not only the cue ball of their physical and chemical environment. Endogenous rhythms and networks controlling photosynthesis and growth buffer plant processes from external fluctuations. This review highlights recent evidence of the importance of dynamic temporal and spatial organization of photosynthesis and of growth in leaves and roots. These central processes for plant performance differ strongly in their dependence on environmental impact and endogenous properties, respectively. Growth involves a wealth of processes ranging from the supply of resources from external and internal sources to the growth processes themselves. In contrast, photosynthesis can only take place when light and CO2 are present and thus clearly requires 'input from the environment'. Nevertheless, growth and photosynthesis are connected to each other via mechanisms that are still not fully understood. Recent advances in imaging technology have provided new insights into the dynamics of plant-environment interactions. Such processes do not only play a crucial role in understanding stress response of plants under extreme environmental conditions. Dynamics of plants under modest growth conditions rise from endogenous mechanisms as well as exogenous impact too. It is thus an important task for future research to identify how dynamic external conditions interact with plant-internal signalling networks to optimize plant behaviour in real time and to understand how plants have adapted to characteristic spatial and temporal properties of the resources from their environment, on which they depend on.     

The role of mesophyll conductance in the economics of nitrogen and water use in photosynthesis

A recent resurgence of interest in formal optimisation theory has begun to improve our understanding of how variations in stomatal conductance and photosynthetic capacity control the response of whole plant photosynthesis and growth to the environment. However, mesophyll conductance exhibits similar variation and has similar impact on photosynthesis as stomatal conductance; yet, the role of mesophyll conductance in the economics of photosynthetic resource use has not been thoroughly explored. In this article, we first briefly summarise the knowledge of how mesophyll conductance varies in relation to environmental factors that also affect stomatal conductance and photosynthetic capacity, and then we use a simple analytical approach to begin to explore how these important controls on photosynthesis should mutually co-vary in a plant canopy in the optimum. Our analysis predicts that when either stomatal or mesophyll conductance is limited by fundamental biophysical constraints in some areas of a canopy, e.g. reduced stomatal conductance in upper canopy leaves due to reduced water potential, the other of the two conductances should increase in those leaves, while photosynthetic capacity should decrease. Our analysis also predicts that if mesophyll conductance depends on nitrogen investment in one or more proteins, then nitrogen investment should shift away from Rubisco and towards mesophyll conductance if hydraulic or other constraints cause chloroplastic CO₂ concentration to decline. Thorough exploration of these issues awaits better knowledge of whether and how mesophyll conductance is itself limited by nitrogen investment, and about how these determinants of photosynthetic CO₂ supply and demand co-vary among leaves in real plant canopies.     

The diurnal time course of net photosynthesis of soybean leaves: Analysis with a physiologically based steady-state photosynthesis model

Summary A physiologically based steady-state model of whole leaf photosynthesis (WHOLEPHOT) is used to analyze observed net photosynthesis daily time courses of soybean, Glycine max (L.) Merr., leaves. Observations during two time periods of the 1978 growing season are analyzed and compared. After adjustment of the model for soybean, net photosynthesis rates are calculated with the model in response to measured incident light intensity, leaf temperature, air carbon dioxide concentration, and leaf diffusion resistance. The steady-state calculations closely approximate observed net photosynthesis. Results of the comparison reveal a decrease in photosynthetic capacity in leaves sampled during the second time period, which is associated with decreasing ability of leaves to respond to light intensity and internal air space carbon dioxide concentration, increasing mesophyll resistance, and increasing stomatal resistance.     

Formation of false stems in Cymopterus longiopes: an uplifting example of growth form change

Summary The leaves of Cymopterus longipes form prostrate rosettes early in the spring. As the weather warms, these leaves are elevated on a pseudoscape (false stem) which develops below the rosette through the elongation of the caudex (in the region between root and shoot). The effect of this growth form change on the water relations and photosynthesis in C. longipes was investigated. Pseudoscape height was not linked to phenology or plant size. Leaf conductance, leaf temperature, and leaf water potential were notably similar between plants with different pseudoscape height growing in different microsites. Experimental manipulation of the microclimate around plants growing naturally allowed us to demonstrate that increased temperature led to an increase in the rate of pseudoscape elongation. By changing the distance above the ground surface of the rosettes of some plants we determined that leaf temperature, leaf to air vapour concentration deficits, leaf conductances, and leaf water potentials were all influenced by pseudoscape height. Leaf conductance in C. longipes had a strong negative relationship with W. Since the temperature response of net photosynthesis was extremely flat it was concluded that pseudoscape elongation may be an important morphological means of increasing water use efficiency.     

Effects of nitrogen supply on the acclimation of photosynthesis to elevated CO2

A common observation in plants grown in elevated CO₂ concentration is that the rate of photosynthesis is lower than expected from the dependence of photosynthesis upon CO₂ concentration in single leaves of plants grown at present CO₂ concentration. Furthermore, it has been suggested that this apparent down regulation of photosynthesis may be larger in leaves of plants at low nitrogen supply than at higher nitrogen supply. However, the available data are rather limited and contradictory. In this paper, particular attention is drawn to the way in which whole plant growth response to N supply constitutes a variable sink strength for carbohydrate usage and how this may affect photosynthesis. The need for further studies of the acclimation of photosynthesis at elevated CO₂ in leaves of plants whose N supply has resulted in well-defined growth rate and sink activity is emphasised, and brief consideration is made of how this might be achieved.Abbreviations A rate of CO₂ assimilation - C_i internal CO₂ concentration - PCR photosynthetic carbon reduction - Rubisco Ribulose 1,5-bisphosphate carboxylase/oxygenase - RuBP ribulose 1,5-bisphosphate     

The Control of Water and Carbon Dioxide Flux in Water-stressed Sugar Beet

Changes in leaf and canopy water potential of sugar beet growingin soil of decreasing water content depended on soil water potentialand were independent of water flux from the plant when thiswas varied by changing the water vapour content of the air.The calculated hydraulic conductance of the plant increasedas flux increased and decreased as leaf water potential decreasedand as the plant aged. The conductances to water vapour of individualleaves and of the canopy decreased as leaf water potential decreasedand increased with increasing humidity of the air. The lattereffect was independent of changes in leaf water potential. Theconductances were not affected by the rate of evaporation orleaf temperature. The rate of photosynthesis was directly relatedto leaf conductance except in severely stressed, mature leavesin which leaf water potential had a more direct effect on photosynthesis.Stomatal conductances, transpiration, and photosynthesis weregreater in young leaves than mature leaves on the same plantand at the same leaf water potential. These results are discussedin relation to current agricultural irrigation practices usedfor sugar beet.     

How plants cope with complete submergence

Flooding is a widespread phenomenon that drastically reduces the growth and survival of terrestrial plants. The dramatic decrease of gas diffusion in water compared with in air is a major problem for terrestrial plants and limits the entry of CO(2) for photosynthesis and of O(2) for respiration. Responses to avoid the adverse effects of submergence are the central theme in this review. These include underwater photosynthesis, aerenchyma formation and enhanced shoot elongation. Aerenchyma facilitates gas diffusion inside plants so that shoot-derived O(2) can diffuse to O(2)-deprived plant parts, such as the roots. The underwater gas-exchange capacity of leaves can be greatly enhanced by a thinner cuticle, reorientation of the chloroplasts towards the epidermis and increased specific leaf area (i.e. thinner leaves). At the same time, plants can outgrow the water through increased shoot elongation, which in some species is preceded by an adjustment of leaf angle to a more vertical position. The molecular regulatory networks involved in these responses, including the putative signals to sense submergence, are discussed and suggestions made on how to unravel the mechanistic basis of the induced expression of various adaptations that alleviate O(2) shortage underwater.     

Elevated CO2 and plant structure: a review

Consequences of increasing atmospheric CO₂ concentration on plant structure, an important determinant of physiological and competitive success, have not received sufficient attention in the literature. Understanding how increasing carbon input will influence plant developmental processes, and resultant form, will help bridge the gap between physiological response and ecosystem level phenomena. Growth in elevated CO₂ alters plant structure through its effects on both primary and secondary meristems of shoots and roots. Although not well established, a review of the literature suggests that cell division, cell expansion, and cell patterning may be affected, driven mainly by increased substrate (sucrose) availability and perhaps also by differential expression of genes involved in cell cycling (e.g. cyclins) or cell expansion (e.g. xyloglucan endotransglycosylase). Few studies, however, have attempted to elucidate the mechanistic basis for increased growth at the cellular level. Regardless of specific mechanisms involved, plant leaf size and anatomy are often altered by growth in elevated CO₂, but the magnitude of these changes, which often decreases as leaves mature, hinges upon plant genetic plasticity, nutrient availability, temperature, and phenology. Increased leaf growth results more often from increased cell expansion rather than increased division. Leaves of crop species exhibit greater increases in leaf thickness than do leaves of wild species. Increased mesophyll and vascular tissue cross-sectional areas, important determinates of photosynthetic rates and assimilate transport capacity, are often reported. Few studies, however, have quantified characteristics more reflective of leaf function such as spatial relationships among chlorenchyma cells (size, orientation, and surface area), intercellular spaces, and conductive tissue. Greater leaf size and/or more leaves per plant are often noted; plants grown in elevated CO₂ exhibited increased leaf area per plant in 66% of studies, compared to 28% of observations reporting no change, and 6% reported a decrease in whole plant leaf area. This resulted in an average net increase in leaf area per plant of 24%. Crop species showed the greatest average increase in whole plant leaf area (+ 37%) compared to tree species (+ 14%) and wild, nonwoody species (+ 15%). Conversely, tree species and wild, nontrees showed the greatest reduction in specific leaf area (– 14% and – 20%) compared to crop plants (– 6%). Alterations in developmental processes at the shoot apex and within the vascular cambium contributed to increased plant height, altered branching characteristics, and increased stem diameters. The ratio of internode length to node number often increased, but the length and sometimes the number of branches per node was greater, suggesting reduced apical dominance. Data concerning effects of elevated CO₂ on stem/branch anatomy, vital for understanding potential shifts in functional relationships of leaves with stems, roots with stems, and leaves with roots, are too few to make generalizations. Growth in elevated CO₂ typically leads to increased root length, diameter, and altered branching patterns. Altered branching characteristics in both shoots and roots may impact competitive relationships above and below the ground. Understanding how increased carbon assimilation affects growth processes (cell division, cell expansion, and cell patterning) will facilitate a better understanding of how plant form will change as atmospheric CO₂ increases. Knowing how basic growth processes respond to increased carbon inputs may also provide a mechanistic basis for the differential phenotypic plasticity exhibited by different plant species/functional types to elevated CO₂.     

Isoprene increases thermotolerance of fosmidomycin-fed leaves

Isoprene is synthesized and emitted in large amounts by a number of plant species, especially oak (Quercus sp.) and aspen (Populus sp.) trees. It has been suggested that isoprene improves thermotolerance by helping photosynthesis cope with high temperature. However, the evidence for the thermotolerance hypothesis is indirect and one of three methods used to support this hypothesis has recently been called into question. More direct evidence required new methods of controlling endogenous isoprene. An inhibitor of the deoxyxylulose 5-phosphate pathway, the alternative pathway to the mevalonic acid pathway and the pathway by which isoprene is made, is now available. Fosmidomycin eliminates isoprene emission without affecting photosynthesis for several hours after feeding to detached leaves. Photosynthesis of fosmidomycin-fed leaves recovered less following a 2-min high-temperature treatment at 46 degrees C than did photosynthesis of leaves fed water or fosmidomycin-fed leaves in air supplemented with isoprene. Photosynthesis of Phaseolus vulgaris leaves, which do not make isoprene, exhibited increased thermotolerance when isoprene was supplied in the airstream flowing over the leaf. Other short-chain alkenes also improved thermotolerance, whereas alkanes reduced thermotolerance. It is concluded that thermotolerance of photosynthesis is a substantial benefit to plants that make isoprene and that this benefit explains why plants make isoprene. The effect may be a general hydrocarbon effect and related to the double bonds in the isoprene molecule.     

斑驳气孔特点及形成机理

气孔是植物叶片内外气体交换的场所。斑驳气孔在形态结构、动态变化、光合气体交换机制等方面都与常见的普通气孔不同,是植物体响应环境变化而形戍的特殊气孔形式。本文介绍了斑驳气孔的特点及其形成机理。     

Regulation of RuBP carboxylase activity associated with photo-inhibition of wheat

Detached wheat leaves were illuminated in air until a steady rate of photosynthesis was established. Then the gas was changed to 1% O₂, 99% N₂ and after 2.5 h further illumination the capacity of the leaves for photosynthesis in air was decreased to approximately 50%. Measurement of RuBP carboxylase activity in extracts showed that inhibition of photosynthesis was accompanied by 70% inactivation of this enzyme. The capacity for photosynthesis and the activity of RuBP carboxylase were recovered when leaves were returned to normal air. Extracts of the leaves made when photosynthesis and carboxylase activity were low, recovered most of the lost carboxylase activity when supplemented with bicarbonate and magnesium ions. The time courses for activation and inactivation of the RuBP carboxylase in these experiments suggests the operation of a mechanism that has not yet been elucidated.     

Plant calcium oxalate crystal formation, function, and its impact on human health

Crystals of calcium oxalate have been observed among members from most taxonomic groups of photosynthetic organisms ranging from the smallest algae to the largest trees.The biological roles for calcium...     

Der Beitrag einzelner Blätter an der Pflanze zur Photosynthese des gesamten Blattapparates im Laufe der Pflanzenentwicklung

Plants ofPlectranthus fructicosus were grown in two controlled environments -“spring” and “summer” conditions - differing in temperature and air humidity (day/night 20/15 and 27/22 °C; 80/98 and 50/80 % relative humidity) in order to study the influence of environmental conditions on the development of photosynthetic characteristics of individual leaves. The contribution of individual leaves to plant photosynthesis was very similar in both environments, the maximum shifting from bottom leaves to leaves of middle insertion levels during plant ontogenesis. On integrating the values of leaf photosynthesis for the whole vegetation period, the 5th leaf in “spring” conditions and the 4th leaf in “summer” conditions showed the highest contribution to plant photosynthesis (29 % resp. 25% of total net CO₂ influx). The “photosynthetically mature” leaves of middle insertion levels played the main role in CO₂ uptake of whole plant.     

Evergreens favored by higher responsiveness to increased CO₂

Physical CO(2) diffusion from sub-stomatal cavities to the chloroplasts where photosynthesis takes place is an important limitation of photosynthesis largely neglected in research related to global climate change. This limitation is particularly important in leaves with robust structures such as evergreen sclerophylls. In these leaves, photosynthesis is less sensitive to changes in stomatal openness, which is considered to be the primary limitation of photosynthesis. In this review we state that, because of large limitations in internal diffusion in C(3) plants, photosynthesis and the intrinsic efficiency of the use of plant water responds more strongly to elevated levels of CO(2) in leaves with more robust structures. This provides an additional explanation for the current apparent expansion of evergreen sclerophylls in many Earth ecosystems, and adds a new perspective to research of the biological effects of increasing atmospheric CO(2).     

Photosynthetic consequences of phenotypic plasticity in response to submergence: Rumex palustris as a case study

Survival and growth of terrestrial plants is negatively affected by complete submergence. This is mainly the result of hampered gas exchange between plants and their environment, since gas diffusion is severely reduced in water compared with air, resulting in O2 deficits which limit aerobic respiration. The continuation of photosynthesis could probably alleviate submergence-stress in terrestrial plants, but its potential under water will be limited as the availability of CO2 is hampered. Several submerged terrestrial plant species, however, express plastic responses of the shoot which may reduce gas diffusion resistance and enhance benefits from underwater photosynthesis. In particular, the plasticity of the flooding-tolerant terrestrial species Rumex palustris turned out to be remarkable, making it a model species suitable for the study of these responses. During submergence, the morphology and anatomy of newly developed leaves changed: 'aquatic' leaves were thinner and had thinner cuticles. As a consequence, internal O2 concentrations and underwater CO2 assimilation rates were higher at the prevailing low CO2 concentrations in water. Compared with heterophyllous amphibious plant species, underwater photosynthesis rates of terrestrial plants may be very limited, but the effects of underwater photosynthesis on underwater survival are impressive. A combination of recently published data allowed quantification of the magnitude of the acclimation response in this species. Gas diffusion resistance in terrestrial leaves underwater was about 15,000 times higher than in air. Strikingly, acclimation to submergence reduced this factor to 400, indicating that acclimated leaves of R. palustris had an approximately 40 times lower gas diffusion resistance than non-acclimated ones.     

The recovery of photosynthesis in tomato subsequent to chilling exposure

The overall success of a plant in coping with low temperature sensitivity of photosynthesis is dependent not only on the maximum extent of inhibition suffered for a given time of low temperature exposure but also on the persistence of the inhibition after normal growth temperatures are restored. Thus the capacity of recovery and the speed with which a plant can recover from the effects of chilling exposure are important parameters in determining how devastating the chilling event will be on season-long growth and yields. We have studied the recovery of CO₂-saturated photosynthesis from the injury caused by exposing intact tomato plants (Lycopersicon esculentum Mill. cv. Floramerica) or detached tomato leaves to a temperature of 1°C in the dark for varying periods of time. We found that net photosynthesis was fully recovered within 12 h after returning the plants to 25°C in the dark, even after chilling exposures as long as 45 h. This was true for intact plants as well as for detached leaves that were supplied with water. When chilling took place in the light (4°C, 1000 E · m^-2 · s^-1, PAR) inhibition of photosynthesis was more severe and appeared more quickly and the recovery was slower and incomplete. A 12 h chilling exposure in the light resulted in injury to net photosynthesis that was not fully recovered even after 50 h. Chilling damage to photosynthesis developing in the light was distinguished from chilling in the dark by the decreased photosynthetic quantum yield. Not only did high intensity illumination enhance chilling damage of photosynthesis but bright light subsequent to the chilling exposure also delayed the recovery of photosynthesis. At none of the three ambient CO₂ concentrations investigated (300, 1500 and 5000 1.1^-1) did the recovery of photosynthesis depend on stomatal conductance.     

Anatomical considerations related to photosynthesis in cotton (Gossypium hirsutum L.) leaves, bracts, and the capsule wall

Light and electron microscopy was used to relate histologicaland ultrastructural differences of cotton (Gossypium hirsutumL.) leaves, bracts, and capsule walls to their different photosyntheticactivities. Light microscopy revealed that the leaf thicknesswas approximately 152µm, had a well-defined internal organizationwith elongated palisade mesophyll cells and loosely packed spongymesophyll cells. In contrast, the bract was thinner (111 µm),lacked a defined palisade layer, and was largely composed ofinternal air spaces. The capsule wall was very thick (1013µm)and composed of numerous tightly packed, paren-chymatous corticalcells with little or no intercellular air space. Chloroplastswith well-defined granal stacks and extensive stroma lamellaewere observed in each of these three tissues, however, theirdensity was always greater in the palisade cells of the leafcompared to spongy mesophyll cells of the bract and the parenchymatouscells of the capsule wall. The low rates of photosynthesis inthe bracts and the capsule wall were associated with the internalorganization of these tissues. Key words: Cotton, photosynthesis, anatomy, cuticle, tissues