Structural and Functional Grounds for Ephedra sinica Expansion in Mongolian Steppe Ecosystems

Morphological and structural characteristics of photosynthetic organs, diurnal changes in photosynthetic and transpiration rates, and the efficiency of water use were studied in three plant species from mountain-steppe ecosystems in Mongolia, Ephedra sinica Stapf, Stipa glareosa P. Smirn., and Allium polyrhizum Furcz. ex Regel. The species studied differed in the structural and functional mechanisms for the adaptation of photosynthetic apparatus to arid conditions. E. sinica has thick, vertical assimilating shoots, which are characterized by a high density (620 mg/cm³) and a small proportion of photosynthetic tissues (13%). The proportion of meso-phyll in the leaves of A. polyrhizum and S. glareosa was two and three times higher, respectively. The low content of phototrophic tissues in E. sinica shoot was compensated for by a high photosynthetic activity of single chloroplasts (25 mg CO₂/(10⁹ chloroplast h)), which was six times higher, than in two other species. Daily course of photosynthesis and transpiration inE. sinica differed from those of A. polyrhizum and S. glareosa by the absence of the midday depression. E. sinica had the highest efficiency of water use (45 mg CO₂/g H₂O) due to a low transpiration rate (0.25 g/g fr wt h). It is concluded that, in E. sinica, the main strategy for adaptation to arid stress is to develop in the shoot a few photosynthesizing cells of high assimilation activity. Such structural organization of photosynthetic organs in ephedra contributes to its higher efficiency of water use and stability of physiological characteristics under changing environmental conditions. These specific features of the structure of assimilating organs and their functional features contribute to a greater expansion of E. sinica with increasing climate aridization in Mongolia.     

Structure of the Photosynthetic Apparatus in Leaves of Freshwater Hydrophytes: 2. Quantitative Characterization of Leaf Mesophyll and the Functional Activity of Leaves with Different Degrees of Submersion

The structure of leaf photosynthetic elements was investigated on 42 boreal plant species characterized by different degrees of submergence (helophytes, neustophytes, and hydatophytes). Six main types of mesophyll structures were identified. Quantitative characteristics for the mesostructure of the photosynthetic apparatus in these groups were determined, such as the size and abundance of cells and chloroplasts in the mesophyll and epidermis, the number of plastids per cell in each tissue, the total surface area of the mesophyll cells, epidermal cells, and chloroplasts per unit leaf area. Analysis showed that quantitative characteristics of the photosynthetic apparatus in hydrophytes are determined by two factors: (a) the degree of leaf submergence and (b) the type of mesophyll structure. With an increasing degree of immersion in water, the mesophyll types change in a sequence isopalisade dorsoventral homogeneous. The leaves become thinner, their weight per unit area diminishes, cells and chloroplasts become less numerous (on a per unit leaf area basis), but their dimensions become larger. Adaptation to aquatic medium is also manifested in the increasing contribution of the epidermal tissue to the overall photosynthesis: in submerged leaves, the epidermis accounts for more than 50% of the photosynthetic activity. The occurrence of six structural types of leaves contrasting in their characteristics was confirmed by discriminatory analysis according to the qualitative parameters of mesophyll.     

Structure of the Photosynthetic Apparatus in Leaves of Freshwater Hydrophytes: 1. General Characteristics of the Leaf Mesophyll and a Comparison with Terrestrial Plants

The structure of photosynthetic elements was investigated in leaves of 42 boreal plant species featuring different degrees of submergence (helophytes, neustophytes, and hydatophytes). The mesophyll structure types were identified for all these species. Chlorenchyma tissues and phototrophic cells were quantitatively described by such characteristics as the sizes of cells and chloroplasts in the mesophyll and epidermis, the abundance of cells and chloroplasts in these tissues, the total surface area of cells and chloroplasts per unit leaf area, the number of plastids per cell, etc. The hydrophytes typically had thick leaves (200–350 m) with a well-developed aerenchyma; their specific density per unit area (100–200 mg/dm²) was lower than in terrestrial plants. Mesophyll cells in aquatic plants occupied a larger volume (5–20 × 10³m³) than epidermal cells (1–15 × 10³m³). The number of mesophyll cells per unit leaf area was nearly 1.5 times higher than that of epidermal cells. Chloroplasts were present in the epidermis of almost all species, including emergent leaves, but the ratio of the chloroplast total number to the number of all plastids varied depending on the degree of leaf submergence. The total number of plastids per unit leaf area (2–6 × 10⁶/cm²) and the surface of chloroplasts per unit leaf area (2–6 cm²/cm²) were lower in hydrophytes than in terrestrial plants from climatically similar habitats. The functional relations between mesophyll parameters were similar for hydrophytes and terrestrial plants (a positive correlation between the leaf weight per unit area, leaf thickness, and the number of mesophyll cells per unit leaf area), although no correlation was found in hydrophytes between the volume of mesophyll cells and the leaf thickness. Phototrophic tissues in aquatic plants contributed a larger fraction to the leaf weight than in terrestrial plants, because the mechanical tissues were less developed in hydrophytes. The CO₂assimilation rates by leaves were lower in hydrophytes than in terrestrial plants, because the total surface area of chloroplasts per unit leaf area is comparatively small in hydrophytes, which reduces the conductivity for carbon dioxide diffusion towards the carboxylation sites.     

锡林郭勒盟气候干燥度的时空变化规律

以锡林郭勒盟15个气象站点1981—2007年的月平均气温、月累积降水量数据为基础,在Arcgis软件的支持下,得到DeMartonne干燥度的空间数据。研究结果表明,锡林郭勒盟27a平均干燥程度自东向西递增;1981—2007年,锡林郭勒盟整体上表现出干燥度数值下降、干旱程度上升的趋势;从干燥度的年代,20世纪80年代和90年代是锡林郭勒盟气候相对湿润时期,21世纪初期,锡林郭勒盟大部分地区的气候呈现干燥度值减小、干燥程度加大的趋势,干性干旱区在空间分布上占据了主导地位,结果也打乱了原有的气候带状交替格局。21世纪初与20世纪80年代相比,各干燥度等值线的位置均发生了明显的东移现象。     

Basic Types of Structural Changes in the Leaf Mesophyll during Adaptation of Eastern Pamir Plants to Mountain Conditions

Quantitative characteristics of mesophyll structure were compared in leaves of eleven alpine plant species grown under natural conditions in the Eastern Pamirs at various altitudes, from 3800 to 4750 m. Basic types of changes in mesophyll structure, associated with plant adaptation to mountain conditions, were characterized. These changes manifested themselves in different numbers of cell layers and cell sizes in the palisade tissue and, as a consequence, in changed leaf thickness and cell number per unit of leaf area. Three plant groups were identified by the changes in the leaf structural characteristics depending on the type of mesophyll structure, ecological group of plant species, and altitude of plant habitat. The first group comprised alpine xerophytes with an isopalisade structure, in which the volume of palisade cells decreased and their number per unit of leaf area increased with the altitude of plant habitat. The number of mesophyll layers and leaf thickness decreased or did not change with altitude. The second group comprised subalpine plant species with a dorsoventral structure of mesophyll; these species occur below the line of continuous night frost. In these plant species, the number of mesophyll layers, leaf thickness, and cell number per unit of leaf area increased with altitude. The third group comprised mesophyte plants with a dorsoventral and homogenous mesophyll structure, which are encountered in a wide range of habitats, including the nival belt (from 4700 to 5000 m). In this group, cell volume increased and cell number per unit of leaf area decreased with altitude. We present a general scheme of leaf structural changes, which explains the changes in the quantitative characteristics of mesophyll as a function of altitude and highland environmental conditions.     

Changes in leaf characteristics as indicator of the alteration of functional types of steppe plants along the aridity gradient

Changes in some leaf characteristics: leaf mass area (LMA), content of photosynthetic pigments and nitrogen in the leaves, leaf mass ratio (LMR) and leaf area ratio (LAR) were investigated in steppe plants of the Volga land along the gradient of aridity. When drought stress became stronger, the content of chlorophylls in the leaves, LMR and LAR decreased, whereas LMA and the proportion of carotenoids in the leaves rose. In the North to South direction, the content of pigments and nitrogen per unit whole plant weight considerably decreased (4 and 2 times, respectively). The relationship between leaf indices (chlorophyll and nitrogen contents and LMA) differed along this gradient. It was concluded that adaptation of steppe plants to drought stress generally depended on predominant development of heterotrophic tissues in the leaf and the whole plant. During aridization, the stress-tolerant species became more numerous.     

Stomatal Conductance, Photosynthetic Rate, and Pigment Content in Ruellia Tuberosa Leaves as Affected by Coal-Smoke Pollution

Study of the effects of air pollution caused by thermal power plant emissions on some foliar traits of Ruellia tuberosa L. has shown that length and width of stomata, length of stomatal pore, stomatal density, photosynthetic rate, stomatal conductance and chlerophyll content were reduced in the polluted plants in pre-flowering, flowering as well as post-flowering phases of plant growth. Intercellular carbon dioxide concentration in the palisade tissue was increased at each stage of plant development. Stomatal index remained almost unchanged at the polluted site, except on the adaxial surface during the preflowering stage where it was higher as compared to the non-polluted plants.     

Decline in the Primary Productivity of Northwestern European Forests as a Consequence of Climate Aridization

Average annual age-dependent changes of carbon accumulation in the stemwood of major forest species (pine, spruce, and birch) of the taiga zone of the northwestern European Russia (Karelia) were analyzed. The changes in carbon accumulation were assessed by comparing carbon reserves in tree stands of various ages. Net primary productivity of photosynthesis (NPP) and the proportionality coefficient between respiratory decarboxylation and carbon reserves in wood were calculated. NPP clearly decreased with increasing climate aridization (aridity index). However, the time of the attainment of climax state by a stand did not depend on the latitudinal climate gradient. Hence, only the size of heterotrophic part of phytomass determines annual carbon losses in northern-taiga stands. It is concluded that the climate dependency of the long-term carbon storage in the phytomass of boreal forests is mainly determined by the climate effect on photosynthetic carbon sequestration.__________Translated from Fiziologiya Rastenii, Vol. 52, No. 4, 2005, pp. 513–517.Original Russian Text Copyright © 2005 by Voronin, Konovalov, Bolondinskii, Kaipiainen, Mao.     

Structural and Functional Rearrangements of Mesophyll as a Probable Basis for the Cytokinin-Dependent Assimilate Translocation in Detached Leaves

The effects of benzyladenine (BA) on the mesophyll functioning, such as osmotic potential (), the effect of the inhibitors of ⁺-ATPase on the influx of ¹⁴C-sucrose, the direction of carbon metabolism, and the rate of dark respiration, were followed in the detached leaves of pumpkin (Cucurbita pepo L.) and broad beans (Vicia faba L.). BA elevated and established a gradient of (_p) between the treated and untreated leaf regions. The inhibitors of H⁺-ATPase did not affect the BA-induced influx of ¹⁴C-sucrose. The changes were accompanied with the elevated synthesis of starch and other polymeric compounds and the diminished synthesis of the substances of relatively low molecular weight. The stimulation of dark respiration was short and inconsiderable. The author concludes that the BA-induced transport was a passive process related to a increase. Leaf expansion accompanied by the synthesis of high-molecular-weight substances essential for cell growth and by starch synthesis apparently increased the sink capacity of the BA-treated detached leaves. The diminished efflux from the leaf blade was probably related to a lowered level of the transportable carbon compounds restricting their entry into the phloem. The influx induction could result from the activation of growth and metabolic processes, the decline in the number of organic molecules per cell volume unit, and the development of _p between the source and sink leaf regions.     

Growth and Respiration in Plants from Various Adaptation Groups as Affected by Mineral Nutrient Deficiency

The effect of the deficiency in mineral nutrients was investigated in plant species representing various adaptation groups (stress-tolerant, competitive, and ruderal plants). Dry and fresh weight, as well as the length of shoots and underground organs, were determined in 20- to 50-day-old seedlings. The ratio between the dry weights of shoot and root (SRR), relative growth rate (RGR), the rate of total dark respiration (R), gross photosynthesis (P _g), and the proportion of the respiratory expenditures to gross photosynthesis (R/P _g) were calculated. When affected by a deficiency in mineral nutrients, the weight of the whole plant decreased. In resistant species of clover (Trifolium pratense L.) and alfalfa (Medicago sativa L.), this reduction was insignificant, whereas, in the ruderal species amaranth (Amaranthus retroflexus L.), it was at its highest. In all the species investigated, the ratio R/P _g was 38–46%. Under stress conditions, this index increased. Given a deficiency in mineral nutrients, the changes in SRR, RGR, and R/P _g were greater in amaranth, suggesting that this plant species is less tolerant to stress. The correlation between RGR and R observed in amaranth under normal conditions indicates that the major energy expenditures are associated with growth. Under stress conditions, such a correlation was not observed. In more resistant species of clover and alfalfa, a weak positive correlation between RGR and R was observed both under normal and stress conditions. In these species, the deficiency in mineral nutrients probably brought about a reduction in the growth component of total dark respiration and a rise in the adaptation component. The complex of indices (R/P _g, RGR, and SRR) and the extent of their variation in the seedlings describe the potential productivity and resistance of particular species to a deficiency in mineral nutrients and may characterize the adaptation type of the plants.     

Comparative Characterization of the Pigment Complex in Emergent, Floating, and Submerged Leaves of Hydrophytes

The content of chlorophylls (Chls) and carotenoids was studied in the leaves of 42 species of boreal aquatic plants with different degree of submergence (emergent, floating, and submerged) and isopalisade, dorsoventral, and homogenous types of mesophyll structure. Hydrophytes were shown to have a low Chl content (1–2 mg/g fr wt) and low Chls/carotenoids ratio (2.3–3.5) as compared to terrestrial plants. The pigment content per dry wt unit and unit leaf area was dependent on the type of mesophyll structure. It was a consequence of the changes in the parameters of leaf mesophyll structure characterizing the density of photosynthetic elements. In a sequence emergent floating submerged forms, the content of Chls and carotenoids decreased, and the photosynthetic capacity decreased due to a reduction in the chloroplast number per unit leaf area. Adaptation of submerged leaves to low illumination and slow CO₂ diffusion changed the functional properties of chloroplasts. An increase in the pigment content in the chloroplasts of submerged leaves (7 × 10^–9 mg Chl, 2 × 10^–9 mg carotenoids) as compared to emergent and floating leaves was accompanied by a decline in the photosynthetic capacity per Chl comprising 1.6 mg CO₂/(mg Chl h) versus 3.9 and 3.8 mg CO₂/(mg Chl h) in emergent and floating leaves, respectively.     

Photosynthetic and Transpiration Rates of Soybean as Affected by Different Irradiances During Growth

The diurnal variation of net photosynthetic (PN) and transpiration (E) rates in soybean [Glycine max (L.) Merr. cv. Fukuyutaka] plants grown under 100, 50, or 25 % of full sun irradiance (I100, I50, I25 plants) were compared. In the morning, activities of the plants were measured at irradiances under which they grew. However, during the afternoon, all the plants were tested under full irradiance. The lower the growth irradiance, the lower PN, E, and mesophyll conductance values were found. Stomatal conductance was considerably lower in I25 plants only. Both the increase in specific leaf area (SLA) and the decrease in nitrogen content per leaf area unit contributed to the PN reduction of soybean plants grown under low irradiances. Though E of the plants grown under different irradiances differed less markedly than PN, the water use efficiency declined from I100 to I25.     

Contribution of Photorespiration to Changes of Carbon Isotope Characteristics in Plants Affected by Stress Factors

Experimental data available in literature on changes in the carbon isotopic composition of biochemical fractions and metabolites isolated from plant biomass (Clusia minor) and photosynthesizing algae (Chlorella stigmatophora) under the action of environmental stress factors are reviewed and analyzed. Within the framework of previously suggested mechanism of carbon isotope fractionation in photosynthesis, all studied fractions and metabolites obtained from plants and photosynthesizing algae can be divided into two groups according to their carbon isotope composition. The first group includes the fractions and metabolite pools that contain carbon stored by cell during the carboxylase phase of Rubisco functioning. The second group consists of those formed primarily by the photorespiratory carbon flow, generated during the oxygenase phase of Rubisco functioning. The first group represents the assimilatory branch of photosynthesis and is enriched in ¹²C relative to carbon of biomass, whereas the second group represents the photorespiratory branch and is enriched in ¹³C. Under the action of environmental stress factors, such as incident light intensity, moisture availability, and salinity; the isotope composition of metabolites and fractions changes, which reflects variable contributions of the assimilatory and photorespiratory flows to the metabolite synthesis. These isotope shifts were used to study biochemical adaptation of plants to stress conditions and to elucidate the role of photorespiration in this adaptation.     

不同载畜率对荒漠草原群落结构和功能群生产力的影响

采用随机区组试验研究了内蒙古高原荒漠草原亚带短花针茅(S tip a brev if lora)草原群落不同载畜率对草原群落结构和功能群生产力的影响。结果表明:随着载畜率的增加,群落的植物种数逐渐减少,在每个载畜率水平下,冷蒿(A rtem isia f rig id a)占有绝对优势地位,优势度为35.66%~41.95%;群落的地上生物量随载畜率的增加而降低,各功能群地上生物量组成中,灌木类处于主体地位,分别占据了群落68%(CK)、77.40%(LG)、73.25%(M G)、76.91%(HG)的生物量;在植物生活型功能组成中,灌木类和杂类草、多年生丛生禾草和杂类草功能群,在生物量上具有生态互补效应(n iche com p lem en tary effect)。     

近20年亚欧大陆植被指数(NDVI)对大尺度气候变化的敏感性(英文)

The influence of climate change on the terrestrial vegetation health (condition) is one of themost significant problems of global change study. The vegetation activity plays a key role in the globalcarbon cycle. The authors investigated the relationship of the advanced very high resolution radiometer-normalized difference vegetation index (AVHRR-NDVI) with the large-scale climate variations on the inter-annual time scale during the period 1982-2000 for the growing seasons (April to October). A singular valuedecomposition analysis was applied to the NDV! and surface air temperature data in the time-domain todetect the most predominant modes coupling them. The first paired-modes explain 60.9%, 39.5% and 24.6%of the squared covariance between NDV! and temperature in spring (April and May), summer (June andAugust), and autumn (September to October), respectively, which implies that there is the highest NDVIsensitivity to temperature in spring and the lowest in autumn. The spatial centers, as revealed by themaximum or minimum vector values corresponding to the leading singular values, indicate the highsensitive regions. Only considering the mode 1, the sensitive center for spring is located in westernSiberia and the neighbor eastern Europe with a sensitivity of about 0.308 0 NDVI/℃. For summer, thereare no predominantly sensitive centers, and on average for the relatively high center over 100^o-120^o E by 45^o-60^o N, the (110^o-140^o E,55^o-65^oN)sitivity is 0.248 0 NDVI/℃. For autumn, the center is located over the high latitudes ofeastern Asia (110^o-140^o E, 55^o-65^o N), and the sensitivity is 0.087 5 NDVI/℃. The coherent patters asrevealed by the singular decomposition analysis remain the same when coarser resolution NDVI data wereused, suggesting a robust and stable climate/vegetation relationship.     

近20年亚欧大陆植被指数(NDVI)对大尺度气候变化的敏感性

利用1982～2000年4～10月的AVHRR-NDVI数据,分析了大尺度的气候(温度)变化对欧亚大陆植被状况的影响.分析方法为奇异值分解,从温度和NDVI的年际变化中检测出二者最重要和最密切的大尺度空间相关特征.用每个奇异值的平方占总的协方差平方和的比例(解释率),可以度量每对模态的重要性.春季(4和5月)、夏季和秋季(9和10月)的解释率分别是60.9%、39.5%和24.6%,这说明整体上春季植被状况对温度的敏感性高于夏季和秋季.奇异值分解的显著模态中心是二者关系最密切的地区,也就是NDVI对温度最敏感的地区,春季为西西伯利亚和东欧东北部,敏感性为 0.308 0 NDVI/℃;夏季没有特别突出的敏感中心,选择与计算春季相同格点数的高值中心,其敏感性为 0.248 0 NDVI/℃;秋季敏感中心在亚洲东部高纬度地区,相同格点大小范围(110°～140° E,55°～65°N)平均敏感性为 0.087 5 NDVI/℃.这种大尺度的NDVI-气温的关系及其敏感性非常稳定,并不随使用的NDVI的空间分辨率的改变而改变.     

nter-annual Changes in Eurasian Continent NDVI and Its ensitivity to the Large-scale Climate Variations in the Last 20 Years

The influence of climate change on the terrestrial vegetation health (condition) is one of the most significant problems of global change study. The vegetation activity plays a key role in the global carbon cycle. The authors investigated the relationship of the advanced very high resolution radiometer-normalized difference vegetation index (AVHRR-NDVI) with the large-scale climate variations on the inter-annual time scale during the period 1982-2000 for the growing seasons (April-October). A singular value decomposition analysis was applied to the NDVI and surface air temperature data in the time-domain to detect the most predominant modes coupling them. The first paired-modes explain 60.9%, 39.5% and 24.6% of the squared covariance between NDVI and temperature in spring (April-May), summer (June-August), and autumn (September-October), respectively, which implies that there is the highest NDVI sensitivity to temperature in spring and the lowest in autumn. The spatial centers, as revealed by the maximum or minimum vector values corresponding to the leading singular values, indicate the high sensitive regions. Only considering the mode 1, the sensitive center for spring is located in western Siberia and the neighbor eastern Europe with a sensitivity of about 0.308 0 NDVI/℃. For summer, there are no predominantly sensitive centers, and on average for the relatively high center over 1000-1200 E by 450-600 N, the sensitivity is 0.248 0 NDVI/℃. For autumn, the center is located over the high latitudes of eastern Asia (1100-1400 E, 550-650 N), and the sensitivity is 0.087 5 NDVI/℃. The coherent patters as revealed by the singular decomposition analysis remain the same when coarser resolution NDVI data were used, suggesting a robust and stable climate/vegetation relationship.     

Dry Matter and Leaf Structure in Young Wheat Plants as Affected by Cadmium, Lead, and Nickel

The effects of 1 mM cadmium, lead and nickel on dry mass, Cd, Pb, and Ni contents, and changes in leaf structure in young wheat plants were studied. In leaves, Cd content was highest, followed by Pb and Ni, in roots Cd content was also highest, but followed by Ni and Pb. Roots accumulated considerably larger amounts of the three heavy metals than leaves. Largest reductions of leaf and root mass were obtained with Cd. Pb and Ni effects were almost equal. Ni excess had a strong negative effect on mesophyll thickness, while Cd mostly reduced the number and size of vascular bundles and vessel diameter. High Pb reduced the diameter of vessels causing their different deformations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamics of Primary Productivity and Soil Organic Matter of Typical Steppe in the Xilin River Basin of Inner Mongolia and Their Response to Climate Change

At the site level, the authors used the Century plant-soil ecosystem model and Landsat remote sensing to estimate the aboveground biomass of Aneurolepidium chinense steppe and Stipa grandis steppe in the Xilin river basin, Inner Mongolia China. The results of century simulation matched well in terms of the seasonal and yearly change of biomass, with those of field moniforing. The results of field monitoring replicated well were about 142.45～144.37 g/m2 and 210. 38~227.44 g/m2 on S. grandis and A. chinense steppe, respectvely, whereas the simulation results were 127. 04～156. 23 g/m2 and 189.25~193.98 g/m2, respectively. Simulated soil organic matter was around ±–25% of the observed data. Normalized differnce vegetation index derived aboveground biomass was around ±25 % of the observed field biomass on the A. chinence and S. grandis steppe, using Landsat TM imagecries on July 31, 1987 and August 11, 1991. The effect of global climate change and elevated CO2 on these steppe was examined, using the climate fields from Global Change Models of Canadian Climate Center and Geophysics Flow Dynamics Laboratory under 1 × CO2 (350 X 10-6) and 2 × CO2 (700 X 10-6) sceneries. Climate change resulted in considerable decrease of primary productivity and soil organic matter of A. chinense and S. grandis steppe, the former being more sensitive to climate change.     

Photosynthetic Pigments and Gas Exchange of in vitro Grown Tobacco Plants as Affected by CO2 Supply

Contents and functioning of photosynthetic pigments and gas exchange of Nicotiana tabacum L. leaves were studied in platlets cultivated in vitro under different CO₂ supply. The plantlets were grown for six weeks either in glass vessels tightly closed with aluminium foil (G-plants) or in polycarbonate Magenta GA-7 vessels covered with closures with microporous vents (M-plants). M-plants (better supplied with CO₂) had higher contents of chlorophyll (Chl) a. Chl b. and β-carotene, higher photochemical activities of photosystem 2 and whole electron transport chain, and lower contents of xanthophyll cycle pigments. Differences in Chl a fluorescence kinetic parameters between G-plants and M-plants were not statistically significant. M-plants had higher net photosynthetic rate, and lower transpiration rate and stomatal conductance than G-plants. This revised version was published online in June 2006 with corrections to the Cover Date.