Photosynthetic Carbon Metabolism in an Amphibious Sedge, Eleocharis baldwinii (Torr.) Chapman: Modified Expression of C4 Characteristics under Submerged Aquatic Conditions

The photosynthetic characteristics of Eleocharis baldwinii (Torr.)Chapman, an amphibious leafless plant in the Cyperaceae, wereinvestigated in both the terrestrial form and the submergedform of the plant. Anatomical observation of the culm, whichis the photosynthetic organ in this plant, revealed that theterrestrial form has the Kranz type of anatomy, whereas thesubmerged form has an inner structure that is similar to thatof submerged aquatic plants, with a reduction in both the numberand the size of bundle sheath cells and vascular bundles andrelatively well developed mesophyll cells. In ¹⁴C-pulse ¹²C-chaseexperiments with the terrestrial form, 80% of the total fixed¹⁴C was incorporated into C₄ dicarboxylic acids after a 10-spulse. The radioactivity in the C₄ acids decreased rapidly,while that in sucrose increased to 36% during a 120-s chase.In the submerged form, 64% and 30% of the total fixed ¹⁴C wasincorporated into C₄ acids and phosphate esters, respectively,after a 10-s pulse. The radioactivity of these compounds decreasedrelatively slowly during a 120-s chase. The specific activitieson a chlorophyll basis of C₄ photosynthetic enzymes that areinvolved in the NAD-ME subtype were high in the terrestrialform, while they were intermediate between those of C₃ and C₄plants in the submerged form. The activity of ribulose 1,5-bisphosphatecarboxylase was 1.5 times higher in the submerged form thanin the terrestrial form. By contrast, the activity of carbonicanhydrase exhibited the reverse tendency. Western blot analysisof soluble proteins extracted from the mesophyll cells and thebundle sheath strands of the terrestrial form demonstrated thatribulose 1,5-bisphosphate carboxylase/oxygenase protein waspresent in the mesophyll cells as well as in the bundle sheathcells, with a higher level in the latter, although phosphoenolpyruvatecarboxylase and pyruvate, P_i dikinase proteins were restrictedto the mesophyll cells. In the submerged form, diurnal fluctuationsin levels of malate were observed with significant fixationof CO₂ at night. However, the diurnal changes of malate weresmaller than those reported for CAM plants. These data indicatethat the terrestrial form of Eleocharis baldwinii fixes atmosphericCO₂ essentially via the C₄ pathway, while the submerged formfixes inorganic carbon via a complex metabolic system that resemblesan intermediate between C₃ and C₄ metabolism in associationwith a CAM-like profile. (Received September 12, 1994; Accepted November 21, 1994)     

基于稳定碳同位素分析宁夏典型林分土壤有机碳分布格局及影响因素

选择宁夏自北向南方向的贺兰山、罗山和六盘山(3座山的降水量呈现逐渐增加的趋势)共有的青海云杉林和油松林土壤作为研究对象,分析两种针叶林土壤有机碳特征[土壤有机碳(SOC)含量、稳定碳同位素组成(δ13C)和有机碳分解速率(β值)]的变化情况,并采用冗余分析法分析土壤化学指标对土壤有机碳特征的影响作用,探究干旱半干旱区土...     

Nitrogen and Carbon Concentrations, and Stable Isotope Ratios in Mediterranean Shrubs Growing in the Proximity of a CO2 spring

Seasonal changes in foliage nitrogen (N) and carbon (C) concentrations and δ¹⁵N and δ¹³C ratios were monitored during a year in Erica arborea, Myrtus communis and Juniperus communis co-occurring at a natural CO₂ spring (elevated [CO₂], about 700 μmol mol⁻¹) and at a nearby control site (ambient [CO₂], 360 μmol mol⁻¹) in a Mediterranean environment. Leaf N concentration was lower in elevated [CO₂] than in ambient [CO₂] for M. communis, higher for J. communis, and dependent on the season for E. arborea. Leaf C concentration was negatively affected by atmospheric CO₂ enrichment, regardless of the species. C/N ratio varied concomitantly to N. Leaves in elevated [CO₂] showed lower δ¹³C, and therefore likely lower water use efficiencies than leaves at the control site, regardless of the species, suggesting substantial photosynthetic acclimation under long-term CO₂-enriched atmosphere. Leaves of E. arborea showed lower values of δ¹⁵N under elevated [CO₂], but this was not the case of M. communis and J. communis foliage. The use of the resources and leaf chemical composition are affected by elevated [CO₂], but such an effect varies during the year, and is species-dependent. The seasonal dependency and species specificity suggest that plants are able to exploit different available water and N resources within Mediterranean sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Relationships among Mercury Concentration,and Stable Isotope Ratios of Carbon and Nitrogen in the Scalp Hair of Residents from Seven Countries: Effects of Marine Fish and C4 Plants Consumption

We analyzed the Hg concentration, and δ¹³C and δ¹⁵N values in the scalp hair of residents from seven countries; Vietnam, New Zealand, Spain, the USA, South Korea, Brazil and Japan. Relationships among the data in each country and among the seven countries were then examined. The highest Hg concentration as well as the highest or higher δ¹⁵N value in each country was found in the hair of a heavy marine fish-eater, whereas the lowest Hg concentration and δ¹⁵N value were found in the hair of a vegetarian or non (marginal)-fish eater. Hg concentrations were positively correlated with the δ¹⁵N values in each country, and increased markedly in samples with δ¹⁵N values exceeding 9.0 ‰, probably due to fish consumption. The highest Hg concentration could be found in sample, with a δ¹³C value between -19 and -18‰, probably reflecting the δ¹³C value of the marine food web.     

Structural characterization of photosynthetic cells in an amphibious sedge, Eleocharis vivipara, in relation to C3 and C4 metabolism

Eleocharis vivipara Link is a unique amphibious leafless sedge. The terrestrial form has Kranz anatomy and the biochemical traits of C₄ plants while the submerged form develops structural and biochemical traits similar to those of C₃ plants. The structural features of the culms, which are the photosynthetic organs, of the two forms were examined and compared. The culms of the terrestrial form have mesophyll cells and three bundle sheaths which consist of three kinds of cell, namely, the innermost Kranz cells that contain large numbers of organelles, the middle mestome sheath cells that lack chloroplasts, and the outermost parenchyma sheath cells that contain chloroplasts. The culms of the submerged form had a tendency towards reduction in numbers and size of Kranz cells and vascular bundles, as compared to the terrestrial form, and they had spherical mesophyll cells that were tightly packed without intercellular spaces inside the epidermis. The submerged form had a higher ratio of cross-sectional area of mesophyll cells plus parenchyma sheath cells to that of Kranz cells than the terrestrial form. The difference was mainly due to a decrease in the number and the size of the Kranz cells and to a marked increase in the size of the mesophyll cells and the parenchyma sheath cells in the submerged form, as compared to the terrestrial form. The Kranz cells of the terrestrial form had basically the structural characteristics of plants of the NAD-malic enzyme type, with the exception of the intracellular location of organelles. The Kranz cells of the submerged form included only a few organelles, and the percentage of organelles partitioned to the Kranz cells was significantly smaller in the submerged form than in the terrestrial form. In addition, the size of chloroplasts of the Kranz cells was 60–70% of that of the terrestrial form. These structural differences between the two forms may be related to the functional differences in their mechanisms of photosynthesis.Abbreviations KC Kranz cell - MC mesophyll cell - PSC parenchyma sheath cell - NAD-ME NAD-malic enzyme - VB vascular bundle This study was supported by Grants-in-Aid from the Ministry of Agriculture, Forestry and Fisheries of Japan (Integrated Research Program for the Use of Biotechnological Procedures for Plant Breeding) and from the Science and Technology Agency of Japan (Enhancement of Center-of-Excellence, the Special Coordination Funds for Promoting Science and Technology).     

Dominance of Epiphytic Filamentous Thiothrix spp. on an Aquatic Macrophyte in a Hydrothermal Vent Flume in Sedge Bay, Yellowstone Lake, Wyoming

Sublacustrine hydrothermal vents, geysers, and fumaroles impart regions of Yellowstone Lake with distinctive chemical compositions that generate unique freshwater habitats and support diverse microbial life. Some microbial communities within Sedge Bay manifest themselves as accumulations of white-colored films on the surfaces of aquatic macrophytes located within the hydrothermal flow of vents. It was hypothesized that the white films were the product of microbial growth, particularly sulfur-oxidizing bacteria. An investigation of the relevant biological compounds in the vent waters was conducted. Microscopy, non-culture molecular techniques, and phylogenetic analysis were used to assay the bacterial diversity associated with the films. Microscopic analysis of the white films revealed the presence of long filaments (>200 μm) that contained sulfur granules. Filaments with these characteristics were not detected on the normal macrophyte samples. Nucleic acids were extracted from the surface of macrophyte coated with the white film (SB1, SB2) and from the surface of an uncoated macrophyte (SC). 16S ribosomal (rRNA) genes were amplified with the polymerase chain reaction (PCR) and cloned. Amplified ribosomal DNA restriction analysis (ARDRA) was used to examine 100 clones from each library and identify unique phylotypes. S_Chao1 and the Shannon Index, mathematical measures of richness and heterogeneity, were employed to assess the ARDRA pattern diversity of each sample. The SC community contained 50 unique phylotypes, predominantly cyanobacteria and proteobacteria, and was the most heterogeneous. SB1 and SB2 communities were less heterogeneous and dominated by Thiothrix. Dilution to extinction PCR conducted with specific primers indicated that the relative abundance of Thiothrix 16S rRNA gene copies in all three samples were similar. However, reduced sulfur compounds from the vent resulted in a more narrow habitat that supported the sulfur-oxidizing Thiothrix in the white film to the exclusion of cyanobacteria and other proteobacteria found on the normal macrophyte. The majority of 16S rRNA gene sequences obtained in this study displayed similarities ≤98% to any known sequence in public data bases which suggests an abundance of new bacterial species in Sedge Bay.     

Immunocytochemical localization of enzymes involved in the C3 and C4 pathways in the photosynthetic cells of an amphibious sedge, Eleocharis vivipara

Eleocharis vivipara link, an amphibious leafless sedge, develops traits of C₄ photosynthesis and Kranz anatomy in the terrestrial form but develops C₃-like traits with non-Kranz anatomy when submerged. The cellular localization of C₃ and C₄ enzymes in the photosynthetic cells of the two forms was investigated by immunogold labeling and electron microscopy. The terrestrial form has mesophyll cells and three kinds of bundle sheath cell, namely, parenchyma sheath cells, non-chlorophyllous mestome sheath cells, and Kranz cells. Phosphoenol-pyruvate carboxylase (PEPCase) was present in the cytosol of both the mesophyll cells and the parenchyma sheath cells, with higher-density labeling in the latter, but not in the Kranz cells. Pyruvate, Pi dikinase (PPDK) was found at high levels in the chloroplasts of both the mesophyll cells and the parenchyma sheath cells with some-what stronger labeling in the latter. This enzyme was also absent from the Kranz cells. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was found in the chloroplasts of all types of photosynthetic cell, but labeling was significantly less intense in the parenchyma sheath cells than in other types of cell. The submerged form also has three types of photosynthetic cell, as well as non-chlorophyllous mestome sheath cells, but it lacks the traits of Kranz anatomy as a consequence of modification of the cells. Rubisco was densely distributed in the chloroplasts of all the photosynthetic cells. However, PEPCase and PPDK were found in both the mesophyll cells and the parenchyma sheath cells but at lower levels than in the terrestrial form. These data reveal that the terrestrial form has a unique pattern of cellular localization of C₃ and C₄ enzymes, and they suggest that this pattern and the changes in the extent of accumulation of the various enzymes are the main factors responsible for the difference in photosynthetic traits between the two forms.Abbreviations CAM crassulacean acid metabolism - MC meso phyll cell - PSC parenchyma sheath cell - KC Kranz cell - PEP-Case phosphoenolpyruvate carboxylase - PPDK pyruvate, Pi dikinase - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - LS large subunit - RuBP ribulose-1,5-bisphosphate This study was supported by Grants-in-Aid from the Ministry of Agriculture, Forestry and Fisheries of Japan (Integrated Research Program for the Use of Biotechnological Procedures for Plant Breeding) and from the Science and Technology Agency of Japan (Enhancement of Center-of-Excellence, the Special Coordination Funds for Promoting Science and Technology). The author is grateful to Drs M. Matsuoka and S. Muto for providing the antisera and Dr. M. Samejima for his advice at the early stages of this study.     

姜寨遗址先民食谱分析

尽管通过C、N稳定同位素分析已对陕西临潼姜寨遗址先民的食物结构和粟作农业进行了初步探索,但研究中的一些重要问题,如不同时期先民食物结构的演变,姜寨与半坡、史家先民食物结构间的差异等,依然未能深入讨论。为此,本文对姜寨遗址出土的不同时期(一期、二期)人骨进行了C、N稳定同位素分析,试图揭示先民食物结构的演变历程,探索姜寨与半坡、史家先民食物结构间的差异,并初步探讨产生这种差异的可能原因。人骨的δ13C平均值(-9.7±1.0‰)和δ15 N平均值(8.5±0.5‰),表明粟类食物(包括粟类作物以及依赖于粟类作物的动物等)在姜寨先民食谱中占据主要地位,且动物资源在食物中的比例相对较低。两期先民的δ13C和δ15N值,无显著性差异,表明先民一直从事粟作农业以及家畜的饲养活动。食谱分析并未发现第二期先民食用更多野生动物的证据,这可能与先民样品量相对偏少、二期先民食用的野生动物比例上升较小、动物类食物在先民食谱中所占比例较小等原因有关。对比地理位置毗邻、文化年代相近的姜寨、史家、半坡遗址先民δ13C值,姜寨(-9.7±1.0‰,N=19)与史家(-10.0±0.7‰,N=9)接近,而远高于半坡(-14.8±1.9‰,N=5),表明半坡遗址粟作农业的种植规模要逊于姜寨和史家遗址。我们认为,不同遗址间先民δ13C值的差异,可能受半坡样品量偏少、遗址间小生态环境不同等因素的影响。     

The Ratios of Carbon,Nitrogen, and Phosphorus in a Wetland Coastal Ecosystem of Southern India

The fertility of the coastal and estuarine waters is of great concern because of its influence on the productivity of these waters. Seasonal variations in the distribution of organic carbon, total nitrogen and total phosphorus in the sediments of Kuttanad Waters, a part of the tropical Cochin Estuary on the south west coast of India, are examined to identify the contribution of sediments to the fertility of the aquatic systems. The adjoining region has considerable agricultural activity. The fresh water zones had higher quantities of silt and clay whereas the estuarine zone was more sandy. Organic carbon, total phosphorus and total nitrogen were higher in the fresh water zones and lower in the estuarine zones. Total phosphorus and organic carbon showed the lowest values during monsoon periods. No significant trends were observed in the seasonal distributions of total nitrogen. Ratios of C/N, C/P and N/P, and the phosphorus and nitrogen content indicate significant modification in the character of the organic matter. Substantial amounts of the organic matter can contribute to reducing conditions and modify diagenetic processes.     

超高产杂交稻剑叶中C4途径酶活性和稳定碳同位素分异作用的变化

以超高产杂交水稻(Oryza sativa L．)“培矮64S／E32”和多年来大面积推广的杂交稻“汕优63”为材料,研究孕穗后剑叶中C4途径酶和对稳定碳同位素分异作用的变化。结果表明,籽粒灌浆期(移栽后68～75d)的两个品种剑叶中NADP—MDH活性最高,随后下降;超高产杂交水稻“培矮64S／E32”的NADP-MDH的活性明显高于“汕优63”;PEPcase和NADP—ME活性在黄熟期之前的叶片中持续上升。不同生育期的叶片与籽粒的△^13C值相近(19．49‰～19．82‰),在成熟期时较高。超高产水稻“培矮64S／E32”叶片的平均△^13C值比“汕优63”高0．43‰。     

Establishment of a Reverse Genetic System of Severe Fever with Thrombocytopenia Syndrome Virus Based on a C4 Strain

Virologica Sinica - Severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging tick-borne bunyavirus that causes hemorrhagic fever-like disease (SFTS) in humans with a case fatality...     

超高产杂交稻剑叶中C4途径酶活性和稳定碳同位素分异作用的变化

以超高产杂交水稻(Oryza sativa L.)"培矮64S/E32"和多年来大面积推广的杂交稻"汕优63"为材料,研究孕穗后剑叶中C4途径酶和对稳定碳同位素分异作用的变化.结果表明,籽粒灌浆期(移栽后68～75 d)的两个品种剑叶中NADP-MDH活性最高,随后下降;超高产杂交水稻"培矮64S/E32"的NADP-MDH的活性明显高于"汕优63";PEPCase和NADP-ME活性在黄熟期之前的叶片中持续上升.不同生育期的叶片与籽粒的△1aC值相近(19.49‰～19.82‰),在成熟期时较高.超高产水稻"培矮64S/E32"叶片的平均△13C值比"汕优63"高0.43‰.     

The Potential of Two Perennial C4 Grasses and a Perennial C4 Sedge as Ligno-cellulosic Fuel Crops in N.W. Europe. Crop Establishment and Yields in E. England

Three perennial C₄ rhizomatous species, Cyperus longus L., Spartinacynosuroides and Spartina pectinata Link, were examined as potentialrenewable energy crops. These species are unusual among C₄ plantsin showing natural distributions which extend into cool temperateregions. This study examined whether these species could beestablished in the cool temperate climate of eastern Englandand whether they could consistently attain the relatively highdry matter yields associated with C₄ plants of warmer regions.Clonally produced material was planted in 1986, on two siteswith contrasting soil types in Essex, eastern England. Plantingwas within a randomized-block design incorporating replicatedplots of each species, both with and without fertilizer. Survivorshipand stem demography were monitored at monthly intervals from1986 to Jun. 1989 for stem recruitment and to Dec. 1991 forstem density. Yields were determined from 1987 (the year followingestablishment) to 1993. Survivorship of the planted propagules over the first 12 monthswas 92% for S. pectinata , 96% for S. cynosuroides and 100%for C. longus. Recruitment of new stems peaked in Apr. of mostyears, although a significant number of new stems appeared asearly as Feb. Stem death peaked in Sep. or early Oct. and allabove-ground stems had died by mid-Nov. Stem density trendsindicated that 2-4 years were required to reach a steady-statedensity, depending upon species. The stem density of the twoSpartina species had reached more than 1000 m^-2 in 1989 althoughthat of S. pectinata fluctuated considerably in the subsequentyears. C. longus stem density rose to approx. 600 m^-2 by 1988and did not change significantly in the subsequent years. In the 6 years following establishment, annual yields averagedacross all fertilizer treatments and both sites were 1·0,1·1 and 1·3 kg m^-2 for C. longus, S. cynosuroidesand S. pectinata, respectively. The average annual yield ofall three species at the site with the heavier soil was 1·3kg m^-2. This was significantly greater than the 1·0 kgm^-2 on the lighter soil. Nitrogen addition did not significantlyincrease yield. Even in the absence of any nitrogen addition,the annual yield of S. pectinata averaged 1·2 kg m^-2over the 6 years, with no evidence of any decline with the increasingage of the stands.Copyright 1995, 1999 Academic Press Cyperus longus, Spartina cynosuroides, Spartina pectinata, energy crop, dry matter yield     

The Influence of Leaf Age on C(4) Photosynthesis and the Accumulation of Inorganic Carbon in Flaveria trinervia, a C(4) Dicot

Characteristics of C₄ photosynthesis were examined in young, mid-age, and mature leaves of Flaveria trinervia (an NADP-malic enzyme-type C₄ dicot). The turnover of [4-¹⁴C] (malate plus aspartate) following a pulse with ¹⁴CO₂ was similar in leaves of different ages (apparent half-time of 18-25 seconds). However, the rate of ¹⁴CO₂ incorporation in mid-age leaves was about 1.5-fold higher than in young leaves, and about 2.5-fold higher than in mature leaves. The rate of ¹⁴CO₂ fixation was proportional to the total active pool of malate plus aspartate but was not correlated with the total photosynthetically derived inorganic carbon pool. The leaf's ability to concentrate inorganic carbon photosynthetically declined during leaf expansion, from 29 down to 7 nanomoles per milligram chlorophyll. Similarly, the active aspartate pool also declined during leaf expansion, from about 123 down to 20 nanomoles per milligram chlorophyll. Enhanced metabolism of aspartate to CO₂ and pyruvate in young leaves is suggested to facilitate the maintenance of high CO₂ levels in bundle sheath cells which are thought to have a higher conductance to CO₂.     

Welfare of Apes in Captive Environments: Comments On,and By,a Specific Group of Apes

Accurately determining the proper captive environment for apes requires adequately assessing the psychological similarities between apes and humans. Scientists currently believe apes lack mental complexity (Millikan, 2006 Millikan, R. G. 2006. “Styles of rationality”. In Rational animals?, Edited by: Hurley, S. and Nudds, M. 117–126. Oxford, , England: Oxford University Press.. [Crossref] , [Google Scholar]), raising questions concerning the evolution of human culture from ape-like societies (Tomasello, 1999 Tomasello, M. 1999. The cultural origins of human cognition, Cambridge, , MA: Harvard University Press..  [Google Scholar]). A long-term cultural study with bonobos suggests less intellectual divergence from humans than currently postulated (Savage-Rumbaugh, 2005 Savage-Rumbaugh, E. S. 2005. “Individual differences in language competencies in apes resulting from unique rearing conditions imposed by different first epistemologies”. In Symbol use and symbolic representation, Edited by: Namy, L. L. 199–219. Mahwah, , NJ: Lawrence Erlbaum Associates, Inc..  [Google Scholar]). Because humans view apes as mentally limited, some current captive environments may appear idyllic while offering only an illusion of appropriate care, derived from a simplistic view of what apes are, rather than what they might be. This perception of apes determines their handling, which determines their mental development, which perpetuates the prevailing perception. Only breaking this cycle will allow the current perception of apes to change. Their usual captive environment limits any demonstration of culture. However, the bonobo study reveals what ape culture can become, which should affect future welfare considerations for at least those species genetically close to humans (bonobos and chimpanzees). Development of a languaged bonobo culture allows these nonhuman animals to provide their own responses regarding adequate ape welfare.     

Partitioning of Lead in Urban Street Dust Based on the Particle Size Distribution and Chemical Environments

The objective of the present study was to investigate the distribution of lead among the physical fractions and between the various chemical forms of urban street dust. In order to achieve this aim, street dust samples were collected from three major roads with high traffic volume and one minor road with a low traffic density in urban areas of Az Zarqa City, Jordan. The dust samples (N = 6 for each site) were split into two portions. One part was employed for physical size fractionation and the other portion for chemical and physical analyses. A sequential extraction procedure was used to determine Pb associated with various chemical and physical fractions. It was found that about half of the lead was associated with the carbonate fraction and Fe-Mn oxides were ranked second, followed by the exchangeable and organic fractions. A general trend of increasing lead levels with decreasing particle size in street dust was observed. The current study showed that leaded gasoline was the major source for the elevated lead levels in street dust. Therefore, for those countries still employing leaded gasoline, such as Jordan, substantial reductions in lead contamination of street dust and roadside soils could be achieved by prohibiting the use of Pb additives. Consequently, many health benefits could be expected for the entire population and especially for children. The accuracy of lead results was checked by periodic analysis of SRM Soil 7. Observed concentrations were within 5% of certified value in analyzed SRM for lead.     

Expression of C3 and C4 photosynthetic characteristics in the amphibious plant Eleocharis vivipara: structure and analysis of the expression of isogenes for pyruvate,orthophosphate dikinase

Eleocharis vivipara, a unique leafless amphibious sedge, adopts the C4 mode of photosynthesis under terrestrial conditions and the C3 mode under submerged aquatic conditions. To analyze the molecular basis of these responses to the contrasting environments, we isolated and characterized two full-length cDNAs for a key C4 enzyme, pyruvate, orthophosphate dikinase (PPDK; EC 2.7.9.1). The isogenes for PPDK, designated ppdk1 and ppdk2, were highly homologous to one another but not identical. The PPDK1 protein, deduced from the nucleotide sequence of the cDNA, contained an extra domain at the amino terminus which, presumably, serves as a chloroplast transit peptide, while PPDK2 lacked this extra domain. It seems likely, therefore, that the ppdk1 and ppdk2 genes encode a chloroplastic and a cytosolic PPDK, respectively. Genomic Southern blot analysis revealed the existence of a small family of genes for PPDK in the genome of E. vivipara. Northern blot analysis indicate that both chloroplastic and cytosolic genes for PPDK are expressed simultaneously in the culms, a photosynthetic organ, of E. vivipara and that the pattern of expression of these genes differs between the growth forms.     

Carbon dioxide exchange of C3 and C4 tree species in the understory of a Hawaiian forest

Summary Field measurements of photosynthetic CO₂ exchange were made on saplings of a C₄ tree species, Euphorbia forbesii, and a C₃ tree species, Claoxylon sandwicense, in a shaded mesic forest on Oahu, Hawaii. Both species had light responses typical of those generally found in shade plants. Light saturated photosynthetic rates were 7.15 and 4.09 mol m² s¹ and light compensation points were 6.3 and 1.7 mol m² s¹ in E. forbesii and C. sandwicense, respectively. E. forbesii maintained a higher mesophyll conductance and a higher water use efficiency than C. sandwicense as is typically found in comparisons of C₄ and C₃ plants. Under natural light regimes, both species maintained positive CO₂ uptake rates over essentially the entire day because of low respiration rates and light compensation points. However, photosynthesis during sunflecks accounted for a large fraction of the daily carbon gain. The results show that the carbon-gaining capacity of E. forbesii is comparable to that of a C₃ species in a moderately cool, shaded forest environment. There appears to be no particular advantage or disadvantage associated with the C₄ photosynthetic pathway of E. forbesii in this environment.