C4 plants in the vegetation of Mongolia: their natural occurrence and geographical distribution in relation to climate

The natural geographical occurrence, carbon assimilation, and structural and biochemical diversity of species with C₄ photosynthesis in the vegetation of Mongolia was studied. The Mongolian flora was screened for C₄ plants by using ¹³C/¹²C isotope fractionation, determining the early products of ¹⁴CO₂ fixation, microscopy of leaf mesophyll cell anatomy, and from reported literature data. Eighty C₄ species were found among eight families: Amaranthaceae, Chenopodiaceae, Euphorbiaceae, Molluginaceae, Poaceae, Polygonaceae, Portulacaceae and Zygophyllaceae. Most of the C4 species were in three families: Chenopodiceae (41 species), Poaceae (25 species) and Polygonaceae, genus Calligonum (6 species). Some new C₄ species in Chenopodiaceae, Poaceae and Polygonaceae were detected. C₄ Chenopodiaceae species make up 45% of the total chenopods and are very important ecologically in saline areas and in cold arid deserts. C₄ grasses make up about 10% of the total Poaceae species and these species naturally concentrate in steppe zones. Naturalized grasses with Kranz anatomy,of genera such as Setaria, Echinochloa, Eragrostis, Panicum and Chloris, were found in almost all the botanical-geographical regions of Mongolia, where they commonly occur in annually disturbed areas and desert oases. We analyzed the relationships between the occurrence of C₄ plants in 16 natural botanical-geographical regions of Mongolia and their major climatic influences. The proportion of C₄ species increases with decreasing geographical latitude and along the north-to-south temperature gradient; however grasses and chenopods differ in their responses to climate. The abundance of Chenopodiaceae species was closely correlated with aridity, but the distribution of the C₄ grasses was more dependent on temperature. Also, we found a unique distribution of different C₄ Chenopodiaceae structural and biochemical subtypes along the aridity gradient. NADP-malic enzyme (NADP-ME) tree-like species with a salsoloid type of Kranz anatomy, such as Haloxylon ammodendron and Iljinia regelii, plus shrubby Salsola and Anabasis species, were the plants most resistant to ecological stress and conditions in highly arid Gobian deserts with less than 100 mm of annual precipitation. Most of the annual C₄ chenopod species were halophytes, succulent, and occurred in saline and arid environments in steppe and desert regions. The relative abundance of C₃ succulent chenopod species also increased along the aridity gradient. Native C₄ grasses were mainly annual and perennial species from the Cynodonteae tribe with NAD-ME and PEP-carboxykinase (PEP-CK) photosynthetic types. They occurred across much of Mongolia, but were most common in steppe zones where they are often dominant in grazing ecosystems. Received: 17 March 1999 / Accepted: 1 November 1999     

Occurrence of C3 and C4 photosynthesis in cotyledons and leaves of Salsola species (Chenopodiaceae)

Most species of the genus Salsola (Chenopodiaceae) that have been examined exhibit C₄ photosynthesis in leaves. Four Salsola species from Central Asia were investigated in this study to determine the structural and functional relationships in photosynthesis of cotyledons compared to leaves, using anatomical (Kranz versus non-Kranz anatomy, chloroplast ultrastructure) and biochemical (activities of photosynthetic enzymes of the C₃ and C₄ pathways, ¹⁴C labeling of primary photosynthesis products and ¹³C/¹²C carbon isotope fractionation) criteria. The species included S. paulsenii from section Salsola, S. richteri from section Coccosalsola, S. laricina from section Caroxylon, and S. gemmascens from section Malpigipila. The results show that all four species have a C₄ type of photosynthesis in leaves with a Salsoloid type Kranz anatomy, whereas both C₃ and C₄ types of photosynthesis were found in cotyledons. S. paulsenii and S. richteri have NADP- (NADP-ME) C₄ type biochemistry with Salsoloid Kranz anatomy in both leaves and cotyledons. In S. laricina, both cotyledons and leaves have NAD-malic enzyme (NAD-ME) C₄ type photosynthesis; however, while the leaves have Salsoloid type Kranz anatomy, cotyledons have Atriplicoid type Kranz anatomy. In S. gemmascens, cotyledons exhibit C₃ type photosynthesis, while leaves perform NAD-ME type photosynthesis. Since the four species studied belong to different Salsola sections, this suggests that differences in photosynthetic types of leaves and cotyledons may be used as a basis or studies of the origin and evolution of C₄ photosynthesis in the family Chenopodiaceae.This revised version was published online in October 2005 with corrections to the Cover Date.     

δ13C values of grass species collected in the northern Sahara desert

Summary ¹³C values were measured for 45 Poaceae species collected in the northern Sahara desert, at the foot of the Saharan Atlas. The results indicate a clear relationship between carbon isotope discrimination and phytogeographical distribution of the grasses. Mediterranean species predominantly had ¹³C values indicating the C₃ pathway of photosynthesis. By contrast, nearly all species belonging to the Saharo-Arabian and /or Sudanian group showed a C₄ like carbon isotope composition. Leaf material of two species, Lygeum spartum and Stipa tenacissima, had ¹³C values in the region of-20, i.e. intermediate between the mean ¹³C values of C₃ and C₄ plants. However, additional speciments of both these grasses obtained from a different source (herbarium of the Hebrew University, Jerusalem) yielded a C₃ like carbon isotope composition.     

Altitudinal changes in the incidence of crassulacean acid metabolism in vascular epiphytes and related life forms in Papua New Guinea

Summary The occurrence of Crassulacean acid metabolism (CAM), as judged from ¹³C values, was investigated in epiphytes and some related plant species at a series of sites covering the approximate altitudinal range of epiphytes in Papua New Guinea. Comprehensive collections were made at each site and the occurrence of water storage tissue and blade thickness was also determined. Some 26% of epiphytic orchids from a lowland rainforest (2–300 m.a.s.l) showed ¹³C values typical of obligate CAM and possessed leaves thicker than 1 mm. A second group of orchids, mostly with succulent leaves, possessed intermediate ¹³C values between -23 and -26% and accounted for 25% of the total species number. Some species of this group may exhibit weak CAM or be facultative CAM plants. The remainder of the lowland rainforest species appeared to be C₃ plants with ¹³C values between -28 and -35%. and generally possessed thin leaves. Obligate CAM species of orchids from a lower montane rainforest (1175 m.a.s.l) comprised 26% of the species total and mostly possessed thick leaves. The remainder of the species were generally thin-leaved with ¹³C values between -26 and -35%. largely indicative of C₃ photosynthesis. Orchids with intermediate ¹³C values were not found in the lower montane rainforest. Obligate CAM appeared to be lacking in highland epiphytes from an upper montane rainforest and subalpine rainforest (2600–3600 m.a.s.l). However the fern, Microsorium cromwellii had a ¹³C value of -21.28%. suggesting some measure of CAM activity. Other highland ferns and orchids showed more negative °¹³C values, up to-33%., typical of C₃ photosynthesis. The highland epiphytic orchids possessed a greater mean leaf thickness than their lowland C₃ counterparts due to the frequent occurrence of water storage tissue located on the adaxial side of the leaf. It is suggested that low daytime temperatures in the highland microhabitats is a major factor in explaining the absence of CAM. The increased frequency of water storage tissue in highland epiphytes may be an adaptation to periodic water stress events in the dry season and/or an adaptation to increased levels of UV light in the tropicalpine environment.     

Photosynthetic pathways and the ecological distribution of the chenopodiaceae in Isreal

Summary Fifty-four species of the Chenopodiaceae in Israel were examined for their anatomical features, ¹³C values, habitat and phytogeographical distribution. 17 species have ¹³C values between -20 and -30and non-Kranz anatomy (NK) and are therefore considered as C₃ plants. 37 species have ¹³C values between -10 and -18 and Kranz or C₄-Suaeda type anatomy and are therefore considered as C₄ plants. Some C₄ plants have leaf structure which seems to be intermediate between the Kranz and the C₄-Suaeda type of leaf anatomy.The segregation of the species into photosynthetic groups shows tribal and phytogeographical grouping. Most of the C₃ Chenopods are either mesoruderal plants or coastal halophytes, with a distribution area which covers the Euro-Siberian as well as the Mediterranean phytogeographical regions. The C₄ Chenopods are mainly desert or steppe xerohalophytes with a distribution area which includes the Saharo-Arabian and/or Irano-Turanian phytogeographical regions.     

Environmental control of crassulacean acid metabolism in Welwitschia mirabilis Hook. Fil. in its range of natural distribution in the Namib desert

Summary Within the area of its natural distribution in South West Africa, Welwitschia mirabilis has a less negative ¹³C value than C₃ plants and a more negative ¹³C value than C₄ species. This indicates that Welwitschia m. assimilates CO₂ partially via CAM when growing in its natural habitat. The difference between the ¹³C values of Welwitschia m. and of the C₃ species is significant in the savanna, whereas it is only small and statistically not significant in the grassland zone. The proportion of CO₂ fixed via CAM is largest in the coastal desert zone. There was no correlation between the ¹³C values and the Cl^- or ash content of the tissue. Thus, CAM in Welwitschia m. seems not to be induced by salt stress. There is no change in the ¹³C values along the persistent Welwitschia m. leaf. The present data indicate that on a broad geographical scale in the area of distribution temperature regime, and water stress as a modifying factor, determine CAM in Welwitschia m. The ecological implications are discussed by comparing the behaviour of Welwitschia m. with other CAM, C₃ and C₄ species of the accompanying flora.     

Carbon-isotope discrimination by leaves of Flaveria species exhibiting different amounts of C3-and C4-cycle co-function

Carbon-isotope ratios were examined as ¹³C values in several C₃, C₄, and C₃–C₄ Flaveria species, and compared to predicted ¹³C, values generated from theoretical models. The measured ¹³C values were within 4 of those predicted from the models. The models were used to identify factors that contribute to C₃-like ¹³C values in C₃–C₄ species that exhibit considerable C₄-cycle activity. Two of the factors contributing to C₃-like ¹³C values are high CO₂ leakiness from the C₄ pathway and pi/pa values that were higher than C₄ congeners. A marked break occurred in the relationship between the percentage of atmospheric CO₂ assimilated through the C₄ cycle and the ¹³C value. Below 50% C₄-cycle assimialtion there was no significant relationship between the variables, but above 50% the ¹³C values became less negative. These results demonstrate that the level of C₄-cycle expression can increase from, 0 to 50% with little integration of carbon transfer from the C₄ to the C₃ cycle. As expression increaces above 50%, however, increased integration of C₃- and C₄-cycle co-function occurs.Abbreviations and symbols RuBP carboxylase ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) - PEP carboxylase phosphoenolpyruvate carboxylase (EC 4.1.1.31) - pa atmospheric CO₂ partial pressure - pi intercellular CO₂ partial pressure - isotope ratio - quantum yield for CO₂ uptake     

Biomass production of C3- and C4-plant species in pure and mixed culture with different water supply

Summary Pure and mixed cultures of the dicotyledons Atriplex hortensis L. (C₃ plant) and Amaranthus retroflexus L (C₄) on the one hand and of the grasses Avena sativa L (C₃) and Panicum miliaceum L. (C₄) on the other hand were maintained in a standard soil with different ground water tables. After 12 weeks the length, dry weight and nitrogen-content of the aboveground and belowground parts of the plants, and in addition the carbon-and ash-content and the ¹³C value of the aboveground parts were determined. It turned out that the length and the dry weight of the shoots of the C₃ species showed on increasing tendency with increased water supply, while the values of the C₄ species were drastically diminished at the highest water level only. The roots showed in most cases an increased length and dry weight at drier conditions, more pronounced in the C₄ than in the C₃ species. The nitrogen content of the shoots was mostly higher in the shoots of the C₃ plants and in the roots of the C₄ plants; it changed in a non-regular manner with variations in water supply. Since the carbon content did not change markedly, the C/N ratio was variable. There was a slight tendency for a higher carbon content and mostly also for a higher C/N-ratio in the shoots of C₄ plants. The ¹³C values of both C₃ as C₄ plants were in general not at all influenced by the water supply; they were fixed genetically. The ash content of the analyzed species did not show a clear relationship to the type of photosynthetic CO₂-fixation or to the water regime.The influence of light intensity was studied with mixed cultures of all four plant species, again with different water supply. There was a strong effect of light intensity on the competitive behaviour of the C₃ and C₄ plants under modified water conditions. The wild C₃ plant Atriplex hortensis was most successful under conditions of relatively low light intensity and high water availability, while the cultivated artificial species Avena sativa showed much less differences between full-light grown and shadow plants. The C₄ plant Amaranthus retroflexus is most successful under competitive conditions at high water stress in full light. The C₄ grass Panicum miliaceum showed maximum shoot growth in light, but was successful under competitive conditions especially also with good water supply. The light intensity had no effect on the ¹³C values. — There was no indication that the soil-type as such has a distinct influence on the success of C₃ or C₄ plants in mixed cultures.Dedicated to Prof. Dr. M. Evenari, Jerusalem, and to Dr. K.F. Springer, Heidelberg     

Responses of C4 grasses to atmospheric CO2 enrichment

Summary The growth and photosynethetic responses to atmospheric CO₂ enrichment of 4 species of C₄ grasses grown at two levels of irradiance were studied. We sought to determine whether CO₂ enrichment would yield proportionally greater growth enhancement in the C₄ grasses when they were grown at low irradiance than when grown at high irradiance. The species studied were Echinochloa crusgalli, Digitaria sanguinalis, Eleusine indica, and Setaria faberi. Plants were grown in controlled environment chambers at 350, 675 and 1,000 l 1^-1 CO₂ and 1,000 or 150 mol m^-2 s^-1 photosynthetic photon flux density (PPFD). An increase in CO₂ concentration and PPFD significantly affected net photosynthesis and total biomass production of all plants. Plants grown at low PPFD had significantly lower rates of photosynthesis, produced less biomass, and had reduced responses to increases in CO₂. Plants grown in CO₂-enriched atmosphere had lower photosynthetic capacity relative to the low CO₂ grown plants when exposed to lower CO₂ concentration at the time of measurement, but had greater rate of photosynthesis when exposed to increasing PPFD. The light level under which the plants were growing did not influence the CO₂ compensation point for photosynthesis.     

Oxygen inhibition of photosynthesis in the C4 species Amaranthus graecizans L.

In the C₄ plant, Amaranthus graecizans, increasing [O₂] from 2% up to 100% inhibited photosynthesis, quantum yield, and the carboxylation efficiency, and increased the CO₂ compensation point () from 2 to about 12 l/l. The O₂ inhibition of photosynthesis was fully reversible. When changing from 2.5 to 40% O₂ and vice versa, about 1 h was required for full equilibration with an O₂ inhibition of 18%; whereas in wheat, a C₃ species, inhibition of photosynthesis and its reversal occurs within minutes after changing [O₂], resulting in 63% inhibition of photosynthesis by 45% O₂. These differences in O₂ inhibition between a C₄ and C₃ species can be explained by high diffusive resistance across bundle-sheath cells of C₄ plants and the increased CO₂/O₂ ratio in bundle-sheath cells which is the consequence of the C₄ cycle. In A. graecizans, increased with increasing [O₂] but tended to reach a maximum at relatively high O₂ levels. The lack of a linear increase in as previously observed for C₃ species indicates that a considerable amount of photorespired CO₂ may be re-fixed with increasing levels of O₂. In comparison to previous reports with other C₄ species, photosynthesis of A. graecizans shows greater sensitivity to O₂, with a noticeable inhibition occurring with shifts from 2 to 21% O₂. A. graecizans has characteristics of other C₄ species with respect to Kranz anatomy, localization of PEP carboxylase in mesophyll cells and RuBP carboxylase in bundle-sheath cells, and little fractionation among carbon isotopes during CO₂ fixation. The basis for the higher sensitivity of photosynthesis of A. graecizans to O₂ may be based upon a lower diffusive resistance of gases across bundle-sheath cells than in some other C₄ species.Abbreviations CE carboxylation efficiency - RuBP ribulose-1,5-bisphosphate - CO₂ compensation point     

Photosynthetic Pathway Types in Rangeland Plant Species from Inner Mongolia,North China

Photosynthetic pathway types, based on ¹³C measurements, were determined for 125 species in 95 genera and 32 families growing in rangelands from Inner Mongolia. Of the total species, 4 species from 3 genera and 2 families had C₄ photosynthesis (2 species in Gramineae and 2 in Chenopodiaceae) and 118 species from 90 genera and 31 families had C₃ photosynthesis. The number of C₄ species differed significantly among four rangeland sites, 4 species in desert, 3 species in steppe, but no C₄ species were identified in meadow and dune. Six species [e.g. Agriophyllum arenarium Bieb., Bassia dasyphylla O. Kuntze, Saussurea japonica (Thunb.) DC.] earlier identified as C₄ species using the enzyme ratio method were found as C₃ species using the carbon isotope ratios (¹³C). Hence the enzyme ratio method for C₃ and C₄ identification may not always be reliable. The ¹³C values of 3 species of Crassulaceae, which had been considered as CAM species, differed remarkably [–25.79 for Sedum aizoon L., –24.42 for Osostachys fimbriatus (Turcz.) Berger, and –16.97 for O. malacophyllus (Pall.) Fisch], suggesting that the use of ¹³C method as a diagnosis for CAM photosynthetic pathway type may not always be reliable and supplementary measurements are needed.     

European plants with C4 photosynthesis: geographical and taxonomic distribution and relations to climate parameters

A survey of C₄ plants in Europe was performed with 216 species based on information in the literature and new studies. C₄ species were found in 10 families: the eudicots Amaranthaceae, Chenopodiaceae, Euphorbiaceae, Molluginaceae, Nyctaginaceae, Polygonaceae, Portulacaceae and Zygophyllaceae and the monocots Cyperaceae and Poaceae. The majority of the C₄ species belong to four families, Amaranthaceae (23), Chenopodiaceae (65), Cyperaceae (27) and Poaceae (88). In central and southern Europe, the abundance of native C₄ plants varied between 44 and 88% of total C₄ plants occurring, the rest being invasive C₄ species. The occurrence of total C₄ species, C₄ monocots and C₄ Chenopodiaceae was assessed for five major phyto‐geographical regions of Europe (north‐west, north‐east, central, south‐west, and south‐east). The abundance of C₄ plants of total C₄ dicots, C₄ Chenopodiaceae, total C₄ monocots, C₄ Poaceae and C₄ Cyperaceae was related to the climatic variables of annual mean daily temperature, annual precipitation and DeMartonne's aridity index. The abundance of total C₄ plants decreases with increasing temperature and expression of aridity (decreasing aridity index) and is not correlated with precipitation. The abundance of total C₄ dicots and C₄ Chenopodiaceae is correlated with precipitation and aridity but not temperature, whereas the abundance of total C₄ monocots, C₄ Poaceae and C₄ Cyperaceae is correlated with temperature and aridity but not precipitation. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 163 , 283–304.     

Differences in Leaf δ13C Among Four Dominant Species in a Secondary Succession Sere on the Loess Plateau of China

Differences in leaf ¹³C among four dominant species as well as the species-specific response to the fluctuations of either soil moisture or monthly mean temperature were examined along a secondary succession sere with a time scale from 3 to 149 y on the Loess Plateau in north-western China. We used leaf ¹³C as a surrogate for water use efficiency (WUE) of the mentioned dominant species. Bothrichloa ischaemun as a dominant species in the final succession stage belongs to C₄ photosynthesis pathway, while the other three dominant species occurring in the first three succession stages belong to C₃ pathway. The overall trend of leaf ¹³C variation among the three C₃ species was Artemisia gmelinii (in the third stage) and Lespedeza davurica (in the second stage) > Artemisia scoparia (in the first stage). This suggests that species with higher WUE (more positive leaf ¹³C) would have substantial competitive advantages in the context of vegetation succession. Furthermore, species with highest WUE (i.e. C₄ pathway) have great potential to be dominant in the final succession stage in the habitats (such as the study area) undergoing strong water stress in growing season. The evolution of WUE among the dominant species occurring in different succession stages strongly depends on the time scale of given stage since abandonment. The longer the time scale is, the more significant the differences among them in terms of leaf ¹³C, hence WUE. Our results support the notions that leaf ¹³C may be more positive when water supply is less favourable.     

Effect of size on the energy acquired in species of the fish from a neotropical reservoir,Brazil

In this paper we analysed autotrophic sources of the carbon ( ¹³C) and the trophic position ( ¹⁵N) of Leporinus friderici in the influence area of Corumbá Reservoir, Brazil. We collected samples of muscles of fish from different sizes riparian vegetation, C₄ grasses, zooplankton, periphyton and particulate organic carbon (POC). There were significant differences for the carbon isotope proportion found in muscles of L.friderici in the different size groups analysed. The highest values of ¹³C recorded for middle sized individuals is attributed to the large contribution of C₄ plants in their diet. Small individuals sampled upstream also receive similar contribution from C₄ plants. In contrast the same size group sampled downstream from the reservoir, has a much smaller of C₄ plants. The ¹³C negative character of small individuals from downstream is due to the larger contribution of C₃ plants (except periphyton). At larger sizes we found intermediate ¹³C values. The ¹⁵N proportions we found for each size group were not significantly different, however we found decreasing mean values with increasing size. The trophic level calculated from the dietary data was higher than that found with the ¹³C concentration in the muscle, except for small individuals, when the values were equal.     

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.     

δ13C values of some succulent plants from Madagascar

Summary ¹³C values were determined in 20 succulents from Madagascar. The values were indicative of Crassulacean Acid Metabolism in 10 species of the Didiereaceae, 4 species of the Euphorbiaceae, 2 species of the Crassulaceae and 1 species of the Cucurbitaceae. The Didiereaceae and Euphorbiaceae studied are major components of a high biomass xerophytic flora in the semi-arid southwest and south of Madagascar. Three species of the Euphorbiaceae with succulent stems and non-succulent leaves, which were cultivated outdoors in the Tananarive Botanic Garden, showed C₃ like ¹³C values for both leaves and stems. ¹³C values of leaf and stem material from a similar species, collected in the south of Madagascar, indicated Crassulacean Acid Metabolism.Abbreviations CAM Crassulacean Acid Metabolism     

Carbon isotope ratios of soil organic matter and their use in assessing community composition changes in Curlew Valley,Utah

Summary Stable carbon isotope ratios of roots and soil organic matter were measured in Curlew Valley, Utah to determine if changes in the relative dominance of two shrub species had occurred in this salt-desert community. Measurements were made on soil cores along transects stretching from monospecific stands of Ceratoides lanata, a C₃ shrub, to monospecific stands of Atriplex confertifolia, a C₄ shrub. ¹³C values of roots and soil organic matter under Ceratoides cover appeared to be in equilibrium with the current plant community. By contrast, ¹³C values of roots and soils under Atriplex portions of the transects were more negative than would be expected for a C₄-dominated community. These results indicate that a change in relative C₃/C₄ dominance has occurred, and suggest that the C₄ shrub Atriplex confertifolia is increasing in importance in this salt-desert community.     

Plant functional types and their ecological responses to salinization in saline grasslands, Northeastern China

Photosynthetic pathways (C₃, C₄, and CAM) and morphological functional types (e.g. shrubs, high perennial grasses, short perennial graminaceous plants, annual grasses, annual forbs, perennial forbs, halophytes, and hydrophytes) were identified for the species from salinity grasslands in Northeastern China, using the data from both stable carbon isotope ratios (¹³C) and from the references published between 1993 and 2002. 150 species, in 99 genera and 37 families, were found with C₃ photosynthesis, and most of these species are dominants [e.g. Leymus chinensis (Trin.) Tzvel., Calamagrostis epigeios (L.), Suaeda corniculata (C.A. Mey.) Bunge]. 40 species in 25 genera and 8 families were identified with C₄ photosynthesis [e.g. Chloris virgata Sw., Aeluropus littoralis (Gouan) Parlat] and 1 species with CAM photosynthesis. Gramineae is the leading family with C₄ photosynthesis (27 species), Chenopodiaceae ranks the second (5 species). The significant increase of C₄ proportions with intense salinity suggested this type plant is remarkable response to the grassland salinization in the region. 191 species were classified into eight morphological functional types and the changes of most of these types (e.g. PEF, HAL, and HPG) were consistent with habitats and vegetation dynamics in the saline grassland. My findings suggest that the photosynthetic pathways, combined with morphological functional types, are efficient means for studying the linkage between species and ecosystems in this type of saline grassland in Northeastern China.This revised version was published online in March 2005 with corrections to the page numbers.     

Does Bienertia cycloptera with the single-cell system of C(4) photosynthesis exhibit a seasonal pattern of delta (13)C values in nature similar to co-existing C (4) Chenopodiaceae having the dual-cell (Kranz) system?

Family Chenopodiaceae is an intriguing lineage, having the largest number of C₄ species among dicots, including a number of anatomical variants of Kranz anatomy and three single-cell C₄ functioning species. In some previous studies, during the culture of Bienertia cycloptera Bunge ex Boiss., carbon isotope values (δ¹³C values) of leaves deviated from C₄ to C₃−C₄ intermediate type, raising questions as to its mode of photosynthesis during growth in natural environments. This species usually co-occurs with several Kranz type C₄ annuals. The development of B. cycloptera morphologically and δ¹³C values derived from plant samples (cotyledons, leaves, bracts, shoots) were analyzed over a complete growing season in a salt flat in north central Iran, along with eight Kranz type C₄ species and one C₃ species. For a number of species, plants were greenhouse-grown from seeds collected from the site, in order to examine leaf anatomy and C₄ biochemical subtype. Among the nine C₄ species, the cotyledons of B. cycloptera, and of the Suaeda spp. have the same respective forms of C₄ anatomy occurring in leaves, while cotyledons of members of tribe Caroxyloneae lack Kranz anatomy, which is reflected in the δ¹³C values found in plants grown in the natural habitat. The nine C₄ species had average seasonal δ¹³C values of −13.9‰ (with a range between species from −11.3 to −15.9‰). The measurements of δ¹³C values over a complete growing season show that B. cycloptera performs C₄ photosynthesis during its life cycle in nature, similar to Kranz type species, with a seasonal average δ¹³C value of −15.2‰. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Incorporation of 14CO2 into C4 acids by leaves of C3-C4 intermediate and C3 species of Moricandia and Panicum at the CO2 compensation concentration

Comparative ¹⁴CO₂ pulse-¹²CO₂ chase studies performed at CO₂ compensation ()-versus air-concentrations of CO₂ demonstrated a four-to eightfold increase in assimilation of ¹⁴CO₂ into the C₄ acids malate and aspartate by leaves of the C₃-C₄ intermediate species Panicum milioides Nees ex Trin., P. decipiens Nees ex Trin., Moricandia arvensis (L.) DC., and M. spinosa Pomel at . Specifically, the distribution of ¹⁴C in malate and aspartate following a 10-s pulse with ¹⁴CO₂ increases from 2% to 17% (P. milioides) and 4% to 16% (M. arvensis) when leaves are illuminated at the CO₂ compensation concentration (20 l CO₂/l, 21% O₂) versus air (340 l CO₂/l, 21% O₂). Chasing recently incorporated ¹⁴C for up to 5 min with ¹²CO₂ failed to show any substantial turnover of label in the C₄ acids or in carbon-4 of malate. The C₄-acid labeling patterns of leaves of the closely related C₃ species, P. laxum Sw. and M. moricandioides (Boiss.) Heywood, were found to be relatively unresponsive to changes in pCO₂ from air to . These data demonstrate that the C₃-C₄ intermediate species of Panicum and Moricandia possess an inherently greater capacity for CO₂ assimilation via phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) at the CO₂ compensation concentration than closely related C₃ species. However, even at , CO₂ fixation by PEP carboxylase is minor compared to that via ribulosebisphosphate carboxylase (EC 4.1.1.39) and the C₃ cycle, and it is, therefore, unlikely to contribute in a major way to the mechanism(s) facilitating reduced photorespiration in the C₃-C₄ intermediate species of Panicum and Moricandia.Abbreviations Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - PEP phosphoenolpyruvate - CO₂ compensation concentration - 3PGA 3-phosphoglycerate - SuP sugar monophosphates - SuP₂ sugar bisphosphates Published as Paper No. 8249, Journal Series, Nebraska Agricultural Research Division