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.     

Photosynthetic Pathway Types of Forage Species Along Grazing Gradient from the Songnen Grassland,Northeastern China

Photosynthetic pathway types (C₃ and C₄ species) and their dynamics along grazing gradient were determined for 42 plant species in 30 genera and 13 families from the Songnen grassland, Northeastern China. Of the total, 10 species in 9 genera and 4 families had C₄ photosynthesis; 32 species in 21 genera and 12 families had C₃ photosynthesis. The proportion of C₄ species in total plants and C₄/C₃ increased with grazing intensity, and peaked in overgrazed plot. Most of the increased C₄ species (6 of 10) along the grazed gradient were annual grasses and halophytes. This indicated that the C₄ species had greater capacity to tolerate environmental stresses (e.g. drought and saline) caused by animal grazing in the Songnen grassland, Northeastern China.     

Photosynthetic Pathways and Life Form Types for Native Plant Species from Hulunbeier Rangelands,Inner Mongolia,North China

Photosynthetic pathway Types (C₃, C₄, and CAM) and life forms of native species from Hulunbeier rangelands, north China were studied. Of the total 258 species, 216 species in 132 genera and 42 families had C₃ photosynthetic pathway, including dominant herbs, e.g. Stipa baicalensis Roshev. and Leymus chinensis (Trin.) Tzvel., Filifolium sibiricum Kitam. and Arudinella hirta (Thunb.) Koidz. 38 species in 28 genera and 10 families were found with C₄ photosynthesis, and 4 species in 2 genera and 1 family had CAM photosynthetic pathway. The occurrence of C₄ species was common in Gramineae and Chenopodiaceae, and the two families were leading ones within C₄ plants. More than 52 % of the total 258 species were in H form, 21 % in Th form, 19 % in G form; the other life form Types, e.g. Ch, M, N, and HH, formed less than 3 %. 68 % of C₄ species were in Th form and 24 % in H form, indicating that these Types were the dominant life forms for C₄ species in the rangeland region. The occurrence of C₄ species was closely related with plant habitats, disturbed lands had the highest C₄ abundance (55 % of the total C₄ species), followed by grasslands and sandy soil, and forests had the lowest C₄ abundance (8 %). Hence the occurrence of C₄ species could be efficient indicator for rangeland dynamics in Hulunbeier rangelands.     

Photosynthetic pathway and morphological functional types in the vegetation from North-Beijing agro-pastoral ecotone, China

Photosynthetic pathways (C₃, C₄, and CAM) and morphological functional types were identified for the species from vegetation in agro-pastoral ecotone, North Beijing. 792 vascular plant species (nearly half of the total species in the ecotone), in 66 families and 317 genera, were identified with C₃, C₄, and CAM photosynthesis (Table 1). 710 species (90 % of the identified species in Table 1) in 268 genera and 64 families were found with C₃ photosynthesis, 68 species (9 % of the total identified species) in 40 genera and 7 families with C₄ photosynthesis, and 14 species in 4 genera and 1 family with CAM photosynthesis. Gramineae is the leading family with C₄ photosynthesis (43 species), Cyperaceae ranks the second (16 species) followed by Chenopodiaceae (5 species). The significant increase of C₄ proportion (C₄/total species) with land deterioration suggested the plants of this type are remarkably responsive to land use in the ecotone. 792 species were classified into nine morphological functional types and the changes of most of these types (e.g. perennial forbs (PEF), annual grasses (ANG), and annual forbs (ANF)) were consistent with habitats and vegetation dynamics in the agro-pastoral ecotone. Hence the photosynthetic pathways, combined with the morphological functional types, are efficient indications for studying the linkage between species and ecosystems in the ecotone.     

Photosynthetic Pathways,Life Forms,and Reproductive Types for Forage Species Along the Desertification Gradient on Hunshandake Desert,North China

Floristic compositions, life forms, reproductive types for forage species, and their responses to desertification in Hunshandake desert were studied. 164 species, in 30 families and 94 genera, were identified with C₃ (137 species), C₄ (25 species), and CAM (2 species) photosynthesis. Of the 25 C₄ species, 76 % were grasses and Chenopodiaceae species (hereafter chenopods). This suggests that the C₄ species mainly occurred in a few families in the desert region. The reduction of C₃ species and the increase of C₄ species with desertification indicated that C₄ species might have higher tolerance to environmental stresses (e.g. dry and poor soil). Relatively more hemicrytophyte and therophyte forms in the desert are related to the local temperate climate and vegetation dynamics. Relatively greater proportions of C₄/C₃ and clonal species/sexual species at mobile dune showed that the C₄ species and clonal species could make greater contribution to sand land restoration in the Hunshandake desert.     

The occurrence of C4 plants and their morphological functional types in the vegetation of Xinjiang, China

Floristic composition, morphological functional types and habitat distributions for C₄ species were studied in Xinjiang, North-western China. 89 species, in 9 families and 41 genera, were identified with C₄ photosynthesis. 48 % of these C₄ species were found in Monocotyledoneae, e.g. Cyperaceae (5 species), Gramineae (38 species), the other 52 % was in Dicotyledoneae, e.g. Chenopodiaceae (29 species), Amaranthaceae (7 species), and Polygonaceae (5 species). Compared with those in semi-arid grasslands in North China and tropical forests in South China, more plant families were found with the occurrence of C₄ plants in this arid region. Relatively higher annual species (63 %), shrubs (18 %), and Chenopodiaceae C₄ species (33 %) compositions were the primary characteristics for the C₄ species occurring in Xinjiang, and this was remarkably related with its arid environment. More Chenopodiaceae C₄ species occurring in the region suggested that this type of C₄ species may have higher capacity to fit the air and soil droughts. There was a strong relationship between C₄ occurrence and habitat distributions, more than half of the total 89 C₄ species were found in disturbed and cultivated lands and early stages of vegetation successions, indicating C₄ occurrence was not only related with climate changes, but also with land uses and vegetation dynamics.     

C<Subscript>3</Subscript> and C<Subscript>4</Subscript> photosynthetic pathways and life form types for native species from agro-forestry region,Northeastern China

Of the total 570 species, 194 species in 116 genera and 52 families were found with C₃ photosynthesis, 24 species in 17 genera and 6 families with C₄ photosynthesis, and 2 species in 1 genera and 1 family with CAM photosynthesis. 90 % of the total species can be found in Changbai Mountain flora, more a half (69 %) in North China flora, and about 1/3 in Mongolian flora and Xinan flora, respectively. The occurrence of C₄ species was not as common as that in adjacent grasslands and deserts, but relatively more than in the adjacent forests. Of the total 24 C₄ species, 63 % C₄ species (15 of 24) was found in Gramineae. Nine life form types can be found, reflecting the moist climate in the region, especially the occurrence of epiphyte and liana forms. Relatively more geophyte life form plants suggested the winter in the region was much colder than in grasslands. These indicated that both ecological studies and land management decisions must take into account plant photosynthetic pathway and life form patterns, for both of them are closely related to climatic changes and land use.     

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 (δ¹³C) 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.     

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.     

δ<Superscript>13</Superscript>C values,photosynthetic pathways,and plant functional types for some plants from saline meadows,Northeastern China

Based on stable carbon isotope ratio (δ¹³C) measurements, photosynthetic pathway types were determined for 61 species in 54 genera and 24 families of flowering plants from the saline meadows of Northeastern China. Of these total vascular plants, 18 species in 17 genera from 6 families were found to have C₄ photosynthesis; 43 species in 38 genera from 20 families had C₃ photosynthesis. Six dicotyledonous species exhibited C₄ pathway, 12 monocotyledonous species were found with C₄ photosynthesis. The dicotyledonous C₄ species had relative greater mean δ¹³C value and less total carbon content than both monocotyledonous C₄ and C₃ species. Most dicotyledonous C₄ species were annual forbs and halophytes. Some C₄ species had been previously documented, but their δ¹³C values varied remarkably from those of the present study. Even though there are some fluctuations for the δ¹³C values of some C₄ species, δ¹³C value was still more reliable for C₃ and C₄ identification than the use of the enzyme ratio method and of low CO₂ compensation concentration.     

The C4 Photosynthetic Pathway and Life Forms in Grassland Species from North China

C₄ photosynthetic pathway and life form were determined for 159 species in 71 genera and 13 families in the grassland of North China. 45 % of the C₄ species were found in Graminae, 19 % in each of Cyperaceae and Chenopodiaceae. More than 51 % of these C₄ species were in therophyta and 36 % hemicryptophyta, while fewer species were in nanophanerophyta (9 %) or geophyta (5 %). The numbers of C₄ species and their life forms were closely related with grassland deterioration and succession in North China. This indicated that the C₄ species had greater capacity to tolerate environmental stress (e.g. drought and salinity) caused by animal grazing and cultivation.     

Occurrence and altitudinal pattern of C<Subscript>4</Subscript> plants on Qinghai Plateau,Qinghai province,China

The natural occurrence and altitudinal pattern of species with C₄ photosynthesis were investigated on Qinghai Plateau, Qinghai province by using stable carbon isotopes in plant leaves and using additional data from references. A total of 58 species belonging to 10 families and 34 genera were identified using C₄ photosynthetic pathway, which is only 1.66 % of total 3 500 plant species in Qinghai province. The leading two families, i.e. Gramineae (23 species) and Chenopodiaceae (22 species) contain 77.6 % of all C₄ plants in the studied area. The number of C₄ species increased from 1 600 to 2 400 m a.s.l. and then decreases quickly till 4 400 m a.s.l. with one half of C₄ species distributing from 2 200 to 2 800 m a.s.l. (48 %). Eight plant species were found above 4 000 m a.s.l., but the distribution of these species is limited to the south of Qinghai province (low latitude area) where annual mean temperature is above 0 °C, suggesting that low temperature may generally limit the distribution of C₄ plants.     

Reassimilation of carbon dioxide by Flaveria (Asteraceae) species representing different types of photosynthesis

The capability to reassimilate CO₂ originating from intracellular decarboxylating processes connected with the photorespiratory glycolate pathway and-or decarboxylation of C₄ acids during C₄ photosynthesis has been investigated with four species of the genus Flaveria (Asteraceae). The C₃-C₄ intermediate species F. pubescens and F. anomala reassimilated CO₂ much more efficiently than the C₃ species F. cronquistii and, with respect to this feature, behaved similarly to the C₄ species F. trinervia. Therefore, under atmospheric conditions the intermediate species photorespired with rates only between 10–20% of that measured with F. cronquistii. At low oxygen concentrations (1,5%) the reassimilation potential of F. anomala approached that of F. trinervia and was distinct from that found with F. pubescens. The data are discussed with respect to a possible sequence of events during evolution of C₄ photosynthesis. If compared with related data for C₃-C₄ intermediate species from other genera they support the hypothesis that, during evolution of C₄ photosynthesis, an efficient capacity for CO₂ reassimilation evolved prior to a CO₂-concentrating mechanism.Abbreviations C₃, C₄ assimilated CO₂ initially found in 3-phosphoglycerate (C₃) or malate and aspartate (C₄) - D reassimilation coefficient - R _n , R _t net, total CO₂ evolution as measured with 0.03 and 3% CO₂, respectively - RuBP ribulose-1,5-bisphosphate - TPS true photosynthesis     

Co-function of C3-and C4-photosynthetic pathways in C3, C4 and C3-C4 intermediate Flaveria species

The potential for C₄ photosynthesis was investigated in five C₃-C₄ intermediate species, one C₃ species, and one C₄ species in the genus Flaveria, using ¹⁴CO₂ pulse-¹²CO₂ chase techniques and quantum-yield measurements. All five intermediate species were capable of incorporating ¹⁴CO₂ into the C₄ acids malate and aspartate, following an 8-s pulse. The proportion of ¹⁴C label in these C₄ products ranged from 50–55% to 20–26% in the C₃-C₄ intermediates F. floridana Johnston and F. linearis Lag. respectively. All of the intermediate species incorporated as much, or more, ¹⁴CO₂ into aspartate as into malate. Generally, about 5–15% of the initial label in these species appeared as other organic acids. There was variation in the capacity for C₄ photosynthesis among the intermediate species based on the apparent rate of conversion of ¹⁴C label from the C₄ cycle to the C₃ cycle. In intermediate species such as F. pubescens Rydb., F. ramosissima Klatt., and F. floridana we observed a substantial decrease in label of C₄-cycle products and an increase in percentage label in C₃-cycle products during chase periods with ¹²CO₂, although the rate of change was slower than in the C₄ species, F. palmeri. In these C₃-C₄ intermediates both sucrose and fumarate were predominant products after a 20-min chase period. In the C₃-C₄ intermediates, F. anomala Robinson and f. linearis we observed no significant decrease in the label of C₄-cycle products during a 3-min chase period and a slow turnover during a 20-min chase, indicating a lower level of functional integration between the C₄ and C₃ cycles in these species, relative to the other intermediates. Although F. cronquistii Powell was previously identified as a C₃ species, 7–18% of the initial label was in malate+aspartate. However, only 40–50% of this label was in the C-4 position, indicating C₄-acid formation as secondary products of photosynthesis in F. cronquistii. In 21% O₂, the absorbed quantum yields for CO₂ uptake (in mol CO₂·[mol quanta]^-1) averaged 0.053 in F. cronquistii (C₃), 0.051 in F. trinervia (Spreng.) Mohr (C₄), 0.052 in F. ramosissima (C₃-C₄), 0.051 in F. anomala (C₃-C₄), 0.050 in F. linearis (C₃-C₄), 0.046 in F. floridana (C₃-C₄), and 0.044 in F. pubescens (C₃-C₄). In 2% O₂ an enhancement of the quantum yield was observed in all of the C₃-C₄ intermediate species, ranging from 21% in F. ramosissima to 43% in F. pubescens. In all intermediates the quantum yields in 2% O₂ were intermediate in value to the C₃ and C₄ species, indicating a co-function of the C₃ and C₄ cycles in CO₂ assimilation. The low quantum-yield values for F. pubescens and F. floridana in 21% O₂ presumably reflect an ineffcient transfer of carbon from the C₄ to the C₃ cycle. The response of the quantum yield to four increasing O₂ concentrations (2–35%) showed lower levels of O₂ inhibition in the C₃-C₄ intermediate F. ramosissima, relative to the C₃ species. This indicates that the co-function of the C₃ and C₄ cycles in this intermediate species leads to an increased CO₂ concentration at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase and a concomitant decrease in the competitive inhibition by O₂.Abbreviations PEP phosphoenolpyruvate - PGA 3-phosphoglycerate - RuBP ribulose-1,5-bisphosphate     

Photosynthetic/photorespiratory characteristics of C3−C4 intermediate species

The extent of photorespiration, the inhibition of apparent photosynthesis (APS) by 21% O₂, and the leaf anatomical and ultrastructural features of the naturally occurring C₃–C₄ intermediate species in the diverse Panicum, Moricandia, and Flaveria genera are between those features of representative C₃ and C₄ plants. The greatest differences between the photosynthetic/photorespiratory CO₂ exchange characteristics of the C₃–C₄ intermediates and C₃ plants occur for the parameters which are measured at low pCO₂ (i.e., the CO₂ compensation concentration and rates of CO₂ evolution into CO₂-free air in the light). The rates of APS by the intermediate species at atmospheric pCO₂ are similar to those of C₃ plants.The mechanisms which are responsible for reducing photorespiration in the C₃–C₄ intermediate species are poorly understood, but two proposals have been advanced. One emphasizes the importance of limited C₄ photosynthesis which reduces O₂ fixation by ribulose 1,5-bisphosphate carboxylase/oxygenase, and, thus, reduces photorespiration by a CO₂-concentrating mechanism, while the other emphasizes the importance of the internal recycling of photorespiratory CO₂ evolved from the chloroplast/mitochondrion-containing bundle-sheath cells. There is no evidence from recent studies that limited C₄ photosynthesis is responsible for reducing photorespiration in the intermediate Panicum and Moricandia species. However, preliminary results suggest that some, but not all, of the intermediate Flaveria species may possess a limited C₄ cycle. The importance of a chlorophyllous bundle-sheath layer in the leaves of intermediate Panicum and Moricandia species in a mechanism based on the recycling of photorespiratory CO₂ is uncertain.Therefore, although they have yet to be clearly delineated, different strategies appear to exist in the C₃–C₄ intermediate group to reduce photorespiration. Of major importance is the finding that some mechanism(s) other than Crassulacean acid metabolism or C₄ photosynthesis has (have) evolved in at least the majority of these terrestrial intermediate species to reduce the seemingly wasteful metabolic process of photorespiration.Abbreviations APS apparent (net) photosynthesis - CAM Crassulacean acid metabolism - CE carboxylation efficiency - T CO₂ compensation concentration - IRGA infrared gas analysis - P_i orthophosphate - PEP phosphoenolpyruvate - RuBP ribulose 1,5-bisphosphate Published as Paper No. 7383, Journal Series, Nebraska Agricultural Experiment Station.     

Photosynthetic Pathways and Life Forms in Different Grassland Types from North China

Photosynthetic pathways (C₄, C₃, and CAM species) and plant life forms of three grassland types in North China were compared. Of the total 201 species, 144 species in 78 genera and 34 families had C₃ photosynthetic pathway, 56 species in 35 genera and 11 families had C₄ photosynthetic pathway, and 1 species had CAM photosynthetic pathway. The number of C₄ species in Songnen meadow was 70–80 % greater than that in Xilinguole steppe and Hunshandak desert grassland, but that for C₃ species did not differ significantly among the three grassland types. The number of therophytes in the Songnen meadow was relatively greater than that of the other two grassland types, but that of hemicryptophytes was lower. Thus the distribution of C₄ species and plant life form is probably related to precipitation.     

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.     

Effects of irradiance and temperature on photosynthesis in C3, C4 and C3/C4 Panicum species

Species in the Laxa and Grandia groups of the genus Panicum are adapted to low, wet areas of tropical and subtropical America. Panicum milioides is a species with C₃ photosynthesis and low apparent photorespiration and has been classified as a C₃/C₄ intermediate. Other species in the Laxa group are C₃ with normal photorespiration. Panicum prionitis is a C₄ species in the Grandia group. Since P. milioides has some leaf characteristics intermediate to C₃ and C₄ species, its photosynthetic response to irradiance and temperature was compared to the closely related C₃ species, P. laxum and P. boliviense and to P. prionitis. The response of apparent photosynthesis to irradiance and temperature was similar to that of P. laxum and P. boliviense, with saturation at a photosynthetic photo flux density of about 1 mmol m^-2 s^-1 at 30°C and temperature optimum near 30°C. In contrast, P. prionitis showed no light saturation up to 2 mmol m^-2 s^-1 and an optimum temperature near 40°C. P. milioides exhibited low CO₂ loss into CO₂-free air in the light and this loss was nearly insensitive to temperature. Loss of CO₂ in the light in the C₃ species, P. laxum and P. boliviense, was several-fold higher than in P. milioides and increased 2- to 5-fold with increases in temperature from 10 to 40°C. The level of dark respiration and its response to temperature were similar in all four Panicum species examined. It is concluded that the low apparent photorespiration in P. milioides does not influence its response of apparent photosynthesis to irradiance and temperature in comparison to closely related C₃ Panicum species.Abbreviations AP apparent photosynthesis - I CO₂ compensation point - gl leaf conductance; gm, mesophyll conductance - PPFD photosynthetic photon flux density - PR apparent photorespiration rate - RuBPC sibulose bisphosphate carboxylase     

C4 Species and their Response to Large-Scale Longitudinal Climate Variables Along the Northeast China Transect (NECT)

Natural occurrence of C₄ species, life forms, and their longitudinal distribution patterns along the Northeast China Transect (NECT) were studied. Six vegetation regions experiencing similar irradiation regimes, but differing in longitude, precipitation, and altitude were selected along the NECT from 108 to 131 °E, around altitude of 43.5 °N. Seventy C₄ species were identified in 41 genera and 13 families. 84 % of the total C₄ species were found in four families: Gramineae (38 species), Chenopodiaceae (11 species), Cyperaceae (5 species), and Amaranthaceae (5 species). C₄ grasses make up 54 % of the total identified C₄ species along the NECT and form the leading C₄ family in meadow, steppe, and desert along the NECT. C₄ Chenopodiaceae species make up about 16 % of the C₄ species and become less important, particularly in the meadow and the eastern end of the NECT. 57 % of the total C₄ species are therophytes and 37 % are hemicryptophytes, which is consistent with floristic composition and land utilization. In general, the number of C₄ species decreased significantly from the west to the east or from dry to moist areas along the NECT, and was remarkably correlated with annual precipitation (r ²= 0.677) and aridity (r ²= 0.912), except for salinized meadow region. The proportion of C₄ species from all the six vegetation regions was considerably correlated with these two climatic parameters (r ²= 0.626 or 0.706, respectively). These findings suggest that the natural occurrence of C₄ species varies significantly along the large-scale longitudinal gradient of the NECT. The notable relationship of C₄ species number and proportion in the flora with variations in annual precipitation and aridity suggest that these two climatic parameters are the main factors controlling the longitudinal distribution patterns of C₄ species along the NECT.