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.
C4 photosynthetic pathway and morphological functional types were determined for 104 species in 45 genera and 10 families from the deserts of China. 67 C4 species (64.4 %) were found in Dicotyledoneae (e.g. Chenopodiaceae, Polygonaceae, and Amaranthaceae), the other 37 species were in Monocotyledoneae (e.g. Gramineae, Cyperaceae, and Commelinaceae). 36.5 % of the Chenopodiaceae species (predominantly members of the genera Anabasis, Atriplex, Kochia, Salsola, and Suaeda) identified in the desert regions were found with C4 photosynthesis, which was about 48 % of the total C4 species. Many C4 species (58.7 %) were annuals (e.g. Amaranthus, Atriplex, Digitaria, Eragrostis, Kochia, and Salsola) and experienced long-term droughts, high temperature, and high irradiance. Relatively more shrub C4 species (28 species of 104) were found in Chenopodiaceae (e.g. Anabasis, Camphorosma, Haloxylon, and Salsola) and Polygonaceae (e.g. Calligonum) in the desert regions. Most of shrub C4 species with small leaf area were no more than 1 m in height and distributed in sandy soils. Composition of relatively more annual species, shrubs, and Chenopodiaceae C4 species was the primary characteristic for the C4 species occurrence in deserts, and this was remarkably related with the arid environmental conditions.
Floristic composition, life forms for C4 species, and the pattern of altitude distribution were studied on Tibetan Plateau. 79 species, in 7 families and 46 genera, were identified with C4 photosynthesis. 95 % of these C4 species belong to Gramineae (51 species), Cyperaceae (14 species), and Chenopodiaceae (10 species), indicating that C4 plants mainly occur in very few families (7 of 204) on the Tibetan Plateau. High altitude distribution for all the Chenopodiaceae C4 species (> 3 000 m above sea level) suggests that plants of this kind have large tolerance to cold, dryness, and strong ultraviolet radiation. Most Gramineae and Cyperaceae C4 species occurrences are consistent with extensive distribution of steppes and meadows in the vast flat of the central Plateau (1 000-3 000 m a.s.l.). Relatively high amount of hemicryptophyte form plants (44 %) in the region indicates that the vegetation, especially grassland, meadows, and steppe, are in good condition. There is a strong relationship between numbers of C4 species and altitude in the Tibetan Plateau. Occurrence of C4 species is significantly less in both high and low altitude plateaux in Tibet. Altitude distribution pattern for C4 species in the region is not only consistent with the altitude and climate, but also with the vegetation types in altitude gradient.
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. C4Chenopodiaceae 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 (r2= 0.677) and aridity (r2= 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 (r2= 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.
Natural occurrence of C4 species, life form, altitude pattern, and infection by the Three Gorges Project (TGP) were studied in the TGP region. 76 species (about 2.5 % of the total 2 685 vascular plant species in the region), in 6 families and 42 genera, were identified with C4 photosynthesis. 91 % of these C4 species belong to Monocotyledoneae, e.g. Cyperaceae (14 species), Gramineae (54 species), and Commelinaceae (1 species). Of these C4 species, Gramineae was the leading C4 family: 54 C4 grass species (71 % of the total C4 species), about 36 % of the total grasses, were identified in the TGP region. 98 % C4 species was found in therophyte (55 %) and hemicryptophyte (43 %). This is consistent with high grass and sedge compositions in the region. Most habitats of more than a half of these C4 species (65 %) will be submerged permanently, but no species will be endangered or extinct, because 95 % C4 species can be found from 500 to 800 m above sea level. The abundance of some C4 species will be dropped due to the reduction of distribution scope. It will take a long-term to explore the effects of the TGP on plants, vegetation, and environment.
The net photosynthetic rate (PN), transpiration rate (E), and water use efficiency (WUE) of two divergent Leymus chinensis populations from the grassland region of Northeast China were compared. The two populations experienced the similar habitats, but differed in leaf colour, stomata numbers, and chlorophyll contents. The leaf PN for the grey-green (GG) population was greater than that for the yellow-green (YG) population, while the leaf E for GG population was lower than that for the YG population. The greater WUE for the GG population suggests that this type is more able to maintain higher PN under drought and is more fit for the rangeland use in this climate region. and R. Z. Wang, Q. Gao.
Net photosynthetic rate (PN), transpiration rate (E), and stomatal conductance (gs) declined from upper leaves to the lower ones during dry and rainy seasons, indicating that long-term carbon budget should take into account PN variations for different leaf types. Relatively greater PN in the dry season suggested that this species is more able to maintain higher PN under drought, but the relatively higher E in the dry season might reduce water use efficiency (PN/E) for the species. Significant correlations between PN and gs indicated that gs may be the critical factor for PN variability in the desert region. and R. Z. Wang ... [et al.].
The intra- and inter-specific variations in net photosynthetic (PN) and transpiration (E) rates and water use efficiency (WUE) of Puccinellia tenuiflora and Puccinellia chinampoensis leaves were compared. The two species experienced a similar habitat, but differed in leaf area, leaf colour, and nitrogen contents. Leaf PN and E for both reproductive and vegetative shoots of the two species declined with leaf age. PN for reproductive shoots was less than for vegetative shoots, but their E was greater than that of vegetative shoots in the dry season. The average PN and E for reproductive shoots of P. tenuiflora were lower than those of P. chinampoensis, but higher for vegetative shoots. and R. Z. Wang, Y. Q. Yuan.
The differences in net photosynthetic rate (PN), transpiration rate (E), and water use efficiency (WUE) between the vegetative and reproductive shoots of three native grass species from the grassland of northeastern China [grey-green and yellow green populations of Leymus chinensis (Trin.) Tzvel., Puccinellia tenuiflora (Griseb) Scrib & Merr, Puccinellia chinampoensis Ohwi] were compared. The two type shoots experienced similar habitats, but differed in leaf life-span and leaf area. The leaf PN and WUE for the vegetative shoots were significantly higher than those for the reproductive shoots in the grasses, while their E were remarked lower in the dry season. Relative lower leaf PN and WUE for the reproductive shoots of grassland grasses may explain the facts of lower seed production and the subordinate role of seed in the grassland renewal in north-eastern China.
Photosynthetic pathways (e.g. C3, C4) and morphological functional types (e.g. trees, shrubs, high perennial grasses, perennial forbs) were identified for the native species from the Saskatchewan mixed prairie, using the data from references published between 1950 and 2003. Of the total 219 identified species in 145 genera and 45 families, 208 species in 137 genera and 44 families were found with C3 photosynthesis, and most of these species are dominants (e.g. Agropyron dasystachyum Hook. and Stipa spartea var. curtiseta Hitchc.). 11 species in 10 genera and 3 families were identified with C4 photosynthesis (e.g. Atriplex argentea Nutt., Andropogon scoparius Michx., Boutelou gracilis Lag., Calamovilfa longifolia Hook.). The amount of total identified C4 species in the region is much less than that from the South Dakota mixed prairie (27 species). Gramineae is the leading family with C4 photosynthesis (8 species), Chenopodiaceae ranks the second (2 species). Relatively less forb types [50 % perennial forbs (PEF) and 12 % annual forbs (ANF)] and more graminoid types (25 %) composition suggested that the rangelands in the region are relatively stable. Lacking of the knowledge on the optimal traits for PFTs classification in the region, further studies (e.g. C3 and C4 plant identification and optimal trait selection) are needed to explore the relationships between PFTs and vegetation variations, as well as land-use and climate changes. and R. Z. Wang, X. Q. Liu, Y. Bai.