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.
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.
Floristic composition, morphological functional types, and altitudinal distribution pattern for C4 species were studied in Yunnan province, South-western China. 159 species, in 6 families and 60 genera, were identified with C4 photosynthesis. 93 % of these C4 species were found in Monocotyledoneae, e.g. Cyperaceae (18 species), Gramineae (129 species), and Commelinaceae (1 species), the other 7 % was in Dicotyledoneae, e.g. Amaranthaceae (5 species), Portulacaceae (4 species), and Chenopodiaceae (2 species). Hence C4 plants mainly occurred in very few families in the tropical region. Compared with those in semi-arid grasslands and arid deserts in North China, more C4 grasses and much less Chenopodiaceae C4 species occurred in the tropical region. This indicates the physiological responses of C4 plants from the two families are very different. Chenopodiaceae C4 species may be more fit semi-arid and arid environments, while C4 grasses are more fit the moist tropical conditions. There was a strong relationship between C4 distribution and altitude in the tropical region. Altitudinal distribution pattern for C4 species in the region was consistent with altitude, climate, and habitats.
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.
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.