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.