Response of photosynthesis of different plant functional types to environmental changes along Northeast China Transect

Net photosynthesis (P-n), transpiration (E), stomatal conductance (g(s)), internal CO2 concentration (C-i), and water use efficiency (WUE) were examined on 215 species from eight plant functional types (PFTs) along a precipitation gradient in northeast China (the Northeast China Transect, or NECT). Among the eight PFTs, meadow steppe grasses had the highest rates of net photosynthesis and forest grasses the lowest and the following order of P-n was noted: meadow steppe grasses >typical steppe grasses >steppe shrubs >desert grasses >forest trees >forest shrubs >desert shrubs >forest grasses (P<0.05). Transpiration tended to be the highest in the steppe grasses and lowest in forest shrubs. Transpiration also decreased rapidly with the appearance of C-3 desert species at the desert end. The forest tree PFT had lower P-n, E, g(s) than the steppe PFTs, whereas WUE values were somewhat greater in the forest tree PFT than the desert shrubs and grasses. Low Ci values along the steppe section (from 400 to 1100 km, east to west) indicated the presence of C-4 species. Of all the PFTs, only shrubs and herbs were noted at all points along the transect. No clear relationship between P-n, E, g(s), WUE of herb and shrub PFTs and annual precipitation was noted - low values were found at both the high and low precipitation ends of the transect. Highest values were noted when precipitation was intermediate.