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)), i nternal CO2 concentration (C-i), and water use efficiency (WUE) were examin ed on 215 species from eight plant functional types (PFTs) along a precipit ation gradient in northeast China (the Northeast China Transect, or NECT). Among the eight PFTs, meadow steppe grasses had the highest rates of net ph otosynthesis and forest grasses the lowest and the following order of P-n w as noted: meadow steppe grasses >typical steppe grasses >steppe shrubs >des ert grasses >forest trees >forest shrubs >desert shrubs >forest grasses (P< 0.05). Transpiration tended to be the highest in the steppe grasses and low est in forest shrubs. Transpiration also decreased rapidly with the appeara nce 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 a long the steppe section (from 400 to 1100 km, east to west) indicated the p resence of C-4 species. Of all the PFTs, only shrubs and herbs were noted a t 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 value s were found at both the high and low precipitation ends of the transect. H ighest values were noted when precipitation was intermediate.