Photosynthesis ( Pn ), transpiration (E) and water use efficiency (WUE) of more than 66 add sand species from different environmental habitats, shifting sand dune, fixed sand dune, lowland and wetland in the Maowusu Sand Area were analyzed and the relation among these characteristics and the resource utilization efficiency, taxonomic categories and growth forms of the species were assessed. The results showed that species from Chenopodiaceae, Gramineae, keguminosae which possessed the C4 photosynthesis pathway, or C3 pathway and also with nitrogen-fixation capacities had higher or the highest Pa values, i.e., 20 ～30μmol CO2·m－2·s－l, while that of evergreen shrub of Pinaceae had the lowest Pa values, i.e., 0 ～ 5 μunol CO2·m－2·s－1. Those species from Compositae, Scrophuladaceae, and Gramineae with C3 pathway but no N- fixation capacity had the highest E rates, i.e., 20 ～30 mmol H2O· m－2·s－1 and again the evergreen shrub together with some species from Salicaceae and Compositae had the lowest E rates, i.e., 0 ~ 5 mmol H2O·m－2·s－1. Species from kegmninosae, Gramineae and Chenopodiaceae with C4 pathway or Cs pathway with N- fixation capacity, both shrubs and grasses, generally had higher WUE. However, even the physiological traits of the same species were habitat- and season-specific. The values of both Pa and E in late summer were much higher than those in early summer, with average increases of 26%, 40% respectively in the four habitats. WUE in late summer was, however, 12% lower. Generally, when the environments became drier as a result of habitats changed, i.e., in the order of wetland, lowland, fixed sand dune and shifting sand dune, Pn and E decreased but WUE increased.
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