Abstract: A hydroponic experiment was conducted to study the short-term effects of isotonic NaCl and mannitol stress on the photosynthesis of  arrow-leaf saltbush (Atriplex triangularis) and maize (Zea mays). Both the NaCl and the mannitol stress decreased the net photosynthetic rate (P_n) of A. triangularis and Z. mays. With the increase of the stress, the mannitol-induced decrement of P_n was much greater than the NaCl-induced one. Under the mild stress of NaCl or mannitol, the decline of P_n was mainly due to stomata limit. When the mannitol stress was below -1.00 MPa, stomata limit gradually turned to non-stomata limit; when the NaCl stress was below -1.00 MPa, stomata limit still dominated. Therefore, isotonic mannitol stress had greater effects than isotonic NaCl stress on the photosynthesis of the  two test plants.

Key words: Sludge, Alluvial soil, Soil enzyme activity, Heavy metal