Abstract: A hydroponic experiment was conducted to study the effects of different arsenic species \[As(III), As(V), and DMA\] at five concentrations (0, 0.3, 1.0, 3.0, and 5.0 mg·L^-1) on the arsenic uptake and phytochelatins (PCs) synthesis by Hydrilla verticillata. The PCs contents were identified by reversed phase-high performance liquid chromatography (RP-HPLC). H. verticillata had an obvious arsenic uptake and accumulation. Low concentrations arsenic promoted the growth of H. verticillata, and the uptake of As(III) by H. verticillata was significantly higher than that of As(V) or DMA. As(III) and As(V) promoted the synthesis of GSH, PC₂, and PC₄ significantly, and the synthesis was significantly positively correlated with the arsenic concentration in H. verticillata(P<0.05). DMA had little effects on the synthesis of PCs, with a detectable synthesis only at 0.3 mg·L^-1 of DMA. With increasing concentration of As(III), the synthesis of GSH and PC₂ decreased after an initial increase, but the synthesis of PC₄ increased. With the increasing concentration of As(V), the synthesis of GSH increased first and decreased then, while the synthesis of PC₂and PC₄ presented an increasing trend. Very few PC₃ was synthesized in all treatments except at 0.3 mg·L^-1 of the test arsenic species. This study indicated that the synthesis of PCs was sensitive to the stress of As(III) and As(V), and the PCs could be used as an biomarker indicating the stress of these two As species onH. verticillata.

Key words: northern grassland transect, soil respiration, precipitation, aboveground biomass, soil organic carbon.