In the process of soil gradual drought, the growth of typical wetland plant Acorus calamus in dry condition and control condition were investigated. The soil water contents of dry group were about 55% (0 th day) , 40% (3 th day) , 30% (6 th day) , 20% (9 th day) , 10% (11 th day) and 5% (12 th day) and average soil water content of the control group was (53. 49依0. 6) % during the experiment period. Meanwhile, Photosystem 域 (PS域) photochemical efficiency (Fv / Fm) , quantum yield (Yield) , photochemical quenching (qP) , non鄄photochemical quenching (qN) were also measured by a submersible, pulse鄄amplitude modulated (PAM) fluorometer: Diving鄄PAM.

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Under light or dark conditions, the change of the radial oxygen loss at the points of 1 / 4, 1 / 2 and 3 / 4 far from root stem base ( root 1 / 4, 1 / 2, 3 / 4) and root tip ( root 1) and its micro鄄interface were measured in鄄situ by soluble oxygen microelectrode for A. calamus seedlings and adult A. calamus plants in a typical wetland. Sediment from natural lakes was used as experimental substrates and a micro motor was used to control the soluble oxygen microelectrode to verify the accuracy of the vertical micro position.The result showed that: there was always an oxygen diffusion layer with an increasing gradient of oxygen saturation from the root surface to the anaerobic layer of sediment in the A. calamus roots in light or dark conditions. Oxygen diffusion layer thickness was 0. 18-0. 68 mm and maximum oxygen saturation was 42. 9% under light condition and oxygen diffusion layer

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