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-interface were measured in-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 thickness was 0.22-0.38mm and maximum oxygen saturation was 21.5% under dark condition.
The oxygen diffusion capacity of root points at 1/2, 3/4, 1 of adult plants was significantly higher than those of the seedlings but was insignificant at the point of 1/4, oxygen diffusion layer thickness increased from 0.40, 0.32, 0.26mm to 0.68, 0.52, 0.46mm and maximum oxygen saturation increased from 6.4%, 3.6%, 4.1% to 42.9%, 22.5%, 10.2% under light condition. Oxygen diffusion layer thickness increased from 0.30, 0.28, 0.24mm to 0.38, 0.34, 0.36mm and maximum oxygen saturation increased from 3.5%, 4.0%, 3.1% to 21.5%, 12.5%, 11.6% under dark condition.
The influence of light on oxygen diffusion capacity of different root part at different plant growth stages were different. Light had significant influence on root 1/2 of seedlings and root 1/2, 3/4 of adult plant (light treatment exceeded dark treatment significantly, P<0.01), but had no significant influence on root 1/4, 3/4, 1 of seedlings and root 1/4, 1 of adult plant (P >0.05). As to the spatial variation of root oxygen release, it showed a tendency of root 1/2> root 3/4, root 1, root 1/4(P<0.01,P >0.05)and root 1/2> root 3/4> root 1> root 1/4(P<0.01)respectively for seedlings and adult plants under light condition. It showed a tendency of no significant difference among root 1/2, 3/4, 1, 1/4 and root 1/2> root 3/4, 1> root 1/4(P<0.01)respectively for seedlings and adult plants under dark condition.
The phenomenon of minimum oxygen diffusion capacity at root 1/4 was mainly induced by the oxygen diffusion barrier in root stem base. Spatial difference of the oxygen diffusion capacity of root 1/2, 3/4, 1 were mainly affected by internal oxygen diffusion capacity and root biomass differences. The stronger the internal oxygen diffusion capacity, the more significant influence on spatial difference of the root oxygen diffusion capacity induced by root biomass differences. On the contrary, root biomass difference would not lead to spatial difference of the root oxygen diffusion capacity. For example, the oxygen diffusion capacity of the seedlings had no significant difference among root 1/2, 3/4, 1 under dark condition.