Abstract: Soil moisture is an important environmental factor that affects plant growth and physiological metabolism.Under water stress conditions, plants can start the protective enzyme/antioxidant enzyme system and adjust the content of osmotic adjustment substances to respond to the environment.To study the P. arundinaceas' responding mechanism of antioxidant enzyme defencing system to different soil moisture,we selected P. arundinaceas seedlings in good growth condition with well preserved rhizome and consistent germination as test materials.Through 50 days indoor potted water control experiment,we set up seven water gradients of (10±0.5)%、(15±0.5)%、(20±0.5)%、(25±0.5)%、(30±0.5)%、(40±0.5)% (saturated soil moisture) and 51% (2 cm flooded) based on the volumetric water content.The soil moisture content was controlled by manual watering method.It was measured with a HH2 soil moisture meter every day at 20:00 PM,calculated the required moisture volume based on the soil moisture status and quantified the supplement to the set value.The effects of different soil moisture content on malondialdehyde (MDA),superoxide dismutase(SOD),peroxidase(POD),catalase(CAT) and soluble protein content were studied using nitroblue tetrazolium method to measure SOD,guaiacol method to measure POD,CAT was measured by potassium permanganate titration method to measure CAT,Glucosinolates barbituric acid method to measure MDA and Coomassie brilliant blue G-250 dyeing method to measure soluble protein.The results showed as follows:(1) The activity of SOD was higher when the soil moisture content was between 20% and 35%,and when the soil moisture content was below 20% or above 35%,the activity of SOD was decreased.The activities of SOD in 50 days were higher than those in 25 days of the experiment under different soil water content. (2) The activities of CAT and POD were extremely significantly correlated with p<0.01,both of which had a trend with a sharp drop at the beginning,and then becoming steady,then going up slightly with the increase of soil moisture content. (3) The content of MDA was opposite to the trend of SOD,and it was decreased with the increase of soil moisture content.The C7 group (flooding 2 cm) was increased slightly in 25 days of the experiment. (4) The content of soluble protein was higher with the value between 20% and 40%,and the plants were growing well.The soluble protein showed a drop trend under drought or flooding stress conditions.So it can be seen that when the P. arundinaceas seedling was exposed to drought or other stress,it will trigger the antioxidant enzyme system to protect the plant tissue,and the antioxidant enzyme defense system would work through a series of antioxidant protection mechanism to increase plant stress resistance ability,reduce or eliminate the damages to the plants,but the long-term stress or the stress which beyond the plant's tolerance (the soil moisture content is less than 20% or the soil moisture content is oversaturated) will destroy the plant's defense system in various degrees thus affecting the plant's growth and development.

Key words: P. arundinacea, antioxidase, Malondialdehyde, soluble protein, soil water content