Effect Of Rhizosphere Dissolved Oxygen Content On Growth And Nitrogen Utilization Of Rice

Dissolved oxygen in paddy field is tightly associated with pH, activity of microbe, availabilityand form of nutrient elements, which directly or indirectly alter the root morphology and physiologicalmetabolism of rice (Oryza Sativa L.). The accumulated deleterious reducing matters and reduced pHvalue due to the deficiency of dissolved oxygen would lead to the weak seedlings at vegetative stageand promoted leaf senescence at grain filling stage, which resulting into the yield decline. Previousstudies have revealed that the aeration condition at rhizosphere would promote plant growth as well asthe N abosorption, however, little work about mechanism responsing to dissolved oxygen and its effecton nitrogen use efficiency was reported. In order to evaluate the dissolved oxygen effect on the plantgrowth and N metabolism, hydroponics experiments were carried out with three dissolved oxygenconcentration (oxygen deficiency(OD):0～1mg·L-1, middle oxygen(MO):2.5～5.5mg·L-1, highoxygen(HO):6.5～8.5mg·L-1, CK:0.5～2.5mg·L-1). In addition, a pot experiment was carried out tosimulate the paddy condition to evaluate the dissolved oxygen effect on the plant growth, grain yield,soil properity as well as N metabolism. Three treatments was carried out: oxygen deficiency treatment(water layer:10cm), aeration treatment(water layer:10cm, water was aerated) and CK. The resultsshowed that:1, MO treatment have greater dry matter and nitrogen accumulation rate, in compared with OD andHO, however, the results were not consistent in both two varieties. In addition, the significantly reducedshoot dry matter accumulation was found in OD condition of Zhong Jiazao17. Zhong Jiazao17wasmore sensitive to dissovled oxygen content than Xiushui134.2, Appropriate oxygen content significantly accelerated the growth and nitrogen metabolism of rice.The acceleration would be reduced by high oxygen content. Dissovled oxygen effect on dry matter andnitrogen accumulation of root, stem and leaf of Xiushui134and Zhong Jiazao17was observed: middleoxygen> high oxygen> CK.3, Under sustaining hypoxia condition, significantly positive effect of mixed nutrition ofammonium and nitrate was observed. And the positive effect varied among varieties. In compare toammonium, plants in mixed nutrition of ammonium and nitrate have greater chlorophyll a, chlorophyllb, nitrogen content and accumulation in both two cultivars. In addtion, the key enzyme activity ofnitrogen metabolism, i.e. glutamine synthetase, nitrate reductase and aminotransferase (GPT, GOT) inroot were improved.4Oxygen deficiency treatment from tillering to heading stage would decrease the tilleringnumbers, leaf area, dry matter, nitrogen accumulation, even the available panicles per plant, grains perpanicle, length of panicle and weight of panicle. However, the aeration treatement will relieve the stressdue to Oxygen deficiency treatment during vegetative stage.Although the parameters were stillsignificantly lower than CK.5, The oxygen content and soil moisture content was coordinated through aeration after headingstage, therefore rice plants has higher leaf photosynthetic nitrogen use efficiency at18days after heading. on the other hand, more dry matter and nitrogen of stem and leaf has more transported topanicle which benfit for improving the grain yield and nitrogen use efficiency, in compared with CK.Root anaerobic respiration consumed large amount of photosynthate, therefore dry matter of stem, leaf,seed setting rate, panicle weight per plant was decrease under oxygen deficiency treatment. Andnitrogen use efficiency was also lowest for nitrogen of stem can’t be effectively transported to panicle.6, Effect of dissovled oxygen on nitrogen form in soil is very complex. The pH, nitrification anddenitrification are influenced by dissovled oxygen, the emission of NH3、N2O is also affected. At sametime, plant selective absorption affects the nitrogen form in soil. Ratio of ammonium and nitrate in soilor nutrient solution was not positive correlated with oxygen content and nitrification.