Effect Of Waterlogging Stress On Growth Of Maize Seedling And Physiological Response Mechanisms

The effects of different waterlogging stress durations on maize photosynthesis and root morphology,such as root length,root surface area,root volume,number of branches,as well as root biomass,nitrogen,phosphorus and potassium concentrations and contents in root,including the correlation between the root morphology and nutrients accumulation and the variations of metabolic enzymes activity,metabolic products,cell membrane integrity and root activities were investigated at seedling stage（4 leaf stage）under simulated condition in the lab.The main results are as follows:1.The main root length,total root length,root surface area,root volume,branch number and crossing number were all increased under the normal growth condition,but they were increased firstly and then decreased under waterlogging condition,which were significantly lower by 53.8%,51%,34.2%,13.3%,49.5%,37.5%than that under normal condition after incubation for 72 h,respectively.2.The content of phosphoenolpyruvate（PEP）in the maize roots increased firstly and then decreased under waterlogging condition which significantly higher by 33.2%than control（normal growth condition）（P<0.05）after incubation for 24h.The activity of pyruvate kinase（PK）significantly increased by 2.2 times than the control after waterlogging stress for 120h.In the meantime,the content of pyruvate in maize roots significantly higher by 33.4%than the control after waterlogging stress for 48h（P<0.05）.The pyruvate carboxylase（PDC）activity was activated by waterlogging stress and its activity was 2.1 folds of control which could catalyze transformation of pyruvate to acetaldehyde.The content of acetaldehyde was significantly higher by 51.4%than the control（P<0.05）after incubation for 24h under waterlogging condition,while the activity of alcohol dehydrogenase（ADH）in the maize roots was 3.3 times higher than control.The content of ethanol was 12.9 folds of the control（P<0.05）.The accumulation of ethanol injured root cells and increased cell membrane permeability.The content of amino acids in cells were only 32.4%times as compared with the control and the root activity decreased significantly,which was lower than that of the control 24.9%.3.The concentrations of nitrogen,phosphorus and potassium in maize roots were gradually increased under the normal growth condition,but the nitrogen concentrations in maize roots firstly increased,and then decreased in the whole period of waterlogging incubation,which were higher than that under the normal growth condition.The phosphorus concentrations in maize roots initially increased and then tended to be stable after incubation for 48h.The potassium concentrations increased initially and then decreased after incubation for 48h under waterlogging condition,which were lower than those under the normal growth condition.The quantities of nitrogen,phosphorus and potassium accumulated in maize roots increased under both the normal and waterlogging condition.The amounts of nitrogen,phosphorus and potassium accumulated in maize roots under waterlogging condition were significantly lower by 7.0%,20.2%,39.1%than that under the normal growth condition after incubation for 72h（P<0.05）.4.There was a significant positive correlation between content of nitrogen,phosphorus,potassium in roots and root surface area under waterlogging stress.The accumulation of nitrogen,phosphorus and potassium had a significant positive correlation with root volume,and the nitrogen content was also significantly correlated with root volume and number of branches.The root surface area was the most influential factor on root nitrogen and phosphorous contents,and their partial regression coefficients were 0.89 and 0.71.The number of branches was the most influential factor on root potassium contents and amounts of nitrogen accumulation accumulated in maize roots,and the partial regression coefficients were-1.46 and-2.09 respectively.Root volume was the most influential factor on amounts of nitrogen and potassium accumulated in maize roots,and the partial regression coefficients were 0.79 and 0.55,respectively..5.The photosynthesis of maize seedlings increased slowly at the beginning of flooding stress,but the photosynthesis of maize seedlings was significantly lower than that of normal growth after 48 hours of flooding stress,and the transpiration rate of maize seedlings increased at 120 hours after flooding stress.Stomatal conductance and intercellular CO₂ concentration were significantly lower by 16.09%,12.36%,33.14%than those under the normal growth condition（P<0.05）.6.The contents of nitrogen and phosphorus in leaves of seedlings with normal growth increased first and then decreased gradually,while the contents of potassium tended to be stable and the contents of nitrogen in leaves of seedlings increased first and then decreased under flooding stress,and the contents of nitrogen and phosphorus in leaves of seedlings increased at first and then decreased with the extension of culture time.However,the contents of phosphorus and potassium in leaves decreased at first.The nitrogen content in leaves was 4.59%higher than that of the control after incubation for 120h under flooding stress,and the content of phosphorus was lower by 10.53%than that of normal growing leaves（P>0.05）,while that of potassium in leaves was lower by 43.28%than that of the normal growth leaves which reached a significant level of difference（P<0.05）.The accumulation of nitrogen,phosphorus and potassium in leaves increased gradually under flooding stress,which was significantly lower than that in normal growth（P<0.05）,and the accumulation of nitrogen,phosphorus and potassium were significantly lower by 33.86%,43.15%and 24.13%than those under the normal growth condition after incubation for120h（P<0.05）.7.The contents of nitrogen and phosphorus in leaves were significantly correlated with stomatal conductance and intercellular CO₂ concentration under flooding stress,in which stomatal conductance was the most influential factor on nitrogen content in leaves and its partial regression coefficient was 1.50.Intercellular CO₂ concentration was the most influential factor on phosphorus content and the partial regression coefficient was-1.75.However,transpiration rate had a significant correlation with potassium content in leaves,and the partial regression coefficient of them was-0.68.There was a positive correlation between the amounts of nitrogen,phosphorus and potassium accumulated in leaves with stomatal conductance under flooding stress.There was also a significantly positive correlation of intercellular CO₂ concentration to nitrogen and potassium accumulation,and partial regression coefficients were 1.69 and 2.15,respectively.Meanwhile,there was a significant correlation between accumulation of nitrogen and transpiration rate.Stomatal conductance has the greatest effect on phosphorus accumulation in leaves.The partial regression coefficient of stomatal conductance to phosphorus accumulation in leaves was-2.15.8.The biomass of roots and leaves were decreased under waterlogging stress,and the biomass of maize plants was significantly lower than that of normal growth by 20%after120 h under flooding stress,which made the growth of the seedlings slow down.In summary,the normal growth of root system was inhibited under flooding stress,which increased the activity of PEP and accelerated the metabolism of PEP to pyruvate,and fermented pyruvate into acetaldehyde,transformed into ethanol.Ethanol in the cell increased permeability of cell membrane and the content of amino acids in root decreased.Meanwhile,flooding stress caused the root activity and photosynthesis of maize seedlings decreased.The absorption of nitrogen,phosphorus and potassium was decreased,and the growth of seedling was inhibited by flooding stress.The increasement of leaf biomass and root biomass were also slowed down by flooding stress.