Effects Of Groundwater Level And Spraying Growth Regulators Under Waterlogging On Agronomic Traits,fiber Quality And Physiological Characteristics Of Ramie

Ramie（Boehmeria nivea L.）is a perennial herbaceous fiber plant belonging to the gene Urtica,and is an important fiber crop in China.At this stage,due to global climate change and frequent extreme rainfall weather,the Yangtze River Basin is susceptible to heavy rain and typhoons.As a result,the second and third crop of ramie are affected by rising groundwater levels or waterlogging stress,and their growth and development are severely restricted and eventually yields are greatly reduced.Therefore,studying the effects of waterlogging on agronomic traits and physiological characteristics of ramie and finding suitable growth regulators to solve the problems caused by waterlogging have become urgent problems in production.This experiment is based on the actual production.Three experiments were performed.Experiment 1 is setting 3 different groundwater levels（20 cm,40 cm,60 cm）in ramie vigorous growth stage for 3 d;Experiment 2,100 mg/L of ABA,SA,and 6-BA were sprayed on each treatment before the 3 d waterlogging treatment in ramie vigorous growth;Experiment 3,100 mg/L of ABA,SA,and 6-BA were sprayed on each treatment after the 3 d waterlogging treatment in ramie vigorous growth,studying the effects of different treatment on agronomic traits,fiber quality,photosynthesis,osmoregulation substance and antioxidant protection systems for the second and third crops of ramie;The main findings are as follows:（1）20 cm and 40 cm groundwater levels will adversely affect the agronomic characteristics,fiber quality and photosynthesis for the second and third crop of ramie.The 60 cm groundwater level doesn’t have any distinctive properties that inhibit the growth and development of ramie.Treatment of the second and third crop at a water level of 20 cm will make the plant height,stem thickness,fresh weight,stem weight and bark weight significantly lower than the water level of 60 cm.The difference is that the diameter of ramie fiber is significantly reduced under the 20 cm water level treatment,the ramie fiber quality is significantly increased,and the elongation at break and fiber diameter are significantly reduced;the 20 cm and 40 cm water levels will significantly reduce the long-term net photosynthetic rate of ramie.However,the net photosynthetic rate of the ramie third crop after 40 cm water level treatment was recovered and the net photosynthetic rate of the ramie third crop after 20 cm water level treatment was still maintained at a low level.Under the water level of 20 cm and40 cm,the contents of MDA proline and soluble sugar in ramie leaves increased significantly,and the activities of SOD,POD and CAT in the antioxidant protection system also increased in varying degrees.（2）Spraying 100 mg/LSA or 6-BA before waterlogging can effectively alleviate a series of effects caused by waterlogging.Compared with CK₁ sprayed with water,the agronomic traits under SA treatment were significantly higher than those of CK₁,but still significantly lower than those of CK₂,the ramie under normal cultivation conditions.There were no significant difference between treatments and CK₁treatment,but SA treatment had better performance.Among the various fiber qualities,the performance of 6-BA treatment is the best,with lower gel content and better breaking strength,elongation at break,and fiber diameter slightly lower than CK₂.Waterlogging will cause the net photosynthetic rate of ramie to decrease significantly,and the more it decreases with time,the spraying of growth regulators can alleviate the restriction caused by waterlogging to varying degrees.Among them,SA and 6-BA can effectively prevent the decrease of net photosynthesis rate.And the effects of SA and 6-BA on photosynthesis were further confirmed by the detection of Rubisco activity.The net photosynthesis of the ramie third crop after SA treatment was also maintained at a high level.Under various treatments,malondialdehyde decreased in different degrees and the content of proline and soluble sugars increased significantly.The activities of SOD,POD and CAT also increased to varying degrees.（3）Spraying 100 mg/L SA during the recovery period can effectively promote the recovery of waterlogged third crop ramie.SA treatment can significantly increase the plant height and single plant tare weight of waterlogged second crop ramie.Although it has certain effects on stem thickness,plant fresh weight,single plant stem weight,and skin thickness,there were no significant difference between treatments and CK₁treatment,but SA treatment had better performance.The performance of third crop ramie was slightly better in SA treatment.Among the various fiber qualities,the SA treatment performed the best,with better breaking strength,elongation at break,and fiber diameter slightly lower than CK₂.After the stress was released,the net photosynthetic rate of CK₁ continued to decrease,and the application of SA and 6-BA could maintain the net photosynthetic rate of ramie plants at a higher level,which was more conducive to the recovery of ramie after stress.The effect of ABA treatment was not good.The detection of Rubisco activity further confirmed this result,and the net photosynthesis of third crop ramie after SA treatment was also maintained at a high level.Under SA and 6-BA treatment,malonaldehyde decreased in varying degrees and the content of proline and soluble sugar increased significantly,but the content of proline and soluble sugar was low after ABA treatment,which was not good.Promote the rapid accumulation of these 2 substances;SOD,POD,and CAT activities also increased to varying degrees after treatment with the three growth regulators.