Effects Of The Aluminum Stress On Physiological Characteristics And Absorption Of Nutrient Elements In Watercress

Watercress（Nasturtium officinale r.r.）,also known as water mustard,belongs to the perennial cruciferous（Brassicaceae）water mustard（Nasturtium）herbs.The soil acidification is becoming more and more serious due to the expanding of the facility area.The soil acidification has led to elevated content of active aluminum and aluminum toxicity has become an important obstacle factor restricting crop production in acidic soils.Long-term production practice and the research showed that flooding can improve the physical and chemical properties of the soil,and the soil pH tends to be neutral.Research showed that,watercress has a partly enrichment capacity for metal elements,and has partly tolerance to aluminum stress,which can significantly improve the water quality of eutrophic water.Therefore,watercress can be used in the production of water and drought rotation mode to improv the soil.For this purpose,the study was conducted with watercress as the research material,setting aluminum concentration gradient（0,300 mg/kg,600 mg/kg,900mg/kg,1200 mg/kg）,To explore the physiological response mechanism of watercress on aluminum stress from the effects of aluminum stress on growth,physiological and biochemical characteristics and nutrient absorption of watercress.At the same time,it also discussed the feasibility of using watercress for water and drought rotation,and provided new materials for the physiological response mechanism of aluminum and the growth and cultivation of watercress.The results of this study were:（1）Under the stress of aluminum,the plant height of watercress was decreased gradually,and under 1200mg/kg,it was significantly lower than the control.The root length,stem thickness and root activity were increased first and then decreased,reaching the highest value at 600mg/kg,300mg/kg,300mg/kg respectively,and then decreased.The dry and fresh weight of the aboveground and underground parts increased first and then decreased.In addition,the dry weight of the aboveground part reached the highest value in the treatment of 300mg/kg,which was the highest in the treatment of 600mg/kg.The root crown was higher than the concentration of aluminum.In general,the growth of watercress was characterized by the change of"low to promote high inhibition".（2）Under the stress of aluminum,the content of SOD and POD activity,Pro,soluble protein and soluble sugar content in watercress leaves showed a trend of first increase and then decrease.As the processing time goes on,the lower concentration（300mg/kg,600mg/kg）gradually increased,but the high concentration has decreased.The CAT activity decreased gradually with the concentration and time of aluminum treatment.APX activity decreased first and then gradually increased.MDA levels continue to rise.In general,the lower concentration of aluminum is beneficial to the expressionofmostenzymesandorganicsinwatercress.When Al³⁺>600mg/kg,aluminum treatment can cause damage to the antioxidant system and cell membrane of watercress.The higher the concentration of aluminum treatment,the longer the stress time,the greater the damage.（3）Under aluminum stress,the chlorophyll synthesis of watercress was stimulated,and the content and total amount of chlorophyll a,b and the total amount of chlorophyll showed a change rule after the first increase.At the 30th day,all three reached the highest value at 600mg/kg,significantly higher than the control;Chlorophyll a/b gradually decreases;With extended time,Al³⁺<600 mg/kg amount of chlorophyll a,b and treatment have been rising,When Al³⁺>600mg/kg,the content of chloroplast a decreased,and the total amount of chlorophyll b and chlorophyll increased slowly.The results showed that the effect of aluminum stress on watercress was decreased,but the chloroplast structure was not destroyed.（4）Under aluminum stress,the chlorophyll fluorescence parameters of watercress Fo,Fm,Fv/Fo,Fv/Fm were reduced after the first rise trend,respectively in 900 mg/kg,600 mg/kg and 300 mg/kg and 300 mg/kg maximum under processing,and then decreased.That low concentration of aluminum processing of watercress PSⅡhave a partly role in promoting,leaf vigor index was increased.The NPQ gradually increased,and the gradual reduction of Y（s）,qP and ETR was significantly lower than that in the treatment of 600mg/kg,300mg/kg,600mg/kg respectively.Show that at the beginning of the aluminum stress（300 mg/kg and 600 mg/kg）,watercress PSⅡsystem affected is not large,as the aluminum stress increase,PSⅡsystem partially closed,photochemical reaction limited,electron transport activity,photosynthetic efficiency is greatly reduced.（5）Under the stress of aluminum,the absorption of nutrient elements by watercress was inhibited by different degrees.The absorption of Al was mainly concentrated in the root system.As the concentration of aluminum was increased,the higher Al content was absorbed,the ability of upward transportation was inhibited,and the aluminum resistance of watercress was demonstrated.The macroelements N,P,K,Ca,Mg gradually decreased,N,P,K inhibition degree was greater than the root,leaf upward transport capacity was restrained,Ca,Mg,slightly higher than that of aboveground root inhibition degree.The amount of Na content increased gradually,and the root system decreased and then increased.900mg/kg was significantly lower than the control,and reached the lowest value.The microelements Fe,Mn,Zn and Cu were all inhibited,and the inhibition effect of Fe and Cu was most obvious,while the upward mobility of Zn was inhibited,and the upward mobility of Cu was promoted.