Effects Of Potassium On The Growth Of Alien Invasive Plant Alternanthera Philoxeroides

Alternanthera philoxeroidesalso known as alligatorweed and revolutionary grass,is an amphibious herbof Alternantherainand Amaranthaceae.Itis amalignant invasive weed recognized worldwide as extremely difficult to control.It has invaded the south of the Yellow River Basin and other areas in China,causing great harm to the environment,ecology and economy.Previous studies have shown that the successful invasion of A.philoxeroides is closely related to its wide adaptability,developed asexual reproduction,strong competitiveness and morphological plasticity.The previous series of studies of the research group showed that the storage root formed by terrestrial A.philoxeroides is the main basis for its overwintering,reproduction and diffusion.However,there are few studies on the role of nutrients in promoting the invasion of A.philoxeroides from the perspective of rhizosphere nutrition.Previous studies have shown that A.philoxeroides is a potassium rich plant,and its roots,stems and leaves are rich in potassium.However,the effect of potassium content in rhizosphere on the growth of A.philoxeroidesis still unclear.Therefore,starting from potassium,this study provides a theoretical basis for further clarifying the correlation between potassium nutrition and the successful invasion of A.philoxeroides and the potassium enrichment mechanism of A.philoxeroides.1、 In Experiment 1,the tissue culture system of the stem segment of A.philoxeroides was established,and 11 treatments that may affect the growth of the stem segment were set up: the intensity of light in the root environment,the use of carrageenan and agar to simulate the substrate with different hardness,the presence or absence of the upper segment of the stem segment,the positive and negative cutting methods of the stem segment,the length of the lower segment of the stem segment was1.5 cm,1 cm,0.5 cm and 0.1 cm respectively,the length of the lower segment of the stem segment was 1.5cm,and the cutting depth was 1.5 cm,1.0 cm and 0.5 cm respectively.The factors that may affect the growth of A.philoxeroides,such as the light conditions of the root system,the hardness of the substrate,the way of inoculation,and the characteristics of the stem segment,were studied.The study found that the ideal tissue culture conditions for the stem segment of A.philoxeroides were as follows: take a stem segment with a length of 4 cm,soak it in 75% alcohol for 1 min after removing the leaves,soak it in 0.1% mercuric chloride for 6 min for disinfection,shake and wash it with sterile water for 5 times,cut the sections at both ends of the stem segment for about 0.3 cm,and then put it into MS medium.After the lateral buds sprouted for about2 cm,cut the lateral buds into MS medium for continuous subculture to obtain sterile seedlings with good growth.The existence of the upper segment of the stem of A.philoxeroides is one of the main factors for its survival and plant formation.Root environment with certain light intensity and hard substrate could promote the differentiation of storage roots of A.philoxeroides.The adventitious roots of A.philoxeroides can be dedifferentiated to form storage roots.The length of the lower part of the explant node and the inoculation depth were directly proportional to the growth of the stem segment and root system of A.philoxeroides.2、The leafless stem segments of A.philoxeroides(1cm long at both ends of the node)were cultured in MS medium with potassium concentrations of 2.2mmol/L,4.53mmol/L,7.27mmol/L,9.96mmol/L and 12.28mmol/L.After 90 days of culture,it was found that A.philoxeroides could survive and grow normally in different potassium environments,and the adventitious roots from the nodes could form storage roots.The total volume of adventitious roots,diameter of storage roots,total volume of storage roots,dry mass of roots,dry mass of storage roots and root shoot ratio of A.philoxeroides in 12.28mmol/L treatment were significantly higher than those in other treatments.The adventitious roots in the internodes of A.philoxeroides in the five treatments did not form storage roots.3 、 On the seventh day of the cutting experiment of A.philoxeroides,Hoaglandnutrient solution with potassium concentration of 0,1,5,10,20,40 and 80 mmol/l was irrigated,of which 0 mmol/l potassium treatment was the control.The samples were taken at the 20 th day(early stage of adventitious root expansion),70 th day(late stage of adventitious root expansion)and 106 th day(late stage of adventitious root expansion)of the growth of A.philoxeroides,and the indexes were measured.The application of potassium at the concentration of 1-20mmol/l could significantly promote the accumulation of biomass and the growth of stolon and root system of A.philoxeroides.In the period of adventitious root expansion,potassium application changed the biomass allocation strategy of A.philoxeroides.When A.philoxeroides was faced with potassium deficiency stress(0 mmol/l treatment),its biomass allocation strategy would be inclined to the root system.The ratio of root to shoot was larger.When the potassium concentration was between 0-10 mmol/l,the biomass allocation strategy gradually tilted to the stem and leaf,and the root shoot ratio gradually decreased,and decreased to the lowest in the 10 mmol/l treatment.When the potassium concentration was between 10-80 mmol/l,the biomass allocation strategy of A.philoxeroides would gradually tilt to the root system,and its root shoot ratio gradually increased to the highest point in the 80 mmol/l treatment.At the later stage of adventitious root expansion,the biomass allocation strategy would be adjusted,and the root shoot ratio among the treatments had no significant difference.In addition,at the late stage of adventitious root expansion,A.philoxeroides would produce more adventitious roots to cope with potassium deficiency stress(0 mmol/l treatment).The storage root diameter and total surface area were not affected by potassium concentration.4、Four treatments were set up on the 7th day of the cutting experiment of A.philoxeroides.The other three treatments were irrigated with 20 mmol/l potassium nutrient solution at the early stage of adventitious root expansion,the stage of adventitious root expansion and the late stage of adventitious root expansion respectively.Sampling and index determination were carried out on the 106 th day of the experiment.The results showed that,compared with the control,the three potassium treatments were beneficial to the increase of biomass and stolon elongation of A.philoxeroides.Potassium application period had a great effect on the stem growth of A.philoxeroides.The application of potassium at the expansion stage of adventitious roots was beneficial to the extension of lateral branches of A.philoxeroides,but also significantly reduced the length of the main stem of A.philoxeroides.Under potassium deficiency stress(CK treatment),more adventitious roots were produced to increase the total volume of adventitious roots,so as to change the root morphology and improve the ability of root to absorb and utilize potassium.The growth strategy was tilted to the root system for storing root growth.The application of 20 mmol/l potassium at the later stage of adventitious root expansion was more conducive to the growth of stolon and adventitious root of A.philoxeroides,but the storage root diameter,total length and surface area of A.philoxeroides were not affected by the application of potassium.In conclusion,external application of potassium could promote the differentiation of storage roots of A.philoxeroides,but had little effect on the growth of storage roots.In the expansion stage of adventitious roots,low concentration of potassium can meet the root growth of A.philoxeroides.At the later stage of adventitious root expansion,A.philoxeroides produced more adventitious roots to cope with low potassium stress.