Effects Of Soil Acidification On Morphological Structure And Stress Physiology In Sedum Aizoon L.

Sedum aizoon L.is also known as Fei vegetables and Nourishing vegetables,which belongs to Crassulaceae Sedum Perennial herbs.It is a kind of green wild vegetable with economic value.Based on the actual situation of soil acidification in more than 40%of the cultivated land in China,this experiment investigated the mechanism of Sedum aizoon L.resistance to soil acid stress by simulating soil acidification,and the following conclusions were obtained through experiments:?1?Soil acidification has a significant effect on the content of soil NPK,and the content of NPK is balanced in the range of ph6.6-7.4.With the decrease of soil pH?5.5,4.6,3.4?and compared with CK?pH6.6?,the available nitrogen decreased by 62.9%,84%and88%,the available phosphorus decreased by 18.4%,49.7%and 65.1%,and the potassium increased by 16%,18.8%and 32.6%,which showed that the content of nitrogen and phosphorus decreased,the content of potassium increased,and unbalance soil nitrogen,phosphorus,potassium content.After soil pH was lower than 4.6,the active aluminum dissolution in soil increased sharply to 22.92mg/kg from 0.53mg/kg of CK,and it began to be associated with aluminum toxicity in the process of soil acid stress.?2?Sedum aizoon L.showed strong resistance to soil acid stress,and it could grow in the range of soil pH 4.6-7.4,and the growth was the best in CK soil.With the decrease of soil pH,the increase of dry fresh weight in the ground was gradually inhibited,and the root growth was shown as the tendency of mild stress promotion,moderate and severe stress suppression.After soil pH was lower than 4.6,severe soil acid stress caused severe damage to root growth and resulted in the death of the root system,causing the plant to grow slowly and even stop growing.?3?The ultrastructure of the leaves showed that the chloroplasts were ellipsoid,evenly distributed along the cell membrane,and the structure was normal in the soil of CK.Soil pH below 4.6,the chloroplasts are no longer uniformly distributed along the cell membrane,take the form of cluster in the cytoplasm,some chloroplasts show irregular spherical,grana lamella appear obvious gap,part of the internal capsule membrane become blurred,osmiophilic particles increased obviously,and produced a large number of large starch grains.?4?The ultrastructural changes of the root system were consistent with the leaves,and the plasmid and mitochondrial structure of the root cells were intact,circular or elliptical,and the structure of the nuclear membrane was clearly visible in the soil pH5.5-7.4.After soil pH was lower than 4.6,soil acid stress caused serious damage to mitochondria,cell nuclear membrane and plasmid in the root cells such as collapse,cause the root of death.?5?Within the range of soil pH 4.6-7.4,the soluble sugar,soluble protein and free proline are accumulated in the plant when the Sedum aizoon L.is stressed by soil acid,and balance the cells inside and outside osmotic potential and ensure normal cell function.After the soil pH less than 4.6,the root MDA content is significantly higher than control59.7%,three kinds of osmotic regulation substances content decreased significantly,the degree of membrane peroxidation exceeds the limit of osmotic regulation,causing serious damage to the root cells.Although the content of soluble sugar and free proline in the late stage of severe stress decreased by 43.4%and 32.5%,but the content of soluble protein is significantly higher than control 154.6%,to a certain extent of stress damage the blade.?6?SOD,CAT,APX and GR play an active role in removing the reactive oxygen species produced in plants under soil acid stress.The production and removal of reactive oxygen free radicals can be well regulated in the range of soil ph4.6-7.4,which can alleviate the stress of the plant.After the soil pH was less than 4.6,with the increase of membrane peroxidation,the activity of protective enzymes changed dramatically,and the production of reactive oxygen species and the clearing balance were broken,which had a serious effect on the normal growth of plants.?7?In the range of soil ph4.6-7.4,with the extension of stress time,Sedum aizoon L.total chlorophyll,the chlorophyll a and chlorophyll b content increased,mild and moderate stress will have certain inhibitory effect on the accumulation of chlorophyll,but does not affect photosynthesis.After soil pH below 4.6,Fo,Fv/Fm,Fm,qP,and?_PS?significantly reduced,NPQ significant increased,PS?reaction centers have been damaged or reversible inactivation,light energy conversion efficiency decreased,photosynthetic electron transport activity is restrained,produce a large amount of excess light energy,causing the chlorophyll degradation,Pn?Gs?Tr?Ci serious decline,a significant rise in Ls,plant photosynthetic ability damage.