Different Of Low Potassium Stress On Leaf Microstructure And Photosynthetic Characteristics Of Soybean Varisties With Different Tolerance

Potassium is one of the major three important essential elements for plant growth.The requirements for K supply increases with the increasing of crop yield and quality.However, potassium defieieney in soils is widespread in China,where low K has become the major limiting factor for obtaining high yield.Soybean[Glycine max(L) Merr.]is the main oilseed crop in north of China,which yield and quality were extremely affected by potassium fertilizer.Planting resistant varieties to low potassium in China is the ease of potassium resource scarcity,promote the sustainable development of agriculture is the most economic and efficient way.Previous studies have shown that different soybean varieties under low potassium leaf symptoms are diverse,there are bigger difference,but not for its microstructure research.In former experiments,potassium tolerant and non-tolerant genotypes had been screened in field.The present study is an attempt to identify the physiological mechanisms implicated in tolerance to low potassium by testing difference of leaf microstructure,photosynthetic characteristics,protective enzyme system and JIP-test of different typical genotypes that differ in tolerance to low K stress.The main conclusions of study were as followed:1.Results showed there was no difference in upper epidermis microstructure between low potassium stress and CK for tolerant variety.For resistant variety,the thickness of upper epidermis greatly increased in low potassium stress,but the length of upper epidermis, density of upper epidermis and length of upper epidermis:Thickness of upper epidermis decreased significantly.With the low potassium level,length of the first line palisade cell in tolerant variety was reduced.However,length and width of the first and second line palisade cell,thickness of palisade tissue are both increased,but the density of palisade cell was decreased.The results showed that the tolerant variety still keep midvein mesophyll cell significant,while the change of resistant variety was not significant.For tolerant variety,the density of sponge tissue greatly decreased in low potassium stress.The radio of thickness of palisade tissue and thickness of sponge tissue of resistant variety increased significantly in low K level.Compared with CK,the thickness of lower epidermis of tolerant variety was incrassate,but there were no difference between tolerant variety and CK in thickness of lower epidermis in low potassium stress.2.In order to study photosynthetic characteristics and protect enzyme system of different K efficient soybean varieties under low potassium stress,we carried out field experiments in Liaozhong county,Liaoning province,with K-efficient soybean varieties Shennong6 and GD1617,K-inefficient soybean varieties Tiefeng31 and Tie95068-5 and two potassium levels(0 and 150kg/hm²).Significant difference of leaf photosynthetic rate(Pn) was found between K-efficient and K-inefficient of soybean under low potassium stress.The results showed that the variance of Pn between two K-efficient varieties was higher than that of two K-inefficient varieties Furthermore the results indicated that the difference of chlorophyll (Ch1) content and Pn of two K-efficient varieties was smaller than those of K-inefficient varieties under low K stress and K-applied.Compared with K-inefficient varieties, K-efficient varieties had much longer green persistent duration,lower stomatal conductance (Gs),and higher intercellular CO₂ concentration(Ci) and transpiration rate(Tr).The protective enzyme system of soybean also responded under low K stress.The SOD,CAT and POD activities of leaves under K stress among all genotypes were higher than those of K-applied.Moreover protective enzyme activities of K-efficient varieties decreased more than those of K-inefficient varieties under low K stress.These suggested leaf of K-efficient varieties had lower oxygen free radicals content through cultivation.On the whole,the K-efficient varieties can hold leaves green and prolong a high photosynthetic capacity and keep oxygen free radicals in a low level for a long time through cultivation,which were a key of increasing biomass and enhancing grain yield under low K stress.3.The difference of F_o,F_m,F_v/F_m and F_v/F_o between two K levels weren't significant for K-efficient variety,while the changes of these parameters were significant difference for K-inefficient variety,including the change of F_v.Except for that,the ratio of energy dissipated by reaction center increased in low K stress for GD8521,and the ratio of transfer energy decreased at the same time,while those change of Jiunong 15 were tiny.