Effect Of Exogenous Selenium On The Growth And Soil Selenium Effectiveness Of Rice With Different Selenium Accumulation

Selenium（Se）is not an essential element for plant growth,but it can promote growth when present in adequate amounts.Excessive Se,however,can be toxic to plants.Different plant species have varying levels of tolerance to Se.Rice is not a hyperaccumulator of this element.Furthermore,different rice varieties have varying abilities to accumulate Se.High Se-accumulating rice varieties exhibit stronger tolerance to high Se toxicity than low Se-accumulating rice varieties,but the specific mechanisms underlying their growth and physiological differences remain unclear.It is also important to determine whether Se application leads to differences in soil selenium availability for different rice varieties.To address these issues,this experiment employed a pot experiment with three Se levels（0,0.5,25mg·kg-1）and selected high and low Se-accumulating rice as test crops.The study aimed to explore the effects of different exogenous Se levels on the growth of high and low Se-accumulating rice and soil Se availability by analyzing the differences in growth and physiological indicators of high and low Se-accumulating rice,as well as the content and proportion of various forms of Se in soil.The main research findings are as follows:（1）With the increasing application of Se,the plant height,tiller number,total biomass,and yield of two rice varieties showed an initial increase followed by a decrease.At a Selevel of 0.5mg·kg^-1,the plant height,tiller number,total biomass,and yield of high-accumulating rice increased by 7.46%,23.08%,22.28%,and 28.91%,respectively,compared to the control,with a greater increase than that of low-accumulating rice.When the Se level increased to 25mg·kg^-1,the decrease in plant height,tiller number,total biomass,and yield of high-accumulating rice was lower than that of low-accumulating rice.The Se content in all parts of the two rice varieties increased with the increase of Se application level.The application of 0.5mg·kg^-1Se significantly increased the grain Se content of high-accumulating rice,promoting the enrichment and transport of Se between roots,stems,leaves,and grains.This indicates that high-accumulating rice has a stronger ability to absorb and utilize Se,as well as greater Se tolerance.（2）With the increasing application of Se,both rice varieties showed a trend of initially increasing and then decreasing in net photosynthetic rate（Pn）,photochemical quantum yield(Φ_PSII),photosynthetic quantum efficiency（ETR）,and photochemical quenching coefficient（q P）,while the non-photochemical quenching coefficient（q N）showed a trend of initially decreasing and then increasing.At a Se level of 0.5mg·kg^-1,there was no significant difference in the parameters between the two rice varieties.However,when the Se level increased to 25mg·kg^-1,the Pn,Φ_PSII,ETR,and q P of the high-accumulating rice decreased by 16.05%,52.5%,22.83%,and 47.37%respectively,compared to the control,while those of the low-accumulating rice decreased by 31.03%,52.94%,37.34%,and 48.15%,respectively.The q N of the high-accumulating rice increased by 20.27%compared to the control,while that of the low-accumulating rice increased by 5.13%.This indicates that under high Se stress,the degree of damage to the photosynthetic structure and the degree of electron transfer inhibition in the low-accumulating rice were higher,and the inhibition of photosynthesis was more severe.Additionally,Se application increased the content of soluble sugars,soluble proteins,and proline in the high-accumulating rice,enhancing its carbon and nitrogen metabolism capacity.（3）With the increasing application of Se,the activities of superoxide dismutase（SOD）,catalase（CAT）,peroxidase（POD）,ascorbic acid（ASA）content,and carotenoid（CAR）content in two rice varieties showed an initial increase followed by a decrease,while the contents of malondialdehyde（MDA）and glutathione（GSH）continued to increase.Compared to the high-accumulating rice,the low-accumulating rice had a significantly higher increase in MDA content,indicating more severe membrane damage.At Se levels of0.5mg·kg^-1and 25mg·kg^-1,the activities of SOD,CAT,POD,and ASA content in high-accumulating rice were significantly higher than those in low-accumulating rice,indicating that high-accumulating rice had stronger enzymatic and non-enzymatic antioxidant systems and a stronger ability to scavenge reactive oxygen species.（4）The application of Se increased the content of various forms of Se in the soil of two rice varieties,although the difference between the two varieties was not significant.The application of 0.5mg·kg^-1Se increased the proportion of water-soluble and exchangeable Se in the soil of high-accumulating rice.This indicates that appropriate external Se levels can promote the transformation of various forms of Se in the soil and increase the effectiveness of Se in the soil.