Study On Root Morphology And Root-shoot Relationship Of Cotton Under Potassium Stress

Potassium is a large number of elements necessary for the growth and development of cotton,and its adequate supply is the basis to ensure the formation of crop yield.About 1/3 of the cultivated land in China is deficient in potassium or seriously deficient in potassium,which reduces the ability of plants to resist adversity and reduces yield;excessive application of potassium fertilizer affects normal physiological activities and easily leads to yield reduction.The root system is the key organ for plants to absorb potassium.The dynamic changes in root morphology and root life characteristics of cotton under potassium stress are not clear.Therefore,the dynamic responses of root-shoot relationship and root phenotype under different potassium levels(low,medium,and high potassium)were studied by in situ root observation device(RhizoPot)in the light culture room in 2022.The main results are as follows:1.Low potassium inhibited the growth and development of cotton aboveground,while high potassium did not affect the growth and development of cotton shoots.In the later stage of the cotton growth period,compared with medium potassium treatment,plant height,stem diameter,leaf area and SPAD of low potassium treatment decreased by 14.00%,4.78%,21.89%,and 29.36%,respectively;net photosynthetic rate,transpiration rate,and stomatal conductance decreased by 56.63%,45.38%,and 40.18%,respectively;maximum photochemical efficiency and actual photochemical efficiency significantly decreased by 41.53%and 58.80%,respectively.Compared with medium potassium treatment,the related indexes of high potassium treatment had no significant change.2.Low potassium and high potassium significantly affected plant dry matter accumulation and root-shoot ratio.The dry matter accumulation of roots stems,leaves,and bolls(buds)of low potassium treatment was significantly lower than that of medium potassium treatment,by 18.14%,20.23%,15.55%,and 15.34%,respectively,and the total dry weight was significantly reduced by 16.40%.The weight of lint and seed cotton per plant decreased significantly by 34.44%and 37.17%,respectively,but there was no significant difference in root/shoot ratio between treatments.Compared with the medium potassium treatment,the root dry matter accumulation of the high potassium treatment significantly decreased by 24.98%,the dry matter accumulation of the stem significantly increased by 11.77%,the seed cotton yield per plant decreased by 8.69%,and the root/shoot ratio decreased by 23.53%.3.Low and high potassium significantly affected potassium content,potassium accumulation,and potassium utilization efficiency in all organs of the plant.Compared with the medium potassium treatment,the low potassium treatment significantly reduced the potassium content in all organs of the plant,and the potassium content of root,stem,leaf,and boll(bud)decreased by 25.30%,21.80%,27.00%,and 17.60%,respectively,and the potassium accumulation decreased by 38.94%,37.41%,38.20%,and 30.14%,respectively.Compared with the medium potassium treatment,the high potassium treatment significantly increased the potassium content of roots,stems,and leaves by 24.49%,46.32%,and 135.44%respectively,but had no significant effect on the potassium content of bolls(buds).The potassium accumulation of plants in high potassium treatment increased significantly,the potassium accumulation in stems and leaves increased significantly by 66.67%and 139.56%respectively,and the potassium fertilizer use efficiency decreased significantly by 15.97%.4.Low potassium and high potassium inhibited the growth and development of the main root and lateral root.Under low potassium stress and high potassium stress,the average daily growth of cotton taproot decreased by 7.44%and 3.56%,respectively.In the later growth stage,the root length density(RLD)of cotton was significantly different,medium potassium treatment>low potassium treatment>high potassium treatment,the root average diameter(AD)of medium potassium treatment was significantly larger than that of low potassium treatment and high potassium treatment,and the AD between low potassium treatment and high potassium treatment was very similar.In addition,the total root length,total root average diameter,total root surface area,and total root volume of cotton plants under low potassium treatment decreased significantly by 14.97%,12.50%,23.67%,and 31.51%,respectively,compared with medium potassium treatment.Under high potassium stress,the total root length,total root diameter,total root surface area,and total root volume decreased significantly by 24.99%,9.38%,31.50%,and 37.52%,respectively,compared with medium potassium treatment.The average lifespan of primary and secondary lateral roots showed as follows;low potassium treatment<medium potassium treatment<high potassium treatment.Compared with medium potassium treatment,the average lifespan of the first and second lateral roots of medium potassium treatment was shortened by 6.40 and 8.56 days,respectively,and that of the first and second lateral roots of high potassium treatment was prolonged by 6.92 and 3.90 days,respectively.It can be seen that the root lifespan is positively correlated with the amount of potassium fertilizer,and the root lifespan is prolonged with the increase of soil potassium fertilizer.5.Low potassium and high potassium significantly affected the length,density,and lifespan of cotton lateral root hair.Compared with medium potassium treatment,the hair length of the first and second lateral roots in low potassium treatment significantly increased by 34.19%and 52.01%,respectively;the hair density of the first lateral root decreased significantly by 10.21%,and the hair density of the second lateral root increased slightly by 5.17%.The root hair average lifespan of the first and second lateral roots was significantly shortened by 3.01 and 1.91 days,respectively.Compared with medium potassium treatment,the root hair length of primary and secondary lateral roots in high potassium treatment was significantly shortened by 7.63%and 12.30%respectively,and the hair density of the first and second lateral roots was significantly reduced by 11.60%and 11.74%,respectively.There was no significant difference in the root hair average lifespan of the first lateral root,and the root hair average lifespan of the second lateral root was significantly shortened by 5.32 days.The above results showed that the response trends of cotton root phenotype and root hair lifespan were similar under low and high potassium conditions.the root length density,root dry weight,total root length,root average diameter,total root surface area,total root volume,and root hair lifespan of the plant were significantly lower than those of medium potassium.The responses of aboveground morphology and photosynthetic characters,root hair length,and lateral root lifespan to low potassium and high potassium were different.Low potassium decreased plant height,stem diameter,leaf area,net photosynthetic rate,fluorescence ability,and lateral root lifespan,and significantly increased root hair length.High potassium had no significant effect on plant aboveground morphology and photosynthesis,mainly by significantly increasing lateral root lifespan and shortening root hair length.The accumulation of potassium was significantly correlated with root phenotype and lifespan.The results of this study enhanced the understanding of cotton root phenotype and longevity under potassium stress and provided a basis for further revealing the response characteristics of the cotton root system under potassium stress.