Effects of potassium fertilizer on dry matter accumulation and potassium absorption characteristics of maize (Zea mays L.) inbred lines with different yield types

In this experiment, 20 different maize inbred lines were used as basic materials, which were divided into high-yield type, middle-yield type and low-yield type by yield cluster analysis. A 3-year long-term positioning field experiment (2016–2018) was carried out to assess the effects of potassium fertilizer on dry matter, potassium absorption and potassium absorption efficiency of maize inbred lines with different yield types. The results showed that the dry matter, potassium absorption and potassium absorption efficiency of leaf, stem, bract, rachis and grain of maize inbred lines have been significantly increased with potassium application in comparison with no potassium application. Potassium fertilizer could improve the dry matter accumulation capacity and potassium absorption characteristics of maize, promote the potassium absorption by maize plants, influence the growth and development of maize, and then improve the maize yield. The decrease of dry matter, potassium absorption and potassium absorption efficiency of high-yield maize inbred lines was smaller under low potassium stress. The high-yield maize inbred lines had stronger ability to maintain higher dry matter accumulation and potassium absorption characteristics under low potassium stress. The study provided a theoretical basis for the breeding of potassium-efficient maize materials.


171
At maturity, the dry matter of leaf and stem of high-yield, middle-yield and low-yield type maize of middle-yield and low-yield type at 0K. The dry matter of bract and rachis of high-yield type maize 178 inbred lines was 1.21 and 1.43 times higher than that of middle-yield and low-yield type at 45K, 1.16 179 and 1.31 times higher than that of middle-yield and low-yield type at 0K. The dry matter of grain of 180 high-yield type maize inbred lines was 1.21 and 1.51 times higher than that of middle-yield and 181 low-yield type at 45K, 1.16 and 1.40 times higher than that of middle-yield and low-yield type at 0K 182 (Fig 4).

183
The dry matter of maize inbred lines with different yield types were shown as follows: high-yield 184 type>middle-yield type>low-yield type, and potassium fertilizer could significantly increase the dry 185 matter of maize.    and low-yield type at 0K. The potassium absorption efficiency of bract and rachis of high-yield type 245 maize inbred lines was 1.49 and 2.14 times higher than that of middle-yield and low-yield type at 45K, 246 1.24 and 1.60 times higher than that of middle-yield and low-yield type at 0K. The potassium 247 absorption efficiency of grain of high-yield type maize inbred lines was 1.41 and 1.86 times higher 248 than that of middle-yield and low-yield type at 45K, 1.41 and 1.75 times higher than that of 249 middle-yield and low-yield type at 0K (Figure 8).

250
The potassium absorption efficiency of maize inbred lines with different yield types were shown as 251 follows: high-yield type>middle-yield type>low-yield type, and potassium fertilizer could significantly 252 increase the potassium absorption efficiency of maize.  Note ： DMLS, DMBR, DMG, PALS, PABR, PAG, PAELS, PAEBR, PAEG indicated the dry matter of leaf and stem, dry matter of bract and rachis, dry matter of grain, potassium absorption of leaf and stem, potassium absorption of bract and rachis, potassium absorption of grain, potassium absorption efficiency of leaf and stem, potassium absorption efficiency of bract and rachis, potassium absorption efficiency of grain respectively.

Discussion
The cluster analysis method can classify different germplasm resources based on genetic differences among varieties objectively and accurately, so as to screen out excellent germplasm resources and provide basic materials for crop breeding and genetic improvement [19,20]. It was an important way to achieve stable and high maize yield by researching the yield differences of different genotypes of maize inbred lines and improving maize varieties so as to improve maize yield [21][22][23]. Therefore, in this study, 20 maize inbred lines were classified into three types by cluster analysis method: high-yield type, middle-yield type and low-yield type. Potassium fertilizer could increase maize yield, the yield of maize inbred lines with high-yield, middle-yield and low-yield type increased by 7.96%~8.45%, 4.72%~5.35% and 2.41%~2.95% at 45K compared with that at 0K. The yield of maize inbred lines with different yield types was as follows: high-yield type>middle-yield type>low-yield type. The test provided basic materials for further research on dry matter accumulation and potassium absorption characteristics of maize inbred lines with different yield types.
The accumulation of dry matter is an important index to improve maize yield [24]. Potassium fertilizer played an important role in promoting the dry matter accumulation of maize [25]. Potassium fertilizer could increase the dry matter of maize leaf, stem, bract, rachis and grain, thus promoting the increase of maize grain yield [26][27][28]. In this study, the dry matter of maize inbred lines with different yield types increased significantly under potassium application level, and the increase range of high-yield type maize inbred lines was greater than that of middle-yield and low-yield type maize inbred lines, indicating that maize inbred lines with high yield had higher dry matter accumulation ability. Under the condition of 0K, the decrease of dry matter of high-yield type maize inbred lines was smaller. The results showed that high-yield type maize inbred lines had stronger ability to maintain higher dry matter accumulation under low potassium stress. The grain dry matter of maize inbred lines with high-yield, middle-yield and low-yield type increased by 14.29%~15.23%, 9.58%~11.71% and 5.81%~7.63% at 45K compared with that at 0K.
Nutrient absorption is the basis of yield formation, which directly affects the yield and fertilizer absorption and utilization efficiency. The potassium absorption capacity of maize is an important factor to obtain high yield [29]. The absorption capacity of maize plants to potassium could directly affect the accumulation and distribution of dry matter, and then affect the formation of maize yield [30,31]. In this study, there were significant differences in potassium absorption and potassium absorption efficiency of maize inbred lines in the silking stage and maturity stage under the two potassium fertilizer levels, which were as follows: high-yield type>middle-yield type>low-yield type. Potassium application increased the amount and efficiency of potassium absorption. The improvement degree of potassium absorption characteristics of high-yield type maize inbred lines was greater than that of middle-yield and low-yield type maize inbred lines. The grain potassium absorption of maize inbred lines with high-yield, middle-yield and low-yield type maize inbred lines increased by The results showed that high-yield type maize inbred lines were more sensitive to potassium fertilizer in improving potassium absorption characteristics, which may be one of the important factors for high-yield type maize inbred lines to gain higher yield. The correlated relationship between maize yield and dry matter accumulation and potassium absorption characteristics was of great significance to guide the breeding of maize materials with high yield and good quality.

Conclusions
20 maize inbred lines were divided into three types, the first type was high-yield type, including FAPW, Potassium fertilizer can improve the dry matter accumulation capacity and potassium absorption efficiency, influence the growth and development of maize, and then improve the grain yield.
High-yield type maize inbred lines have stronger ability to maintain higher dry matter accumulation and potassium absorption characteristics under low potassium stress, which can be one of the important factors for high yield of high-yield type maize inbred lines.