Study On The Effect Of Soybean-maize Relay Strip Intercropping Systems To The Abscission Of Soybean Flower And Pod And Its Physiological Mechanism

The abscission of flower and pod organs is not only a common problem in soybean production,but also an important factor affecting the increase of soybean yield.In the soybean-maize relay strip intercropping,soybean was shaded by maize during the vegetative growth period,resulting in changes in the structure and function of its source-sink organs.The effect of this change on the development and abscission of flower and pod organs in the reproductive period of soybean is not clear.Therefore,this thesis takes the soybean under the soybean-maize relay strip intercropping as the object to study the effect of the intercropping system on the abscission law of soybean flower and pod organs and its physiological mechanism.First of all,two field experiments were set up from 2016 to 2017 to study the flower and pod abscission characteristics of soybean varieties and planting patterns on relay strip intercropping soybean,and the relationship between flower and pod abscission characteristics and yield changes.At the same time,the flowering and pod differences of soybean flower and pod organs under strip intercropping system were further analyzed by simulated shading experiment in 2022.Secondly,a three-year field experiment was set up from 2018 to 2020 to study the physiological regulation mechanism of strip intercropping pattern on soybean flower and pod abscission.Using two-factor split zone design,the main factors were soybean varieties Nandou 25（ND）,Guixia 3（GX）and Gongqiudou 8（GQ）,and the side factors were soybean monoculture（SS）,soybean-maize relay intercropping（RI）and soybean-maize strip intercropping（SI）.This paper mainly studied the regulation mechanism of photosynthetic capacity,matter accumulation and distribution,carbon and nitrogen metabolism and endogenous hormones on the growth,development and abscission of flowers and pods in soybean.The main results are as follows:1.Through the study on the abscission characteristics of flower and pod organs of ribbon intercropping soybean varieties,it was found that soybean varieties could be divided into three categories by principal component analysis and cluster analysis,among which Nandou 12 and GX belonged to high-yield varieties,because the high-yield varieties had shorter flower-pod symbiosis period,more flowering and pod setting,and less flower and pod drop.Banded intercropping changed the abscission time and position of flowers and pods of soybean.The falling flowers of ND and GQ were mainly concentrated in the middle and lower parts,while those of GX were mainly concentrated in the middle and upper layers.The rate of falling flowers was determined by the number of falling flowers.The falling rate of ND and GX intercropping was significantly lower than that of single cropping.The intercropping mode had a greater effect on ND and GX,because intercropping reduced the number of falling flowers of ND and GX,but increased the total flowering number of GX.There was no difference in the total number of flowering in GQ single cropping system between years,and the planting pattern had the least effect on it.The pod drop of ND and GQ was mainly in the middle and upper layer,while the performance of GX was different,mainly in the canopy in 2016 and at the bottom in 2017.The pod drop rate depends on the number of pods.The pod drop characteristic of GX is more stable in two years,while only the pod number of GQ is stable between years,which indicates the importance of pod number to the final yield.2.After maize harvest,soybean entered the reproductive growth stage,and the soybean entered the recovery growth stage under this time and intercropping mode.The light transmittance of intercropping and intercropping,especially in the middle and lower layer of intercropping soybean,was significantly higher than that of monoculture,and the interrow temperature,relative humidity and CO₂ concentration of intercropping were lower than those of monoculture.The interrow microenvironment of intercropping was better than that of monoculture,which was beneficial to the development of pods in the later stage of soybean reproductive growth.In 2018,the flower bud differentiation of three soybean varieties showed that GQ was faster than ND and GX.At 47 and 61 days after emergence,soybean was in the late stage of vegetative growth and early stage of reproductive growth,and the difference among different planting patterns was the greatest,showing that the process of flower bud differentiation in intercropping and intercropping was slightly faster than that in monoculture.In 2019,the flower bud differentiation process of soybean in the critical period from vegetative growth to reproductive growth（54 days after emergence）was observed.It was found that the three soybean varieties all showed canopy>middle>bottom,but the performance was different under different models.The flower bud differentiation process of ND and GX under SS mode was slower than that of RI and SI model,and the difference of GQ flower bud differentiation among the three planting models was not significant.3.Reasonable vegetative growth will regulate the distribution range of flowering and podding of soybean.The leaf area and leaf area of banded intercropping and intercropping soybean increased significantly at 80-100 days after emergence,and reached the peak at about 110 days,and then showed a significant downward trend.During the period of vegetative growth,the photosynthetic rate of intercropping was lower than that of monoculture,but after resuming light,the photosynthetic rate of intercropping and intercropping increased gradually.At the full pod stage（R4）,the net photosynthetic rate of different varieties under intercropping with ND and GX was higher than that of single cropping.At this time,the daily growth rate of total biomass of ND intercropping was higher than that of monoculture,but larger than that of intercropping,and the time required to reach the maximum biomass of intercropping was longer than that of monoculture and intercropping,so the final total biomass of intercropping was 4.0%lower than that of monoculture,but 9.4%higher than that of intercropping.The flowering order of soybean plants is from bottom to top,and the shading from the vegetative growth stage will change the flowering and pod distribution of the main stem of soybean.The flowering distribution of soybean under intercropping is mainly distributed between 3 and 17 nodes.With the extension of shading time,the distribution range of flowering is reduced to 4-12 nodes,while shading from the reproductive growth period mainly affects the flowering number between 6-12 nodes of soybean.In intercropping,shading during vegetative growth will delay the peak time of flower and pod organ abscission,and the total number of flowers in different parts decreases from top to bottom,while the distribution of pods is mainly concentrated in the central region.4.The effectiveness of soybean assimilate supply regulates the abscission of flowers and pods by affecting the balance of carbon and nitrogen and the change of hormone content.80 days after emergence,the soluble sugar content and nitrogen content of ND and GX intercropping were lower than those of single cropping.At the fifth triple compound leaf stage（V5）and R4 stage,there was no difference in sucrose synthase（SS1）activity among different cropping patterns,but the SS1 activity of GX monoculture in R2 stage was 14.2%and 16.2%higher than that of intercropping and intercropping,respectively.At V5 stage,the sucrose phosphate synthase（SPS）of ND under intercropping was significantly lower than that of monoculture and intercropping by 25.8%and 23.8%,respectively.When it developed to R2 stage,there was no difference in SPS among different cropping patterns,but in R4 stage,intercropping and intercropping were 15.4%and 18.5%higher than that of monoculture,respectively.The order of glutamine synthase（GS）activity among varieties in R2 stage was GX>ND>GQ,but there was no difference among varieties in R4 stage,the GS activity of intercropping in R2 stage was 19.4%and23.3%higher than that of single cropping and intercropping,and that of intercropping in R4 stage was 24.2%and 17.1%higher than that of single cropping and intercropping,respectively.The activity of glutamate synthase（GOGAT）among different varieties was GX>GQ>ND in R2 stage,and GQ>ND>GX;in R4 stage.The difference of GOGAT activity among different planting patterns in R2 and R4 stage was SI>SS>RI.At R2stage,the cellulase（AC）activity of flower organs in different varieties showed GQ>ND>GX.At this time,the relative expression of Gm AC gene in intercropping was up-regulated by 32.6%and 47.0%,while GQ was significantly down-regulated.At R2 stage,the ABA content of flower organs in ND monoculture was significantly higher than that in intercropping and intercropping,while in R4 stage,the ABA content in pod organs in intercropping was significantly lower than that in monoculture and intercropping.The GA₃content in leaves and floral organs of intercropping,intercropping and intercropping was significantly higher than that of monoculture,while the floral organ GA₃content of GX was significantly lower than that of monoculture.In conclusion,soybean-maize relay strip intercropping can promote the transformation of soybean flower buds from vegetative growth to reproductive growth,and material accumulation and transport can be carried out during the period of flowers and pods after light recovery.At the same time,because shading affects the growth and photosynthesis of intercropping leaves,the balance of carbon and nitrogen between source and sink organs is changed,resulting in nutrient stress.Therefore,the consumption of soluble sugar in the late reproductive stage is a signal to cause abscission,with the change of the content of endogenous hormones ABA and GA₃,and the changes of cellulase,polygalacturonase and Gm AC genes related to abscission,resulting in the abscission of flowers or pods.