| Rice(Oryza sativa L.)is one of the most important food crops in the world.About 60%of people in China take rice as their staple food.Rice machine transplanting has the advantage of reducing labor intensity and saving labor.The development of mechanized rice planting is of great significance to promoting the transfer of rural labor force,improving labor productivity and arable land productivity,and stabilizing the total yield of rice in China.However,in the existing machine-transplanting technology,in order to ensure the basic number of seedlings and improve the quality of machine-planting,it is often achieved by high seeding rate.With the increase of the seeding rate,new problems such as poor seedling rate,irregular seedling emergence and weak seedling quality have been brought about.Light is one of the most important environmental factors for plant growth and development.Plant growth is not only restricted by light intensity and light time,but also affected by light quality.Therefore,it is of great significance to study the interaction between different light intensity and sowing density and the interaction between different light quality and sowing density on rice,so as to cultivate robust and neat seedlings suitable for machine transplanting.In this study,‘XZX 32’,‘XZX45’,‘ZZ 39’,‘ZLY 819’,‘YZX’,‘XWX 17’,‘WFY T025’and‘TY 553’were used as experimental materials to determine the seedling quality,antioxidant enzyme activity,MDA content,soluble protein content and total nitrogen content of machine transplanted seedlings,To explore the physiological regulation mechanism of different varieties’response to light intensity and light quality under different sowing density.The main results are as follows:(1)Through the investigation of seedling quality of 8 rice varieties under different light intensity and sowing density,the indexes of plant height,leaf age,number of green leaves,stem base width,dry and fresh weight and root morphology were compared.It was found that increasing light intensity can significantly improve the leaf age and number of green leaves,promote the accumulation of dry matter and improve the root morphology of seedlings.Reducing sowing density can effectively enhance the quality of machine transplanted seedlings,improve the dry and fresh weight of aboveground and underground parts,and increase the number of root tips.(2)Through the analysis of physiological characteristics,photosynthetic pigment content and total nitrogen content of seedlings of machine-transplanted seedlings of 8 rice varieties under different light intensity and sowing density,it was found that the changes of photosynthetic pigment content showed a trend of increasing significantly with the increase of light intensity,the change of photosynthetic pigment content showed a trend of increasing significantly with the increase of light intensity,under the three sowing density treatments,but different light intensity treatments had no effect on physiological indexes and total nitrogen content of seedlings.Reducing sowing density can effectively increase the contents of chlorophyll a,chlorophyll b and total chlorophyll,CAT activity,soluble protein and total nitrogen content of seedlings.(3)The correlation results showed that leaf age was positively correlated with soluble protein content(p<0.01),and negatively correlated with the number of white roots(p<0.05).Three factor analysis of variance showed that the single factor of variety,light intensity and sowing density and their two factor interaction and three factor interaction had significant effects on the leaf age of seedlings(p<0.001).Through comprehensive analysis obtain that high light intensity(25000 Lux)+low density(2 grains/cm~2),the growth of rice seedlings is the best,and‘ZLY 819’and‘XZX 45’can be selected as the best varieties to adapt to light intensity and sowing density.(4)Through the investigation of seedling quality of machine-transplanted seedlings of 8 machine transplanted rice varieties under different light quality and sowing density,and comparing the indexes of seedling plant height,leaf age,number of green leaves,stem base width,dry and fresh weight and root morphology,it was found that red light treatment significantly increased plant height,blue light treatment significantly increased leaf age and number of green leaves,increased aboveground fresh and dry weight and aboveground fresh and dry weight,and accelerated the establishment of root morphology.The seedling quality,aboveground fresh and dry weight and root morphology of low-density treatment were significantly higher than those of high-density treatment.(5)Through the analysis of physiological characteristics,photosynthetic pigment content and plant total nitrogen content of seedlings of 8 machine transplanted rice varieties under different light quality and sowing density,it is found that the photosynthetic pigment content decreases with the increase of sowing density,and the photosynthetic pigment content can be increased by blue light treatment in medium and high density treatment.Red light(wavelength 660～665nm)+low density(2 grains/cm~2)treatment can effectively improve SOD and POD activity,total nitrogen content and reduce malondialdehyde content,while blue light(wavelength 450～455nm)+low density(2 grains/cm~2)treatment can effectively improve CAT activity.(6)Correlation analysis showed that the average root diameter was positively correlated with the fresh weight of aboveground and underground parts(p<0.01),and negatively correlated with the number of root tips and CAT activity(p<0.05).Three factor analysis of variance showed that there were significant differences in leaf age,chlorophyll a,chlorophyll b,total chlorophyll content,SOD activity,POD activity,CAT activity and MDA content among variety treatment,light quality treatment,sowing density treatment and two factor interaction treatment and three factor interaction treatment(p<0.001).Blue light(wavelength450～455nm)+low density(2 grains/cm~2).Through cluster analysis,it was found that‘YZX’,‘ZLY 819’and‘ZZ 39’were the best varieties for the interaction of light quality and sowing density.In conclusion,in the process of industrialized seedling raising of rice,rice seedlings suitable for machine planting can be cultivated by using high light intensity(25000 Lux)+low density(2 grains/cm~2)or blue light(wavelength 450～455nm)+low density(2 grains/cm~2),and‘ZLY 819’is the most suitable rice variety.This study provides an important reference for industrialized seedling raising of rice. |
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