Effects Of LED Supplemental Light On Pepper Seedling Growth And Arbuscular Mycorrhizal Fungi Colonization

Vegetable seedling cultivation is an extremely important part in the process of vegetable production,which will directly affect the yield and quality of vegetables.Through appropriate seedling management measure,it can not only cultivate high-quality seedlings,but also adapt them to the growing environment of the field in advance,providing quality guarantee for vegetables later.In facility production,problems such as low temperature and poor soil have greatly restricted the sustainable production of pepper and other facility vegetables.Therefore,it is very important to improve the stress resistance and adaptability to soil environment during seedlings management.Light supplement is an important means of light environment regulation in the process of vegetable production,which can effectively promote the growth and development of vegetable crops.It is an important choice to improve the yield and quality of vegetable crops by scientific light supplementation methods.Light quality and intensity can be precisely controlled through LED light supplement,which can not only meet the needs of plant growth and development,but also significantly reduce energy consumption and production costs compared with other light sources.In recent years,it has been widely used in facility production.In this paper,using pepper（Capsicum annuum L.）as the research object,plant physiology,molecular biology and other means as the research methods,we explored the effects of far-red light supplementation on the growth and resistance of pepper seedlings;we studied the effects of supplemental light on the growth,photosynthesis,carbon and nitrogen metabolism of pepper seedlings;we researched the effects of supplemental light in seedling stage on the colonization of arbuscular mycorrhizal fungi and phosphorus absorption in pepper.The main results obtained are as follows:1.The effects of supplementing 6%FR on the biomass,strong seedling index and stress resistance of pepper seedling on the bases of the control spectrum(R:B=3:1,PPFD is 150μmol m^-2s^-1)were studied.The results showed that compared with the control,supplementation of 6%FR was beneficial to the increase of the biomass of pepper seedlings,and the strong seedling index also increased significantly.At the same time,supplementation of 6%FR increased the maximum photochemical efficiency（Fv/Fm）,ABA content and CBF1 gene expression level of pepper seedlings under low temperature stress,improved the activity of antioxidant enzymes such as SOD,POD,GR and the expression of antioxidant enzyme related genes such as Cu/Zn-SOD,GR,POD,and suppressed the increase of relative conductivity.In addition,supplementation of 6%FR increased the actual photochemical efficiency(Φ_PSII)and ABA content of pepper seedlings under drought stress,inhibited non-photochemical quenching（NPQ）and increased relative conductivity,improved antioxidant enzymes activity such as SOD,POD and APX.The above results showed that red and blue light combined with appropriate amount of far-red light was conductive to regulate the morphology of pepper plants,increased the biomass of seedlings and the resistance to abiotic stresses such as low temperature and drought.2.The effects of different light quality on the growth,photosynthesis,carbon and nitrogen metabolism of pepper seedlings were studied.The total light intensity of the study is 160μmol m^-2s^-1,and the light intensity of the supplementary light source is 25μmol m^-2s^-1.The results showed that compared with the control,the supplement of red light and blue light could significantly increase the biomass and seedling index of pepper seedlings.At the same time,supplementing red light was most conducive to the increase of net photosynthetic rate,and supplementing blue light had a significant effect on improving stomatal conductance and transpiration rate.We further explored the role of HY5 in it,it was found that supplementing red light enhanced the expression of HY5.It was further detected that the expression of SWEET10a,SWEET11a and SWEET11b was significantly up-regulated,and the proportion of total sugar and sucrose content in roots increased significantly.In addition,supplementing red light was beneficial to the up-regulation of NRT1.1,NRT2.1,NRT2.2,NRT2.4,NRT2.5 gene expression and the increase of total nitrogen content.The above results indicated that supplementing red light played an important role in growth,photosynthesis,carbon and nitrogen metabolism of pepper seedlings.3.The effects of supplemental light in the seedling stage on subsequent arbuscular mycorrhizal fungi colonization and phosphorus uptake in pepper were clarified.The results showed that the leaves of the control groups which were not inoculated with arbuscular mycorrhizal fungi fell off from bottom to top,and the upper leaves were thin and small.However,the leaves of the experimental plants which were inoculated with arbuscular mycorrhizal fungi fell less,especially the treatment groups seedling supplemented with red and blue light grew well.At the same time,compared with the control groups,the expression of CCD7,CCD8 and MAX1 genes in the experimental groups were significantly up-regulated,the accumulation of strigolactones content in roots increased,the expression of PT4 and PT5 genes were up-regulated,the dry weight,phosphorus content and concentration of phosphorus increased.Among them,the effect of supplementing the red light on group during the seedling stage was the most significant.In addition,the arbuscular mycorrhizal fungi colonization rate of the treatment group supplemented with red light at the seedling stage was also the highest.The above results indicated that supplementing red light at the seedling stage could significantly promote the phosphorus absorption of pepper seedlings under phosphorus deficiency stress after planting,and was conducive to the colonization of arbuscular mycorrhizal fungi.Based on the above research results,we have clarified the plan for supplementing light during the seedling stage under the environmental conditions such as low temperature,phosphorus deficiency and poor soil,which provides a new scientific basis for facility production and application.