Research On The Mechanism Of Nano-lanthanum Priming On Switchgrass Seed Vigor And Seedling Salt Tolerance

Switchgrass（Panicum virgatum L.）is a perennial C₄ herb plant of the genus Panicum in the family Poaceae.It has the advantages of drought tolerance,salt-alkali tolerance,barren tolerance,and strong adaptability.However,the low seed germination rate in the cultivation process is the bottleneck problem limiting its field production.Seed priming with rare earth elements can promote seed germination,increase seedling survival rate and crop yield.Domestic and foreign reports about anti-stress effects of rare earth elements on plants are mainly concentrated on food crops and cash crops,less attention has been paid to energy crops.Thus a in-depth research on its site of action and the physiological characteristics of photosynthesis is needed.Based on previous studies,this study investigated the effects of different concentrations of nano-lanthanum and lanthanum nitrate priming on the germination characteristics,water absorption,and metabolic processes of switchgrass seeds,as well as the photosynthetic characteristics,antioxidant system and osmotic system of switchgrass seedlings under salt stress after priming with lanthanum.The main results are as follows:1.Nano-lanthanum and lanthanum nitrate priming significantly improved the seed germination energy,germination rate and germination index of switchgrass（P<0.05）,and the optimal priming concentration is 200 mg·L^-1 and 600 mg·L^-1,respectively,and it significantly increased the water absorption rate of seeds and enhanced amylase activity（P<0.05）;Energy dispersive X-ray analysis found that the nano-lanthanum particles are mainly concentrated in the seed coat,and a small amount of particles are also present in the aleurone and endosperm,indicating that the nano-lanthanum particles can enter the inside of the seed and affect its germination,however,La³⁺only concentrated on the seed coat,and there is almost no endosperm,indicating that NO₃^-may play an important role in promoting seed germination.2.Nano-lanthanum and lanthanum nitrate priming can alleviate the influence of Na Cl stress on switchgrass seedling growth.Concentration≤300 mg·L^-1 nano-lanthanum priming and 600 mg·L^-1 nano-lanthanum priming the best relief effect,and 400～500 mg·L^-1lanthanum nitrate priming the relief effect optimal;Under the two lanthanum priming treatments,switchgrass seedlings and root MDA increased continuously with the increasing concentration of Na Cl solution.However,the concentration of≤300 mg·L^-1nano-lanthanum,100～400 mg·L^-1 and 600 mg·L^-1 lanthanum nitrate priming seedling MDA lower than CK;Under the two lanthanum priming treatments,the soluble protein content of switchgrass seedlings and roots gradually decreased with the increase of salt concentration,but the soluble protein of seedlings was higher than that of CK,which could alleviate the damage to chlorophyll.The proline content gradually increased with the increase of salt concentration,and the root proline was higher than CK;With the increase of the concentration of Na Cl solution,concentration≤200 mg·L^-1 nano-lanthanum and 400～600mg·L^-1 lanthanum nitrate priming could increase activity of SOD,CAT,and POD in seedlings.The root system increased at first then decreased.3.Chlorophyll content increased under low-concentration salt stress(100 mmol·L^-1),and the increase of nano-lanthanum priming treatment was larger,the increase was28.2%～101.9%.Salinity reduced the content of chlorophyll,and it slowed down its decline rate by nano-lanthanum priming,especially the effect on the content of chlorophyll was more obvious.The chlorophyll content by 100～300 mg·L^–1 nano-lanthanum and 600 mg·L^–1lanthanum nitrate priming were higher than that of CK.Under Na Cl stress,most of the fluorescence characteristics（Fm,Fv/Fm,Fv/Fo,Fv′/Fm′andΦPSⅡ）of switchgrass seedlings increased after priming,and only q P decreased,indicating that salt stress could not inhibit the PSⅡoriginal light energy conversion efficiency of switchgrass seedlings and the potential activity of PSⅡ,and reduce the non-radiative energy dissipation of PSⅡ.This study indicated that Lanthanum priming effectively improves the germination characteristics of switchgrass seeds by increasing water absorption and enhancing amylase activity.This advantage is mainly reflected in photosynthetic characteristics and stress resistance in subsequent growth,thereby improving the cultivation and planting process and the survival of seedlings.The optimal concentration of nano-lanthanum and lanthanum nitrate priming are 100～300 mg·L^–1 and 400～600 mg·L^–1,respectively.This research provides references for enriching rare earth element priming and plant seed germination and growth process theory,as well as increasing the application of switchgrass.