| In this paper, black locust (Robinia pseudoacacia) seedlings inoculated with arbuscularmycorrhizal (AM) fungi Rhizophagus irregularis or Glomus versiforme were studied, and theseedlings growth, root morphology, nutrient, leaf anatomy structure, gas exchange,chlorophyll fluorescence, carbon content, calorific value, delignification, enzymatichydrolysis were tested. Simultaneously, energy accumulation and carbon accumulation werecalculated in this research. The mechanisms of AM fungi affecting black locust growth,carbon assimilation and biofuel traits were discussed. Furthermore, physiological andecological characters such as gas exchange, carbon and lignin content, salt resistance of blacklocust colonized by AM fungi under salt stress were researched, for energy plants breedingshould use less productive soils and enhancing usage efficiency of salty soils. The mainresults as follows:1. Effects of AM fungi on the growth, root morphology, and N, P, Mg content of blacklocustSeedlings inoculated with R. irregularis had higher colonization rate than that ofseedlings inoculated with G. versiforme. The AM colonization rate of seedlings inoculatedwith R. irregularis was75.0%at the third week. However, the AM colonization rate ofseedlings inoculated with G. versiforme was76.5%at the ninth week. Both R. irregularis andG. versiforme improved the growth and root system development. The root length, rootsurface, root volume, root tips, and root forks of seedlings inoculated with R. irregularis werehigher than those of the control by46.1%,118.1%,217.6%,134.6%, and165.3%,respectively. Seedlings inoculated with G. versiforme had higher root length, root surface, androot forks than the control by33.0%,14.5%, and43.4%. AM seedlings had higher P, Mgcontents, especially seedlings inoculated with R. irregularis. There were significant positivecorrelations between biomass (r=0.958, p <0.01), or root surface (r=0.938, p <0.01), orroot volume (r=0.932, p <0.01) and AM colonization rate. AM fungi enhanced biomass byAM fungi promoting root systems development and P, Mg uptake of black locust.2. Effects of AM fungi on leaf anatomy structure and photosynthesis of black locustLeaf palisade cells of AM seedlings lined up tightly and the tissue were thicker. Leaf palisade tissues of seedlings inoculated with R. irregularis or G. versiforme were25.9%and23.1%thicker than that of control. AM fungi greatly promoted the photosynthetic ability ofblack locust. Seedlings inoculated with R. irregularis had significant advantages in leaf area,chlorophyll contents and net photosynthesis rate over non-mycorrhizal seedlings by460.0%,19.4%, and13.0%, and those of seedlings inoculated with G. versiforme over controlseedlings by491.0%,33.6%, and19.6%, respectively. Seedlings inoculated with G.versiforme had89.0%higher carboxylation efficiency than that of control, indicating that G.versiforme significantly enhanced carbon assimilation of black locust. AM fungi alsosignificantly increased the effective photochemical efficiency of photosystem II and electrontransport rate, which lead seedlings absorbe more light energy.3. Effects of AM fungi on calorific value, carbon and ash content of black locustAM fungi significantly increased the biomass, calorific value, energy accumulation, andcarbon accumulation of black locust. The biomass, energy accumulation and carbonaccumulation of5-month black locust colonized by R. irregularis were311.0%,345.2%,364.0%greater; and by G. versiforme were353.0%,395.2%, and393.7%greater than thoseof the control seedlings, respectively. The calorific values of root, stem, and leaf in5-monthblack locust colonized by R. irregularis were10.0%,5.4%,5.5%higher, and by G. versiformewere9.5%,9.5%,7.3%higher than those of control, respectively. The biomass, energyaccumulation and carbon accumulation of14-month black locust colonized by R. irregulariswere89.6%,102.2%, and93.3%greater, and by G. versiforme were91.3%,94.2%, and77.2%greater than those of control, respectively. In addition, energy and carbonaccumulations in leaves and roots were higher than those in stems. G. versiforme hadadvantages over R. irregularis in enhancing biomass, energy and carbon accumulations of5-month seedlings. However, R. irregularis was more excellent than G. versiforme inenhancing calorific value, energy and carbon accumulations of14-month seedlings.4. Effects of AM fungi on delignification and enzymatic hydrolysis of black locustAM fungi enhanced cellulose and lignin contents of black locust;5-month seedlingsinoculated with R. irregularis had cellulose and lignin contents11.2%and13.4%greater thanthose of the control;14-month seedlings inoculated with R. irregularis only had lignin content11.6%greater than that of the control. Five and14-month seedlings inoculated with G.versiforme only had lignin content12.4%and7.9%greater than the control. Fourteen-monthseedlings had higher lignin content which might have inhibition to enzymatic hydrolysis ofcellulose. The glucose yield of14-month seedlings colonized by R. irregularis was56.1%,however, which of5-month non-mycorrhizal seedlings was69.7%. Photographs by scanningelectron microscope (SEM) showed that AM fungi affected the lignocellulose structures. Non-mycorrhizal and G. versiforme seedlings after aqueous ammonia pretreatment, thesurface were coarse, rough and with many pores, which were benefit for enzymatic hydrolysis.The structures after enzymatic hydrolysis were evidently different between non-mycorrhizaland mycorrhizal seedlings.5. Photosynthetic carbon fixation and biofuel traits of AM black locust under salt stressAM colonization rates of black locust were obviously lower under1.5g kg-1NaCl stress.R. irregularis enhanced chlorophyll content, leaf area, and net photosynthesis rate by15.5%,197.2%, and39.9%higher, while G. versiforme enhanced chlorophyll content, leaf area by8.3%and151.0%higher, than those of non-mycorrhizal seedlings under1.5g kg-1NaClstress. So, AM fungi increased resistance to NaCl stress by the stronger growth andphotosynthetic ability of AM seedlings. AM fungi enhanced calorific value and carboncontent of black locust under1.5g kg-1NaCl stress. AM fungi increased cell wall and lignincontents of black locust in0g kg-1soils. In addition, there were linear relations between netphotosynthetic rate, or calorific value and AM colonization rate, which were y=0.089x+3.632(R2=0.733, p <0.01) and y=0.022x+16.386(R2=0.434, p <0.01), respectively.Therefore, AM fungi improved the photosynthetic carbon fixation and biofuel traits of blacklocust in different salinity.In conlusion, AM fungi enhanced biofuel traits of black locust through increment N, P,Mg nutrient uptake and CO2fixation. AM fungi could influence aqueous ammoniapretreatment and enzymatic hydrolysis of black locust for higher lignin content. In addition,AM fungi had the positive effects in improving the growth and biofuel traits of black locustunder NaCl stress. |
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