Effect Of Mycorrhizal Fungi Inoculation And Phosphorus Supply For Betula Alnoides Seedlings

Betula alnoides is an indigenous valuable broad-leaved tree species mainly distributed in tropical and south subtropical regions of China.Its wood is of good quality and usually used for making floor,high-grade furniture,musical instruments and so on.The bark of B.alnoides also has a higher economic value since it can be used for treating a variety of diseases.Furthermore,B.alnoides also plays an important role in biodiversity and soil fertility maintain,water conservation and carbon fixation etc.Nowadays,it has been widely used for the construction of ecological forest and precious timber forest in south China.Robust seedling cultivation is the basis for artificial afforestation.Mycorrhiza,a symbiont of mycorrhiza fungi and plant root,can significantly accelerate seedling growth and improve its stress resistance.B.alnoides both has exogenous and arbuscular mycorrhizas,mycorrhizal seedlings is thus an important measure for robust seedling cultivation.This study selected 6 universal arbuscular mycorrhiza fungi（AMF）and 6 easily isolated ectomycorrhiza fungi（ECMF）to conduct seedling single inoculation,mixed inoculation as well as inoculation and phosphate fertilizing experiments on four clones of B.alnoides（FB4、BY1、FB4⁺、A5）with large scale promotion.The study could reveal the effects of single and mixed inoculation and its difference between B.alnoides clones,select the optimal AMF,ECMF species and its combination for young seedling of B.alnoides,explore the effect of phosphate fertilizing on inoculation of mycorrhiza and select the optimal amount of phosphate fertilizing based on the mycorrhizal inoculation rate,growth performance of seedling,root morphology,nutrient content,photosynthetic physiology and many other indexes after inoculation.In addition,surface soil collected from 12 B.alnoides plantations was used for local mycorrhizal fungi inoculation experiments to reveal the correlation among mycorrhizal colonization,growth performance,nutrient status and photosyntheticphysiology,explore the internal mechanism of adaptation to soil condition and provide basis for exploration and application of local mycorrhizal fungi species.The main results are as follows:（1）The results of AMF inoculation experiment showed that all six AMF were effective in arbuscular mycorrhiza of B.alonoides clones,the colonization rate was 14%³9%.Only the Glomus intraradices had a medium dependence with 4 clones and the other AMF had weak dependences.Inoculating with Glomus intraradices and Glomus mosseae HUN03B significantly enhanced seedling growth,net photosynthetic rate,water use efficiency,chlorophyll contents and fluorescence parameters（P<0.05）,thus the affinity between these two AMF and clones was superior to other AMF and the two AMF can be used for mycorrhizal seedlings cultivation.There were non-significant differences of colonization rate among four clones,but the promotion effect of AM5 on FB4 and BY1 were better than on FB4⁺and A5significantly.（2）The results of ECMF inoculation experiment indicated that,all six ECMF could colonize seedling roots of B.alnoides clones,the colonization rate was 3%⁸6%.The dependence between Scleroderma polyrhizum,Scleroderma flavidum and FB4,BY1,FB4⁺clones were higher than others,and the colonization rate exceeded 80%.Inoculation of Scleroderma polyrhizum and Scleroderma flavidum significantly enhanced seedling growth and nutrient accumulation（P<0.05）,inferring that affinity of these two ECMF to clones was superior to those of other ECMF.It suggested that these two ECMF could be used for mycorrhizal seedlings production.Similar to AMF,there were also no significant differences in mycorrhizal colonization rate among four clones,while the positive effects of ECMF on growth of FB4 and BY1 were remarkably better than those of FB4⁺and A5.（3）Based on above selected superior AMF and ECMF,we designed mixed inoculation experiment on clone FB4.Six treatments including Glomus intraradices+Scleroderma polyrhizum,Glomus mosseae HUN03B+Glomus intraradices,Scleroderma polyrhizum+Scleroderma flavidum,Glomus intraradices,Scleroderma polyrhizum and the control were conducted.The results showed that all these inoculation treatments could colonize seedling roots well.The colonization rate was the highest for treatment Glomus intraradices+Scleroderma polyrhizum,the colonization rate was 27.6%for ECMF and 78.3%for AMF.The seedling biomass,total root length,N and P content of underground part,chlorophyll content and actual photosynthetic efficiency of this treatment were significantly higher than other treatments.The second was the single inoculation treatment with Scleroderma polyrhizum.Additionally,an interesting phenomenon was that the effect of single ECMF inoculation with Scleroderma polyrhizum was better than that of mixed inoculation with Scleroderma polyrhizum+Scleroderma flavidum,while the effect of mixed AMF inoculation with Glomus intraradices+Scleroderma polyrhizum was superior than that of single inoculation with Glomus intraradices.（4）Inoculation and fertilizing experiment was carried out on clone FB4 including a inoculated treatment with Glomus intraradices+Scleroderma polyrhizum and a control（without inoculation）,then each treatment contained six levels application dose of dissoluble phosphorus(0、20、40、80、100、200 mg P·plant^-1).The colonization rate of Glomus intraradices+Scleroderma polyrhizum increased and then decreased with the increasing application amount of phosphorus.The highest colonization rate emerged at the application amount of 80 and 100 mg P·plant^-1.Growth performance,nutrient and photosynthetic physiological indexes of inoculated seedlings were all higher than that of seedlings without inoculation,and growth performance reached significance at the levels of 40,80 and 100 mg P·plant^-1,the root morphology developed to the direction that was much easier for water and nutrient absorption.The accumulation of nutrient in trees increased and photosynthetic capacity also improved.For treatments without inoculation,growth,nutrient and photosynthetic physiological indexes still had an increasing trend even at the application amount of 200 mg P·plant^-1,while for treatments with inoculation,most of these indexes begun to decrease at the application amount of 100 mg P·plant^-1,and the growth was restrained at the application amount of 200 mg P·plant^-1.In conclusion,inoculation could significantly reduce the application amount of phosphorus,and the effect of inoculation of mycorrhiza fungi on seedling growth was best at the application amounts between 80¹20 mg P·plant^-1.（5）The results of inoculation experiment of indigenous mycorrhizal fungi showed that the mycorrhizal colonization rate was of no significant difference among four clones（P≥0.05）,while it was significantly different among soil treatments.Especially,S12 had remarkably higher colonization rate than other soils（P<0.05）.Significant differences were observed in growth performance,root properties,leaf nutrition,chlorophyll content,photosynthetic and chlorophyll fluorescenceparametersamong four clones as well as 12 soils,and the interaction between clone and soil had remarkable effects on seedling height,leaf area,total root length,root biomass and leaf total phosphorus concentrationnet photosynthetic rate,intercellular CO2concentration,transpiration rate,water utilization efficient,chlorophyll a content and PSⅡactual photosynthetic efficiency.Seedlings grown in soil coded as S12 performed better with higher concentrations of nutrients,chlorophyll content,photosynthetic and chlorophyll fluorescence parameters than those of other soils,this is in accordance with high productivity of the plantation where the soils were collected.Clones FB4 and BY1 were performed better than other two clones as grown with 12 soils,demonstrating that FB4 and BY1 were more adaptable to these soils.The correlation analysis also showed that the mycorrhizal colonization rate was positively correlated with seedling growth,leaf nutrient and total chlorophyll cotents,net photosynthetic rate,PSⅡmaximal photochemical efficiency as well as actual photochemical efficiency.The present study swelected two superior AMF（Glomus intraradices and Glomus mosseae）and two ECMF（Scleroderma polyrhizum and Scleroderma flavidum）,found out that mixed inoculation with Glomus intraradices and Scleroderma polyrhizum as well as single inoculation with Scleroderma polyrhizum had the optimal effect on growth performance of B.alnoides,proved that mycorrhizal fungi inoculation could significantly reduce the application amount of phosphorus and the optimal application range was from 80 to 100 mg P·plant^-1,and discussed the feasibility of indigenous mycorrhizal fungi inoculation on robust seedling cultivation for B.alnoides.The present results could provide scientific basis and technical support for mycorrhizal seedling cultivation and even the sustainable management of artificial forests.Next,we will use the surface soil for comparison and find out the optimal mycorrhizal fungi and explore the interaction between them so as to furtherly improve the mycorrhizal seedling technology of B.alnoides.