Genetic Response Of Toona Ciliata Var. Pubescens Families To Soil Nitrogen And Phosphorus Level

Toona ciliata var. pubescens is a fast-growing tree species belonging to Genus Toona ofMeliaceae in subtropical area of China, with excellent wood quality as building, furniture anddecorative timber, and has be planted for wood production in many provinces.The plangting sites in mountainous southern China are complex and variable, and evendegradated along with the cultivation cycles. So breeding Toona ciliata var. pubescensgenotype which could utilize site productivity efficiently, or has a strong tolerance withenvironmental factors of site, should be encouraged for ensuring the development of Toonaciliata var. pubescens plantation.The investigation on the family test plantation of the species in Kaihua County ofZhejiang, Nanling County of Anhui, Yongfeng County of Jiangxi, showed that there weresignificant differences among families and treatments. The tree height and the diameter was notcorrelated with the geographical or climatic factors. Among the element content in thesoil,nitrogen and phosphorus were correlated highter with the tree height and the diameter ofthe species.In this paper,8representative families were choosed in the pot test of available N and Plevels to study the genetic differences of growth, root morphology, biomass, nutrition andphotosynthetic physiological characteristics and their relationship with the nitrogen andphosphorus environment. The result revealed the traits difference and genetic response of thetoona to nitrogen and phosphorus nutrient, illustrated the adaptive mechanism of the species tolow N and P stress, and some families of high N and P utilizing efficiency were selected.1. Response of different families of T. ciliata var. pubescens to nitrogen(1) There were genetic differences of growth response between the8families at differentN levels. The difference of seedling height, basal diameter, total biomass, root morphologicalcharacter parameters were significant among families and treatments. With the concentration ofN increasing, each growth character increased first and then decreased, and had maximum at N1level. N1may be determined as the optimum concentration to the growth of seedlings. Ineach N level, the traits of the species had significant differences among families, it showed thatthere was great genetic variation in the response of T. ciliata var. pubescens families to soilNitrogen, which was the premise for the genetic improvement.(2) With the concentration of N increasing, Fv/F0, Fv/Fm, ΦPS Ⅱand NRA activityincreased first and then decreased, and SPAD increased continuously. It indicated that lownitrogen concentration inhibited photosynthetic and physiological metabolism, however, SPADincreased slightly, but photosynthetic efficiency was inhibited at exorbitant nitrogen level.Family of low nitrogen tolerance had more content of chlorophyll, stronger PSⅡ activity,higher NRA activity; In the same way, family of high nitrogen efficiency had similarcharacteristics in the better nitrogen environment.(3) With concentration of nitrogen increasing, root-shoot ratio of Toona ciliata var.pubescens seedlings decreased continuously, and had maximum under low nitrogen stress,which was a initiative adapt mechanism to low nitrogen stress. Among the rootparameters,Length of roots in diameter of0-1.0mm, Number of fibrous roots and Surface areaof roots played an important role to the adaption to low nitrogen stress, but Roots in diameterof more than1mm, Root volume play a much smaller overall role. Under low nitrogen stress,more biomass of Toona ciliata var. pubescens was distributed to the Roots in diameter of0-1mm.(4) The correlation analysis showed that biomass accumulation of T. ciliata var. pubescenshad significant positive correlation with nitrogen accumulation, but was weakly correlated withnitrogen utilization efficiency,which indicated that the uptake of nitrogen by roots played amajor role on accumulation ability of biomass at each N level. Under low nitrogen stress(N0),Surface area of the roots, Length of roots in diameter of0-0.5and Number of fibrous roots hada higher correlation with biomass accumulation; Under N1level, Root volume, Surface area ofthe roots and Length of roots in diameter>2mm had a higher correlation with biomassaccumulation. (5) The analysis of the family heritablities of traits of the species showed that tree height,basal diameter, biomass accumulation and the root parameters were under strong geneticcontro（l0.6305~0.9773）. With concentration of nitrogen increasing, family heritablities of thetraits (except root/shoot ratio) decreased, but still Keep at high levels.(6)Through the correlation analysis and the of the family heritablities analysis, weconfirmed Surface area of root, Number of fibrous, Length of roots in diameter of0-0.5mm asthe special characteristics of family with low nitrogen tolerance, and confirmed that Rootvolume and Surface area of roots were of families with high nitrogen efficiency.(7) Through the analysis of the special characteristics of the families, and considering withthe growth situation of them, we confirmed GX1, JX1, JX2as the family with low nitrogentolerance that can grow better under low nitrogen stress; We confirmed GX1, GX2, JL1as thefamily with high nitrogen efficiency that can grow better in better nitrogen environment2. Response of different families of T. ciliata var. pubescens to phosphorus(1) There was genetic variation in growth response of8Toona ciliata var. pubescensfamilies at different P levels. There were significant differences of height, basal diameter, totalbiomass, root parameterss of Toona ciliata var. pubescens seedlings among different familiesand treatments. With P level increasing, each growth character increased continously, and hadmaximum at P2level. In each P level, the traits of the species had significant differences amongfamilies, it showed that there was great genetic variation in the response of T. ciliata var.pubescens families to soil Nitrogen, which was the premise for the genetic improvement.(2) There was a minium of SPAD、Fv/F0、Fv/Fm、ΦPSⅡand qP under low phosphorus stress,and they increased continuously with the increasing of phosphorus level, but qN decreasedcontinuously. It indicated that low phosphorus concentration had an inhibitory action onphotosynthesis. There was an maximum of Apase activity under low phosphorus, which was aninitiative adaptive mechanism coping with low phosphorus stress. Family of low phosphorustolerance had more content of chlorophyll, stronger PSⅡ activity, higher apase activity, andfamily of high nitrogen efficiency had similar characteristics in the better phosphorusenvironment. (3) With concentration of nitrogen increasing, there was no significant variation ofroot-shoot ratio of the species seedlings.The species changed the root characters to adapt thelow P stress: Number of fibrous, Length of roots in diameter of0-0.5mm, Total length of rootsand Surface area of roots played an important role to the adaption to low P stress, but Length ofroots in diameter>1.0mm and Root volume play a much smaller overall role.(4) The correlation analysis showed that biomass accumulation of T. ciliata var. pubescenshad significant positive correlation with phosphorus accumulation, but was weakly correlatedwith phosphorus utilization efficiency, which indicated that the uptake of nitrogen by rootsplayed a major role on accumulation ability of biomass at each P level, which was the same tothe result of nitrogen pot test. Under low phosphorus stress(P0), Number of fibrousroots,Surface area of the roots and Length of roots in diameter of0-0.5mm and had a highercorrelation with biomass accumulation; Under P2level, Root volume and Length of roots indiameter>1mm had a higher correlation with biomass accumulation.(5) The analysis of the family heritablities of traits of the species showed that tree height,basal diameter, biomass accumulation and the root parameters were under strong geneticcontro（l0.6714~0.9951）. With concentration of P increasing, family heritablities of the traitsdecreased, but still keep at high levels.(6) Through the correlation analysis and the of the family heritablities analysis, weconfirmed Number of fibrous roots,Surface area of the roots and Length of roots in diameterof0-0.5mm as the special characteristics of family with low P tolerance, and confirmed thatRoot volume and roots in diameter>1were of families with high nitrogen efficiency.(7) Through the analysis of the special characteristics of the families, and considering withthe growth situation of them, we confirmed XJ2, GX2as the family with low phosphorustolerance that can grow better under low phosphorus stress; We confirmed XJ2, JX1, JL1as thefamily with high phosphorus efficiency that can grow better in better phosphorus environment.