Research On Fertilizer Utilization Difference And Root Transcriptome Comparison Among Different Eucalyptus Species

Eucalyptus is an important fast-growing tree species in China.By 2013,the area of Eucalyptus plantations in China was approximately 4.5 million hectares,accounting for 5.8% of the total planted forest area in China.Annual output of wood accounted for about 20% of China's total timber production,and it protects China's timber and ecological security.This paper compares the biomass composition,nutrient accumulation and distribution,differences in fertilizer utilization,and root morphological characteristics of 9 species of Eucalyptus trees(E.cloeziana,E.pellita,Corymbia torelliana,E.robusta,E.camaldulensis,E.grandis,E.urophylla,E.exserta,E.tereticornis)that were 1-year-old Eucalyptus in the same soil and fertilization management conditions.The transcriptomes were sequenced from the roots of the two Eucalyptus trees with the highest difference in fertilizer utilization.Transcriptome information was obtained and assembled.The difference in the level of the transcriptional sequence was compared,and the mechanism of nutrient utilization difference of Eucalyptus was explored at the level of gene expression.The main results are as follows:(1)Among the nine species of 1-year-old Eucalyptus,the largest amount of biomass was E.camaldulensis which was 711.20 g per plant,followed by C.torelliana,E.pellita,E.grandis,E.robusta,E.tereticornis,E.urophylla and E.cloeziana.The minimum biomass was E.exserta which was 69.20 g per plant.In each organ,the distribution ratio of biomass of tree trunk or leaves was the largest,and the distribution ratio of bark or branch tree biomass was the smallest.The biomass of the eucalyptus trees with larger biomass,such as E.camaldulensis,C.torelliana and E.pellita,also has a larger proportion of root biomass.While the biomass with the smallest amount of biomass has the smallest proportion of underground biomass,such as E.cloeziana and E.exserta.(2)Roots,trunks,barks,leaves and branches of the nine species of eucalyptus,the content of nitrogen,phosphorus and potassium in the leaves were the highest,followed by branches,bark and roots,and the nutrient content in the trunk was the lowest.The contents of three elements in the five kinds of organs showed that nitrogen and potassium were higher and phosphorus was lower.The cumulative amounts of nutrients in nine species of Eucalyptus and the ratio of N,P,K needed were different.The total nitrogen,phosphorus and potassium accumulation of E.camaldulensis was the largest,and the cumulative absorption rate of N,P and K was 12.96:1:11.37.Followed by C.torelliana,E.grandis,E.robusta,E.pellita,E.tereticornis,E.urophylla which cumulative of N,P and K absorption ratio was 10.11:1:8.74,12.05:1:7.74,10.57:1:9.30,11.33:1:8.01,11.33:1:7.80,12.71:1:10.26,respectively.The accumulation of N,P and K in the E.cloeziana and E.exserta were the smallest,and the absorption ratios were 12.68:1:7.24 and 11.75:1:8.80,respectively.(3)Nine kinds of Eucalyptus nitrogen utilization rate ranged from 0.80% to 7.69%.Phosphorus use efficiency ranged from 0.11% to 1.32%.Potassium utilization rate ranged from 0.61% to 10.38%.The utilization rate of nitrogen,phosphorus and potassium of in E.camaldulensis was the highest and E.cloeziana was the lowest.(4)The correlations among length,surface area,volume,and connection number of nine species of Eucalyptus trees were highly significant.The four indicators of E.camaldulensis were higher than other tree species,and the E.cloeziana and E.exserta were the smallest.The average diameters of different tree species were not significantly different.The positive correlation between mean diameter and surface area and volume was not significant,but negatively correlated with length and number of connections.The fractal dimension of E.camaldulensis was the largest(1.60),the fractal dimension of E.tereticornis was the smallest,only 1.32.There was a significant positive correlation between volume and number of connections.(5)The root lengths of the fine roots(d?2.0mm)in the nine species Eucalyptus were the largest,and the root surface areas of the roots(2.0~10.0mm)were the largest,and the coarse roots(d?10.0mm)had the largest volume.There was a significant positive correlation between the length,surface area,volume,N-utilization,P-utilization,K-utilization,and total biomass of the nine species of eucalyptus,and the correlation coefficient was 0.551 to 0.994.There was a strong positive correlation between root morphology indicators and nutrient utilization.In short,one-year-old E.camaldulensis has better nutrient uptake capacity than the other eight Eucalyptus trees of the same age,followed by E.pellita,E.grandis,E.tereticornis,E.robusta,C.torelliana,E.urophylla,E.cloeziana,and E.exserta.(6)The transcriptomes were sequenced from the root materials of E.camaldulensis and E.cloeziana,and a total of 16.41 Gb of valid data was obtained.A total of 9,544 pairs of single-copy homologous genes were found in the two trees,and 1,810 pairs of Ka/Ks values greater than 0.5 were positively selected.These positive selection genes were enriched in metabolic processes,cellular processes,single organism processes,biological regulation,binding,catalytic activity,cells,cell parts,etc.The selection genes may be the differences in resistance to barrenness,salinity stress,and fertilizer use efficiency in E.camaldulensis and E.cloeziana.Among them,carbonic anhydrase CA gene and cyclic nucleotide gated channel(CNGCs)gene were particularly worthy of attention in respect of nutrient and environmental stress.