Revealing the changes of labile nitrogen(LN)fractions in soil aggregates of eucalypt plantations at different ages is of great significance for better understanding of soil nitrogen cycles in such plantations.In this study,the state-owned Daguishan forest farm in Guangxi was selected as the research area,and the soil of eucalypt plantations with different ages(1,2,4 years)along with some adjacent abandoned land(control)during traditional rotation period were selected as the research objects.The undisturbed soil samples of the 0～20 cm soil layer were collected and divided into 4 granular aggregates by the wet sieving method,including＞2 mm,1～2 mm,0.25～1 mm and＜0.25 mm.The contents of LN fractions in soil aggregates of different sizes were determined.The LN components include Particulate Organic Nitrogen(PON),Microbial Biomass Nitrogen(MBN),Ammonium Nitrogen(Ammonium Nitrogen),Nitrate Nitrogen(NH4+-N),Nitrate Nitrogen(NO3--N)and Alkali-hydrolyzable Nitrogen(AN).The results showed that the content of LN in soil aggregates increased significantly as aggregate size decreased in the soil of eucalypt plantations of different ages,resulting in more soil LN distributed in＜0.25 mm aggregates.Overall,the content of LN in soil increased at first and then decreased after the planting of eucalypts,and the highest content was found when the plantation was 2-year-old,indicating that the soil nitrogen availability of eucalypt plantations was the highest at this age.Therefore,after eucalypt plantations reach age 2 years,attention should be paid to supplementing soil LN so as to maintain the nitrogen supply levels of eucalypt plantation soils.
In order to develop Eucalyptus cloeziana plantations,10 families of E.cloeziana were introduced from Australia to the southern Fujian mountains.The results showed that families 1212 and 1202 were the most excellent families,with average preservation rates of 85.56%at age 6 years.The average diameter at breast height(DBH),tree height,crown width,volume with bark and volume without bark were 15.42 cm,12.73 m,4.46 m,0.137 9 m3 and 0.116 4 m3,respectively.The genetic gains of above indicators were 8.56%,1.86%,4.83%,16.50%and 4.55%,respectively.The coefficient of variation of DBH,tree height,crown width,volume with bark and volume without bark ranged from 0.27%to 30.04%,belonging to the range of relatively small to moderate variation.The growth of trees within the family was relatively uniform,and the average wind damage index of selected families was 17.02%,lower than the population average of 14.98%.
The forest resources of Guangxi underwent great changes during the period from 2000 to 2021.The forest area increased from 9.819 million hm2 to 14.864 million hm2.The forest stock volume increased from 370.76 million m3 to 978.22 million m3.The forest covering rate increased from 41.32%to 62.55%.The forest land usage rate increased from 71.84%to 92.11%.The average annual growth rate increased from 4.09 m3·hm-2 to 7.97 m3·hm-2.The stock volume per hectare of forest land increased from 48.80 m3·hm-2 to 84.25 m3·hm-2.The annual growth of forests increased from 40.18 million m3 to 91.37 million m3,and the annual timber production increased from 16.37 million m3 to 38.99 million m3.Based on the results of continuous forest resource inventory in Guangxi from 2000 to 2021,the forest qualities were evaluated using the Analytic Hierarchy Process(AHP)that included 5 main aspects(forest origin,forest structure,forest productivity,forest health,forest value)and 37 sub-classification indicators.The results showed that the forest quality increased from passing grade to good grade from 2000 to 2021.The reasons for improving forest quality were systematically analyzed,and the important factors for improving forest quality were policy driven,market lead and increased investment along with strong,scientific and technological support which provided for scientific resource management.In order to further increase the forest resource quantity and promote forest quality in Guangxi,adjusting the structure of forest types,forest species structure,stand age group structure,tending of young stands,moderately reducing forest harvesting in the future were proposed.
Tissue culture technology is an important means for the regeneration and reproduction of woody plants.This paper summarizes the research progress of tissue culture technology and molecular regulation mechanism of organ re-generation in woody plants.This scrutiny of research progress has made it clear that establishment of regeneration sys-tems for woody plants is closely related to internal factors(explant genotypes,physiological states,etc.)and external factors(plant hormones,culture conditions,etc.).Gene expression,hormone signaling pathways and other signaling pathways play key regulatory roles in the process of de novo regeneration of woody plant organs.The difficulty in induc-ing adventitious buds and roots can be a bottleneck in the regeneration of woody plants.In the future,regulatory mecha-nism of regeneration of woody plants should be further studied to improve the regeneration efficiency and quality of woody plants.
To identify key NAC transcription factors involved in wood formation,a NAC transcription factor gene EugNAC007 of the clone DH32-29 of Eucalyptus urophylla×E.grandis was cloned based on RNA sequencing data and its function analyzed.The coding DNA sequence length of the EugNAC007 gene was found to be 1 711 bp and encodes an acidic protein with 569 amino acid residues of molecular weight of 64.32 KD.The EugNAC007 protein contained a typical NAC domain at the N terminus and shared relatively high homology with the Arabidopsis NAC with TRANSMEMBRANE MOTIF1(AtNTM1)that regulates cell division.The results of RT-qPCR showed that EugNAC007 was predominantly expressed in xylem tissues.Overexpression of EugNAC007 in poplar suppressed growth of tree height.These results indicated that the EugNAC007 may participate in the processes of wood formation through the regulation of cell division,but the regulation mechanism is still unclear.This study advanced deep excavation of NAC transcription factors involved in wood formation processes in Eucalyptus.
