Study On Artificial Induction Of Heartwood Formation And Related Signal Substances Of Dalbergia Odorifera

Dalbergia odorifera?D.odorifera?is famous for its precious heartwood;however,its heartwood grows very slowly and trading market is very tight.The key technology in the efficient cultivation of D.odorifera plantation is how to speed up the growth of D.odorifera plantation,induce the formation of heartwood,improve the yield and quality of heartwood,and shorten the rotation period.Therefore,in this study,we carried out four experiments of water control of forest land,exogenous plant growth regulators and chemical reagents of trunk,and pruning of potted plants and investigated the effects of different treatments on the formation of heartwood and the dynamic process of corresponding physiological parameters,to provide the basic data for the research on the artificially induced the formation of heartwood.The main findings are as follows:?1?Compared with CK,DI treatment increased and HD decreased the growth,respectively.Heartwood formation ratio of HD and LD was as high as 60⁷0%,while DI and CK were only about 40%.The heartwood length of HD and LD were about 1.4 cm,while DI and CK were only 0.3⁰.8 cm.There was a significant difference in heartwood density among treatments,with the order of HD = LD > DI = CK.The oil content of HD was generally more than 1%,and other treatments were all below 1%.HD and LD can both promote the heartwood formation of D.odorifera,and have no significant effect on the composition of heartwood essential oil and the ratio of various components.HD and LD treatments increased the conversion of starch to soluble sugar in sapwood during the dry season and increased the substrate material for the synthesis of heartwood compounds,which may provide some theoretical basis for that drought can promote the heartwood formation of D.odorifera.The study suggests that in the cultivation practice of D.odorifera plantation,the dry-season irrigation should be implemented in the young forests for a long time.HD treatment is suitable for promoting the heartwood formation in medium-aged or mature forests of D.odorifera,which have a large DBH but a small proportion of heartwood,and LD is suitable for promoting the heartwood formation of young or medium-aged trees with a faster growth.In terms of different site conditions,under conditions of rich rainfall,well-distributed and deep soil,drought treatments should be used to increase the proportion of heartwood and the quality of heartwood before harvest;Under the thin soil conditions,appropriate irrigation should be used in the young or middle forests in the dry season to promote early growth and achieve a reasonable DBH.?2?The increments of DBH in SA and ABA were 80.32% and 47.62% of CK?Wounding?,respectively.The increments of tree height and crown in ABA were only 45.21% and 30.53% of CK?Wounding?.After one month of treatment,the axial discoloration of the SA treatment was the largest,followed by Me JA and ABA,and the ETH treatment was small.The discoloration length and area were only about 20% and 15% of the SA treatment,respectively.However,ETH was significantly higher than that of other treatments after 3 months,and the difference further increased after 6 months.The range of discoloration after 3 months and 6 months of ETH treatment were 60 times and 100 times that of 1 month,respectively.After one month of treatment,the relative moisture contents of all the discolored sapwoods were about 42%,which were significantly higher than that of NH 36.78%,and they were close to NH after 6 months.After one month of treatment,the densities of the discolored sapwoods were all close to NH.After 6 months,the density of the discolored sapwood of ETH treatment was significantly greater than that of NH,which was 1.28 times that of NH.After one month of treatment,the oil contents of discoloration sapwood of all treatments were significantly lower than that of NH.After 6 months,the oil content of ETH treatment was 1.42%,which was significantly higher than that of NH.The ETH treatment can induce almost discoloration of the all-over tree.Although the initial effect is slower,finally it has the most complete heartwood composition,the highest content and is closest to the natural heartwood.Thus,it is feasible that ETH treatment induces the heartwood formation of D.odorifera,while the effects of Me JA,SA and ABA treatments are poor.?3?Compared with CK?Wounding?,the increment in DBH,tree height,and crown width of H⁺ treatment decreased by 34.92%,25.53%,and 32.78%,respectively,and there was no difference among other treatments.The H⁺ treatment induced the greatest range of sapwood discoloration,but the duration of action was shorter.The H₂O₂ treatment took the second place,and had a long duration of action.After one month of treatment,the densities of the discolored sapwood of all treatments were lower than that of NH.After 6 months,the density of the discolored sapwood treated with H₂O₂ was significantly greater than that of NH.After 1 month of treatment,the oil contents of all treatments were significantly lower than that of NH.After 6 months,the oil content of H₂O₂ treatment was 0.98%,which was significantly greater than that of NH 0.82%.Although H⁺ treatment had the largest induction range,it severely inhibited tree growth.The oil contents and heartwood composition treated with H⁺ and Na Cl did not reach the level of natural heartwood.The induction range of H₂O₂ treatment was large,the action time was long,the composition of the induced heartwood was the most,and the basic wood properties also reached the level of natural heartwood.Therefore,H₂O₂ treatment may induce the heartwood formation of D.odorifera,while H⁺ and Na Cl treatments have poor induction effects.?4?In the process of sapwood discoloration induced by plant growth regulators and chemical reagents,axial and ray parenchymal cells consumed starch and other sugars to largely synthesize the heartwood substances such as lipids and phenolic.These substances passed through the pit pairs between the parenchyma cells and vessels or fibers,then continuously transported to the vessels and the fiber tracheids.When the heartwood substances are evenly distributed in the wood,the heartwood finally forms.?5?Mechanical wounding induced bimodal bursts of ethylene and H₂O₂ in the xylem of D.odorifera,and both of them were significantly inhibited by their specific inhibitors.AVG and As A significantly inhibited the PVO,oil content,and synthesis of heartwood substances.After 6 weeks,the PVO of air,water,AVG,and As A treatments were 80.24,76.92,19.6,and 27.46%,respectively,and the oil contents were 0.45,0.47,0.13,and 0.18%,respectively.The heartwood substances of air and water treatments contained 9 components,while the AVG and As A treatments contained only 2 and 4 components,respectively.Thus,both of Ethylene and H₂O₂ play important roles in the signaling chain that mediates D.odorifera's response to mechanical wounding.In general,H₂O₂ is in the upstream of the signal transduction chain and is responsible for receiving and delivering external wounding,stimulating the synthesis of downstream ethylene,etc.,to regulate the expression of key enzymes and ultimately induce the synthesis of heartwood substances.?6?The results of the experiments of plant growth regulators,chemical reagents and pruning validate each other,and consistently indicate that both of ETH and H₂O₂ play important roles in the process of the heartwood formation of D.odorifera.They are both effective methods for further research on the induction of heartwood formation of D.odorifera,and can also provide some inspiration for exploring the mechanism of the heartwood formation of D.odorifera.