Effects Of Nitrogen And Gibberellin On Growth And Foliar Nutrient Status Of Dalbergia Odorifera

Dalbergia odorifera,a national class II protected plant,is extremely valuable for its excellent heartwood,and show great demand in market because of its high economic and medicinal value.However,due to its long rotation period,the current plantation regeneration rate can not keep pace with the increasing consumer demand.Therefore,how to accelerate the growth of D.odorifera and improve the quality of plantation has become an important research content in the high efficiency cultivation technology of D.odorifera.Seedlings are the basic guarantee for afforestation,which show great impacts on survival rate,growth performance and stress resistance after afforestation,so perfecting the cultivation techniques of D.odorifera can not only improve seedling quality,increase yield,but can also be helpful in forming a better shape,decreasing the cost and improving afforestation effectiveness during the plantation establishement and management.In this study,a nitrogen fertilizer dosage test and a gibberellin dosage experiment were set up to explore the effects on growth and nutrient status of D.odorifera seedlings and saplings.The main research results were summarized as follows:（1）Five dosages（0,400,800,1200,1600 mg nitrogen per seeding）of nitrogen（N）were applied on 6-month old D.odorifera seedlings with an average seedling height of 21.5 cm through an exponential fertilization pot trail.The results showed that seedling height,ground diameter,biomass,leaf area,chlorophyll content and gas exchange parameters of D.odorifera seedlings were significantly different among different nitrogen supply levels（P<0.05）,seedling growth increasd with the amount of fertlizer applied first and then decreased when 1200 mg N per seeding was applied.The root/shoot ratio showed a downward trend with the increasing of fertilization amount（P<0.05）.The N and potassium（K）contents of leaves increased with the increase of fertilizer application,while the phosphorus（P）content tends to be stable,which indicate that the demand for N and K of D.odorifera is much higher than those of P.Application of N can significantly increase the leaf chlorophyll content and photosynthesis intensity.According to the critical level approach,the optimum range of N,K content and N/P ratio for D.odorifera were 26.53-41.16 g·kg^-1,25.86-39.18 g·kg^-1 and 13.79-21.42,respectively.Based on these data,it could indicate that 800-1200 mg N per seeding would be the optimal fertilizer amount for 6-month old D.odorifera seedlings.（2）Five gibberellin concentrations(0,10,50,100,200 mg·L^-1per seedling)were applied on 6-month old D.odorifera seedlings to carry out foliar spray pot experiment.The results showed that there existed statistical differences among different gibberellin treatments on height,ground diameter,biomass,leaf area and chlorophyll content of D odorifera seedlings（P<0.05）.Biomass and leaf area showed a tendency of increasing first and then decreasing with the further increase of gibberellin concentration.In terms of seedling biomass and leaf area,both 50 mg·L^-1 and 100 mg·L^-1 gibberellin treatments had a significant promotion effect,the maximum values of the height,ground diameter,total biomass and leaf area were 55.78 cm,6.22 cm,12.24 g and582.75 cm²,which were 1.1,1.47,1.24 and 1.46 times of the control treatment（P<0.05）,respectively;foliar application of gibberellin could significantly increase the leaf and stem biomass of seedlings,but no significantly different were observed on root biomass accumulation.Leaf N content increased significantly with the increase of gibberellin concentration,while P and K content kept stable.Leaf spraying of gibberellin can increase the accumulation of N content in D odorifera seedlings,and the accumulation of P and K also increased slightly,however,no significantly different were observed among different concentrations,which indicates that foliar application of gibberellin could not significantly increase the accumulation of nutrients in D.odorifera.The content and total amount of chlorophyll a and b in seedlings,as well as the net photosynthetic rate,stomatal conductance,intercellular CO₂ concentration and transpiration rate of the seedlings showed a trend of increasing first and then decreasing with the increase of gibberellin concentration.,the maximum value is achieved when the gibberellin concentration were 50 mg·L^-1.The results of the study showed that:foliar spraying 50 mg·L^-1 GA₃ was the best application concentration to promote the growth of 6-month old D.odorifera seedlings.（3）Field trials of nitrogen and gibberellin application showed that nitrogen could promote significant differences on growth of 3-year-old D.odorifera saplings.Tree height,DBH and leaf area were increased with the increase of N amount.All gibberellin treatments significantly stimulated height growth,and 100 mg·L^-1 GA₃ significantly promoted DBH growth.The application of nitrogen and gibberellin showed no significant effects on leaf contents of N,P and K of 3-year-old D.odorifera saplings.