| Eucalypts, together with poplars and pines are known worldwide as the three groups ofthe fastest growing forest trees. In southern China, Eucalyptus urophylla×E.grandis cloneDH32-29has mang advantages including short rotations, fast growth and high yields, straighttrunk,good natural pruning and relatively wide adaptability for their timber.Consequently thearea of the eucalypt plantation resource has increased rapidly over the past20years or so,inmost China’s southern provinces.This rapid increase in plantation areas in conjunction withrelative short lengths used for these species has resulted in the eucalypt seedling demands oftenexceedling supply.At present empirical fertilization methodologies are commonly used during thepropagation of eucalypt nursery stock（seedlings and vegetative propagules） in mostnurseries;the fertilizers are supplied intensively,periodically and equivalently.However,thiskind of methodology supplies unnecessarily high nutrient quantities during early growthstages,resulting in wastage of fertilizer,sub-optimal quality seedlings/propagules andenvironmental pollution.So the techologies for nutritional regulation in the growing stage ofseedlings and propagules has already become one of the key techniques of propagating highquality eucalypt propagules.In the study reported here,fertilization technologies were studied at the stages of thenursery propagation and early plantation growth for Eucalyptus urophylla×E.grandis cloneDH32-29vegetative propagules. Growth, physiology, photosynthetic indices and nutrientdemands of propagules were studied with different fertilization methods and fertilizer quantitesduring the propagation period.The results are as follows:（1） An exponential fertilization trial was conducted with five dose levels of nitrogen(applying a total of0,50,100,150,200mg propagule-1) to assess the effects of nitrogen levelson growth, quality and nutrient status of E. urophylla×E. grandis propagules. The objective of this study was to reveal the nitrogen demand and determine the optimal nitrogen amount for E.urophylla×E. grandis propagules.Height, ground diameter, total plant biomass, soil and plantanalyzer development（SPAD） value and quality index of propagules increased with increasingN supply up to100mg propagules-1. At rates above this level, ground diameter, total plantbiomass and quality index remain unchanged, but height and SPAD value decreased markable.Quality index showed a significant positive correlation with height（R=0.423）, grounddiameter（R=0.645）,and total plant biomass（R=0.834）. The critical level approach was used foridentifying N, P and K deficiencies of propagules, and the critical values of those nutrientswere26.6,3.8and16.5g kg-1respectively, while their optimal concentrations ranged from26.6to38.5,3.8to5.3,16.5to21.4g kg-1, respectively. In conclusion,100mg propagules-1would be the optimal nitrogen amount for E. urophylla×E. grandis propagules.（2） The effects of nitrogen treatments with the exponential fertilization method, meanfertilization method and non-fertilization on the growth and physiological indices of E.urophylla×E. grandis tissue culture propagules in light media were studied during athree-month period. The results indicated that increasing N supply could significantly increasethe growth and chlorophyll contents of propagules （P<0.05）.The treatment with60mg Nplant-1provided for significantly higher（P<0.05）ground diameter, root volume, leaf area, leaflength, leaf width and chlorophyll contents than all the other8treatments. N, P contents ofroots, stems and leaves of propagules subject to exponential fertilization treatment were higherthan those given the mean fertilization treatment, but K content of different tissues ofpropagules given the mean fertilization treatment were higher. Principal component analyses ofthe different treatments showed that the exponential fertilization methodology was better thanthe average fertilization methodology with N concentrations in descending sequential orderwas60mg propagule-1,80mg propagule-1,40mg propagule-1and20mg propagule-1.Thetreatment of exponential fertilization methodology with60mg propagule-1N was the optimaltreatment in this study. （3） Growth, biomass allocation and photosynthetic characteristics of E. urophylla×E.grandis propagules coming out from nursery was studied by pot culture method in agreenhouse, the results showed that growth, biomass of different tissues and photosyntheticindices of propagules under16treatments（3fertilization methods×5N supply levels,andnon-fertilization） were significantly different （P<0.05）. According to the different SPAD valueof new and old leaves, the propagules stability in different fertilization methods from strong toweak is: exponential fertilization> linear fertilization> mean fertilization; Ground diameter,leaf dry weight, stem dry weight, aboveground dry weight, total biomass and netphotosynthetic ratio（Pn） from the exponential fertilization treatment with2000mg N plant-1were all the maximums in all treatments. It was concluded that propagules given exponentialfertilization method were superior to the propagules under other fertilization methods; thetreatment combination of exponential fertilization method with2000mg N propagule-1was theoptimal one in this experiment.（4） In this study, the effects of nitrogen treatments with different fertilization method onthe biomass and morphology parameters in roots of E. urophylla×E. grandis propagulescoming out from nursery were studied during a three-month period. The results suggested thatthe biomass and morphology parameters were significantly differennt among the treatments（P<0.05）. In the same nitrogen application concentration, root biomass, root length and rootsurface-area of propagules from different fertilization methods ranked as exponentialfertilization> linear fertilization> mean fertilization> non-fertilization. Degree of fitting of theParaboloid model equation was superior to that of linear model equation. As a multi-variatenonlinear model, the Paraboloid model when applied to the simulations involving both heightand ground diameter, provided a better fit for both root biomass and specific root length withhigher correlation coefficient（R2）and lower residual sum of squares （RSS）... |
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