Nutrient Diagnosis And Nitrogen Fertilization Of Betula Alnoides Seedlings

Nutrient diagnosis and fertilization for seedlings plays an important role in guiding to grow robust seedling, thus improve seedling quality and enhance survival rate of plantations. The requirement and efficiency of nitrogen in plants has always been a focal issue of nutritionists and physiologists since nitrogen is one of the elements widely distributed in plant. Betula alnoides Buck. -Ham. ex D. Don is a valuable indigenous hardwood species with large-scale development in tropical and warm subtropical areas, while less study has been reported on its nutrient requirement and fertilization. Therefore, trials of macronutrient deficiency and nitrogen exponential fertilization were conducted for its seedlings. We determined the responses of B. alnoides seedlings to deficiencies of these nutrients in terms of foliar symptoms, growth attributes, pigment composition concentration and mineral element contents, examined the growth and nutrient dynamics of B. alnoides seedlings under different nitrogen addition levels, and to determine the optimum nitrogen amount based on critical level method and the relationship between nutrient supplied quantity, biomass and nutrient condition. The findings provide a theoretical foundation for plantation forestry of B. alnoides and optimizing techniques for growing its seedlings.Macronutrient deficiency trial was carried out using healthy tissue cultured seedlings of B. alnoides with almost uniform height of 14.5 cm in sand culture with seven treatments: i.e., complete nutrient mixture (Control), minus nitrogen (-N), minus phosphorus (-P), minus potassium (-K), minus calcium (-Ca), minus magnesium (-Mg), and minus sulfur (-S) nutrient solutions. It was indicated that: (1) The foliar symptoms of no-N, no-K, and no-Mg seedlings were most apparent including leaf discoloration, bronze patches, leaf twisting, and interveinal chlorosis; (2) Apart from no-Mg and no sulfur (no-S) treatments, seedlings lacking other nutrients showed significant decreases in the height, root collar diameter, number of branches, leaf area as well as biomass of B. alnoides seedlings, but an increase in root/shoot ratio; (3) Phosphorous deficiency had no significant effect on all fractions of pigments, while the other nutrient deficiency treatments resulted in significant reductions of photosynthetic ability of seedlings; and (4) Vector analyses showed that there was obvious synergism or antagonism between different nutrients in B. alnoides seedlings under different treatments of nutrient deficiency.An exponential fertilization trial was conducted with seven dose levels involved (applying a total of 0, 50, 100, 200, 300, 400, 600 mg N seedling^-1 in the experiment), using healthy seedlings of B. alnoides with almost uniform height of 4cm. It was showed that: (1) The root collar diameter, height, biomass and whole plant nutrient contents of all nitrogen treatment seedlings followed an exponential function as the time advanced, while the root and shoot ratio gradually reduced; As for the whole plant nutrient concentrations, P concentration increased with time, while N and K concentrations decreased followed by increasing or consistently raised; (2) There were significant differences in the root collar diameter, height, biomass and leaf area of B. alnoides seedlings between treatments, and 200 mg N seedling^-1 was the critical amount meeting growth of B. alnoides seedlings; (3) The extent of requirements for N, P and K were different, the leaf and whole plant phosphorus concentrations became stable when nitrogen supply was more than 100 mg N seedling^-1, whole plant N and K concentrations were stable as nitrogen supply more than 300 mg N seedling^-1, while leaf N and K concentrations kept on increasing when nitrogen supply more than 200 mg N seedling^-1, suggesting that the requirement for P was less than N and K; and (4) Based on critical level method and relationship between nutrient supply and biomass and nutrient conditions, it could be inferred that 200 - 400 mg N seedling^-1 was the optimal nitrogen amount for B. alnoides seedlings, indicating that B. alnoides is grow-fasting and fertilizing species.