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Growth and nutrient uptake dynamics of Mytilaria laosensis seedlings under exponential and conventional fertilizations

The growth characteristics and nutrient uptake dynamics of Mytilaria laosensis Lec. seedlings treated weekly with conventional and exponential fertilizations were investigated at intervals of 3 weeks for 12 weeks in a greenhouse. Leaf area and pigment compositions were also examined at the final harvest. The fertility treatments (mg nitrogen seedling–1) included two conventional (50C and 100C) and four exponential (50E, 100E, 200E and 400E) fertilizations, and no fertilization (0) as control. The biomass and nutrient contents of M. laosensis seedlings increased exponentially with time. Steady-state nutrition of nitrogen (N) and phosphorus (P) were achieved under exponential fertilization treatment of 50 mg N seedling−1 (50E) and conventional fertilization treatment of 100 mg N seedling–1 (100C), resulting from simultaneous increase of their biomass and nutrient contents. The nutrient uptake efficiency continuously increased over time in conventionally fertilized seedlings, but it increased initially and declined or remained stable from 11 weeks after transplanting in the exponentially fertilized seedlings. At the end of the experiment, the conventionally fertilized seedlings performed remarkably better than all exponentially fertilized seedlings except for seedlings in the exponential treatment of 200 mg N seedling–1 (200E) in height, root collar diameter and biomass. The optimum N and P uptake occurred in 200E seedlings because their N and P contents were 71%/60% and 14%/9% higher than both conventionally fertilized seedlings (50C/100C) without significant differences in growth performance between them. The leaf areas and chlorophyll contents of seedlings increased significantly with the increase of fertilizer levels and nearly peaked at the range from 100 to 200 mg N seedling–1, whereas the delivery schedule (conventional and exponential) had little effect on leaf areas and chlorophyll contents of seedlings at the same nutrient level (50 or 100 mg N seedling–1). These findings will provide evidence to make guidelines on fertilization for nursery production of M. laosensis, and help understand the nutrient demands for this species and further benefit the development of its plantations.