Exponential nutrient loading shortens the cultural period of Larix olgensis seedlings

Traditional nursery culture of Changbai larch (Larix olgensis Henry) in Northeast China requires up to a 2-year nursery production period. The high cost of seedling culture for this duration has been identified as a constraint. As a potential means to help to shorten the cultural period, we evaluated growth, biomass accumulation, and nitrogen (N) uptake dynamics of 1-year-old seedlings subjected to nutrient-loading treatments at intensive rates of 500 mg N seedling(-1) supplied exponentially (E500) and 135 mg N seedling(-1) supplied exponentially (E135) or conventionally (constant). Also included were an unfertilized control and the standard fertilizer regime for 2-year-old seedling production (77 mg N seedling(-1) supplied conventionally over 2 years). At the end of nursery culture, though seedlings in the constant treatment had more biomass and N accumulation at the whole-seedling level, much of this was allocated to needles. While seedlings in the E500 treatment exhibited signs of toxicity, those in the E135 treatment had equivalent end-of-nursery N concentration in woody tissues to those produced over 2 years; root collar increment and survival 69 d after outplanting were also similar. Our results suggest that exponential nutrient loading at an optimal rate could increase available nutrient reserves in woody tissues of deciduous tree seedlings, therefore having the potential to improve seedling performance after outplanting.