The Effect Of Fertilization On N And P Utilizations In Larix Olgensis Seedlings

Larix olgensis Henry. is one of the most important timber species planted in northeastern China. Bareroot stocks are the main type of seedlings cultured as production in local nurseries, for which high rate fertilization is widely operated. This was believed to degrade their seedling quality and result in a big fertilizer-waste. Based on operational culture practice and classic theories, such as "Target seedling" and "Nutrient reserves", and aiming at improving seedling quality at an economical rate, we studied responses of above- and below-ground growths and N and P uptake and utilization in seedlings with different sizes to inorganic fertilization, steady-state nutrient loading and late-season nutrient addition. Carbohydrate accumulation and depletion in early spring, summer nutrient retranslocation, fall nutrient reserves and fine root development were monitored. Germinated (1-0) seedlings subjected to nutrient loading in nursery were compared, for the first time, with transplanted (1-1) gradeâ… seedlings in their early performance after out-planting, so as to determine the possibility of a cost culture-regime with a shortened culture period.The results revealed that:(1) significant response of 1-0 seedlings to fertilization treatments began in late summer locally; (2) Compared to the inorganic fertilization treatment at a rate of 200 kg N and P hm-2, that at the rate of 100 kg N and P hm-2 could improve larger seedling growth and nutrient uptake, decrease nutrient leaching, and raise their carbohydrate accumulation rate in following early spring, so did organic fertilization treatment (10000 kg FM Chicken manure hm"2); (3) Basal fertilization treatment at a low rate of 23.76 kg N hm-2 and 60.72 kg P hm-2 could enhance nutrient uptake from current soils, decrease nutrient leaching and retranslocation, and tended to strengthen nutrient reserves in 1-1 seedlings; (4) Late-season fertilization at a rate of 30 kg P hm-2 and 60 kg N hm-2 could increase nutrient accumulation in reserves in 1-1 seedlings without affecting their growth; (5) GS activity was higher in needles and lower in roots of seedlings subjected to the treatment of N to P supply ratio of 2:1 than other treatments, while AP activity was higher in roots and lower in needles of seedlings subjected to the treatment of N to P supply ratio of 1:2 than other treatments; (6) Relative to the rate of 500 mg N seedling-1, seedlings subjected to the nutrient loading treatment at a rate of 135 mg N seedling-1 had lower chlorophyll and soluble protein contents, but higher nutrient utilization efficiency, and they had a mortality as low as gradeâ… 1-1 seedlings after planting.