Growth Response of Sequoia sempervirens Seedlings to N Nutrients

In this paper,the growth response of one-year-old Sequoia sempervirens seedlings to N nutrients level was studied in a six-month period.In greenhouse, the plants were sand-cultured in pots supplied with various N mass concentration(0,0.05,0.11,0.16,0.21,0.32,0.42 and 0.63 g·L-1,0.21 g·L-1 as control).The results suggested:(1)When the seedlings were supplied with normal levels of nitrogen,they grew well and their net increase heights were 31.2 cm;when they were supplied with less nitrogen as 0.11,0.05 amd 0 g·L-1,or oversupplied with nitrogen as 0.63 g·L-1,they grew slowly and their net increase heights were 92.6%,83.0%,29.8% and 70.8% of those supplied with normal nitrogen respectively.(2)When supplied with less N nutrients,the seedlings changed below-ground and above-ground biomass by regulating partitioning of photosynthates between them.Deficient nitrogen supply caused increments of biomass partitioning to roots in order to increase root growth and the ratio was 56%.When the seedlings were oversupplied with nitrogen,and the ratios of below-ground to whole biomass evidently decreased.(3)Under the conditions of less nitrogen,the specific root length of the seedlings fine roots significantly increased,helpful for the seedlings to absorb more nutrients and water.It was 14.9 m·g-1,when supplied with 0 g·L-1.When oversupplied with nitrogen as 0.63 g·L-1,their specific root length was 6.0 m·g-1.