北美红杉幼苗对不同供N水平的生长反应

Growth Response of Sequoia sempervirens Seedlings to N Nutrients

采用温室盆栽的方法探讨了北美红杉1年生幼苗对不同N供应水平(0、0.05、0.11、0.16、0.21、0.32、0.42和0.63 g·L-1,0.21 g·L-1为对照)的生长反应,结果表明:(1)幼苗在完全供N水平(对照)时,苗高净增量为31.2 cm;当供N水平降到一半(0.11 g·L-1)以下时(N3～ N1),苗木的生长明显减缓,苗高净增量分别是对照的92.6%、83.0%和29.8%;供N水平增加2 倍(0.63 g·L-1)时,苗高净增量为对照的70.8%.(2)当N供应水平降低(N4～ N2)或缺N(N1)时,幼苗地下部分与地上部分比率(R/S)增加,缺N时为对照的2.1 倍;净增生物量分配给根系的比例也明显增大,缺N时为56%.(3)在低N供应条件下,幼苗细根(D≤2 mm)的特定根长增加尤为明显,缺N时为14.9 m·g-1 ,是对照的169%;N供应过量时,细根的特定根长减小,在0.63 g·L-1供N水平(N8)时为6.0 m·g-1 ,约为对照的68% .

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 was6.0 m · g^-1