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31.2cm;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%。

本文对两类处于不同演替阶段的天然次生林,从直径生长、胸高断面积生长、材积生长、林木死亡率等方面进行了对比分析。研究结果表明:随着演替的进程,天然次生林直径生长、胸高断面生长和材积生长呈现下降趋势,林木死亡率也呈现明显的下降趋势,其主要原因是,在演替的早期阶段,速生喜光先锋种在林分中占据较高比例,进而林分表现出较高的死亡率和较高的生长力,但是随着演替的进行,喜光先锋速生树种逐步被耐荫的顶级或亚顶级树种所取代,进而表现出低生长和低的死亡率。

In order to understand the dynamic change of soil chemical characteristics along with the succession stages for supporting forest restoration,the soil chemical characteristics in different succession stages were compared and analyzed. The results indicated that with the progress of succession, pH value, available P,and total K showed a decreasing trend while organic matters, total P, total N, alkaline hydrolytic N, and available K showed a trend of increase. The correlation analysis indicated that there was an significant correlation between soil chemical characteristics such as total N, alkaline hydrolytic N, available P and organic matters of different horizon in different succession stages. The correlation analysis somehow signified the main source of soil N and P was organic matters. During the forest restoration process, forest litters should be protected so as to increase soil organic matter and improve soil fertilization.