川西亚高山65年人工云杉林种子雨、种子库和幼苗定居研究
收稿日期: 2010-04-14
录用日期: 2010-06-03
网络出版日期: 2011-01-24
Seed rain, soil seed bank and seedling regeneration in a 65-year Picea asperata plantation in subalpine coniferous, western Sichuan, China
Received date: 2010-04-14
Accepted date: 2010-06-03
Online published: 2011-01-24
川西亚高山人工针叶林已成为亚高山森林的重要组成部分, 它们是否具有持续的自然更新能力, 是决定川西亚高山针叶林群落演替方向和维持该区针叶林大面积存在的基础。以川西米亚罗亚高山人工云杉(Picea asperata)林(65 a)为研究对象, 对种子雨量年际变化、土壤种子库动态、种子萌发和幼苗定居等更新过程的关键环节进行了连续7年(2002-2008年)的野外观测, 以研究人工云杉林更新潜力及影响其更新的限制因素。结果表明: 该区云杉林种子雨一般从每年的10月初开始下落, 一直到翌年的1月底或2月初结束; 云杉种子散落存在明显的大小年现象, 种子散落周期为4年, 且大小年之间种子产量差异极大; 云杉种子从下落到土壤到种子完全失去活力不到1年时间, 属于Thompson和Grime定义的第II类土壤种子库类型。腐烂死亡和动物取食是土壤种子库损耗的主要因素, 而种子通过萌发真正转化为幼苗的比例非常低, 仅占2002年下落种子总量的3.6%。种子萌发后, 环境筛的作用导致云杉幼苗大量死亡, 尤其是在种子萌发后的一个生长季节内, 其死亡率高达78%。凋落物和苔藓是构成人工云杉林下地表的两种主要地被物类型, 二者占所有调查幼苗数量的93%左右; 两种地被物类型上0-2 cm层幼苗存活率最高, 分别占存活幼苗总数的76.07%和86.72%, 随地被物厚度增加, 幼苗存活率呈明显下降趋势, 而幼苗死亡率呈明显升高的趋势, 表明林下地被物厚度也是影响云杉幼苗定居的重要因素。两种地被物对幼苗生长的影响不同, 除株高之外, 分布在苔藓上的云杉幼苗生长参数(地径、分枝数、干重以及干重年增长率)明显高于分布于凋落物上的幼苗, 表明苔藓地被物更有利于云杉幼苗定居。尽管该区大量云杉种子下落, 但由于种子的高损耗率、幼苗的低输出率以及萌发幼苗的高死亡率, 使得人工云杉林下种子通过萌发转为实生幼苗的数量非常少, 最终真正能补充到云杉种群的个体数量非常有限。
尹华军, 程新颖, 赖挺, 林波, 刘庆 . 川西亚高山65年人工云杉林种子雨、种子库和幼苗定居研究[J]. 植物生态学报, 2011 , 35(1) : 35 -44 . DOI: 10.3724/SP.J.1258.2011.00035
Aims Picea asperata is one of the keystone spruce species used for reforestation in subalpine coniferous forest of western Sichuan, China. A total of ca. 13 000 hm2 of plantations are dominated by this species in this region. Our objective was to assess (a) potential for natural regeneration and (b) critical factors limiting regeneration of this tree species in spruce plantations.
Methods We conducted field studies on the seed rain, soil seed bank dynamics and seedling establishment in a 65-year spruce plantation in Miyaluo subalpine coniferous forest of western Sichuan, China from 2002 to 2008. We used seed traps, sieved to determine the soil seed bank, and recorded seedlings.
Important findings Pinus asperata seed rain commonly lasted from early October to the end of January or early February. There was a large annual variation in seed production, with mast years at 4-year intervals. We concluded that seed availability was not a limiting factor for natural regeneration, at least in mast years. The seed bank was transient, with losses from seed decay and seed predation being the two most important factors affecting seed bank dynamics. Only a small fraction of seeds germinated and produced seedlings, e.g., 3.6% in 2002. Higher seedling mortality greatly reduced the total number of germinated seedlings, and few seedlings survived after one growing season. Deep litter and moss were the most common substrates for P. asperata regeneration, having 93% of all germinated seedlings. Most surviving seedlings occurred with a substrate depth of 0-2 cm, and seedling mortality increased with greater depth, suggesting substrate depth is an important constraint on natural regeneration. Seedlings on moss substrate had greater root collar diameter, number of green shoots, estimated dry weight and annual dry weight increment but less height than those on litter substrate. In conclusion, despite a substantial seed production, high depletion of soil seed, low germination and high seedling mortality limit natural regeneration of P. asperata.
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