藏东南巨柏土壤种子库的时空分布格局

Spatial and Temporal Distribution Pattern of Soil Seed Bank of Cupressus gigantea in Southeast Tibet

为深入了解巨柏天然更新基础——土壤种子库,以巨柏稀疏纯林为研究对象,在巨柏主要分布区的雅江中游朗县选择2种地类(台地、坡地)、4个径级(0~10、10~30、30~50 cm和>50 cm)每径级选1株共8株巨柏标准木单株进行土壤种子库时空特征调查。结果显示:(1)巨柏土壤种子库中其种子密度较小,平均为299粒/m^(2),集中分布在距树干1~5 m和土层0~5 cm深度的范围内,分别占种子库储量的93.4%和89%,种子库的数量随地表覆盖度的增加呈波动增加趋势;(2)不同地类巨柏土壤种子库大小存在显著差异,坡地345.9粒/m^(2)主要分布在偏西方向;台地种子库密度为252.1粒/m^(2),主要分布在偏北方向上;(3)巨柏种子库整体质量较差,有活力的种子仅占21.9%;不同径级巨柏土壤种子库变异系数在54.9%~67.5%之间;(4)两期调查土壤种子库大小差异显著,12月巨柏种子库数量达到稳定期,到翌年5月种子经过了萌发期,种子库密度从平均311.9粒/m^(2)降到176.4粒/m^(2),减少了43.4%。研究表明,环境异质性、地表覆盖物的遮挡均对巨柏种子库产生了重要影响;巨柏种子库较小、失活率较高一定程度上影响了其天然更新基础。

In order to deeply understand the soil seed bank,which is the basis of natural regeneration of Cupressus gigantea,this paper investigated the spatial and temporal characteristics of the seed bank and its potential impact on the subsequent life history of C.gigantea in two types of terraces and slope land with four diameter classes(0-0,10-30,30-50 cm and>50 cm)in LANGXIAN County,the middle reaches of Yajiang river.The results showed that:(1)The number of soil seed bank was small,and the average seed number was only 299 seeds/m 2,which concentrated in the range of 1-5 m away from the tree trunk and 0-5 cm depth from the soil layer,accounting for 93.4%and 89%of the seed bank reserves respectively.At the same time,the number of seed banks increased with the increase of land cover;(2)The seed bank density of slope land waS345.9 seeds/m 2,which was higher than 252.1 seeds/m 2 of terrace,and had typical directional heterogeneity.Affected by wind direction,they are distributed in the West and north directions respectively;(3)The overall quality of the seed bank was poor,and only 21.9%of the seeds were active;the coefficient of variation of the soil seed bank of different diameter classes ranged from 54.9%to 67.5%;(4)In December,the number of seed banks reached a stable stage.In May of the next year,the size of seed banks in the two periods was significantly different.The average size of seed banks decreased from 311.9 seeds/m 2 to 176.4 seeds/m 2,a decrease of 43.4%.This study indicated that the heterogeneity of the environment and the shelter of the surface cover had an important impact on the seed bank.The small seed bank and high inactivation rate of C.gigantea affected the foundation of natural regeneration to a certain extent.