石羊河中游沙漠化逆转过程土壤种子库的动态变化

在石羊河中游,应用空间代替时间的方法,选择流动沙丘以及封育恢复5a、15a和25a的沙漠化逆转过程序列,研究了沙漠化逆转过程土壤种子库的变化特征。结果表明:石羊河中游沙漠化土地土壤种子库由4科12种植物组成,种子库主要分布于表层0-5cm。在沙漠化逆转过程中,土壤种子库物种数趋于增加,物种组成以1年生草本植物占优势逐渐向多年生草本植物和半灌木植物转变;种子库密度、表层土壤种子比例、物种多样性指数、与地上植被的相似性呈现先增大后降低趋势;沙漠化土地生态恢复间隔的时间越长,土壤种子库间的相似性程度越低;沙漠化土地与地带性植被区种子库的相似性逐渐增大,但是恢复25a沙漠化土地也仅达到0.36。研究认为,沙漠化逆转过程也是沙漠化土地土壤种子库向地带性植被土壤种子库演变的过程,而且是一个十分缓慢的过程,该研究有助于丰富干旱区土壤种子库的理论和指导干旱内陆河流域沙漠化土地的生态恢复实践。

Dynamics of soil seed banks in the reversion process of desertification in the middle reaches of the Shiyang River

Soil seed bank is an important indicator for plants responding to changes of the land utilization and climate, also an important tool for the understanding vegetation dynamics. However, little information is available about the dynamics of soil seed banks in the reversion process of desertification in arid areas. With the method of substituting time with space, the mobile sand dune and desertified lands closed for 5, 15 and 25 years were selected as a restoration stage series in the reversion process of desertification, and the adjacent native vegetation habitat was took as the reference site to look into the change characteristics of soil seed bank in the middle reaches of the Shiyang River. The results showed that the soil seed bank of the desertified land in the middle reaches of the Shiyang River consisted of 12 species, belonging to 4 families, with a simple composition, and the seed density, diversity index and similarity coefficient were relatively low. In the reversion process of desertification,(1)the species number of soil seed bank showed a gradual increasing trend, and the species composition of soil seed bank was changing from annual plants to perennial and semi-shrub plants;(2)the soil seed bank was concentrated in the topsoil layer (0-5 cm). Except for mobile sand dunes, the ratio of topsoil seeds to total seeds in the desertified lands closed for 5, 15, 25 years and the adjacent native vegetation habitat were all over 90%. The seed density of the topsoil layer (0-5 cm) showed an increase first and then a reduction, but the seed density of the 5-10 cm soil layer showed an increasing trend. The seed density of the 0-10 cm soil layer of the mobile sand dune was 141 seeds/m² which only accounted for 13.5% of that the desertified land closed for 15 years; (3) the seed density, ratio of topsoil seeds to the total seeds, species diversity and similarity coefficient between standing vegetation and the soil seed bank showed an increase first and then a reduction. The longer the interval between the reversion stages, the little the similarity coefficient among the seed banks was; (4) the similarity between the desertified land and native vegetation habitat in the soil seed bank showed an increasing trend, while the similarity coefficient between the desertified land closed for 25 years and the native vegetation habitat was only 0.36. So the reversion process of desertification in the middle reaches of the Shiyang River was a changing process from the desertified land soil seed bank toward the native vegetation habitat with a very slow process. The results could enrich the theories of soil seed bank and support the ecological restoration practices of desertified land in arid inland river basins.