锡林郭勒退化草原不同禁牧恢复演替阶段土壤种子库比较

Soil seed banks in different grazing exclusion restoring succession stages in the Xiligole degraded steppe

以冷蒿(Artemisia frigida)+糙隐子草(Cleistogenes squarrosa)退化草原经过长期围栏禁牧恢复演替(23a和10a)群落为研究对象,并对比围栏外退化的冷蒿+糙隐子草草原,揭示锡林郭勒退化草原长期围栏禁牧后的土壤种子库特征。随着群落的恢复演替,土壤总种子库物种组成和密度均增加,但持久性土壤种子库占土壤总种子库的比例下降。代表土壤总种子库的4月份取样,围栏禁牧23a、10a和围栏外退化样地土壤种子库密度平均值分别为4433、4756粒.m-2和856粒.m-2,在0.001水平上差异显著,基本代表持久土壤种子库(persistent soil seed bank)的6月底取样,3个样地土壤种子库密度在0.05水平上差异显著;多数植物土壤种子库主要分布在0～3cm层,各样地种子库密度随土壤深度的增加而减少;围栏禁牧23a、10a和围栏外重度退化样地的持久土壤种子库密度分别为土壤总种子库的52.6%、47.4%和90.9%,;各样地一年生植物,构成了草原土壤种子库密度的主要组成部分。结果表明,对于严重退化的冷蒿+糙隐子草群落,只要在恢复起点仍有零星分布的羊草和大针茅植株,经过长期围栏禁牧可恢复其土壤种子库物种组成和种子库规模。

The soil seed bank is important for vegetation regeneration and natural succession, and it may change as a result of management, for example in response to varying grazing pressure. However, almost nothing is known about the on the soil seed banks in the restored steppe, and steppe degraded by grazing in Inner Mongolia. Here, we aimed to： （1） investigate the composition and soil seed density in three vertical layers in restored steppe after long-term exclusion （ 10 and 23 years） of grazing, and compare this with steppe degraded by grazing; （2） examine and compare the total and persistent soil seed bank in restored steppe versus degraded grazing steppe ; （3） relate the similarity of seed bank composition with that of the standing vegetation. In August 2004, we investigated the community of three sites in Xilingole： （ 1 ） two areas of previously degraded steppe where grazing had been excluded for either 10 or 23 years, and （2） a degraded steppe where grazing had been continued. The species present in the vegetation was assessed using five 1 m 1 m quadrats distributed randomly in each area. In spring 2005, in the same sites, fifteen soil cores （ 15 cm × 15 cm ×3 cm） were collected from three depth layers （0 -3 cm, 3 -6 cm and 6 -9 cm） for each three treatments. The composition and density of the soil seed bank was evaluated by monitoring seedling emergence. The similarity of soil seed bank and the standing vegetation was assessed using the Sorensen index. Heavy grazing can cause the lack of soil seed reserves, and long term-grazing exclusion can restore the composition and density of soil seed banks steppe. In April 2005, the total soil seed banks （0 - 9 cm depth ） after 10 and 23 years enclosure had 4756 and 4433 seeds＇m^-2 respectively but only 856 seeds＇m^-2 for the degraded steppe. In June results were lower but showed the same pattern （i. e. 2255, 2333 and 778 s seeds＇m^-2）. The difference in results between April and June can be considered as the spring germinable seeds. The persistent soil seed banks of the 10, 23 years enclosed steppe, and degraded steppe were 53% ,47% and 91% of the total soil seed bank. Most soil seeds were found in the top 0-6 cm, and there was a decrease with depth. Annuals constituted a major component of the steppe soil seed bank, and most seeds were classified as transient members of the transient soil seed bank, such as annual Chenopodium album and perennial Allium tenuissimum. The Sorensen similarity index of seed bank composition and standing vegetation was 0.49 - 0.54.