沙坡头地区生物结皮覆盖区土壤种子库组成及垂直分布特征

采用野外随机取样和室内萌发试验相结合的方法,对沙坡头人工植被区的藓类结皮、地衣结皮和裸沙覆盖区土壤种子库的组成及垂直分布特征进行了研究。结果表明:1)人工植被区土壤种子库的物种组成简单,以1年生草本为主,相较于裸沙,两种生物结皮的存在显著增加了土壤种子库的密度(P0.01),但降低了土壤种子库的物种多样性及其与地上植被的相似性;2)两种生物结皮覆盖区土壤种子库的总密度虽无显著差异,但在0—2 cm土层中,地衣结皮土壤种子库的密度显著高于藓类结皮(P0.05),而在2—5 cm和5—10 cm土层中,藓类结皮土壤种子库的密度高于地衣结皮,但差异不显著;3)不同生物结皮覆盖区土壤种子库的垂直分布特征存在差异,藓类结皮覆盖土壤中有活力的种子主要分布在0—5 cm土层中,而地衣结皮和裸沙覆盖土壤中有活力的种子主要分布在0—2 cm土层中,且随着深度的增加,土壤中有活力的种子急剧减少。该研究表明,相较于裸沙,生物结皮的存在不仅增加了土壤种子库的大小,还改变了土壤种子库的垂直分布格局。生物结皮层下仍有相当比例有活力的小种子,这些种子欠缺萌发条件,对地上植被的贡献作用较小,但它们的存在对荒漠生态系统健康及可持续发展具有重要意义。

The composition and vertical distribution characteristics of soil seed banks in soil coverage with biocrusts in the Shapotou Region

Using random sampling in the field and observing the emergence of seedlings, we studied the structure, the density and vertical distribution of soil seed banks in moss crusts, lichen crusts, and bare sands in the artificially re-vegetated region of Shapotou. We found that the soil seed banks of this region were mainly composed of annual herbs and had a simple species composition and a significantly higher seed density in soil covered by biocrusts than in bare sands (P < 0.01). However, the existence of biocrusts decreased the species diversity of soil seed banks and the similarity of soil seed banks with corresponding ground vegetation. Furthermore, although the total density of soil seed was not significantly different between the two types of crusts, there were differences in the distribution within the different soil layers. Specifically, the soil seed density in the 0-2 cm soil layer of lichen crusts was significantly higher than in the corresponding layer in moss crusts (P < 0.05), while that of moss crusts was higher in the 2-5 cm and 5-10 cm soil layers. Finally, the effects of biocrusts on vertical distribution of soil seed banks varied with biocrust types. For example, germinative seeds were primarily distributed in the 0-5 cm soil layer for moss crusts and in the 0-2 cm soil layer for lichen crusts and bare sands, and their abundance decreased with soil depths. These results suggest that biocrusts increase the soil seed bank density, but also change the vertical distribution pattern of soil seed banks in artificially re-vegetated regions. A substantial proportion of small seeds are present in soil covered by biocrusts, and these seeds lack germination potential and contribute little to the above-ground vegetation. However, they play a significant role in ecosystem stability and the sustainable development of deserts.