围栏封育对不同退化高寒草地土壤种子库及地上植物群落的影响

Effects of fence enclosure on soil seed bank and aboveground plant communities in alpine grasslands with different degradation levels

关键词:  围栏, 高寒草甸, 高寒草原, 土壤种子库, 地上植物群落, 物种多样性, 物种相似性

Key words:  fence, alpine meadow, alpine steppe, soil seed bank, aboveground plant community, species diversity, species similarity

摘要:

围栏封育是青藏高原退化草地的主要恢复措施之一,其对轻度或中度退化草地恢复效果显著,但对沙化草地恢复效果有限,其原因尚不清楚。该研究以西藏那曲地区轻度退化和沙化(沙坑)高寒草甸和高寒草原为研究对象,系统分析了围栏内外不同退化程度草地的土壤种子库特征及其与地上植被的关系,重点探讨了围栏对沙化草地恢复效果不佳是否与土壤种子库中目标植物缺乏相关的科学假设。结果表明:(1)高寒草甸和高寒草原土壤种子库密度分别在184～2 162 seeds·m^-2和74～812 seeds·m^-2之间,其中高寒草甸沙化草地土壤种子库密度显著高于轻度退化草地,高寒草原则相反; 围栏显著提高了两种草地类型轻度退化草地土壤种子库密度,但对沙化草地无显著影响; 围栏内外土壤种子库物种相似性较高,表明土壤种子库间物种组成差异小。(2)总体上不同草地类型和退化程度以及围栏对土壤种子库物种多样性无显著影响。(3)无论围栏内外,尽管高寒草甸和高寒草原沙化草地土壤种子库中均含有利于恢复的目标植物的种子,但是其密度远低于杂类草植物种子密度。(4)高寒草甸和高寒草原的土壤种子库与地上植物群落物种组成相似性系数分别在0.33～0.43和0.22～0.33之间,均属低相似性,物种组成差异大。因此,该研究结果证实土壤种子库在沙化草地恢复过程中起重要作用,而目标植物种子库的缺乏是制约沙化草地自然恢复的关键因素之一,建议结合补播目标植物种子等人工干预措施来促进沙化草地的生态恢复。

Abstract:

Fence enclosure is one of the primary restoration measures for degraded grasslands on the Qinghai-Xizang Plateau, demonstrating significant effectiveness in restoring lightly or moderately degraded grasslands but limited success in desertified grasslands, the reasons for which remain unclear. This study focused on lightly degraded and desertified(sand patches)alpine meadows and alpine steppes in Nagqu, Xizang, systematically analyzing the characteristics of soil seed banks and their relationship with aboveground vegetation in grasslands of different degradation levels inside and outside fence. The study specifically investigated the scientific hypothesis that the poor restoration effect of fence on desertified grasslands is related to the lack of target plant species in the soil seed bank. The results were as follows:(1)The soil seed bank densities of alpine meadow and alpine steppe ranged from 184 to 2 162 seeds·m^-2 and 74 to 812 seeds·m^-2, respectively. Notably, in alpine meadow, the soil seed bank density of desertified grassland was significantly higher than that of lightly degraded grassland, while the opposite was observed in alpine steppe. Fence significantly increased the soil seed bank density of lightly degraded grasslands in both grassland types but had no significant effect on desertified grasslands. The high species similarity between inside and outside fences of the soil seed bank suggested minimal differences in species composition.(2)Overall, grassland type, degradation level, and fence had no significant impact on soil seed bank species diversity.(3)Regardless of fence, although the soil seed banks of alpine meadow and desertified alpine steppe contained seeds of target plants beneficial for restoration, but their densities were far lower than those of weed species.(4)The similarity coefficients between soil seed banks and species composition of aboveground plant communities ranged from 0.33 to 0.43 in alpine meadow and 0.22 to 0.33 in alpine steppe, both indicating low similarity and substantial differences in species composition. Therefore, this study confirms the critical role of the soil seed bank in the restoration of desertified grasslands, with the scarcity of target plant seeds being a key limiting factor for natural restoration of desertified grasslands. It is recommended that artificial interventions, such as reseeding target plant species, be implemented to enhance the ecological restoration of desertified grasslands.