荒漠草原“土岛”生境群落物种共存机制

经过长期破碎化, 荒漠草原原生硬质灰钙土斑块散布在广大沙化土地中, 形成类似“土岛”的土被结构。为揭示土岛生境的群落物种共存机制, 2016年在宁夏盐池县皖记沟村选取大(200-300 m²)、中(约100 m²)、小(约50 m²)土岛各3个开展调查, 采用Jaccard相异系数、物种生态位宽度和生态位重叠度、零模型、Meta分析, 综合计算和分析土岛内部与外部植物群落相似性、物种生态位宽度和生态位重叠、物种共存格局及其影响因子。研究发现, (1)随着破碎化加剧, 土岛内部植物多样性整体呈现下降趋势, 群落优势种从短花针茅(Stipa breviflora)转变为猪毛蒿(Artemisia scoparia)和短花针茅共优种, 土岛内外群落相似性增加。(2)土岛内外绝大多数物种生态位重叠较小, 生态位重叠在土岛内呈集中分布, 而土岛外则呈均匀发散分布。(3)环境过滤为主的生态过程决定了土岛生境群落物种的共存格局, 随着土岛面积减小, 环境因子对群落物种共存的调控强度降低, 关键性环境因子由土壤细砂粒和黏粒转变为粗砂粒, 显著性竞争物种共存格局在小岛出现。综上所述, 土岛生境对于维持草原物种具有重要作用, 环境过滤主导了荒漠草原物种共存格局。随着生境破碎化加剧或土岛面积减小, 物种共存格局及其调控因子发生转变。保护面积在200 m²以上的大土岛对于恢复荒漠草原区草原成分种和其物种多样性机制都十分必要。

Co-existence mechanisms of plant species within “soil islands” habitat of desert steppe

Extensive fragmentation has led to the original desert steppe soils of hard sierozem to become isolated in the desertified lands, forming the so-called “soil islands”. We aimed to reveal the effect of fragmentation on the co-existence of plant species within “soil islands” habitat. To this end, we characterized the plant communities on three large (200-300 m²), medium (about 100 m²) and small (about 50 m²) soil islands each, in the Wanjigou Village of Yanchi County in Ningxia Hui Autonomous Region of China. We analyzed the similarity of plant community within and outside those soil islands, the breadth and overlap of plant ecological niche, the species co-existence pattern and its influencing factors using Jaccard similarity coefficient, niche overlapping degree formula, null model analysis, and meta-analysis. Our results showed that: (1) with increased fragmentation, plant diversity within the soil island decreased, and the dominant plant species changed from Stipa breviflora to a combination of Artemisia scoparia and S. breviflora, and the plant communities within soil islands became more similar to communities outside; (2) most species showed relatively small ecological niche overlap between within and outside soil islands, with the overlap showing concentrated distribution within soil islands but scattered distribution outside the islands; (3) environmental filtering was the main driver of species co-existence patterns. As soil islands became larger, the effect of environmental factors on species co-existence decreased, and the key environmental factor that explained species composition changed from clay and fine sand to coarse sand. Notably, a competition was a key driver of co-existence patterns within small “soil islands”. In summary, “soil islands” provide an important habitat for representative plant species in the desert steppe and environmental factors influenced species co-existence patterns. Both processes were disrupted by fragmentation. Maintaining soil islands larger than 200 m² would be critical for restoring representative plant species and preserving plant diversity of the desert steppe ecosystems.