青海海北植物群落类型与土壤线虫群落相互关系

土壤线虫是良好的指示生物, 是植物群落演替的重要驱动力, 其生态功能影响着生态系统正常生态效应的发挥。该研究以海北矮生嵩草(Kobresia humilis)草甸、西藏嵩草(Kobresia tibetica)沼泽化草甸、暗褐薹草(Carex atrofusca)沼泽化草甸和金露梅(Potentilla fruticosa)灌丛4种不同植物群落类型的土壤线虫为研究对象, 研究不同植物群落类型下的土壤线虫群落组成、分布特征、物种多样性及其营养类群组成, 分析植物类群结构与土壤线虫群落之间的相关性。主要研究结果: (1)在4种植物群落土壤样本中共分离线虫3 800条, 分属于2纲5目15科30属, 线虫平均个体密度为每100 g干土580条, 随土壤深度增加而递减, 具有明显的表聚性。不同植物群落间的土壤线虫群落组成存在一定差异, 矮生嵩草草甸0-40 cm土壤线虫总数(1 811条·392.5 cm^-3)显著高于其他植物群落类型, 暗褐薹草沼泽化草甸的土壤线虫总数最少(324条·392.5 cm^-3)。4种植物群落下土壤线虫的优势属和营养类群组成存在差异, 这种差异在矮生嵩草草甸与暗褐薹草沼泽化草甸之间表现得尤为明显。 (2)不同植物群落下土壤线虫的多样性指数(H′)和均匀度指数(J′)均为金露梅灌丛最高, 暗褐薹草沼泽化草甸最低, 其两种植物群落间H′差异显著, 而优势度指数(λ)相反, 为暗褐薹草沼泽化草甸最高, 金露梅灌丛最低。表明金露梅灌丛土壤线虫群落多样性最高, 暗褐薹草沼泽化草甸土壤线虫群落多样性最低, 土壤线虫群落趋于单一化。4种植物群落土壤有机质的分解途径均以细菌通道为主。西藏嵩草沼泽化草甸的瓦斯乐斯卡指数(WI)显著高于矮生嵩草草甸, 表明从高寒沼泽化草甸过渡到高寒灌丛、高寒草甸, 土壤肥力不断降低, 沼泽化草甸有利于食微生物线虫的生长。暗褐薹草沼泽化草甸的植物寄生线虫指数(PPI)、成熟度指数(MI)均表现为最低, 表明其生态系统的成熟度较低, 这与暗褐薹草沼泽化草甸土壤含水量较高有关。不同植物群落下的富集指数(EI)、结构指数(SI)均为暗褐薹草沼泽化草甸最高, 由此可以看出暗褐薹草沼泽化草甸的食物网相对连通性较高, 食物链较长, 食物网的阻力相对较小。(3)主成分分析(PCA)结果显示4种植物群落最大贡献属不同。相关性分析表明: 食细菌性线虫数量与西藏嵩草沼泽化草甸有显著的正相关关系; 金露梅灌丛的植物多样性与线虫的H′、J′有显著的负相关关系, 与λ则有显著的正相关关系; WI与矮生嵩草草甸的植物多样性有显著的正相关关系, PPI与矮生嵩草草甸的物种多样性指数有显著的负相关关系。综上所述, 植物群落深刻地影响着土壤线虫群落的多样性。

Relationship between plant community types and soil nematode communities in Haibei,Qinghai, China

Aims Soil nematodes are good indicator organisms and considered to be one of the important driving forces for the succession of plant communities. Therefore, understanding the relationship between soil nematodes and aboveground communities is particularly important. Methods This study took the soil nematodes in four different types of alpine plant communities, Kobresia humilis meadow, Kobresia tibetica swamp meadow, Carex atrofusca swamp meadow, Potentilla fruticosa shrubland as the research objects in Haibei, Qinghai, China. Nematode community composition, distribution characteristics, species diversity and trophic group composition were studied for the different plant communities. Important findings (1) A total of 3 800 nematodes were extracted with 30 genus, 15 families, 5 orders and 2 phyla. The average individual density of the nematodes was 580 ind.·100 g^-1 dry soil. The number of nematodes decreased with the increase of soil depth. The majority of them were observed in the top soil layer. Different nematode communities vary dramatically among different plant communities. The total number of soil nematodes in K. humilis meadow (1 811 ind.·392.5 cm^-3) was significantly higher than ones from other plant community types. C. atrofusca swamp meadow (324 ind.·392.5 cm^-3) was the least. The composition of dominant genera and trophic groups of soil nematodes saw a significant difference in four plant communities, which is particularly obvious between K. humilis meadow and C. atrofusca swamp meadow. (2) The soil nematode Shannon index (H′) and evenness index (J′) are highest in the P. fruticosa shrubland, and lowest in the C. atrofusca swamp meadow. However, the dominance index (λ) showed opposite patterns. H′ and λ had significant differences between the two plant communities. Potentilla fruticosa shrubland soil nematode community has the highest diversity. Carex atrofusca swamp meadow soil nematode community was lower than those in the other plant meadows, and the nematode community tends to be simplified. The four plant communities rely on the bacterial decomposition pathways. Wasilewska index (WI) of C. atrofusca swamp meadow is the highest and K. humilis meadow is the lowest. It indicates that the state of soil fertility is constantly decreasing in transition from alpine swamp meadow to alpine shrub and alpine meadow. Swamp meadow is beneficial to the growth of microbial nematodes. Plant parasite index (PPI) and maturity index (MI) indexes were the lowest of C. atrofusca swamp meadow. It shows that the maturity of its ecosystem is low. This is related to the higher soil water content in the C. atrofusca swamp meadow. Enrichment index (EI) and structure index (SI) of different plant communities are both the highest in C. atrofusca swamp meadow. It can be seen that the food web of C. atrofusca swamp meadow is relatively connected, with less resistance, and a longer food chain. (3) Principal component analysis (PCA) shows that the four plant communities have different main contribution species. Correlation analysis showed that: bacterivorous nematodes number have a significant positive correlation with K. tibetica swamp meadow; P. fruticosa shrubland has a significant negative correlation with nematode H′, J′, and a significant positive correlation with λ; WI has a significant positive correlation with the plant diversity of K. humilis meadow, while PPI has a significant negative correlation. In summary, plant communities have a profound impact on the diversity of soil nematode communities.