藏北高寒草甸植物群落对土壤线虫群落功能结构的影响

Abstract

2011年5-11月,对西藏北部高寒草甸3种典型植物群落下0-30cm范围内不同深度土层的土壤线虫群落进行调查,采用浅盆法分离线虫,土壤性质指标,如pH、含水量、电导率分别采用电位法、烘干法、电导率仪法进行测定,应用营养类群组成、c-p类群结构及营养结构特征指数,以及营养类群、c-p类群与土壤性质之间的关系等特征值分析高寒环境下土壤线虫群落的功能结构特征,以了解高寒环境下植被对土壤线虫群落功能结构的影响。调查共分离得到33038条土壤线虫,隶属于2纲6目51科93属;线虫个体密度平均为847条/100g干土;表聚性明显。研究结果表明,高寒草甸不同植物群落的土壤线虫群落营养类群组成及分布特征均存在一定差异,植食性线虫和食细菌性线虫是调查区域的主要营养类群,不同植物群落间植食性线虫和杂食/捕食性线虫的相对多度差异明显。c-p类群组成结构特征结果表明:3种植物群落的土壤线虫cp2类群均为优势类群,生活策略以r-对策为主;高山嵩草植物群落土壤中的线虫食物资源在3种植物群落中最丰富;藏北嵩草群落土壤线虫数量低的可能原因是线虫食物资源的减少限制了cp1、cp2类群的增殖。<em>PPI</em>值表明:委陵菜群落受扰动的影响程度大于其余两种植被类型,而<em>MI、PPI/MI</em>值及cp5类群数量的结果则表明:委陵菜群落的稳定性较高,受到的干扰在3种植物群落中最少。<em>F/B</em>及<em>NCR</em>值均说明了3种植物群落的土壤有机质分解均主要依靠细菌分解途径。相关性分析结果表明:杂食/捕食性线虫在枯草期明显受到土壤含水量的影响;食真菌性线虫与土壤pH之间的关系密切,在盛长期则明显受到土壤电导率的影响;食细菌性线虫仅在返青期与pH有相关性。不同植物群落下土壤线虫群落功能结构特征的分异显示出线虫指示环境因子影响土壤生态系统的潜力。;Northern Tibet lies within the remote regions of the Tibetan Plateau, features a dry and cold climate, and forms a broad strip of land sensitive to global warming. Meadows are the largest and most important ecosystems in northern Tibet. Alpine meadows are extensively distributed in the northern Tibetan Plateau and are typical features of the region. The alpine meadow soil type in the study area is seasonally frozen. We chose three representative plant communities as samples areas, which we identified as <em>Potentilla</em> spp., <em>Kobresia pygmaea</em>, and <em>Kobresia littledalei</em> based on the dominant species of each community to study soil nematode communities. The plots are situated at Dejixiangdaga village at N31°31'38″-31°32'02″, E92°04'03″-92°04'16″ in Naqu County in the Naqu region of the Tibet Autonomous Region, China. Soil nematode communities in the upper 0-30 cm soil were investigated in three typical plant communities in alpine meadows of northern Tibet from May to November 2011. The soil nematodes were collected using the shallow basin method. The following soil chemical properties were tested: pH, potentiometry, soil water content (oven drying method), and electricity conductivity. The trophic composition, c-p group structure and functional structure index, as well as the characteristic values between trophic groups, c-p groups and soil properties, were analyzed to understand the effect of cold alpine conditions on soil nematode functional diversity. A total of 33038 nematodes, which were classified to nematode phylum, 2 classes, 6 orders, 51 families and 93 genera, were collected during the surveys. Average individual density was 847 nematodes per 100g dry soil. The results were mostly within the scope of previous reports, and nematodes obviously appeared to aggregate in the upper soil layers. The research indicated soil nematode tropic composition varied from one plant community to another in alpine meadows. Herbivorous and bacterivorous nematodes were the major nematode communities in the area. The relative abundance of herbivorous to omnivorous and/or predatory nematodes obviously varied in different plant communities. An analysis of the constitution of the c-p groups showed all cp2 groups were the predominant groups in all three plant communities, and all c-p groups were mainly <em>r</em>-strategists. <em>Kobresia pygmaea</em> was the most common food source for nematodes. <em>Kobresia littledalei</em> had the lowest nematode density, possibly because limited food availability limits the reproduction of cp1 and cp2 nematodes. The result of analysis of the plant parasite index indicated the <em>Potentilla</em> community was easier for nematodes to populate when compared to the other two vegetation types, whereas the data from the maturity index (<em>MI</em>), <em>PPI/MI</em> and cp5 demonstrated nematode stability in <em>Potentilla</em> was highest among three vegetation types. The fungal to bacterial feeder ratio and Nematode Channel Ratio showed bacterial decomposition was the major decomposition pathway in the soil organic substance decomposition system. Correlation of nutritional groups and environmental factors showed omnivorous/predatory nematodes were affected significantly by water content during dry periods, while a close relationship was found between soil pH and fungivorous nematodes, which was obviously affected by electrical conductivity (<em>EC</em>) during periods of rapid growth. The abundance of bacterivorous nematodes was only correlated to pH during the dry season. The presence of different plant communities leads to effects on water content, soil formation and the distribution of nutrients. The analysis related to water content, pH and <em>EC</em> reveals plant communities have important influences on the functional structure of nematode communities. Differences in nematode community structure in different meadows preliminarily indicate the potential for using nematodes as environmental indicator species.