厚荚相思和尾叶桉人工林土壤线虫群落研究

Soil nematode community in Acacia crassicapa and Eucalyptus urophylla plantations

相思树和桉树等树种因其生长迅速、耐性好以及适合制作纸浆等特点,近年来在华南地区大面积种植,带来了巨大的经济利益,但是相思树和桉树如何影响林下土壤生物多样性和土壤肥力还不清楚,科学评价其林下土壤健康水平十分必要。土壤线虫的种类和数量十分丰富,在土壤食物网各营养级中占据重要位置,对土壤环境变化反应敏感,作为土壤健康的指示生物被广泛应用。本文以幼龄厚荚相思Acacia crassicapa和尾叶桉Eucalyptus urophylla人工林为研究对象,于干季和湿季分别对2个林分根区和非根区土壤线虫进行研究,探讨土壤线虫这种指示生物的数量、各营养类群比例和多样性的变化规律,以及它们和环境因子的关系。主要结果表明:(1)厚荚相思土壤线虫总数为每公斤干土6 741条,显著高于尾叶桉线虫总数的28.3%。厚荚相思人工林土壤食细菌线虫的百分比相比尾叶桉人工林高6.3%,且差异显著。(2)土壤线虫的群落组成变化具有明显的季节波动,湿季土壤食细菌线虫比例上升,而植物寄生线虫的比例下降,多样性指数由干季的0.87减小到0.75,统计差异均达到了显著水平。(3)根区比非根区显著提高了线虫数量的89.1%,这是由根区积累更多的有机碳和总氮引起的。总之,厚荚相思人工林为土壤自由生活线虫提供了优良环境,且在幼龄期没有表现出土壤酸化,生态效应优于尾叶桉人工林,在华南地区人工林营林过程中可适当增加厚荚相思林分面积。

Wide areas of Acacia crassicapa and Eucalyptus urophylla were planted in South China recently due to their rapid growth, strong tolerance and suitability for paper pulp. However, it is still not clear how these two tree species impact soil biodiversity and fertility. It is necessary to evaluate their soil health condition scientifically. The number and variety of soil nematodes are abundant. Soil nematodes occupy the key positions in trophic levels of soil food web and are sensitive to environmental changes. As indicator of soil health, nematodes are used in ecology widely. In this study, soil nematodes were investigated in young Acacia crassicapa and Eucalyptus urophylla plantations with different seasons and sampling positions, to analyze the patterns of soil nematode individuals, community composition and diversity index, as well as relationships with environmental factors. The main results showed that：（1） Total nematode individuals in Acacia crassicapa plantation were 674.1/100 g dry soil, more 28.3%than Eucalyptus urophylla plantation significantly. Percentages of bacterivores in Acacia crassicapa plantation were more 6.3%than Eucalyptus urophylla significantly. （2） Community composition of soil nematodes varied with the season. The percentage of bacterivores increased, whereas the percentage of plant parasites decreased in wet season. Diversity index decreased from 0.87 in dry season to 0.75 in wet season. Statistic differences were all significant. （3） Nematode density in rhizosphere was more 89.1%than non-rhizosphere which attributed to accumulated organic carbon and nitrogen in rhizosphere. In conclusion, Acacia crassicapa plantation provide optimal environment for soil free living nematodes, whereas soil acidification do not happen in young forest period. For ecological effects of Acacia crassicapa plantation are superior to Eucalyptus urophylla, planting areas of Acacia crassicapa may be expanded in South China in future.