一个年龄序列巨桉人工林植物和土壤生物多样性

Abstract

为了全面、系统研究和评价退耕后桉树人工林生物多样性,采用立地条件控制及空间代替时间法,对四川丹棱县退耕营造的巨桉 (<em>Eucalyptus grands</em>) 人工林 (1-10a) 植物和土壤生物多样性进行了同步研究。结果显示,植物和土壤动物的物种数、密度和多样性指数及土壤微生物数量呈相似变化趋势,即轮伐期前同步(4a左右)降低,此后随林龄显著增加。CCA分析显示,植物生活型随林龄由藤本植物、地面芽和1年生植物向多年生草本高位芽和高位芽植物过渡。土壤微生物以细菌占据数量优势;土壤动物以腐食性功能团占据优势,杂食性次之。腐食性功能团1-7a降低而后升高,杂食性呈S型升高趋势;植食性和捕食性功能团百分比较低随林龄显著降低。土壤动物优势类群中线虫纲个体百分比随林龄显著降低,蜱螨目百分比和A/C值(蜱螨目/弹尾目数量比)呈S型上升趋势。各林龄巨桉林地植物多样性均显著高于对照农耕地;除1, 2a及4-7a样地植物多样性显著低于对照马尾松林,其余均与其无显著差异。土壤生物多样性,轮伐期前巨桉林地与对照农耕地差异不显著,此后则显著高于农耕地;各林龄样地土壤生物多样性均显著低于对照马尾松林。植物和土壤生物多样性指标显著相关,且相关系数随土壤层次加深而降低。;Issues around the loss of diversity caused by fast-growing tree plantations such as <em>Eucalyptus</em> have aroused controversy for many years. It is generally believed that <em>Eucaluptus </em>plantations bring about a decrease of plant's biodiversity by influencing resource competitions, allelopathy, or the level of soil fertility. Above and below-ground of forest ecosystems interact implicitly. Complex interactions between above-belowground biodiversity may provide important feedbacks regulating ecosystem. However, seldom information was available on the soil organism's diversity in <em>Eucalyptus</em> plantations. Furthermore, most of the previous studies were being conducted in the short-term rotation <em>Eucalyptus </em>plantations with a certain plantation age, which might limit our understanding of the actual plantation ecosystem process. Therefore, the abundance and diversity of plants and soil biodiversity were simultaneously measured across a range of eucalypt plantation ages (1-10 years) in southwest China to determine how <em>Eucalyptus grandis</em> afforestation of agricultural lands affected the native biodiversity. The present results showed that afforestation of <em>E. grandis</em> caused changes in plant and soil biodiversity with soil depth and was dependent on the stand age. The species richness, abundance and the diversity of understory plants and soil organisms showed a parallel development during the process of the succession, viz. both of them increased significantly with time but with a‘dip' around 4 years old. CCA analysis showed that the plant's life forms transited from liana, hemicryptophytes and therophytes into perennial herbaceous-phanerophytes and phanerophytes. Bacteria quantitatively dominated the soil microbe in <em>E. grandis </em>regardless of plantation age. The individual proportion of saprozoic group quantitatively dominated in the soils of the all the study sites, followed by omnivorous group. The proportion of saprozoic groups decreased in 1-7 year old stands and then increased significantly with time. The proportion of omnivorous group increased as S shape with the plantation age. The proportion of predators and phytophage groups decreased significantly with time. The individual percentage of nematode decreased with the plantation age, but that of acarina and the number ratio of the acarina and collembola present the S shape increasing trend over time. The multiple comparisons test showed that plant diversity of the understory vegetation in 1, 2 and 4-7 years-old plantations were significantly lower than that in the control forests (<em>Pinus massoniana</em>). Plant diversity in 1-10 year-old <em>E. grandis</em> plantations were significantly higher than that of the control arable land. Soil biodiversity in the plantations before the rotation period has no significant differences compared with agricultural lands, but were significantly higher in the plantations on or after the rotation period than the crop land. There were significant correlations between the plant' s and soil organism's diversity index and the correlation coefficient decreased with soil depth.