桉-桤不同混合比例凋落物分解过程中 土壤动物群落动态

采用凋落物分解袋法研究了10:0(TⅠ)、7:3(TⅡ)5:5(TⅢ)、3:7(TⅣ)和0:10(TV)巨桉(Eucalyptus grandis)和台湾桤木(Alnus formosana)混合凋落物分解过程中的土壤动物群落特征.从5种类型、3种规格的810只凋落袋中共收集土壤动物75651只,隶属2门10纲20目,其中弹尾目(Collembola)和蜱螨目(Acarina)为优势类群.土壤动物个体数最高是7-8月,大型土壤动物个体数最高是7月,中小型土壤动物个体数最高是7-8月.大型、中小型土壤动物类群数各月间均波动较小.与30目和6目相比,260目网袋中弹尾目和蜱螨目等中小型土壤动物数量更高.相对台湾桤木(TV)而言,巨桉(TⅠ)凋落物中弹尾目数量更多.啮虫目(Psocoptera)在台湾桤木(TV)凋落物中的数量远远高于其它凋落物,后孔寡毛目(Opisthopora)在混合凋落物中数量较高.不同比例的凋落物混合可改变凋落物中土壤动物的数量和组成.桤木、混合凋落物中大型土壤动物的个体数高于巨桉凋落物,而且上述凋落物的分解速率亦明显快于巨桉凋落物,这意味着大型土壤动物的活动可加速凋落物的分解.因此,在巨桉人工纯林中混栽台湾桤木,可显著提高大型土壤动物的数量,促进凋落物的分解.

Dynamics on soil faunal community during the decomposition of mixed eucalypt and alder litters

Eucalypt (Eucalyptus grandis) is widely used to develop the short-term rotation industrial plantation in south China due to the characteristics of fast growth, higher yield, higher cellulose content, and straight trunk. However, extensive eucalypt pure plantation gives rise to a series of ecological problems such as native biodiversity loss, soil fertility decline, "green desert", and plant disease outbreak. In order to avoid or lower the ecological and economic risks of pure plantation, therefore, forest managers and researchers begin to plant the mixture of eucalypt tree with native trees. Alder (Alnus formosana) is a nitrogen-fixing tree species, which can increase soil fertility and accelerate the decay of lower-quality litter and nutrient cycling, implying that the alder may become the accompanying tree species in the eucalypt plantation. Meanwhile, soil faunal community plays important roles in maintaining soil fertility, decomposing plant residues and other soil processes. In order to evaluate the effect of mixed eucalypt and alder plantation on soil ecological process in the hilly region of Southwestern Sichuan, therefore, 10-g litters with the ratios of eucalypt to alder 10:0 (TI), 7:3 (TII), 5:5 (TIII), 3:7 (TIV) and 0:10 (TV) were kept in nylon bags with the sizes of 260-mesh, 30-mesh and 6-mesh, and were placed on the forest floor in the plantations with different ratios of eucalypt and alder trees, respectively. Consequently, the structure and composition of soil faunal community during the decomposition of mixed eucalypt and alder litters were investigated from May 2009 to April 2010. Soil macrofauna in litters was picked up by hand in the fields. Mesofauna and microfauna were collected and separated from the soil samples by Tullgren methods. 75651 specimens, which belong to 2 phyla, 10 classes and 20 orders, were found in five mixed leaf litters and three sizes of litterbags. Acarina and Collembola were the dominant groups, accounting for 97.24% of the total. The litters had the maximum peak of soil faunal quantity from July to August. Similarly, the maximum peak of soil macrofaunal quantity was observed in July, and that of meso- and micro-fauna in July and August, respectively. No obvious difference on the faunal groups was found among months. More meso- and microfaunal individuals existed in 260-mesh litterbags than in 30-mesh and 6-mesh litterbags. Eucalypt litter had higher amount of Collembola in comparison with the alder litter. TV litter had more Psocoptera compared with the others. Mixed litter had more Opisthopora. The structure of soil faunal community in litters varied with the mixed ratios of eucalypt to alder litters. These results implied that the soil macrofauna prefers to live in the alder litter and mixed litters rather than the eucalypt litter, and accelerates the rate of leaf litter breakdown. Therefore, alder litter and mixed litters had higher decomposition rates compared with the eucalypt litter. These results demonstrated that the alder was an accompanying tree species in the eucalypt plantation, and alder trees planted in the pure eucalypt plantation will be of benefit to accelerating the decay of eucalypt leaf litters and to maintaining the soil fertility. The results provide with scientific basis for reasonable mixed eucalypt plantation.