Scheu S, Falca M
Institut für Zoologie, Technische Universität Darmstadt, Schnittspahnstraße 3, D-64287 Darmstadt, Germany e-mail
Institutul de Biologia, Academia Romana, Splaiul Independentei 296, 79651 Bucuresti, Romania, , , , , , RO.
Oecologia. 2000 May;123(2):285-296. doi: 10.1007/s004420051015.
The structure of the soil food web in two beech (Fagus sylvatica) forests, the Göttinger Wald and the Solling forest (Northern Germany), was investigated using variations in tissue N concentrations of animal species or taxa. The Göttinger Wald is located on a limestone plateau and characterized by mull humus with high macrofauna activity, particularly of Lumbricidae, Diplopoda and Isopoda. In contrast, the Solling forest is located on a sandstone mountain range and characterized by moder humus. The soil fauna of this forest is dominated by mesofauna, particularly by Collembola, Enchytraeidae and Oribatida. In June 1995 soil fauna was sampled using heat extraction. Three soil layers were analysed at each of the sites. N/N ratios of bulk material increased strongly with soil depth in both forests. This also applied to the water-soluble fraction at the Göttinger Wald, but not at the Solling. Generally, the water-soluble fraction was more enriched in N than the bulk materials. For most animals studied N/N ratios varied little with soil depth. In both forests soil animals could be classified either as saprophages, including microphytophages, or predators. On average, the δN of predatory taxa (Chilopoda, Araneida, Gamasina, Staphylinidae) exceeded that of saprophagous or microphytophagous taxa (Lumbricidae, Isopoda, Diplopoda, Collembola, Oribatida, Enchytraeidae) by 4.4 and 3.9‰ for the Göttinger Wald and the Solling, respectively. We assume that most of the saprophagous or microphytophagous taxa studied consist of primary and secondary decomposers and hypothesize that predators prey more on secondary than primary decomposers. Generally, average δN values differed little between saprophagous (Lumbricidae, Diplopoda, Isopoda) and microphytophagous taxa (Collembola, Oribatida). The variations in δN values of species within these taxa consistently exceeded the variation between them, indicating that the species of each of these taxa form a continuum from primary to secondary decomposers. Also, variations in δN values within predatory taxa in most cases exceeded that between taxa excluding top predators like Sorex. We conclude that using higher taxonomic units in soil food web analysis is problematic and in general not consistent with nature. Higher taxonomic units may only be useful for depicting very general trophic groupings such as predators or microbi-detritivores.
利用动物物种或类群组织中氮浓度的变化，对德国北部的哥廷根森林（Göttinger Wald）和索林根森林（Solling forest）这两片山毛榉（Fagus sylvatica）林的土壤食物网结构进行了研究。哥廷根森林位于石灰岩高原上，其特征是有大量土壤动物活动的腐殖质，特别是蚯蚓、倍足纲动物和等足目动物。相比之下，索林根森林位于砂岩山脉上，其特征是半腐殖质。这片森林的土壤动物以小型土壤动物为主，特别是弹尾目、线蚓科和甲螨目。1995年6月，采用热萃取法对土壤动物进行采样。在每个地点分析了三个土壤层。在这两片森林中，土壤总体物质的氮/氮比均随土壤深度显著增加。哥廷根森林的水溶性部分也是如此，但索林根森林并非如此。一般来说，水溶性部分的氮含量比总体物质更高。对于大多数所研究的动物，氮/氮比随土壤深度变化不大。在这两片森林中，土壤动物可分为腐食性动物（包括微植食性动物）或捕食性动物。平均而言，在哥廷根森林和索林根森林中，捕食性类群（唇足纲、蜘蛛纲、革螨亚目昆虫、隐翅虫科）的δN值分别比腐食性或微植食性类群（蚯蚓、等足目动物、倍足纲动物、弹尾目、甲螨目、线蚓科）高出4.4‰和3.9‰。我们假设，所研究的大多数腐食性或微植食性类群由初级和次级分解者组成，并推测捕食性动物捕食次级分解者的数量多于初级分解者。一般来说，腐食性类群（蚯蚓、倍足纲动物、等足目动物）和微植食性类群（弹尾目、甲螨目）之间的平均δN值差异不大。这些类群中物种的δN值变化始终超过它们之间的差异，表明这些类群中的每个物种都形成了一个从初级分解者到次级分解者的连续体。此外，在大多数情况下，捕食性类群内的δN值变化超过了不包括鼩鼱等顶级捕食者的类群之间δN值的变化。我们得出结论，在土壤食物网分析中使用较高的分类单元存在问题，总体上与自然情况不一致。较高的分类单元可能仅有助于描绘非常一般的营养类群，如捕食者或微生物碎屑食性动物。
