Soil biota effects on soil structure: Interactions between arbuscular mycorrhizal fungal mycelium and collembola

Soil aggregation is an important ecosystem process mediated by soil organisms. Collembola and arbuscular mycorrhizal (AM) fungi are major soil biota representing different functional groups, and are known as two key promoters of soil aggregation. Although several studies have experimentally demonstrated that AM fungi and, more recently, collembola affect soil structure, there is no study investigating how both soil organisms affect soil aggregation excluding the influence of plant roots, another important driver of soil aggregation. Considering the importance of AM fungi and collembola in terrestrial ecosystems, here we asked if both organisms have any influence on soil aggregation when roots are not present. In order to examine this question we conducted a completely factorial greenhouse study manipulating the presence of both collembola and AM fungi and excluded the roots of Plantago lanceolata using a 38 mu m nylon screen compartment. We quantified soil aggregation as water stable soil aggregates in four size classes in the hyphal compartment and monitored a number of other explanatory variables, including AM (and non-AM) fungal soil hyphal length. The soil in the hyphal compartment showed greater soil aggregation with larger mean weight diameter when collembola were present, and a similar result was found in the presence of AM fungi, compared to control treatments. Moreover, combined presence of both AM fungi and collembola resulted in a non-additive increase of soil aggregation. Our study clearly indicated that collembola can enhance soil aggregation, that they can partially complement effects of AM fungi, and that these effects are independent of roots. (C) 2012 Elsevier Ltd. All rights reserved.