This meta-analysis finds that biodiversity across groups, especially between bacteria and fungi, contributes more to soil aggregation than species from just one group acting alone. For example, fungi specialize in binding macroaggregates, while bacteria can also bind microaggregates, and earthworms can “grind and remould ingested particles into new aggregates” [Lehmann 2017: 1]. There were no such effects from within-group biodiversity, however.
Soil biota potentially contribute to soil aggregation in a number of ways. For example, bacteria can exude biopolymers that act as binding agents for aggregates on the micrometre scale, fungal hyphae can entangle particles to hold them together (on the micrometre to millimetre scale) and geophagous animals, such as earthworms, grind and remould ingested particles into new aggregates and create biopores (on the millimetre to centimetre scale). Due to these various contributions of soil biota to soil aggregation, there is also a clear potential for complementarity among soil aggregation mechanisms, as has been shown in isolated studies [Lehmann 2017: 1].
These findings support the hypothesis that there is functional complementarity contributing to soil aggregation, and the results highlight that this functional complementarity mainly resides at the level of the HTC [Higher Taxonomic Category] . The presence of pronounced organismal interaction effects highlights the opportunity to use soil biota mixtures tailored for enhancing soil aggregation (for example, inoculation for use in restoration). This result also emphasizes the need to manage for overall high levels of soil biodiversity, especially across HTCs, in agroecosystems, which would facilitate the development of such interactions [Lehmann 2017: 4].
Lehmann, Annika, Weishuang Zheng & Matthias C. Rillig, 2017, Soil biota contributions to soil aggregation, Nature Ecology and Evolution, https://www.nature.com/articles/s41559-017-0344-y.