Fungal Traits Important for Soil Aggregation

Abstract

Soil structure, the complex arrangement of soil into aggregates and pore spaces, is a key feature of soils and soil biota. Among them, filamentous saprobic fungi have welldocumented effects on soil aggregation. However, it is unclear what properties, or traits, determine the overall positive effect of fungi on soil aggregation. To achieve progress, it would be helpful to systematically investigate a broad suite of fungal species for their trait expression and the relation of these traits to soil aggregation. Here, we apply a trait-based approach to a set of 15 traits measured under standardized conditions on 31 fungal strains including Ascomycota, Basidiomycota, and Mucoromycota, all isolated from the same soil. We find large differences among these fungi in their ability to aggregate soil, including neutral to positive effects, and we document large differences in trait expression among strains. We identify biomass density, i.e., the density with which a mycelium grows (positive effects), leucine aminopeptidase activity (negative effects) and phylogeny as important factors explaining differences in soil aggregate formation (SAF) among fungal strains; importantly, growth rate was not among the important traits. Our results point to a typical suite of traits characterizing fungi that are good soil aggregators, and our findings illustrate the power of employing a trait-based approach to unravel biological mechanisms underpinning soil aggregation. Such an approach could now be extended also to other soil biota groups. In an applied context of restoration and agriculture, such trait information can inform management, for example to prioritize practices that favor the expression of more desirable fungal traits.

Protists and collembolans alter microbial community composition, C dynamics and soil aggregation in simplified consumer–prey systems

“…For example, good aggregators were reported for species of the bacterial genera Bacillus and Pseudomonas (Caesar-TonThat et al, 2007, 2014 and of the fungal genera Chaetomium, Mucor and Aspergillus (Swaby, 1949). Enhanced aggregative ability was related to higher lipid and protein content in bacterial EPSs (Liu et al, 2013) and to higher density of mycelial growth (Lehmann et al, 2020). Such developments with a microbial focus bring us closer to understanding how the diversity of microbes drive biogeochemical cycles and soil aggregation, but they fail to connect how these processes are modified in the presence of higher trophic levels.…”

“…Bacteria influence soil aggregation mainly through the production of extracellular polymeric substances (EPSs), which adsorb onto mineral surfaces, increase the viscosity of the soil solution and enhance soil particle cohesion (Chenu, 1993;Sandhya and Ali, 2014;Liu et al, 2013). Filamentous fungi promote soil aggregation in various ways including (i) the enmeshment of soil particles (Degens et al, 1996;Tisdall et al, 1997;Baldock, 2002); (ii) the secretion of polymeric substances (Chenu, 1989;Caesar-TonThat and Cochran, 2000;Daynes et al, 2012), enhancing mineral particle cohesion similar to bacterial EPSs; and (iii) the release of a variety of molecules, such as hydrophobins (Linder et al, 2005;Zheng et al, 2016) and phenolic acids (Caesar-Tonthat and Cochran, 2000), reducing wettability and preventing soil aggregates from collapsing when the soil is rewetted. However, effects vary between microbial strains.…”

National Forest Inventories capture the multifunctionality of managed forests in Germany

“…Higher species richness of soil fungal communities has been associated with higher functional diversity (Courty et al 2010;Clemmensen et al 2013) and therefore healthier forests, as fungi have different roles in decomposition (van der Wal et al 2013), water and nutrient uptake (Courty et al 2010;Pena et al 2013;Pena and Polle 2014), enzyme production (Buee et al 2007;Pritsch and Garbaye 2011), and soil health (Lehmann et al 2019). We sampled the whole fungal community following the above-mentioned description of the joint soil-campaign campaign.…”

Ecological mechanisms underlying aridity thresholds in global drylands

“…Besides, the species-specific role of plantmycorrhizal symbioses connects tightly the plant and mycorrhizal communities, so shifting plant communities usually involve shifts in mycorrhiza and, thus, the whole nutrient economy mechanisms (Bahram et al 2020). As a final note, poor nutrient soils show less stable aggregates associated with certain mycorrhizal groups (Lehmann et al 2020) and are more sensitive to erosion (Xiaojun et al 2013) connecting biogeochemical mechanisms with the erosive pathway and closing the cycle among the three pathways described for the soil disruption phase. Although, as evidenced here, the biogeochemical pathway is of strategic concern for studying thresholds, their role as a feedback 3.C The biogeochemical pathway mechanism producing abrupt shifts is poorly understood.…”