Pore-Scale Monitoring of the Effect of Microarchitecture on Fungal Growth in a Two-Dimensional Soil-Like Micromodel

Abstract

In spite of the very significant role that fungi are called to play in agricultural production and climate change over the next two decades, very little is known at this point about the parameters that control the spread of fungal hyphae in the pore space of soils. Monitoring of this process in 3 dimensions is not technically feasible at the moment. The use of transparent micromodels simulating the internal geometry of real soils affords an opportunity to approach the problem in 2 dimensions, provided it is confirmed that fungi would actually want to propagate in such artificial systems. In this context, the key objectives of the research described in this article are to ascertain, first, that the fungus Rhizoctonia solani can indeed grow in a micromodel of a sandy loam soil, and, second, to identify and analyze in detail the pattern by which it spreads in the tortuous pores of the micromodel. Experimental observations show that hyphae penetrate easily inside the micromodel, where they bend frequently to adapt to the confinement to which they are subjected, and branch at irregular intervals, unlike in current computer models of the growth of hyphae, which tend to describe them as series of straight tubular segments. A portion of the time, hyphae in the micromodels also exhibit thigmotropism, i.e., tend to follow solid surfaces closely. Sub-apical branching, which in unconfined situations seems to be controlled by the fungus, appears to be closely connected with the bending of the hyphae, resulting from their interactions with surfaces. These different observations not only indicate different directions to follow to modify current mesoscopic models of fungal growth, so they can apply to soils, but they also suggest a wealth of further experiments using the same set-up, involving for example competing fungal hyphae, or the coexistence of fungi and bacteria in the same pore space.

Transparent soil microcosms for live-cell imaging and non-destructive stable isotope probing of soil microorganisms

“…Moreover, M. fragilis hyphae grown in TS show less variation in width and a more tortuous growth habit (as defined by deviation from straight lines of growth) than M. fragilis hyphae are grown without TS ( Figure 5C ). This suggests a possible influence of narrow pore space and touch stimuli offered by particles on fungal branching and morphology ( Soufan et al, 2018 ).…”

Fungal foraging behaviour and hyphal space exploration in micro-structured Soil Chips

“…The unique abilities of these systems to confine single cells and manipulate minute concentrations of liquids [27] make them ideal for simulating the microscale heterogeneity of soil systems [28]. Microfluidic chips have proven useful to study fungal hyphae [29][30][31], and can be applied to address a wide range of questions in soil ecology [32].…”

Bypass and hyperbole in soil research: Worrisome practices critically reviewed through examples

“…Similarly, for various reasons, and in particular the need in some experiments to use replicate soil columns, a number of authors have found it convenient to isolate uniformly sized aggregates from soils, and to repack them in a reproducible manner, prior to experiments to study a wide range of processes occurring within interaggregate pores (e.g., Juyal et al, 2019; Pot et al, 2015). As long as the repacked soil materials are not confused with the original soils, one could again consider that no real harm is done, as is the case also to some extent when one works with soil‐like micromodels (e.g., Soufan et al, 2018). Given the opportunity, it would always make more sense to work directly with undisturbed soil samples, in spite of their inherent heterogeneity, but as more reproducible alternatives, one has to acknowledge that repacked columns may occasionally be useful.…”