# Micro-Landscape Dependent Changes in Arbuscular Mycorrhizal Fungal Community Structure
## 1 Introduction  
Arbuscular mycorrhizal (AM) associations form direct nutritional symboises between the roots of most terrestrial plants and a monophyletic group of soil-borne fungi belonging to the phylum Glomeromycota [1]. AM associations have attracted a lot of attention because they can promote net primary productivity (NPP) and agricultural production [2, 3]. NPP gains can partially determine how AM fungal communities in plant roots are structured [4, 5, 6]. As a result, a lot of the literature addresses practices that likely select for more beneficial communities of Glomeromycota in plant roots (e.g., [7, 8]) and environmental parameters and practices that determine AM fungal community structure (e.g., [7, 9, 10]). An alternative way to ask this question is via questioning how AM fungal diversity varies in space and time (i.e., which entails addressing the fraction of variance which is often classified in models as \"unexplained\"; [11, 12]). Our general understanding so far is that AM fungal assemblages in the roots are non-random. This has been shown both in relation to null-model analyses [13, 14], which assess the degree to which chance exclusively could have generated the observed community table (i.e., the occurrences of AM fungal species across root samples) of the study, and models exploring species-abundance distributions [15, 16], which essentially test whether particular groups of species have been more abundant than expected by chance. Many studies observing preferential establishment of AMF taxa in specific habitats also hint towards this direction (e.g., [9, 17]). Specific biotic and abiotic parameters of the habitat (besides exerting selectivity to specific AM fungal taxa), however, might also alter ourability to predict (i.e., modify the predictability of) mycorrhizal community structure in nature, but this point remains underexplored. Two syntheses which addressed this question found that anthropogenic disturbances, environmental heterogeneity and a plant host identity (i.e., being a monocotyledon) render AM fungal communities less predictable (i.e., more divergent) than they would have been expected to be by chance alone [18,19]. More recently, [PERSON] et al. [20] assayed AM fungal communities in the field to determine the degree to which AM fungal communities diverge with spatial distance but also when sampling from the root systems of the same or from a different plant-host individual. [PERSON] et al. [20] observed small differences in AMF community turnover between adjacent neighbouring plants (as compared to sampling from the same individual) but also that AMF community turnover increased for plant individuals further away from each other. A particular feature of AM fungi is that they are obligate symbionts, meaning that they cannot fulfil their life cycle in the absence of a suitable host. This limits their ability to colonize soil in some environments because their vegetative growth ceases at distances of about 50 cm from the closest colonized root [21]. There is a large body of literature addressing how dispersal constraints modify the community structure of organisms addressing variable types of landscape which can also occur at a micro level such as in soil in which case we can refer to them as micro-landscapes or meta-communities. There is a consensus that meta-communities simultaneously reduce local (\(\alpha\)-) diversity and increase global (\(\gamma\)-) diversity because they make local community structure less predictable (e.g., [22]) which potentially allows persistence of less competitive species [23]. This point remains underexplored in relation to AM-associations [24]. Here we present a synthesis from three controlled studies with an overall aim to address how spatial structure in plant mesocosms alters predictability in AM fungal communities.