The diversity and abundance of plant root-associated fungi is determined by both the biotic and abiotic environment. However, the relative importance of these drivers to fungal communities and, to what extent these drivers are context-specific, remains under-explored. We quantified plant root-associated fungal communities from six UK salt marshes across two distinct geographic regions (Essex and Lancashire) during Winter and Summer seasons, using extremely high resolution DNA metabarcoding (ca. 77 million sequences). Models on fungal richness and abundance showed that abiotic variables were generally better predictors than biotic variables but the ability of these variables to describe fungal richness and abundance varied considerably between sites and scales. Moreover, models of fungal richness in relation to environmental variables generalised poorly between sites, providing evidence that general environment-diversity relationships may not exist in fungal communities. Finally, we found that functionally similar fungi tended to respond similarly to environmental variables, and that the responses of different fungal functional groups varied markedly. This suggests that whilst fungal communities may exhibit a high degree of functional redundancy, they may not be resilient to environmental change. Our results show that both geographic location and functional group are important contextual aspects of fungal community ecology.