Context dependency of effect of fungal connections between plants and biocrusts

Conceptual context: Species interactions may couple the resource dynamics of different primary producers and may enhance productivity by reducing loss from the system. In low-resource systems, this biotic control may be especially important for maintaining productivity. In drylands, the activities of vascular plants and biological soil crusts can be decoupled in space because biocrusts grow on the soil surface but plant roots are underground, and decoupled in time due to biocrusts activating with smaller precipitation events than plants. Soil fungi are hypothesized to functionally couple the plants and biocrusts by transporting nutrients. We studied whether disrupting fungi between biocrusts and plants reduces nitrogen transfer and retention and decreases primary production as predicted by the fungal loop hypothesis. Additionally, we compared varying precipitation regimes that can drive different timing and depth of biological activities. Methodological approach: We used field mesocosms in which the potential for fungal connections between biocrusts and roots remained intact or were impeded by mesh. We imposed a precipitation regime of small, frequent or large, infrequent rain events. We used 15N to track fungal-mediated nitrogen (N) transfer. We quantified microbial carbon use efficiency and plant and biocrust production and N content.