Coastal dunes are an ecogeomorphological system whereby biotic components feedback on abiotic system organization as ecosystem engineers and vice versa. Storms can devegetate microcosms among dunes, creating unvegetated bowls inherent among healthy and recently storm effected systems that buffer upland areas worldwide. Disturbances are felt most strongly in the foredune, the first dune mound and thus first line of defense during storms. Plant recolonization and establishment post-storm are likely controlled by biotic components of the intact successional gradient surrounding these areas, and could push the system to alternative stable states. We are studying the development of bowls created by Superstorm Sandy, October 2012, among a model barrier island coastal dune system, Island Beach State Park, NJ. Ammophila breviligulata (AB) and Carex kobomugi (CK) are the dominant pioneers. Ammophila is dependent on obligate arbuscular mycorrhizal fungi (AMF) and Carex is non-mycorrhizal such that alteration of substrate infectivity may favor certain species for recolonization. We collected a total of 114 spatially referenced random core samples among the foredune from a saucer bowl, AB and CK stands abutting bowl edges, and foredune faces at three sites each 500+m apart in May and December 2016. We used diluted core substrate to conduct mean inoculation potential (MIP) assays with a sorghum-sudan grass hybrid host. After 45 days, we stained 0.5g fresh host roots with trypan blue and used the grid-line intersect method to calculate root colonization as a proxy for soil infectivity.
Though high abiotic heterogeneity exists at various scales within dunes, we found no differences in biotic AMF infectivity among our sites. In bowls, we did not find differences in infectivity between the east and west side though AMF density and diversity has been shown to increase with growing habitat complexity. Similarly, bowl infectivity was not related to distance to the bowl edge, and thus vegetation, or distance to the center, where infectivity should be theoretically lowest. Among vegetation, Ammophila had greater infectivity than all other areas and both Carex, which appears facultative mycorrhizal, and Ammophila had greater infectivity than foredune face and bowl areas. We observed decreasing infectivity from the crest, suggesting decreasing AMF complexity within the sere compared to the general pattern of increasing complexity along the successional gradient. The mediating effects of these plant-soil feedbacks have direct implications for dune stability and morphology and thus indirect implications for the buffering of increasingly vulnerable upland areas to the effects of climate change.