Factors Affecting Arbuscular Mycorrhizal Fungi Spore Density in the Chilean Mediterranean-Type Ecosystem

Arbuscular mycorrhizal fungi (AMF) are highly important for plant communities in dry or seasonally dry ecosystems, such as the South American Mediterranean-type ecosystem (MTE), considered a biodiversity hotspot. While AMF hold potential for sustainable MTE management and conservation, they have been under investigated on this ecosystem and little is known about AMF spore bank dynamics. In this study, we analyzed the effect of physico-chemical soil factors, phytobiont species, and seasonality on the AMF spore soil density in two sclerophyllous forests (Malloa and San Vicente). We sampled soil once per season during 1 year and beneath four representative tree species for each site. The results show a strong season effect at both sites, while physical-chemical parameters differed between sites. At Malloa, clay content and electrical conductivity were positively correlated with spore density, while available phosphorous showed a negative correlation. At San Vicente, clay content and total nitrogen were positively correlated with spore density, while soil organic matter showed a negative effect. Overall, spore number reached a minimum value in winter and higher values during the growing season at both sites. These results indicate a strong regulation of AMF spore density by seasonal climate, while physico-chemical soil properties exert a host-independent but site-specific effect in both forests.