Abstract
California’s riparian forests are important ecosystems that support a large array of species and are among the most productive of natural systems in the state. However, years of deforestation, agriculture, and livestock grazing have resulted in the loss or degradation of these forests. Consequently, natural resource agencies in California have invested considerable resources into the conservation and restoration of these systems. Arbuscular mycorrhizal (AM) fungi, which form symbiotic relationships with plant roots, may be important to the early development and structuring of restored riparian forests, and thus to the overall success of restoration efforts. AM fungi serve many ecosystem functions, including nutrient acquisition for their plant hosts, soil stabilization, and facilitation of seedling establishment. However, there is little research examining how ecological restoration impacts AM fungal diversity and community structure. This study tested the following hypotheses: 1) diversity of AM fungi decreases following restoration; 2) the frequency of pioneer species in the AM fungal community will increase following restoration; and 3) the frequency of AM fungal species present in commercial inoculum species will be higher in blocks treated with inoculum compared to untreated sites. To tests these hypotheses, AM fungal diversity was compared before and after restoration by DNA sequencing. This study was conducted at the restoration of Cordova Creek in Rancho Cordova, CA. Four 50-meter-wide blocks extending from the creek into the adjacent wetland and riparian plant communities were inoculated with Glomus intraradices propagules and paired with four unamended blocks. Thirty-two soil samples were collected before and after restoration. AM species present in the soil were identified by PCR with AM fungal-specific primers followed by cloning and sequencing. There was a high level of diversity prior to restoration, and though diversity decreased following restoration, it was only significant at the genus-level and was not consistent across the entire site. Different inoculum treatments and plant communities harbored different fungal communities from each other. Due to the high heterogeneity of the fungal community prior to restoration, these communities did not differ significantly from the pre-restoration community and there was no increase in the relative frequency of pioneer species following restoration. The inoculum could not be genetically distinguished from the native species, but plots inoculated with mycorrhizal propagules were not dominated by either the introduced or associated native species. The question of whether to use inoculum or not in restoration is one that needs to be considered by project managers. These results suggest that while restoration influences the diversity and community composition of AM fungi, when there is a relatively high fungal diversity prior to restoration, that it can persist on the through restoration.