Maintenance of biodiversity through mutualistic networks between arbuscular mycorrhizal fungi and plants: robustness against human disturbance and climate change

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Arbuscular mycorrhizal fungi (Glomeromycota) are the most prominent mycobionts in the tropics and crucial for providing minerals to the vast majority of plants including nearly all tree species in the nutrient poor environments. Thus, knowledge of the mutualistic plant-fungus associations is indispensable for understanding the biology and ecology of tropical ecosystems and give guidelines for monitoring and conservation efforts under global change expectations. In contrast to surveys on birds, mammals, soil arthropods or aquatic animals, arbuscular mycorrhizal fungal communities have been rarely studied in the tropics, and nothing is known from the high elevation Ecuadorian Páramos. The main reason for the widespread underestimation of the importance of mycobionts in ecological studies and the lack of a monitoring system is the technically difficult approach to the organisms. During recent years molecular methods were increasingly applied to identify the arbuscular mycorrhizal fungi (AMF) because morphological features proved as insufficient even with detailed description. Meanwhile, nested PCR, cloning and Sanger sequencing are well-established methods for identification of the fungi and a comprehensive data set of AMF sequences has been provided for the Andean tropical mountain forest based on these methods by the applicant. Application of ecological network theory revealed that all studied AMF-assemblages were significantly nested. According to network simulations, significant nestedness, the observation that rarely linked species preferentially link to subsets of highly linked species, indicates that richness of fungi and plants are promoted by the mutualistic interaction. AMF, therefore, not only improve nutrition of individual plants but also integrate and thus preserve locally rare plant species and fungi in a common network. Thus, monitoring the changes of AMF communities among plots along a large elevation gradient as present in the Ecuadorian Andeans will supply data that can be interpreted on a functional level with respect to climate changes. Similar analyses can be carried out for fire-destroyed sites, most common in Ecuador, in comparison to undisturbed sites. The sensitivity of AMF to site elevation and fire needs to be assessed. It is necessary to know if AMF can shift among the modules related to elevation and disturbance to evaluate in as much the mycobionts are resilient or sensitive to climate change or fire affection with consequences for plant establishment and growth. Thus, to install a monitoring system for AMF, further investigation together with the Ecuadorian partners including low and high elevation is necessary to estimate the sensitivity of AMF as indicator organisms for climate change and fire destructions.