The importance of integration and scale in the arbuscular mycorrhizal symbiosis

The arbuscular mycorrhizal (AM) fungus contributes to system processes and functions at various hierarchical organizational levels, through their esta blishment of linkages and feedbacks between whole-plants and nutrient cycle s. Even though these fungal mediated feedbacks and linkages involve lower-o rganizational level processes (e.g. photo-assimilate partitioning, interfac ial assimilate uptake and transport mechanisms, intraradical versus extrara dical fungal growth), they influence higher-organizational scales that affe ct community and ecosystem behavior (e.g. whole-plant photosynthesis, biodi versity, nutrient and carbon cycling, soil structure). Hence, incorporating AM fungi into research directed at understanding many of the diverse envir onmental issues confronting society will require knowledge of how these fun gi respond to or initiate changes in vegetation dynamics, soil fertility or both. Within the last few years, the rapid advancement in the development of analytical tools has increased the resolution by which we are able to qu antify the mycorrhizal symbiosis. It is important that these tools are appl ied within a conceptual framework that is temporally and spatially relevant to fungus and host. Unfortunately, many of the studies being conducted on the mycorrhizal symbiosis at lower organizational scales are concerned with questions directed solely at understanding fungus or host without awarenes s of what the plant physiologist or ecologist needs for integrating the myc orrhizal association into larger organizational scales or process levels. W e show by using the flow of C from plant-to-fungus-to-soil, that through th oughtful integration, we have the ability to bridge different organizationa l scales. Thus, an essential need of mycorrhizal research is not only to be tter integrate the various disciplines of mycorrhizal research, but also to identify those relevant links and scales needing further investigation for understanding the larger-organizational level responses.