Intraspecific variation in mycorrhizal response is much larger than ecological literature suggests

Katherine N. Stahlhut and Jonathan T. Bauer, Department of Biology, Miami University, Oxford, OH, Megan A. Conway and Chase M. Mason, Department of Biology, University of Central Florida, Orlando, FL

Background/Question/Methods
Mycorrhizal response is the most common metric for characterizing how much benefit a plant derives from arbuscular mycorrhizal (AM) symbiosis. Traditionally, ecologists have used these metrics to generalize response in plant species, ignoring the potential for plant intraspecific variation to alter the outcome of the mutualism. Recent genomic work has identified many unique genes within a species that regulate this symbiosis, which suggests that accounting for intraspecific variation in mycorrhizal response could be more important than previously believed. In order for mean trait values to be useful as a functional trait to describe a species, as has been attempted for mycorrhizal response traits, interspecific variation must be much larger than intraspecific variation, but while interspecific variation has been extensively studied with respect to mycorrhizal response traits, intraspecific variation has rarely been examined. To address this gap in knowledge, we conducted a systematic review and analyzed how much intraspecific variation for mycorrhizal growth and nutrient response typically exists within a plant species.
Results/Conclusions
We assessed 17 publications that included 29 individual studies testing mycorrhizal response in at least five genotypes of a plant species, and we found that variation in mycorrhizal response was generally very large and highly variable depending on study design. The degree of variation ranged from 0.1 to 3.5, representing a 10% to 350% range in the change in biomass when inoculated with AM fungi in a given plant species, and 21 of the studies included genotypes that had positive and negative responses. Mycorrhizal phosphorus response was measured in 11 studies. The degree of variation for the effects on phosphorus content was 0.2 to 5.1, representing a 20% to 510% range in the change of phosphorus content. We also determined that mycorrhizal growth response is further confounded by plant genotype-fungal isolate interactions. Our analysis highlights the lack of research that has been done on the scale of intraspecific variation of mycorrhizal responses in plant species, indicating that researchers should be wary about generalizing mycorrhizal response traits across a plant species.