Intraspecific interactions in the annual legume Medicago minima are shaped by both genetic variation for competitive ability and reduced competition among kin

Documenting if plants exhibit kin competition avoidance in intraspecific plant interactions is relevant both to improve crop growth, and to understand diversity and composition in natural plant communities. However, a number of confounding mechanisms complicates detecting kin competition avoidance from experiments comparing plants growing with kin and non-kin neighbors. We conducted complementary greenhouse experiments using genotypes from four populations of the annual Medicago minima, which in a previous study showed higher survival when interacting with kin relative to non-kin. We show that genotypes vary in kin competition avoidance, and in competitive ability, but find no indication of complementary resource use. Importantly, from our first experiment of root growth behavior, we know that some genotypes exhibit kin competition avoidance. Yet, the variation in competitive ability we find in our second experiment, where plants grow in mini communities together with either kin or unrelated genotypes, can alone explain the variation we observe in growth and biomass among communities. In our case, the genotypes with highest competitive ability were also those that showed kin competition avoidance. This confounding effect obscured the disentangling of mechanisms underlying difference in growth between kin and non-kin interactions. When silencing root exudates by adding activated carbon to a subset of our genotype combinations, we found increased size asymmetry of plants grown together, and mostly in kin communities. This suggests that plants recognize the identity of neighbors via root exudates, and compete less with neighbors recognized as kin. To detect kin competition avoidance we suggest designing experiments that pair unrelated genotypes with similar competitive abilities. Such design, combined with silencing root exudates would be powerful to detect whether plants show kin competition avoidance or not. (C) 2021 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.

Automated summary

Plant genotypes show variation in kin competition avoidance and competitive ability, with some genotypes exhibiting avoidance of kin competition. However, there is no evidence of complementary resource use among genotypes. The study suggests that designing experiments pairing unrelated genotypes with similar competitive abilities, combined with silencing root exudates, can help detect whether plants exhibit kin competition avoidance.