DOI: 10.5061/dryad.8gg5mk2
title: Data from: Soil microbial communities alter conspecific and congeneric competition consistent with patterns of field coexistence in three Trifolium congeners

description: 1. Coexistence and diversity in plant communities depend upon outcomes of
 plant competition. Competition and coexistence can be mediated by abiotic
 soil nutrient differences as well as by soil microbial communities. The
 latter effects occur through various mechanisms including negative
 plant-soil feedbacks, when plants foster the build-up of specialized
 pathogenic microbes, which ultimately reduce conspecific, but not
 heterospecific, densities. Microbial mutualists can have generalized
 associations with host plants, and by associating with multiple species
 might affect coexistence by conferring different levels of benefit to
 hosts. 2. We examined the effects of abiotic differences and soil
 microbial communities, including mutualistic nitrogen-fixing rhizobial
 bacteria, on coexistence processes and asked whether these interactions
 inform patterns of co-occurrence in natural communities. We measured
 plant-soil feedbacks in the greenhouse for three native Trifolium species
 that either highly co-occurred or were spatially repulsed at our field
 site. Using size-fractioned soil microbial inocula prepared from
 field-collected soils, we explored the effect of soil microbes on
 nodulation and the outcome of competition (RII). We also examined the
 effects of soil origin (home versus away soil) on the outcome of
 competition between species. 3. Soil microbes had strong positive effects
 on plant growth and nodulation. Microbes in general reduced the strength
 of plant competition relative to competition in sterilized soil and
 altered the relative strength of interactions with conspecific vs.
 congeneric neighbours, which often occurred in ways predicted to enhance
 coexistence. In one pair of highly co-occurring Trifolium, competition was
 strong in sterilized soils, but these species facilitated one other in
 presence of the full microbial community. Outcomes of competition in live
 soil treatments, though quite different from those in sterilized soil,
 best agreed with the observed field co-occurrence patterns of our three
 Trifolium species. The net effect of these microbes in general reduced
 competition while also increasing performance over that in sterilized
 soil, suggesting a role for soil microbial mutualists in coexistence. 4.
 Synthesis. Our results demonstrate that interactions between plants and
 diverse soil communities can alter plant-plant interactions and plant soil
 feedback. Both can generate frequency-dependence that enables coexistence
 of congeneric species in natural communities.
description: field_cooccurrence_dataField Co-occurrence Data for 3 Trifolium speciesgreenhouse_competition_soil_extract_experimentPlant biomass and nodulation data in a greenhouse experiment manipulating competition and soil extracts.fuc_mdn_nodC_field2015OTU counts of nodC genotypes measured on nodules from experimental plants in the field.clean_nodC_field2015_OTU_seqsOTU sequences of nodC genotypes measured on nodules from experimental plants in the field.soil_chemistrySoil chemistry data in relation to the distribution of our three Trifolium species.