The variation among species in their responses to cues in the soil environment has implications for community structure. Soil heterogeneity concentrates intraspecific interactions in small portions of the soil. Consequently, competition intensity increases leading to resource pre-emption by strong competitors, reducing overall diversity of the community. We investigated the effect of belowground competition on community structure by growing three communities in patchy and even soils. A complete community of seven species was compared to two reduced communities: one lacking Plantago lanceolata, which has strong competitive effects but low foraging precision, and one lacking Poa pratensis, which is a weak competitor with high foraging precision. Patchy soils consisted of a grid of 5cm square patches of 60:40, 75:25, and 90:10 sand:compost and even soils consisted of all 75:25 sand:compost. For each community, three or four individuals of each species were planted in semi-random locations. Aboveground and belowground community structure was measured.
Results/Conclusions
Above and belowground biomass was higher in patchy pots compared to even pots. The size variation of the shoots across all species was increased in patchy pots as compared to pots with even nutrient distribution, suggesting more intense competition in patchy pots. Aboveground diversity was higher in pots with a community arrangement containing both Plantago and Poa competitors. In the reduced communities lacking either Plantago or Poa, diversity decreased in patchy pots. This result is surprising as we expect to see diversity increase in communities lacking Plantago if competition by Plantago is important. If precision of Poa is important, then it is expected that communities lacking Poa would experience higher diversity in patchy pots. However, this is not the case as reduced communities experience reduced diversity, possibly suggesting other species’ competition and precision is driving community outcomes.