*For correspondence:
Email: andrew.kulmatiski@usu.edu
Abstract
  1. Plant-soil feedback (PSF) has gained attention as a mechanism promoting plant growth and coexistence. However, most PSF research has measured monoculture growth in greenhouse conditions. Translating PSFs into effects on plant growth in field communities remains an important frontier for PSF research.
  2. Using a four-year, factorial field experiment in Jena, Germany, we measured the growth of nine grassland species on soils conditioned by each of the target species (i.e., PSF). Plant community models were parameterized with or without these PSF effects, and model predictions were compared to plant biomass production in new and existing diversity-productivity experiments.
  3. Plants created soils that changed subsequent plant biomass by 36%. However, because they were both positive and negative, the net PSF effect was 14% less growth on ‘home’ than ‘away’ soils (i.e., the average PSF value was -0.14). At the species level, seven of nine species realized non-neutral PSFs. At the species*soil type level, 31 of 72 PSFs differed from zero. The two dominant species grew only 2% less on home than away soils.
  4. In current and pre-existing diversity-productivity experiments, nine-species plant communities produced 37 to 29% more biomass than monocultures due primarily to selection effects. Null and PSF models predicted 29 to 28% more biomass for polycultures than monocultures, again due primarily to selection effects.
  5. Synthesis: In field conditions, PSFs were consistent and large enough to be expected to affect plant growth and coexistence. However, overyielding in plant communities was caused by selection effects so complementarity effects caused by PSF were not important in these communities. We identified several reasons that even large PSFs may not affect plant productivity. In general, we found that both large positive and large negative PSFs were associated with subdominant species. Because of this, we suggest there may be selective pressure for plants to create neutral PSF. Broadly, testing PSFs in plant communities in field conditions, highlighted new directions for understanding PSF effects in communities in the context of other species traits.
Keywords: aboveground-belowground interactions, biodiversity-ecosystem functioning, dominance, plant community model, plant identity, biomass