Plant community responses to alterations in soil abiotic and biotic conditions are decoupled for above- and below-ground traits

Plant functional traits are increasingly recognised as being impacted by soil abiotic and biotic factors. Yet, the question to what extent the coupling between community-level above- and below-ground traits is affected by soil conditions remains open. In a field experiment in dune grassland, we quantified the responses of both community-level leaf and root traits to changes in soil abiotic and biotic conditions using soil inoculation by living and sterile soil inocula originated from different dune ecosystems. Altered soil conditions resulted in a strong decoupling in responses of community-level leaf and root traits. Changes in soil abiotic conditions imposed by soil inoculation were more important in determining the decoupling of the leaf vs root relationships than additions of soil biota. Altered soil abiotic factors influenced both leaf and root traits at the community level and caused the entire community-level trait spectrum to shift, while experimental additions of living soil inocula only significantly influenced root traits towards longer and thinner roots. Synthesis. Our results bring direct evidence that, at a plant community level, the dynamics of plant above-ground traits are not informative of below-ground traits. Particularly, below-ground abiotic processes are a major driver of commonly observed trait spectra. We suggest that future study is required to test the general pattern of leaf and root correlations across different ecosystems under field conditions.