Data from: Plant species richness promotes soil carbon and nitrogen stocks in grasslands without legumes

1. The storage of carbon (C) and nitrogen (N) in soil are important
ecosystem functions. Grassland biodiversity experiments have shown a
positive effect of plant diversity on soil C and N storage. However, these
experiments all included legumes, which constitute an important N input
through N2-fixation. Indeed, the results of these experiments suggest that
N2-fixation by legumes is a major driver of soil C and N storage. 2. We
studied whether plant diversity affects soil C and N storage in the
absence of legumes. In an 11-years grassland biodiversity experiment
without legumes, we measured soil C and N stocks. We further determined
above-ground biomass productivity, standing root biomass, soil organic
matter decomposition and N mineralization rates to understand the
mechanisms underlying the change in soil C and N stocks in relation to
plant diversity and their feedbacks to plant productivity. 3. We found
that soil C and N stocks increased by 18 and 16% in eight-species mixtures
compared to the average of monocultures of the same species, respectively.
Increased soil C and N stocks were mainly driven by increased C input and
N retention, resulting from enhanced plant productivity, which surpassed
enhanced C loss from decomposition. Importantly, higher soil C and N
stocks were associated with enhanced soil N mineralization rates, which
can explain the strengthening of the positive diversity-productivity
relationship observed in the last years of the experiment. 4. Synthesis:
We demonstrated that also in the absence of legumes plant species richness
promotes soil carbon (C) and nitrogen (N) stocks via increased plant
productivity. In turn, enhanced soil C and N stocks showed a positive
feedback to plant productivity via enhanced N mineralization, which could
further accelerate soil C and N storage in the long term.