Plant, soil and faunal responses to a contrived pH gradient

Purpose To build a more holistic understanding of soil pH change we assessed the synchronised effects of a contrived soil pH change on soil chemistry, vegetation growth and nutrition, and soil faunal abundance and diversity. Methods We established a fifteen year old field experiment with a contrived pH gradient (pH 4.3 to 6.3) and measured the effect on soil chemistry, plant biomass and elemental composition and the impact of these changes on soil fauna (earthworms, nematodes, rotifers and tardigrades) and biological indices (based on ecological group structures of earthworms and nematodes). A single 20 × 20 × 20 cm soil block was excavated from each sample site to directly attribute biotic parameters in the block to the abiotic (soil) conditions. Results Acidification affected the extractable concentrations of Al, Ca, Mn and P and the C:N ratio of the soil and caused a reduction in plant Ca (r s for pH vs Ca = 0.804 p < 0.01), an increase in plant Mn (r s = −0.450 p = 0.019), along with significant decrease in root:shoot ratio (r s = 0.638, p < 0.01). There was a significant positive correlation between pH and earthworm index (r s = 0.606, p < 0.01), and a negative correlation between pH and nematode index (r s = −0.515, p < 0.01). Conclusion Soil pH influenced the mobility of Ca, Al, Mn and P, which in turn has impacted on plant tissue chemistry and plant biomass ratios. Linked changes in soil chemistry and vegetation had a corresponding effect on the abundance and diversity of nematodes and earthworms in the soil blocks.