Long-term acidification of pH neutral grasslands affects soil biodiversity, fertility and function in a heathland restoration

In the wider context of heathland restoration, we investigated how field scale experimental acidification with sulphur (sulfur)affected soil biodiversity, fertility and function over a period of 17 years. A field experiment was conducted in the Isle of Purbeck, England, using ferrous sulphate and elemental sulphur as acidifying agents. We tested the effects of acidification on soil fertility, plant communities, litter decomposition, microbiology (including fungi bacteria and actinomycetes), arbuscular and ericoid mycorrhizal colonisation, and soil fauna (including earthworms, nematodes, rotifers and tardigrades). We found that elemental sulphur had a considerable and persistent effect on soil pH, lowering it to levels found in the surrounding reference acid grassland and heathland sites. A newly adapted heathland restoration index based on soil chemistry, found that elemental sulphur was by far the most successful treatment leading to soil conditions similar to the heathlands. Overall, acidification caused a loss of base cations and an increase in toxic aluminium compounds. Consequently the more mesotrophic components of soil biology were reduced by acidification during the course of the experiment. This transformed the soil biological system into one typical of acid grasslands and heathlands. Concomitant litter decomposition was similarly inhibited by acidification, with the microbiota more strongly hindered in acidified soil than the macroscopic fauna. Acidification resulted in a reduction in nematode and rotifer abundance and earthworm biomass. The vegetation community was also strongly modified by the elemental sulphur treatments and, where grazing was restricted, soil acidification allowed a restored heathland community to endure. Arbuscular mycorrhizal colonisation of grasses was reduced where heather plants were established, while ericoid mycorrhizas had developed sufficient populations in the acidified pastures to match the colonisation rate in the native heathlands