Protist diversity on a nature reserve in NW England − with particular reference to their role in soil biogenic silicon pools

•Considering only a few groups of microorganisms greatly increases the known diversity of a nature reserve.•This microbial diversity is important in many ecological processes.•Diatoms and some testate amoebae create hotspots of Si in the soil.•Testate amoebae are particularly important in mor humus soils.•Quantifying microbial population sizes provides data that can be used to start to estimate their functional role in the soil.