Optimized assay and storage conditions for enzyme activity profiling of ectomycorrhizae

The aim of a joint effort by different research teams was to provide an improved procedure for enzyme activity profiling of field-sampled ectomycorrhizae, including recommendations on the best conditions and maximum duration for storage of ectomycorrhizal samples. A more simplified and efficient protocol compared to formerly published procedures was achieved by using manufactured 96-filter plates in combination with a vacuum manifold and by optimizing incubation times. Major improvements were achieved by performing the series of eight enzyme assays with a single series of root samples instead of two series, reducing the time needed for sample preparation, minimizing error-prone steps such as pipetting and morphotyping, and facilitating subsequent DNA analyses due to the reduced sequencing effort. The best preservation of samples proved to be storage in soil at 4-6 °C in the form of undisturbed soil cores containing roots. Enzyme activities were maintained for up to 4 weeks under these conditions. Short-term storage of washed roots and ectomycorrhizal tips overnight in water did not cause substantial changes in enzyme activity profiles. No optimal means for longer-term storage by freezing at -20 °C or storage in 100% ethanol were recommended.