Considerations in the storage of soil samples for enzyme activity analysis

The most accurate means of assessing soil enzyme activity involves analyzing fresh soil samples very recently taken from the field. Because of the extensive handling times involved, however, such an approach is frequently impossible when moderate to large numbers of soil samples are involved. Therefore, soil samples are frequently stored, either frozen or dried, prior to analysis. Unfortunately, depending on soil type and enzyme, both freezing and drying may significantly alter enzyme activity. In many cases such a storage effect is tolerable as long as the relationships among “treatments” remain unaltered as a consequence of storage. In this study we used two soils (previously determined to possess significantly different enzyme activities) as proxies for experimental treatments, and calculated the ratio of one soil's activity to that of the other for fresh, frozen and dried samples to determine whether soil storage influenced the relationship between the soils. The enzymes included 1,4-β-cellobiohydrolase (CBase), acid phosphatase (Pase), and β-N-acetylglucosaminidase (NAGase). The ratio of activity of the two soils was significantly affected by freezing and drying when compared to the fresh control for all three enzymes, but the ratio generally changed much less as a consequence of freezing than as a consequence of drying. Each investigator should consider whether soil storage affects within-experiment treatment comparisons of soil enzyme activity.

► Storage of soil may alter its enzyme activities.
► Storage effects may be tolerable if relationships among “treatments” are unaltered.
► We used two soils as proxies for treatments and calculated their ratio of activity.
► The ratio changed less as a consequence of freezing than drying.
► Change of treatment relationships by storage must be considered by researchers.