Measuring enzymatic activity to integrate biological, chemical, and physical soil health indicators – a case study in a dry coniferous forest

The quantification of soil health is typically split up in the measurement of physical, chemical, and biological indicators. Such a disciplinary approach requires a manifold of different methods that are often time consuming and are difficult to be integrated into a concise description of soil health status. A possible candidate for a comprehensive description is the extracellular enzymatic activity of the soil. The enzymatic activity as biological indicator plays a pivotal role in the physico-chemical cycles of carbon, nitrogen, phosphorus, and sulfur. In addition, it characterizes the degradation of organic matter and structure formation that controls physical processes like aeration and rainfall partitioning (infiltration and runoff). To represent various functions of enzymes and biogeochemical processes, we measured the activity of five enzymes using SEAR (Soil Enzymatic Activity Reader). SEAR determines the extracellular enzymatic activity using a fluorescent substrate. We applied this method to measure the enzymatic activity in a forest in a dry region of Switzerland that suffers from reduced rainfall amounts, resulting in hydrophobic conditions that affect rainfall partitioning and the soil water balance. Preliminary results for a pine stand show a slight decrease of the activity of enzymes that are responsible for carbon decomposition and nitrogen mineralization during the dry summer period, indicating that the soil functions are disturbed during the dry period. We will compare these findings with results from a spruce stand and discuss the soil functions and soil health status during drought periods.