Should we go the easy way? Realism in decomposition studies

Decomposition of organic matter is a critical function in streams and is important for their food webs. Because of this, organic matter decomposition is the subject of many studies. In this blog post, Verena Schreiner talks about a recently published paper in which decomposition was analysed using different substrates.


Studying the ecosystem function of organic matter decomposition can be done in a traditional and well-proven way – by using e.g., leaves or other organic matter from natural sources. This provides realistic results but also has several disadvantages. Collecting and quality sorting the necessary material can be very time-consuming and is not following a unified procedure. Furthermore, leaves or other natural materials differ in their composition depending on their sources. Even leaves from the same tree species but from different locations can vary in their composition, which results in differences in decomposition. To overcome this, artificial substrates have been developed to be used as standardised surrogates. But until today, it was not studied if these standardised substrates are decomposed similarly to leaves.

Experiment and Findings

We compared the microbial (only by fungi and bacteria) and total (microbial + macroinvertebrate) decomposition of leaves and two standardised substrates – cotton strips and decotabs (Figure 1) – across 70 streams in a Germany-wide monitoring study. We additionally identified the most influential environmental variables for each of the substrates.

Figure 1: The used substrates from left to right: Leaves, cotton strips, and decotabs.

The decomposition of leaves was barely related to that of the two standardised substrates (Figure 2). Only the two standardised substrates were moderately related. This is likely explained by the fact that both standardised substrates are mainly composed of cellulose, while leaves contain many different chemicals, including other macromolecules which can only be decomposed by specialised organisms. Different variables were identified as most influential for the different substrates. While the flow velocity and the arsenic concentration were most relevant for the microbial decomposition of leaves, the proportion of agriculture and fungicide toxicity were most relevant for cotton strips and decotabs respectively. A proxy for the pesticide impact on the macroinvertebrate community was most relevant for the total decomposition of leaves, while the total phosphorous concentration was most relevant for the total decomposition of decotabs.

Figure 2: Comparison of microbial decomposition of the three substrates. The decomposition of all substrates was normalized for deployment duration and temperature (degree day, dday) A: Decomposed mass of decotabs versus decomposed mass of leaves: B: Tension loss of cotton strips versus decomposed mass of leaves; C: Tension loss of cotton strips versus decomposed mass of decotabs. The decomposed mass of decotabs is displayed on a logarithmic scale.


This study shows that standardised substrates do not show the same decomposition patterns as leaves, which makes them unsuitable surrogates when studying natural decomposition and effects on whole food webs.

For further information about the project, “The lowland stream monitoring” (KgM, Kleingewässer-Monitoring) see our previous blog post: Pesticides threaten vulnerable invertebrates in streams

The paper was authored by Verena C. Schreiner, Liana Liebmann, Alexander Feckler, Matthias Liess, Moritz Link, AnkeSchneeweiss, Amélie Truchy, Wolf von Tümpling, Philipp Vormeier, Oliver Weisner, Ralf B. Schäfer, MircoBundschuh can be accessed free of charge in Environmental Toxicology and Chemistry.