How feedback loops between meso- and macrofauna and organic residues contrasting in chemical quality determine decomposition dynamics in soils

The concept of feedback loops between changes in chemical quality of decomposing organic residues and changes in faunal communities was employed in studying how such feedback loops, representing distinct ecological successional stages, determine decomposition dynamics in soils. A 52-week litterbag decomposition study was superimposed onto an 18-year long term field experiment. Four types of organic residues contrasting in chemical quality (i.e., nitrogen (N), lignin, polyphenols, cellulose) were incorporated into soil annually to assess decomposition and associated meso-and macrofauna communities. In the first 4 weeks after residue incorporation (loop #1), the abundances (densities) of both mesofauna and macrofauna were positively influ-enced by labile cellulose and N. The mesofauna Collembola and Acari contributed 70-100% and 0-30% to the decomposition, respectively, while the macrofauna beetles and flies contributed 20-90% and 10-66%, respectively. The abundances were highest under groundnut (high N, low lignin) ([1.35 and 0.85 individual number (g dry litter)-1] for mesofauna and macrofauna, respectively). The presence of macrofauna at week 2 led to a mass loss (R2 = 0.67**), indicating that macrofauna preceded mesofauna in degrading residue. In week 8 (transition of loop #2 to #3), only macrofauna (beetles dominated contributing 65%) played an important role in lignin decomposition (R2 = 0.56**), resulting in a mass loss (R2 = 0.52**). In week 52 (loop #4) macrofauna, ants (Formicidae) replaced beetles as the dominant decomposers showing a feedback reaction to availability of protected cellulose. The Formicidans contributed 94% to the decom-position and influenced losses of mass (R2 = 0.36*) and N (R2 = 0.78***). The feedback loop concept provides a more comprehensive two-sided view into decomposition, as regulated simultaneously by two factors, than earlier one-sided approaches to soil fauna-mediated decomposition.

Automated summary

This study employed the concept of feedback loops between changes in chemical quality of decomposing organic residues and changes in faunal communities to determine decomposition dynamics in soils. A 52-week litterbag decomposition study was conducted in conjunction with an 18-year long term field experiment. Different types of organic residues were incorporated into the soil annually, and the decomposition and associated fauna communities were assessed. The results showed that both mesofauna and macrofauna abundances were influenced by labile cellulose and N in the first 4 weeks after residue incorporation, and the contribution of different fauna to decomposition varied over time.