Crop residues used as food drive enzyme activation and enzymatic stoichiometry in casts of the earthworm Aporrectodea caliginosa (Savigny, 1826)

Earthworms are drivers of important soil processes such as the nutrient cycle. Earthworms provide soil microbiota with mucus, temperature, and organic resources in their guts, enhancing organic matter decomposition. However, very little is known about the effect of different crop rotations on soil microbiota activation mediated by earthworm activity. We aimed to evaluate the effect of different crop rotations on enzymatic activity in A. caliginosa casts and on enzymatic stoichiometry patterns related to C, N, and P acquisition activities. We conducted a microcosm study using different crop residues as food supply: soybean (S), soybean plus maize (SM), vetch, maize, and soybean (VMS), and with no residue addition (NR). We measured α-glucosidase (AGLU), β-glucosidase (BGLU), cellobiohydrolase (CEL), acetylesterase (ACE), N-acetyl-glucosaminidase (NAG), and phosmonoesterase (PME) activities in A. caliginosa casts, immediately before starting the experiment for evaluating the initial condition (IC) and after the experiment in each residue treatment. SM and VMS residues enhanced BGLU, CEL, and NAG activity regarding S, NR, and IC treatments. S had similar or lower activity than NR and IC for all the analyzed enzymes. There was a positive, strong, and significant relationship among C, N, and P acquiring enzymes regardless of the treatment. We found lower ratios for C and N acquisition related to P acquisition than for C: N acquisition activity ratios. This result suggests P as the limiting nutrient for earthworm microbiomes. Our results indicate that soybean residue is unsuitable for A. caliginosa food requirements and that diversifying crop residues and the inclusion of maize as food enhance enzymatic activity mediated by earthworms and thus organic matter decomposition. We suggest differential activation and likely changes in microbiota composition as mechanisms responsible for higher enzymatic activation when earthworms are fed with different combination of crop residues.