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

Abstract

Earthworms are drivers of soil processes as soil structure formation and organic mattercycling. Through providing soil microbiota with mucus, temperature, and organicresources within their guts, earthworms enhance their activity and organic matterdecomposition. In agricultural fields, this phenomenon is linked to crop residues astrophic resources. However, very little is known about the effect of different croprotations on soil microbiota activation mediated by earthworm activity. We aimed toevaluate the effect of diversifying crop rotation on enzymatic activity in A. caliginosacasts and on enzymatic stoichiometry patterns related to C, N, and P acquisitionactivities. We conducted a microcosm essay using different crop residues as foodsupply: soybean (S), soybean and maize (SM), vetch, maize, and soybean (VMS), andwith no residue addition (NR). We measured α-glucosidase (AGLU), β-glucosidase(BGLU), cellobiohydrolase (CEL), N-acetyl-glucosaminidase (NAG),phosmonoesterase (PME), and acetylesterase (ACE) activity in A. caliginosa castsimmediately before starting the essay for evaluating the initial condition (IC) and afterthe essay 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 activitythan NR and IC for all the analyzed enzymes. There was a positive, strong, andsignificant relation 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: Nacquisition activity ratios. This result suggests P as the limiting nutrient for earthwormmicrobiomes. Our results indicate that soybean residue is unsuitable for A. caliginosafood requirements and that both diversified crop residues enhance enzymatic activitymediated by earthworms and thus organic matter decomposition. We suggestdifferential activation and likely changes in microbiota composition as mechanismsresponsible for higher enzymatic activation when earthworms were fed withheterogeneous residues.