Nutrient cycling and microbial responses to termite and earthworm activity in soils amended with woody residues in the Sudano-Sahel

Abstract

Termites and earthworms are the main groups of invertebrates in dry tropical ecosystems and exert significant effects on bioturbation and soil reorganization. The dynamics of microbial communities, enzymes and substrates associated with the flux of energy and nutrients induced by their diverse biogenic structures are still under-investigated in agroecological-based cropping systems. The objective of this study was to determine whether the biogenic structures produced by a grass-woody forager termite (Nasutitermes torquatus) and an endogeic earthworm (Millsonia inermis) shift soil organic C (OC), nutrients, enzyme activities and microbial communities in soils amended with woody residues. The experiment was a randomized block design conducted in a Sudano-Sahelian cropping system that was amended annually with woody residues (3 Mg ha−1) or not amended (control soils) for six consecutive years. Samples were taken from fresh sheetings and casts (produced respectively by N. torquatus and M. inermis) and bulk soils in amended plots as well as from control soils in nonamended plots. Samples were analyzed for soil texture, OC, total nitrogen (N), available phosphorus (P), pH, enzyme activity and microbial composition. The results showed that sheetings and casts altered soil biochemical properties significantly. Sheetings and casts were remarkably enriched in OC (45–55% and 82–94%, respectively) and P (20–55% and 73–130%) compared to bulk soils and control soils. Sheetings and casts substantially stimulated β-glucosidase (153–178% and 158–183%, respectively) and N-acetyl-β-glucosaminidase (43–53% and 84–93%) activity, likely due to gut mucus excretions and favorable physicochemical conditions. Sheetings and casts did not fundamentally alter the microbial diversity but raised soil conditions favorable to selective microbial growth. Overall, casts exhibited higher nutrient content (N, P), enzyme activity, and larger total microbial biomass than sheetings. Both structures stimulated soil microbial communities and enzyme activity associated with the increase of pH, OC and nutrients. Earthworm casts and termite sheetings have ecological significance in OC dynamics in plant residues amended soils.