.. . / zy Eur. zyxwvutsrqpon J. Soil Biol. 36 (2000) 177-198 O 2000 Éditions scientifiques et médicales Elsevier SAS. All rights reserved S1164556300010621/REV zyxwvutsrq Regulation of zyxw soil organic matter dynamics and microbial activity z in the drilosphere and the role of interactions with other edaphic functional domainss George G. Browna’”*, Isabelle Baroisa, Patric zy i L- -- a Departamedto de Biología de Suelos, Instituto de Ecologia, A.C., A.P. 63, Xalapa, IJer. 91000, Mexico LEST, IRD et université Paris-VI, 32, av. Henri-Varagnat, 93143 Bondy, France Received 10 November 1999; accepted 28 September 2000 010024175 zyxwvutsrq l __ . . _._ - Abstract - The moment the soil enters into contact with zyxwvu an earthworm, both superficially and intemally, physicochemical and biological changes take place. The drilosphere represents the whole soil volume under earthworm influence. Thus it includes the body surfaces, the gut and all the internal features of the worm that are in contact with the ingested soil, as well as the external structures (casts, burrows, middens) created by earthworm activities. The extent of t he drilosphere and its particular characteristics depend on the species and ecological categories of the earthworm community present as well as the spatial and temporal scale of interest. Spatially, the drilosphere can interact with other soil functional domains and lead to significant changes in the litter system or detritusphere (generally decreasing litter stocks) and the rhizosphere (affecting both root biomass and density), the two main sources of organic matter (OM) additions to the soil, as well as in the aggregatusphere and the porosphere. Drilosphere effects on microbial activity and OM decomposition can be completely different (and opposite) depending on the spatio-temporal scale of observation. At the level of the gut, microbial activity is dramatically stimulated in a matter of a few hours via a mutualistic digestion system. In this process, water and soluble-C in the form of intestinal mucus (the Kiss) produced by the earthworm (Prince Charming) awakens the dormant microflora (Sleeping Beauties), thereby increasing decomposition of the stable forms of soil OM ingested. During gut passage populations of other organisms (e.g. protozoa, nematodes, fungi) may decline with digestion, although these organisms probably form a minor component of the earthworm’s energy needs. In the casts and on the burrow walls, the abundant nutrient resources for soil microflora continue the priming effect of the gut, increasing over a short time period mineralization rates and plant nutrient bio-availability. However as castings, particularly of the ‘compacting group’, and burrow walls begin to dry and stabilize with age (days to weeks), OM decomposition, nutrient mineralization and microbial activity decrease, often reaching levels lower than uningested soil due to ‘protection’. Finally at the scale of years to decades and soil profile, it,appears that the drilosphere can exert an important regulation on OM incorporation and tumover rates, and soil C stocks. O 2000 Editions scientifiques et médicales Elsevier SAS I ~~~~~~~~~~ I drilosphere / earthworms / soil properties / micro-organisms / organic matter dynamics 1. INTRODUCTION Researching the interactions between soil macro- fauna and micro-organisms is like finding one’s way through a maze of below-ground processes in which the path sometimes leads in one direction and then another, back along the same or another track, and then * zyxwvutsrqpon Correspondence arid repriltts. fax +52 28 18 78 09. E-171uiZ address: browng@ecologia.edu.mx (G.G. Brown). S Paper presented at the 16th World Congress of Soil Science, 20-26 August 1998, Montpellier, France. finally forward again. These shifts in direction, exem- plified by the large number of publications showing apparently conflicting results in this subject, are very likely due to the different approaches used to investi- gate soil interactive phenomena, as well as to the great diversity of species and functions performed by soil organisms and their effects on soil organic matter (SOM) dynamics and microbial activity at different scales of space and time. An example of this is the role that earthworms may play in both acceleration of decomposition and mineralization processes (C loss) and in carbon storage or protection from decomposi- tion (C accumulation) in stable aggregates.