Regulation of soil organic matter dynamics and microbial activity in the drilosphere and the role of interactions with other edaphic functional domains

The moment the soil enters into contact with an earthworm, both superficial ly and internally, physicochemical and biological changes take place. The d rilosphere represents the whole soil volume under earthworm influence. Thus it includes the body surfaces, the gut and all the internal features of th e worm that are in contact with the ingested soil, as well as the external structures (casts, burrows, middens) created by earthworm activities. The e xtent of the drilosphere and its particular characteristics depend on the s pecies 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 cha nges in the litter system or detritusphere (generally decreasing litter sto cks) 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 t he aggregatusphere and the porosphere. Drilosphere effects on microbial act ivity and OM decomposition can be completely different (and opposite) depen ding 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 vi a a mutualistic digestion system. In this process, water and soluble-C in t he form of intestinal mucus (the Kiss) produced by the earthworm (Prince Ch arming) awakens the dormant microflora (Sleeping Beauties), thereby increas ing decomposition of the stable forms of soil OM ingested. During gut passa ge populations of other organisms (e.g. protozoa, nematodes, fungi) may dec line with digestion, although these organisms probably form a minor compone nt of the earthworm's energy needs. In the casts and on the burrow walls, t he abundant nutrient resources for soil microflora continue the priming eff ect of the gut, increasing over a short time period mineralization rates an d 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 act ivity decrease, often reaching levels lower than uningested soil due to 'pr otection'. Finally at the scale of years to decades and soil profile, it ap pears that the drilosphere can exert an important regulation on OM Incorpor ation and turnover rates, and soil C stocks. (C) 2000 Editions scientifique s et medicales Elsevier SAS.