TROPHIC RELATIONSHIPS IN THE SOIL MICROFOOD-WEB - PREDICTING THE RESPONSES TO A CHANGING GLOBAL ENVIRONMENT

In this article, we evaluate how global environmental change may affec t microfood-webs and trophic interactions in the soil, and the implica tions of this at the ecosystem level. First we outline how bottom-up ( resource control) and top-down (predation-control) forces regulate foo d-web components. Food-web components can respond either positively or negatively to shifts in NPP resulting from global change, thus creati ng difficulties in developing general principles about the response of soil biota to global change phenomena. We also demonstrate that top-d own effects can be important in soil food-webs, creating negative feed -backs which may partially counter bottom-up effects. Secondly we dete rmine how soil food-webs and the processes they regulate respond to va rious global change phenomena. Enhanced atmospheric CO2 levels can hav e two main effects on plants which are relevant for the sail food-web, i.e. enhanced NPP (often positive) and diminished organic matter qual ity (with negative effects, at least in the short term). Climate chang e effects resulting from elevated CO2 levels may be mainly secondary t hrough alteration of vegetation, as shown by examples. Intensification of land management is usually associated with greater disturbance, wh ich alters soil food-web composition and key processes; this is partic ularly apparent in comparisons of conventionally tilled and nontilled agroecosystems. Global change involves shifts in plant species composi tion and diversity, possibly affecting soil food-webs; we interpret th is in terms of theories relating biodiversity to ecosystem function. W e conclude that a more detailed understanding of interactions between NPP, soil organic matter and components of the soil food-web, as well as their regulation of biogeochemical processes and ultimately ecosyst em-level properties, is essential in better understanding longterm asp ects of global change phenomena.