Soil food webs in agricultural ecosystems - Microbial Ecology in Sustainable Agroecosystems - page 62

chapter 4
Soil food webs in agricultural ecosystems
John C. Moore
Colorado State University
Peter C. de Ruiter
Wageningen University
Contents
4.1 Introduction .......................................................................................................................... 63
4.2 Soil food web descriptions and models............................................................................ 66
4.2.1 The connectedness food web ................................................................................. 66
4.2.2 The energy lux food web ....................................................................................... 67
4.2.3 The functional food web......................................................................................... 69
4.3 Patterns in energy lux and interaction strength ............................................................ 72
4.4 Patterns and stability........................................................................................................... 74
4.5 Impacts of agricultural practices ....................................................................................... 78
4.5.1 Effects of tillage on soil organic matter and nutrient dynamics....................... 78
4.5.2 Effects on soil food webs ........................................................................................ 79
4.6 Discussion and conclusions ............................................................................................... 84
Acknowledgments ........................................................................................................................ 86
References....................................................................................................................................... 86
4.1 Introduction
Odum (1969) provided a framework for viewing the relationships between plant com-
munities and biogeochemical cycles in his seminal article, “The Strategy of Ecosystem
Development.” The framework is a compilation of ecosystem thinking of that time that
juxtaposes ecosystem properties of early development communities with mature commu-
nities, revealing an end game of homeostasis and balance between plants and nutrients
( Table 4.1 ) . The transition from early developmental communities to mature communities
is characterized structurally and functionally by a transition from r -selected to k -selected
plant species, from food chains that rely primarily on primary production to ones that rely
on both primary production and detritus, and from biogeochemical cycles that are open
with exogenous inputs and high exports of plant-limiting nutrients to ones that are more
closed and dependent on symbiotic interactions that promote internal cycling of nutrients
and nutrient exchanges (Wall and Moore, 1999).
Agricultural practices affect many of these key structural and functional attributes
of ecosystems in ways that transform mature ecosystems to ones that are in a managed
developmental state. The regular additions of inorganic or organic fertilizers and amend-
ments and harvesting of crops have the potential to shift the elemental balance of a system.
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