Characterizing soil biota in Canadian agroecosystems: State of knowledge in relation to soil organic matter

Organic residues resulting from crop and animal production either become incorporated in the soil or remain on the surface and, thus, provide much of the nutrient and energy sources for many soil organisms. Characterizing the response of soil biota to these organic materials is a challenging undertaking due to the complexity of the soil ecosystem with respect to the magnitude of biodiversity involved, the possibilities for interrelationships with biochemical and biophysical processes, and the immense range of scale of observation from particle, through to aggregate, field, landscape and regional levels. The objectives of this paper were to review the available research pertaining to Canadian agroecosystems, which characterize the response of soil biota to soil organic matter dynamics, and to identify the issues, challenges and knowledge gaps. The response by soil organisms is discussed from two approaches: (1) their state of occurrence in terms of population response to soil organic matter as a nutrient and carbon/energy source, and (2) the extent of their influence in contributing to organic matter dynamics, that is, assessing their functional role. For the most part, Canadian research has emphasized comparative studies based on population responses by broad soil biota groups to soil organic matter additions or losses as an outcome of undertaking various agronomic practices. Studies that evaluate the extent of contributions by soil biota to soil organic matter dynamics are few, and rare at the species level. For Canadian agroecosystems, there is currently a great need for research initiatives that address the immense knowledge gaps that exist in relation to (a) identifying the specific contributions to soil organic matter processes and interactions of soil biota both at species and community level, (b) predicting outcomes of the contributions of soil biota groups in regulating or controlling soil organic matter processes both spatially and temporally across landscapes, and (c) assessing the risk to soil biodiversity in various agroecosystems in being able to sustain these functional roles.