Linking Physical and Biogeochemical Properties and Processes in the Drilosphere

Earthworms have long been recognized as ecosystem engineers, and their activity has been linked to increases in plant growth and yield in agroecosystems. Past research has demonstrated many positive impacts of earthworm activity on soil physical properties such as infiltration, aggregate stability, and water-holding capacity. In most cases, these studies have been conducted at the mesocosm, pedon, or plot scale and do not address the fine-scale reorganization of soil structure and molecular alteration of drilosphere soil ultimately responsible for increased plant growth. Past studies have also largely focused on determining the impact of earthworms on a single soil property or process. By using a combination of relatively new methodologies such as tomography and advanced microspectroscopic tools, the consequences of spatial reorganization by earthworms on biogeochemical properties may be determined. Likewise, microscale information on the biochemical environment will help elucidate processes through which earthworms alter soil physical properties. These types of microscale spatially explicit studies will be especially important in understanding how soil ecosystem engineers influence water and nutrient uptake by plants. This article focuses on reviewing our current state of knowledge regarding earthworm influences on physical properties and drilosphere-level studies of biogeochemical properties and processes. Examples of emerging techniques that are capable of studying drilosphere properties are given.