Plant and Animal Activity Below the Solum
if soil depth is defined by the depth of organism activity, then the generalized concept of useful soil depth is much too shallow. While climate and geologic features combine to limit the extent of biologic activity in some soils, this review indicates many instances where such activity continues to great depths. Arbitrarily selecting a 1.5-m lower limit to the solum, we review reports of plant root, root symbiont, and vertebrate and invertebrate activity below this depth. The evidence for plant activity is given by the mere presence of roots as well as observations of water and solute uptake. Water uptake evidence comes from (i) observations of plant roots in the capillary fringe, or at or beneath a water table, (ii) water depletion from unconsolidated regolith with no water table present, and (iii) presence of roots in saprolite and weathered or fractured rock. These observations are numerous and demonstrate root activity to a depth of 40 m under certain conditions. Solute uptake is less readily documented. The few occurrences reported generally range in depth from 2 to 3 m, with one for U at 20 m. Root symbionts (rhizobia and mycorrhiza-forming fungus) also are present at depth (3-34-m) but, like solutes, reports are few. The depth range for faunal activity is from several to 100 m. Clearly, the material below the solum, usually considered not affected by soil-forming processes, is often well inhabited by flora and fauna. The importance of these subsoil volumes is still unclear apart from water withdrawal, but obviously relate to the belowground environment and the adaptation of species to this environment. An excessive concentration of attention in the surface 20 to 40 cm of soil seems often unwarranted.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © 1994. . Copyright © 1994 by the Soil Science Society of America, Inc., 5585 Guilford Rd., Madison, WI 53711 USA