Soil Anaerobiosis, Microorganisms, and Root Function

Abstract

Anaerobic (oxygen-free or anoxic) conditions result from restriction by excess water of the free diffusion and convection of oxygen between the atmosphere and the soil. The ensuing changes in the chemical and biological properties of the waterlogged soil greatly affect the activities of soil microor­ ganisms and plant roots, and depress the growth of plants not especially adapted to wet-land conditions. Characteristic symptoms of damage during temporary waterlogging in herbaceous and woody species when tempera­ tures are high include a slowing of leaf and shoot extension and a yellowing of the older (lower) leaves suggesting premature senescence. Wilting, leaf epinasty, and leaf abscission may occur; in Gramineae tillering is sup­ pressed; and some diseases may become more prevalent. Phloem transport from the shoots into the original roots is soon inhibited (51, 205) and the roots cease extension and dry matter accumulation and often degenerate, particularly at the apex (23,51,93, 165,214,215). Prolonged waterlogging can lead to death of the entire plant in species that do not adapt (203). The effects of poor soil aeration on root function and plant growth have been the subject of an extensive literature (reviewed in 18, 71, 88, 203) but the causes of injury to plants, particularly the role of soil microorganisms, remain obscure, perhaps because of the multiplicity of mechanisms. The primary cause of impairment to root metabolism is still a matter for conjec­ ture. One possibility is that the generation of ATP in anaerobic respiration is inadequate for maintenance of cell metabolism in higher plant cells. With