ROOT OXYGEN DEPRAVATION AND THE REDUCTION OF LEAF STOMATAL APERTURE AND GAS EXCHANGE

Authors: Sojka, Robert; OOSTERHUIS, D - UNIVERSITY OF ARKANSAS; SCOTT, H - MOUNT OLIVE COLLEGE

Submitted to: Handbook of Photosynthesis
Publication Type: Book / Chapter
Publication Acceptance Date: 2/4/2004
Publication Date: 1/1/2005
Citation: Sojka, R.E., Oosterhuis, D.M., Scott, H.D. 2005. Root oxygen deprivation and the reduction of leaf stomatal aperture and gas exchange. In: Pessarakli, M., editor. Handbook of Photosynthesis. 2nd edition. New York, NY: Taylor & Francis. p. 299-314.

Interpretive Summary: It has long been noted that despite being in contact with free water, flooded plants soon wilt and suffer severe physiological stress. When plants wilt, the small pores in leaves that allow the exchange of internal gases within the plant close. In healthy plants, these pores, called stomata, normally act to regulate the flow of water vapor and carbon dioxide to allow evaporative cooling of the leaf and provide the necessary molecules for photosynthesis. Photosynthesis is process that allows light to convert carbon dioxide into sugars, which are ultimately converted to pectins, starch and cellulose, the building blocks of plant growth. When plant roots are flooded, the water prevents the roots from exchanging oxygen in respiration. In a sense the roots suffocate. Because the roots supply water and important biochemicals to the leaves, the loss of oxygen to the roots impairs a number of processes in the plant, affecting growth, crop yield and ultimately survivability. This chapter explores the extent of our knowledge of how flooding stress occurs, what steps bring about the stress response, and how these can be used to diagnose stress, choose flood resistant plants for wet environments, and manage soil-plant systems to avoid flood damage.

Technical Abstract: Flooding in most plant species has been found to induce wilting, usually after about 48 hours of inundation. As with wilting from water deficit stress, flood-induced wilting has been found to be accompanied by loss of turgor in stomatal guard cells, leading to stomatal closure and reduction of leaf gas exchange. Several studies have determined that the physiological stress induced by flooding is predominately the result of root hypoxia. Root hypoxia leads to a cascading series of soil and plant chemical and biochemical shifts that affect membrane permeability and selective ion transfers in root cells. These shifts are propagated through the xylem, affecting the permeability and ion balance of guard cells, resulting in loss of turgor and stomatal closure. Stomatal closure in turn impedes exchange of water vapor and carbon dioxide, resulting in elevated leaf temperatures and a precipitous reduction in photosynthetic rate. This chapter explores the extent of literature on this topic, catalogues the species for which the phenomena is documented and explores the internal physiological mechanisms that bring about the response and how various other environmental queues interact to exacerbate or reduce its severity. The chapter notes the potential value of this physiological indicator for stress resistance comparison among species and cultivars, as an early indication of hypoxic stress, and for soil-plant system modeling of root hypoxia response.