Effects of Flooding on Plant Disease

Root Oxygen Deprivation and the Reduction of Leaf Stomatal Aperture and Gas Exchange

“…The curvilinear regressions of R L against ODR for numerous species have shown sharp response thresholds occurring at or near ODR values of 20 x 10 -8 g/cm 2/min. This same ODR value is a recognized threshold for a variety of plant growth, physiological and nutritional responses [8,79].…”

“…As the amount of water in the soil environment shifts from shortage to plentiful and on to excess, the populations and functional dominance of competing organisms also shift. Under excessively wet or flooded conditions, disease organisms are often favored [8]. Water affects the heat capacity, heat conductivity, and evaporative properties of soil in a way that generally tends to cool soil when wet.…”

“…and surfaces of plant roots also increases. The thickness of these water films greatly influences the transfer of oxygen from the soil environment to respiration sites in roots and microorganisms [8]. Oxygen diffuses 104 times more slowly through water than through air [19] and only one-fourth as rapidly through dense protoplasm as through water [20,21].…”

“…The dominant literature, of course, relates to flooding; however, a number of studies have manipulated soil oxygen independently of flooding, providing important insights to the phenomena [8]. Also, since oxygen unavailability is probably the dominant direct trigger for most of the plant responses that ultimately manifest themselves as familiar visual and otherwise easily monitored physiological responses.…”

“…These fall into about five categories: obstruction of xylem elements by disease organisms, reduced root system extent or root system/membrane water conductance, altered soil-plant nutritional status, production or imbalancing of plant hormones or biochemical signaling compounds, and the action of soil-or plantproduced toxins [2,[6][7][8][9][10][11].…”