Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Ron D. DeLaune

Abstract

Laboratory studies pertaining to effects of soil redox conditions on gas exchange and plant responses were undertaken. A colorimetric method for assaying O$\sb2$ concentration in the root rhizosphere was used to quantify radial O$\sb2$ loss from plant roots. The oxidizing power of seven rice cultivars, grown under aerobic and hypoxic conditions, was measured colorimetrically with titanium-citrate solution. Oxygen release rate was calculated by extrapolation of measured absorbance to standard curves after placing plant roots in the solution for 6 h. Since Ti$\sp{3+}$ ions readily react with O$\sb2$ as it is released from roots, the technique provides a sensitive measurement of dissolved O$\sb2$. Variations in O$\sb2$ release rates existed among cultivars and between aeration status. Values ranged from 10.0 to 18.6 $\mu$mol O$\sb2$ plant$\sp{-1}$ d$\sp{-1}$ in the aerobic treatments, and from 10.4 to 33.2 $\mu$mol plant$\sp{-1}$ d$\sp{-1}$ in the hypoxic treatments. Oxygen leakage from hypoxic treatments was highly correlated to root porosity in some cultivars, which may explain their success in low-land cultivation in Louisiana. There were interactive effects of cultivar type and straw application rate on rice growth and gaseous transport. Results indicated that inhibition of CH$\sb4$ emissions at high straw dosage was not due to inhibition of methanogenesis but due to plant-related factors that influence net CH$\sb4$ emissions. Soil reduction intensity affected porosity and gas transport in the two test plants, Oryza sativa and Spartina patens. Plants were grown in Crowley soil (Typic Albaqualf) and Mississippi alluvial soil (Typic Fluvaquent), respectively, under controlled redox intensity levels, +200, $-$200 and $-$300 mV. Results demonstrated that soil Eh influences net CH$\sb4$ emissions by (1) directly determining the amount and rate of CH$\sb4$ production in the soil, and (2) initiating morphological and physiological changes in aquatic plants that affect gas exchange between the soil and the atmosphere. Plant growth and CO$\sb2$ fixation responded differently to soil redox intensity and capacity, while other parameters measured did not respond to redox capacity. Soil redox intensity and capacity must therefore be considered for properly evaluating physiological responses of wetland plants to reducing conditions in the root medium.

Pages

169

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