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Gaseous Exchange and Wetland Plant Response to Soil Redox Intensity and Capacity

IRRI, P.O. Box 933, 1099 Manila, Philippines

R. D. DeLaune

Wetland Biogeochemistry Inst., Center for Coastal, Energy and Environmental Resources, Louisiana State Univ., Baton Rouge, LA 70803-7511

*Corresponding author (hkludze{at}irri.cgnet.com).

ABSTRACT

Although reports on plant responses to wetland conditions abound, limited information is available to relate such responses to well-defined soil redox conditions. Laboratory experiments were conducted to evaluate differences in plant response to soil redox intensity (Eh) and capacity. Mississippi floodplain soil (Mhoon; fine-silty, mixed, nonacid, thermic Typic Fluvaquent) and rice paddy soil (Crowley; fine, montmorillonitic, thermic Typic Albaqualf) were used to grow saltmeadow cordgrass [Spartina patens (Aiton) Muhlenb.] and rice (Oryza sativa L.), respectively. Plants were grown under controlled Eh levels of 100, 0, –100, and –200 mV to examine the effect of Eh on CO₂ fixation. Treatments for the soil redox capacity experiment were imposed by application of different levels of extra energy source while maintaining Eh at -200 mV. Redox capacity effects on plant growth, CO₂ fixation, root porosity (POR), radial oxygen loss (ROL), and CH₄ emissions were also evaluated. In both test plants, CO₂ fixation did not respond to soil Eh until –100 mV. Although POR was unaffected, plant growth, CO₂ fixation, and CH₄ emissions were significantly decreased with increase in soil O₂ demand, thus suggesting a complex relationship between soil redox capacity and plant physiological functions. Plant O₂ transport to the root environment (ROL) was also governed by soil redox capacity. Results indicate that plants may respond differently in magnitude to soil redox intensity and redox capacity. Evaluating responses, especially ROL, of flood-tolerant plant species therefore requires proper quantification of the soil redox condition or substrate O₂ demand in which the plants are grown.

This study was conducted at Louisiana State Univ., Baton Rouge, LA. Funding for this research was provided by the National Institute for Global Environmental Change (funded by the Department of Energy).

Received for publication May 23, 1994.