GROWTH AND ROOT OXYGEN RELEASE BY TYPHA-LATIFOLIA AND ITS EFFECTS ON SEDIMENT METHANOGENESIS

Growth of Typha latifolia L. and its effects on sediment methanogenesi s were examined in a natural organic sediment and a sediment enriched with acetate to a concentration of 25 mM in the interstitial water. Th e lower redox potential and higher oxygen demand of the acetate-enrich ed sediment did not significantly impede growth of T. latifolia despit e some differences in growth pattern and root morphology. Plants grown in acetate-enriched sediment were ca. 15% shorter than plants grown i n natural sediment, but the former produced more secondary shoots at e arlier stages, which resulted in similar total biomasses after 7 weeks of growth in the two sediment types. Plants grown in acetate-enriched sediment had thicker and much shorter roots than plants grown in natu ral sediment. This difference did not significantly affect the release of oxygen from the roots when measured under laboratory conditions, w hich was 0.12-0.20 mmol O-2 g(-1) DW h(-1). Enrichment with acetate re sulted in much higher sediment methanogenesis rates (643 vs. 90 nmol C H4 g(-1) sediment DW h(-1)). Growth of T. latifolia significantly redu ced methanogenesis in both types of sediment, but the effect was twice as marked in the natural sediment (34%) as in the acetate-enriched se diment (18%), although in absolute terms the reduction was higher in t he enriched sediment. The data suggest that this effect of plant growt h was via root oxygen release and its effect on redox conditions. In t he natural sediment, oxygen release resulted in a significantly higher redox potential and lower sediment oxygen demand, whereas there were no significant changes in the acetate-enriched sediment. The very high oxygen demand of this sediment probably masked the effect of root oxy gen release so that a significant reduction in methanogenesis occurred without any significant increase in the redox potential. This demonst rates how root oxygen release from plants like T. latifolia can signif icantly alter rates of biogeochemical processes such as methanogenesis .