OXYGEN LOSS FROM SPARTINA-ALTERNIFLORA AND ITS RELATIONSHIP TO SALT-MARSH OXYGEN BALANCE

Spartina alterniflora has been reported to lose significant amounts of oxygen to its rhizosphere with potentially important effects on salt- marsh biogeochemical cycling and plant productivity. The potential sig nificance of this oxidative pathway was evaluated using laboratory spl it-chamber experiments to quantify oxygen loss from intact root system s under a wide variety of pre-treatment and incubation conditions incl uding antibiotics to inhibit microbial respiration. The aerenchyma sys tem of S. alterniflora was found to transport O2, N2, Ar, and CH4 from above-ground sources to its below-ground roots and rhizomes. While no n-respiratory gases were observed to move from the lacunae to water ba thing the root systems, net 02 loss did not occur; instead oxygen pres ent outside of the roots/rhizomes was consumed. Net oxygen loss was fo und when resistance to gas transport was reduced in the lacunae-rhizos phere pathway by placing the root systems in a gas phase and when plan t respiration was significantly reduced. Root system respiration appea red to be the major variable in the plant oxygen balance. When root an d rhizome respiration was inhibited using poisons or lowered by coolin g, the oxygen deficit was greatly reduced and oxygen loss was indicate d. The effect of seasonal temperature changes on root system ''oxygen deficit'' presents a possible explanation as to why Spartina produces root systems with respiration rates that cannot be supported by gas tr ansport. Overall, while oxygen loss from individual plant roots is lik ely, integrating measured root system oxygen loss with geochemical dat a indicates that the mass amount of oxygen lost from S. alterniflora r oot systems is small compared to the total oxygen balance of vegetated salt marsh sediments.