ABSTRACT: Standing dead plant litter of emergent macrophytes often forms a considerable portion of the detrital mass in wetland habitats. We examined the effects of varying environmental conditions on the diel respiratory activity (rate of CO₂ evolution) of microbial assemblages associated with standing dead litter of the emergent macrophyte Juncus effusus L. from a small freshwater wetland in central Alabama, USA. Availability of water was a major factor affecting rates of respiration in standing litter. Under field conditions, rates of CO₂ evolution from plant litter fluctuated greatly, with the highest rates occurring at night and in the early morning hours, coinciding with increasing relative humidity (>90%) and plant litter water potentials (>-1.0 MPa). Rates ranged from 2 to 285 µg CO₂-C g^-1 organic mass h^-1 over 24 h. Daily CO₂ flux from microbial decomposers inhabiting standing litter ranged between 1.37 and 3.35 g C m^-2 d^-1. After controlled laboratory additions of water, rates of CO₂ evolution from standing litter increased significantly, with sustained maximal rates occurring within 5 min after being wetted (>100 µg CO₂-C g^-1 organic mass h^-1). Results of these investigations establish that J. effusus litter is colonized by active microbial decomposers while in the standing dead phase. Furthermore, these microbial assemblages make significant contributions to ecosystem metabolism and may represent an important CO₂ output not previously recognized or incorporated in estimates of CO₂ flux from wetland habitats.

KEY WORDS: Freshwater wetlands · CO₂ emissions · Juncus effusus · Standing litter · Fungi

Published in AME Vol. 14, No. 2 (1998) on February 13
Print ISSN: 0948-3055; Online ISSN: 1616-1564. Copyright © Inter-Research, Oldendorf/Luhe, 1998