Diel fluctuations in rates of CO2 evolution from standing dead leaf litter of the emergent macrophyte Juncus effusus

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 mu g CO2-Cg(-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 mu g CO2-Cg(-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.