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 consi derable portion of the detrital mass in wetland habitats. We examined the effects of varying environmental conditions on the diel respirator y 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. Availabilit y of water was a major factor affecting rates of respiration in standi ng litter. Under field conditions, rates of CO2 evolution from plant l itter fluctuated greatly, with the highest rates occurring at night an d in the early morning hours, coinciding with increasing relative humi dity (>90%) and plant litter water potentials (>-1.0 MPa). Rates range d from 2 to 285 mu g CO2-Cg(-1) organic mass h(-1) over 24 h. Daily CO 2 flux from microbial decomposers inhabiting standing litter ranged be tween 1.37 and 3.35 g C m(-2) d(-1). After controlled laboratory addit ions of water, rates of CO2 evolution from standing litter increased s ignificantly, with sustained maximal rates occurring within 5 min afte r being wetted (>100 mu g CO2-Cg(-1) organic mass h(-1)). Results of t hese investigations establish that J. effusus litter is colonized by a ctive microbial decomposers while in the standing dead phase. Furtherm ore, these microbial assemblages make significant contributions to eco system metabolism and may represent an important CO2 output not previo usly recognized or incorporated in estimates of CO2 flux from wetland habitats.