PRODUCTIVITIES OF MICROBIAL DECOMPOSERS DURING EARLY STAGES OF DECOMPOSITION OF LEAVES OF A FRESH-WATER SEDGE

1. We examined standing-senescing, standing-dead and recently fallen l eaf blades of Carer walteriana in fens of the Okefenokee Swamp to dete rmine the nature of the microbial decomposers in the early stages of d ecomposition, measuring both standing crops and productivities ([H-3]l eucine-->protein method for bacteria, [C-14]acetate-->ergosterol for f ungi). 2. Fungal standing crops (ergosterol) became detectable at the mid-senescence stage (leaves about half yellow-brown) and rose to 14-3 1 mg living-fungal C g(-1) organic mass of the decaying system; bacter ial standing crops (direct microscopy) were less than or equal to 0.2 mgC g(-1) until the fallen-leaf stage, when they rose to as high as 0. 9 mgC g(-1). 3. Potential microbial specific growth rates were similar between fungi and bacteria, at about 0.03-0.06 day(-1), but potential production of fungal mass was 115-512 mu gC g(-1) organic mass day(-1 ), compared with 0-22 mu gC g(-1) day(-1) for bacteria. Rates of funga l production were about 6-fold lower on average than previously found for a saltmarsh grass, perhaps because much lower phosphorus concentra tions in the freshwater fen limit fungal activity. 4. There was little change in lignocellulose (LC) percentage of decaying leaves, although net loss of organic mass at the fallen, broken stage was estimated to be 59%, suggesting that LC was lost at rates proportional to those fo r total organics during decay. Monomers of fungal-wall polymers (gluco samine and mannose) accumulated 2- to 4-fold during leaf decay. This m ay indicate that an increase found for proximate (acid-detergent) lign in could be at least partially due to accumulation of refractory funga l-wall material, including melanin. 5. A common sequence in decaying a quatic grasses is suggested: principally fungal alteration of LC durin g standing decay, followed by a trend toward bacterial decomposition o f the LC after leaves fall and break into particles.