Jan Jun 



SUB- 

 MERGED 

 IN BAYOU 



Jan Jun Jan Jun 



STREAMSIDE INLAND 



MARSH MARSH 



Figure 53. Decomposition rates (mg/g/day) 

 of S. a1 ter niflora litter incubated in 



different 



2-mm mesh bags 

 (Kirby 1971). 



in 



locations 



roeme nanus 



slow to decompose. J_ 



decomposes rapidly for a species with a 

 low surface to volume ratio. S_. falcata , 

 a broad-leaved monocot with high leaf 

 N content, decomposes extremely rapidly, 

 apparently at any tenperature. 



Nitrogen availability often limits 

 the decay rate of detritus (Teal 1983). 

 Since most animals have low C:N ratios 

 (under 10) while litter from such plants 

 as S_. al terniflora has a ratio well over 

 20, the decomposers must either select 

 high H residues from the litter or sup- 

 plement the litter with N from other 

 sources. 



In a laboratory test Gosselink and 

 Kirby (1974) found that litter became 

 increasingly fragmented as it decomposed, 

 and that the C:N ratio, after an initial 

 increase, dropped rapidly so that the 

 finely decomposed material had a N content 

 up to 8 percent (C:N = 6). This increase 

 in N was not simply a concentration of 

 litter N by respiration of the C. Rather, 

 N was absorbed from inorganic sources in 

 the environment. This is not surprising 

 since it has been known for many years 

 that when a mulch is used in an agricul- 



Tabl e 20. Range and mean loss rates 

 (mg/g/day) of litter from different marsh 

 plant species (summarized from Appendix 

 2). 



Species 



Range 



Mean 



Sal t marsh 

 Spartina al terni f1 ora 

 Spartina cynosuroides 

 Distichl is spicata 

 Juncus roemerianus 



Bracki sh inarsh 

 Spartina patens 



Intennediate & fresh m 

 Phragmites austral i s 

 Sagittaria falcata " 



tural crop the soil micro-organisms use it 

 as an energy substrate and compete with 

 the crop plant for available nitrogen. 



Although this laboratory test 

 suggested that litter can be converted to 

 high protein microbial biomass efficient- 

 ly, several recent studies showed that the 

 bacterial and fungal biomass associated 

 with detritus is quite small (Rublee et 

 al. 1978, Wiebe and Pomeroy 1972). This 

 may be at least partially because the 

 bacteria are cropped as rapidly as they 

 are produced by the ineiofauna. 



Other forms of nitrogen are 

 extracellular coinpounds produced by 

 microbes and proteins bound to oxidized 

 phenolic compounds (degradation products 

 of plant lignins). Many of these 

 compounds are relatively resistant to 

 decomposition and poor sources of organic 

 energy to detritus feeders. 



The aerobic decomposers comprise a 

 bewildering array of species and 

 physiological strains. Meyers et al . 

 (1971) identified the species Pichia 

 spartinae and Kluyveromyces drosophil arum 

 as dominant yeasts in the sTTt marsh 

 sediment surface. Hood and Colmer (1971) 

 characterized a number of physiological 

 groups of bacteria. They found that the 

 soil -root interface of the grass was the 

 site of most intense microbial activity. 

 Maltby (1982) found that the ratios of 

 actinomycetes to bacteria and of 



59 



