Effect of litter nitrogen on decomposition and microbial biomass inSpartina alterniflora

Abstract

The effect on decomposition of 4 different levels of nitrogen in aerial tissue ofSpartina alterniflora, collected at the end of its growing season litter, was studied in laboratory percolators for 56 days at 20‡C. The CO2 evolution and the release of organic nitrogen and organic carbon were monitored. From these data, the ash-free dry weight (AFDW), nitrogen (N) content, and carbon∶nitrogen (C/N) ratio were calculated at various times during decomposition. Fungal biomass, bacterial biomass, and the relative autoradiographic activity of bacteria were measured at the end of the study. Decomposition was significantly affected by the nitrogen content of the litter. A 55% increase in plant N increased overall weight loss and k by 50% and 40%, respectively. Furthermore, k (calculated from time course weight loss data) responded linearly to the 4 different levels of nitrogen inSpartina tissue. Fungi appear to dominate the microbial community. At the end of the experiment, fungal biomass was between 2.23 and 3.08% of the AFDW, and was calculated to contain 12 to 22% of the nitrogen in the litter. Bacterial biomass was 1/10 of the fungal biomass, and 12-17% of the bacteria were active. The total microbial biomass was not affected by increased plant nitrogen. In the course of decomposition, the organic nitrogen and carbon were highest in the effluent water in all treatments during the first 8 days. The respiration rate (CO2 evolution) first increased to a maximum at day 18 and then decreased to a constant rate (1-2 mg C/day/g detritus). Respiration was highest in the high N litter. The C/N ratio in all treatments increased from the start to day 8, then decreased to day 20. In low N litter, C/N then increased again as a result of increased total organic nitrogen (TON) loss relative to carbon mineralization. In the high N, this was reversed.

Processes that influence carbon isotope variations in salt marsh sediments

“…Furthermore, the bacteria would most likely have to derive its nutrition from a source other than S. alterniflora, since heterotrophic bacteria apparently do not differ greatly in isotopic composition from that of their carbon source (Fry & Sherr 1984, Blair et al 1985 Schwingharner ct d. (1983) reporled ihai bacterial biomass contributed 1.3 % to the total sedimentary carbon. Marinucci et al (1983) found a total microbial carbon content of 2.6 % of total carbon in aerobically degraded S. alterniflora litter. Therefore, it is unlikely that such a small standing stock of bacterial carbon per se could influence the isotopic composition of SOM.…”

Effects of pH and plant source on lignocellulose biodegradation rates in two wetland ecosystems, the Okefenokee Swamp and a Georgia salt marsh1,2,3

“…The lignocelluloses from these herbaceous plants were mineralized several times faster than that from the hardwood, R. mangle. In various studies of the relationship between biodegradability of lignocellulosic material and chemical composition, lignin content (Cromack 1973;Fogel and Cromack 1977) and nitrogen content (Godshalk and Wetzel 1978;Marinucci et al 1983) are often highly correlated with biodegradability. Melillo et al (1982) found that the mass of hardwood leaf litter remaining in litter bags in the Hubbard Brook Experimental Forest after 1 year was more highly correlated with initial lignin-to-nitrogen ratios of leaf material than with lignin or nitrogen content alone.…”

Decomposition in salt marsh ecosystems: phenolic dynamics during decay of litter of Spartina alterniflora

“…The effect of nitrogen is presumably due to stimulation of microbial activity (Witkamp 1966, Satchel1 & Lowe 1967, Harrison 1982, Marinucci et al 1983. The effect also may be the result of an interaction with phenolic compounds.…”