Diagenesis of belowground biomass of Spartina alterniflora in salt‐marsh sediments

Abstract

Belowground biomass of Spartina alterniflora lost 55% of its organic matter during 18 months of decomposition in salt-marsh sediments. Significant losses of lignin were observed under highly reducing conditions confirming previous reports of lignin degradation in the absence of molecular oxygen. The submolecular components of lignin varied in susceptibility to degradation and were ranked in the following descending order of resistance to decomposition: V-P> S-C. The preferential degradation of 1 he cinnamyl and syringyl components constrains the quantitative usefulness of these compounds for estimating the contributions ofherbaceous and angiosperm tissues to pools of dissolved and particulate organic matter. The relative concentration of lignin increased about 1.6-fold during decomposition owing to the more rapid loss of polysaccharides.Two phases in nitrogen dynamics were evident during the decomposition study. During the first 4 months of decomposition there was a net loss of N from Spartina tissues at a rate of about 10 gg N g-l tissue d-I. After this initial phase of net N loss, a phase of N immobilization was evident and was tightly coupled with rates of microbial degradation of the tissues. Net rates of N immobilization were -19 pg N g-' tissue d -I; by the end of the 18-month study more N had accumulated in the tissues than was initially present. Stable N isotope composilions of decaying Spartina were also very dynamic and reflected the sources of N that were immobilized during decomposition and the N transformations that occurred on the detrital particles.The stable C isotope composition of the polysaccharide components of Spartina was -6%~ heavier than that of the lignin component. The isotopic compositions of these components retained the 6o/oo difference throughout the 18-month study. The stable C isotope composition of the bulk tissues, however, decreased gradually during decomposition as the isotopically heavier polysaccharides were preferentially lost. Residual material was relatively enriched in the isotopically lighter, lignin-deriveci C.'

Drivers of Sediment Accumulation and Nutrient Burial in Coastal Stormwater Detention Ponds, South Carolina, USA

“…The oldest sediments have had the most time for mineralization processes to occur. N concentrations decreased more rapidly with depth than did C, which suggests preferential remineralization of N rich compounds (Benner 1991;Hopkinson and others 1997). P sediment depth profiles were more variable, showing no broad down core trends.…”

Litter decomposition in a subtropical plantation in Qianyanzhou, China

“…Mellilo et al (1989) showed a non-linear pattern in a 77-month period, with 15 N depletion during the initial 22 months and slight 15 N enrichment during the remainder of 55 months. Benner et al (1991) reported that significant 15 N depletion occurred during a period of 18 months. Connin et al (2001) did not show a clear pattern for 15 N dynamics during litter decomposition over 6 years.…”

“…Numerous studies have suggested that 15 N enrichment occurred in the remaining litter with decomposition time (Nadelhoffer and Fry 1988;Asada et al 2005). However, a non-linear pattern was observed in a red pine plantation during a 77-month period (Mellilo et al 1989) while significant 15 N depletion was found during 18 months of decomposition of belowground parts in salt-marsh sediments (Benner et al 1991). Over a period of 6 years, there was no clear pattern for 15 N dynamics during litter decomposition (Connin et al 2001).…”

The faunal role in the degradation of the common intertidal salt marsh plant Scirpus maritimus

“…Concerning the plant material, Morrisson (1989) verified, after temporal measurements, that litter had a lower C:N ratio due to heterotrophic bacteria colonization. On the other hand, Benner et al (1997) found that the N content in decomposing Spartina tissues was highly variable, which was reflected in the wide range of C:N values, and that a major fraction (>50%) of the initial N in the tissue was lost during the early stages of decomposition, followed by the slow accumulation of exogenous N. No significant differences were found concerning the sediment C:N and N:P ratios during the degradation period. It has been shown that bacteria grow very rapidly in shallow water estuaries where efflux from the sediment dominates the dynamics in the water column (Hopkinson et al, 1998).…”

“…In fact, it has been shown for other plant species that, in undisturbed marsh sediments, the major fate of below-ground production appears to be microbial decomposition (Benner et al, 1997), although the presence of meiofauna may also enhance the degradation (e.g. DeMesel et al, 2004).…”