Microbial biomass and productivity in seagrass beds

Abstract

Different methods for measuring the rates of processes mediated by bacteria in sediments and the rates of bacterial cell production have been compared. In addition, net production of the seagrass Zostera capricorni and bacterial production have been compared and some interrelationships with the nitrogen cycle discussed. Seagrass productivity was estimated by measuring the plastochrone interval using a leaf stapling technique. The average productivity over four seasons was 1.28 +/- 0.28 g C m-2 day-1 (mean +/- standard deviation, n = 4). Bacterial productivity was measured five times throughout a year using the rate of tritiated thymidine incorporated into DNA. Average values were 33 +/- 12 mg C m-2 day-1 for sediment and 23 +/- 4 for water column (n = 5). Spatial variability between samples was greater than seasonal variation for both seagrass productivity and bacterial productivity. On one occasion, bacterial productivity was measured using the rate of 32P incorporated into phospholipid. The values were comparable to those obtained with tritiated thymidine. The rate of sulfate reduction was 10 mmol SO4(-2) m-2 day-1. The rate of methanogenesis was low, being 5.6 mg CH4 produced m-2 day-1. A comparison of C flux measured using rates of sulfate reduction and DNA synthesis indicated that anaerobic processes were predominant in these sediments. An analysis of microbial biomass and community structure, using techniques of phospholipid analysis, showed that bacteria were predominant members of the microbial biomass and that of these, strictly anaerobic bacteria were the main components. Ammonia concentration in interstitial water varied from 23 to 71 micromoles. Estimates of the amount of ammonia required by seagrass showed that the ammonia would turn over about once per day. Rapid recycling of nitrogen by bacteria and bacterial grazers is probably important.

Benthic microbial metabolism in seagrass meadows along a carbonate gradient in Sulawesi, Indonesia

“…(Table 6). These rates are comparable to the high end of the range of rates measured in other seagrass environments (Oremland 1975, Moriarty et al 1985.…”

Estimation of the microbial biomass in tidal flat sediment by fumigation-extraction

“…Findlay et al (1989) found by direct counts a 3 to 4 times smaller microbial biomass than by phospholipid analysis. The phospholipid content of 1 g bacterial biomass varies between 50 ~mol (Findlay et al, 1989) and 250 [tmol (Moriarty et al, 1985). The factor of the fumigation-extraction method to convert CHC13-1abile C to microbial biomass C is less variable (Kaiser et al, 1992), but also not completely satisfactory because it was calibrated mainly for agricultural soils and not for oxic and anoxic sediments (Jenkinson, 1988;Wu et al, 1990).…”

“…The microbial biomass is defined as the sum of organisms smaller than 5 • 103 ~m 3 (Jenkinson & Ladd, 1981) and is recognized as the most important fraction of organic matter in different sediments (Moriarty et al, 1985;Alongi, 1988). Heterotrophic microorganisms mineralize the greatest part of all organic material that enters the sediment ecosystem, converting it to simple inorganic compounds that can be used again by autotrophic organisms.…”

Sulfate Reduction and Sulfur Cycles at Two Seagrass Beds Inhabited by Cold Affinity Zostera marina and Warm Affinity Halophila nipponica in Temperate Coastal Waters

“…The positive correlation between the SRR and BGB (Fig. 5c) suggested that a substantial amount of dissolved organic carbon (DOC) is released via roots and rhizomes (Moriarty et al 1985;Blackburn et al 1994;Holmer et al 2006). Considering the general positive relationship between the SRR and BGB, further correlation analyses for individual seagrass species revealed that the correlation between the SRR (Fig.…”