Macrophytes nitrogen

Fig. 1. Model depicting nitrogen flows in a kelp bed community. Primary production by macrophytes is partitioned into particulate (POM) and dissolved (DOM) components. Filter-feeders feed on detritus consisting of POM, bacteria and animal faeces. Recycling of nitrogen via the feedback loop provided by faeces is indicated by heavy lines. Fig. la) shows the model under downwelling conditions, when phytoplankton is imported with surface water from offshore. Fig. lb) shows the model under upwelling conditions when it is assumed that phytoplankton in the upwelling water is negligible and excess detritus is exported in surface water.

Fig. 2. Model output showing the percentage of different food components available to filter feeders with varying water transport (0-7 water column turnovers per day). The nitrogen content of all food available to filter feeders is shown below, and is much higher when the system is "closed" (0 turnovers). Fig. 2a) shows food proportions and quantities under upwelling conditions when all food is derived from macrophytes. Fig. 2b) depicts downwelling conditions when phytoplankton is an additional component (After Wickens and Field, 1985).

Under conditions of continuous downwelling, phytoplankton imported from outside the system becomes increasingly important with faster rates of water transport (Fig. 2b) and at rates faster than one water-column turnover per day, phytoplankton contribute more nitrogen to filter-feeder food than macrophyte particulate matter or recycled faeces. 

Wetzel, R. G., and B. A. Manny. 1972. Secretion of dissolved organic carbon and nitrogen by aquatic macrophytes. Verhandlungen der Internationale Vereiningung fur Theoretische und Angewandte Limnologie 18 162—170. 

Rice, D.L., and Tenore, K.R. (1981) Dynamics of carbon and nitrogen during the decomposition of detritus derived from estuarine macrophytes. Estuar. Coastal Shelf Sci. 13, 681-690. 

Doyle, R. D. 1991. Primary production and nitrogen cycling within the periphyton community associated with emergent aquatic macrophytes in an Amazon floodplain lake. Ph.D. Thesis, University of Maryland, p. 269. 

In benthic environments, ranging from the rhizosphere of shallow water macrophyte communities such as Zostera, Thalassia and Spartim hundreds of different diazotrophic strains have been isolated, and these are typically microaerophyUic or anaerobic, and often are sulfate respiring bacteria. These diazotrophs make significant contributions to the nitrogen economy of their respective plant communities. 

The influence of benthic macrophytes on nitrogen cycle processes... 

Numerous biotic factors influence N processing within sediments, including the composition of the microbial, macrofaunal, and macrophyte communities, behaviors of the various infaunal communities, and trophic transfer of carbon and nitrogen between communities. Interactions between benthic communities may be physical, chemical, or biological in nature and, in turn, are influenced by the physical nature of the environment, sediment composition, and autotrophic dominance (Fig. 19.3). 

Haines, K. C., and Wheeler, P. A. (1978). Ammonium and nitrate uptake by the marine macrophytes Hypnea musciformis (Rhodophyta) 2nd. Macrocystis pyrifera (Phaeophyta). J. Phycol. 14, 319—324. Hanisak, M. D. (1979). Nitrogen limitation of Codium fragile ssp. tomentosoides as determined by tissue analysis. Mar. Biol. 50, 333—337. 

Oligotrophic. Refers to waters low in nutrient loading with low primary production of organic material by algae and/or macrophytes. Growth in an oligotrophic water is often limited by low levels of phosphorus and nitrogen (see also eutrophic and mesotrophic). 

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