Community Ecology

The limited number of vascular plant species has made salt marshes very suitable for both descriptive and manipulative studies. Early researchers attributed plant species distributions to their physiological tolerance for the abiotic environment, without regard to species interactions. J. A. Silander and J. Antonovics used perturbation-response methods to determine that biotic forces also affected species distributions. Others effectively used reciprocal transplanting to examine the relative importance of abiotic conditions and interspecific competition to species distributions. For example, S. Pennings and R. Callaway revealed interspecific interactions among southern California halophytes, and S. Hacker and M. Bertness reported interspecific interactions among New England halophytes. Manipulative transplantation has shown that species distributions respond to abiotic conditions, facilitation, and competition.

The wide latitudinal range of salt marshes allowed study of community structure and function in relation to sea-level variations, for example, James Morris documented and modeled interannual variations in salinity and its effect on S. alterniflora growth. Such studies led to predictions of changes in response to global climate change.

Ecosystem Functioning

The monotypic nature of USA Atlantic Coast salt marshes aided early studies of vascular plant productivity and considerable literature developed around the rates of productivity and alternative methods of calculating gross and net productivity - work that transferred to grasslands and other nonwoody vegetation. Nitrogen dynamics were a later focus. The first marine system to have a nitrogen budget was Great Sippewisset Marsh in Massachusetts. The budget quantified nitrogen inputs from groundwater, precipitation, nitrogen fixation, and tidal flow, and nitrogen outputs from tidal exchange, denitrification, and buried sediments.

Integrating Structure and Function

A long controversy over the causes of height variation in Spartina spp. has involved USA researchers on both the Atlantic and Pacific Coasts and has linked plant and ecosystem ecology. The most convincing evidence for a genetic ('nature') component is that of D. Seliskar and J. Gallagher, who grew genotypes from Massachusetts, Georgia, and Delaware for 11 years in a common garden and documented persistent phenotypic differences. A series of papers on soil biogeochemistry explained the role of 'nurture'. Nitrogen was shown to be a key limiting factor for S. alterniflora plant growth because nitrate is quickly reduced to ammonia by bacteria in poorly drained areas away from creeks, where soils have lower soil redox potential. Sulfate-reducing bacteria were also implicated, because they reduce sulfate to sulfide, which impairs the growth of sensitive plant species. Increased soil redox potential and greater pore water turnover in creek-side habitat contributes to taller height forms of S. alterniflora. Thus, both genetics and environment influence height forms of S. alterniflora, an outcome of both community and ecosystem research.

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