Patterns in Nutrient Availability and Plant Diversity of Temperate North American Wetlands

Abstract

Few wetland studies from temperate North America have related either species richness or plant community composition to any direct measure of nutrient availability, or examined changes in species composition following experimental nutrient additions. Studies of wetlands in western Europe and of other terrestrial ecosystems in North America frequently show that nutrient enrichment leads to changes in species composition, declines in overall plant species diversity, and loss of rare and uncommon species. We therefore used an extensive literature survey and analysis of data on plant species composition, species richness, productivity or standing crop, and C:N:P stoichiometry in plant tissues and surface soils to draw conclusions about the nature of nutrient limitation in temperate North American bogs, fens, marshes, and swamps, and to infer their potential response to nutrient enrichment. We searched all major bibliographic data bases for studies containing such data (through March 1998) and added relevant data from our own ongoing research. We analyzed plant and soil data sets by wetland type and by wetland soil type, and the plant data set also by growth form. Existing studies appear to confirm common generalizations: (1) plant community type changes across broad nutrient gradients; (2) species richness declines as various indicators of nutrient availability increase beyond some threshold; and (3) rare and uncommon species are almost always associated with species‐rich communities. However, (1) these generalizations do not always hold within community types; (2) for many community types, the threshold beyond which richness declines has not been established, and high or low diversity may occur below that threshold; and (3) the failure of many studies to include bryophytes precludes drawing strong conclusions about nutrient availability and diversity in peatlands. Marshes had significantly lower mean nitrogen:phosphorus (N:P) ratios in live tissue than other wetland types (bogs, fens, and swamps), which did not differ significantly from each other. Mean N:P ratios in live tissues were significantly higher in peatlands than in mineral‐soil wetlands. Nitrogen:phosporus ratios in litter did not differ significantly between peatlands and mineral‐soil wetlands but were higher than in live tissues. Among growth forms, the highest mean N:P ratios in live tissues occurred in bryophytes, and the lowest in vascular herbaceous species. Only bryophyte live tissues differed significantly from other growth forms; litter N:P ratios were not significantly different among growth forms. Average N:P ratios in surface soils were lower in marshes and swamps than in bogs and fens. Wetlands on mineral soils had lower average N:P ratios than wetlands on peat soils. Average surface soil N:P ratios rose sharply at high soil organic‐matter contents (≥90%) and were generally greater than 16 at organic‐matter concentrations above 20%. In combination, plant tissue and surface soil N:P ratios suggest that a large proportion of North American wetla...

Foliar nitrogen and phosphorus stoichiometry of three wetland plants distributed along an elevation gradient in Dongting Lake, China

“…also reported low foliar P concentrations for wetland vegetation in China compared to global averages 29 . Low P levels might be due to P in the soil being highly insoluble compared to N. Furthermore, a dense root system is usually needed for plants to extract significant amounts of P from soil 13 . However, in Dongting Lake, these 3 macrophyte species tend to have shallow root systems to acclimate to flooding stresses, which might be unfavourable for P absorption.…”

“…In some North American wetlands, the structure of plant communities changes significantly with nutrient gradients, while species richness declines with increasing nutrient availability 13 . The Resource Ratio Hypothesis suggests that when the limiting resource in a given vegetation community changes, the dominant species changes due to altered growth performance and competition.…”

Phenotypic plasticity of introduced versus native purple loosestrife: univariate and multivariate reaction norm approaches

“…On 30 May 2006, seedlings were transplanted into individual plastic pots (30 cm diameter 9 25 cm deep), and placed in plastic wading pools (1.4 m diameter 9 30 cm deep). The pots contained Sunshine LC1 potting soil (Sun Gro Horticulture Canada, Seba Beach, AB, Canada), which has an initial nutrient charge that would correspond to high nutrient levels found in natural wetland soils, i.e., approximating three times the average N content (Bridgham et al 1996;Bedford et al 1999). Because that initial charge is highly water-soluble and provides the equivalent of approximately one application of a liquid fertilizer (Sun Gro Horticulture, personal communication), nutrients were supplemented as described below.…”

“…The Osmocote applied in the high-nutrient treatment followed the manufacturer's recommendation for the amount and rate that is generally used to achieve high levels of fertilization (i.e., one application for the 3-to 4-month growing period). Consequently, the low-and high-nutrient treatments were designed to be reasonable approximations of nutrient levels that would be encountered under natural field conditions (cf., Bridgham et al 1996;Thormann and Bayley 1997;Bedford et al 1999). The date of first flowering by each plant was recorded throughout the experimental period.…”

Biotic and Abiotic Conditions in Michigan Prairie Fen Invaded by Glossy Buckthorn (Frangula alnus)

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