Nutrient limitation and botanical diversity in wetlands: Can fertilisation raise species richness?

S. Gusewell, K.M. Bailey, W.J. Roem, B.L. Bedford

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71 Citations (Scopus)


The 'resource balance hypothesis' proposes that the species richness of grassland vegetation is potentially highest when the N:P ratio of plant tissues is 10-15 (co-limitation), so that species richness could be raised by fertilisation with N or P at sites with lower or higher N:P ratios, respectively. Here we use data from field surveys in Swiss, Dutch and American fens or wet grasslands to analyse what changes in N:P ratios might produce noticeable changes in species richness. Plant species numbers, above-ground biomass, tissue N and P concentrations and soil pH were recorded in plots of 0.06-4 m2. In each data set, plots with intermediate tissue N:P ratios (6-20) were on average most species-rich, but N:P ratios explained only 5-37% of the variation in species richness. Moreover, these effects were partially confounded with those of vegetation biomass and/or soil pH. The unique effects of N:P ratios (excluding those shared with biomass and pH) explained 11-17% of variation in species richness. The relationship between species richness and N:P ratios was asymmetric: plots with high N:P ratios were more species-poor than those with low N:P ratios. This was paralleled by a smaller species pool size at high N:P ratios (estimated from species numbers in multiple records), suggesting that fewer species are adapted to P-limited conditions than to N-limited conditions. According to these data, species richness in wetlands may possibly be raised by P-fertilisation when the initial N:P ratio of the vegetation is well above 20, but this option is not recommended for nature conservation as it might promote common species at the expense of rare ones
Original languageEnglish
Pages (from-to)71-80
Issue number1
Publication statusPublished - 2005


  • north-american wetlands
  • n-p ratios
  • environmental variables
  • european vegetation
  • regional patterns
  • community biomass
  • pool hypothesis
  • plant diversity
  • arctic tundra
  • nitrogen


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