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

• Published in: Oikos
• Main Authors: Gusewell, S., Bailey, K.M., Roem, W.J., Bedford, B.L.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2005
• Subjects: arctic tundra; community biomass; environmental variables; european vegetation; n-p ratios; nitrogen; north-american wetlands; plant diversity; pool hypothesis; regional patterns; Arctic; Tundra
• Online Access: https://research.wur.nl/en/publications/nutrient-limitation-and-botanical-diversity-in-wetlands-can-ferti; https://doi.org/10.1111/j.0030-1299.2005.13587.x

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