The demographic consequences of nitrogen fertilization of a population of sundew, Drosera rotundifolia

This paper reports the result of a 4-year fertilization experiment using nitrogen, on a level with current deposition, on the demography of a Drosera rotundifolia L. population on a raised bog. Five different fertilization treatments were employed: (i) control with no extra nitrogen, (ii) 0-5, (iii) 10, (iv) 2 0, and (v) 40 g N m “ 2 year -l. Spearman rank correlation test unveiled a significant increase in the daily killing power in relation to the amount of nitrogen fertilization. This was valid for all cohorts studied during the 4 years. The addition of nitrogen fertilizer influenced the reproductive behaviour of the D. rotundifolia plants. The proportion of flowering individuals increased in the second year, after which the frequency of flowering gradually decreased compared with the control plots. The number of flowers per individual was not influenced by the nitrogen treatment. The population size in the control plots remained rather constant over the 4 years. Population size also remained constant when low-concentration fertilizer was added. In these nitrogen-treated plots, however, the three youngest age classes represented more than 55% of the total population compared with less than 40% in the control plots. In the plots treated with 2-0 and 4 0 N m-2 year-', the population size decreased dramatically between the first 2 years. From then and up to the end of the study these populations remained at a nearly constant low level. The nitrogen treatment resulted in a significantly increased density of both Andromeda polifolia and Eriophorum vaginatum.