AOBPreview published online on February 13, 2007
Annals of Botany, doi:10.1093/aob/mcl289
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Sensitivity of the Invasive Geophyte Oxalis pes-caprae to Nutrient Availability and Competition
1 Division of Biological Sciences, The University of Montana, Missoula, MT 59812, USA
2 Department of Environmental Sciences, University of Girona, Campus de Montilivi s/n 17071, Girona, Spain
3 Center for Ecological Research and Forestry Applications (CREAF) and Department of Animal Biology, Plant Biology and Ecology, Edifici C, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Catalonia, Spain
* For correspondence. E-mail sala{at}mso.umt.edu
Received: 29 June 2006 Returned for revision: 30 August 2006 Accepted: 4 December 2006
BACKGROUND AND AIMS: Invasion by alien plants may be partially related to disturbance-related increases in nutrient availability and decreases of competition with native species, and to superior competitive ability of the invader. Oxalis pes-caprae is an invasive winter geophyte in the Mediterranean Islands that reproduces vegetatively via bulbs. An investigation was made into the relative responses of O. pes-caprae and the native annual grass Lolium rigidum to nutrient availability and to competition with each other in order to understand patterns of invasion in the field. Because Oxalis accumulates oxalic acid in its leaves, which could ameliorate soil phosphorous availability, field observations were made to determine whether the presence of Oxalis alters soil P availability.
METHODS: A full-factorial glasshouse experiment was conducted with nutrient availability (high and low) and competition (Lolium alone, Oxalis alone, and Lolium and Oxalis together). Plant performance was assessed by determining (1) above- and below-ground biomass at the time of Oxalis maximum biomass and (2) reproductive output of Oxalis and Lolium at the end of their respective growth cycles. Measurements were also taken for leaf N and P content. Soil samples were taken in the field from paired Oxalis-invaded and non-invaded plots located in Menorca (Balearic Islands) and available P was determined.
KEY RESULTS: High nutrient availability increased Oxalis and Lolium vegetative biomass and reproductive output to a similar degree. Competition with Lolium had a much stronger negative effect on Oxalis bulb production than reduced nutrients. Lolium was a superior competitor than Oxalis; the latter did not affect Lolium maximum biomass and spike production. Significantly greater soil-P availability in Oxalis-invaded field soils relative to paired non-invaded soils suggest that Oxalis influences soil P cycling.
CONCLUSIONS: Oxalis is a poor competitor. This is consistent with the preferential distribution of Oxalis in disturbed areas such as ruderal habitats, and might explain its low influence on the cover of native species in invaded sites. The results also suggest that certain disturbances (e.g. autumn ploughing) may greatly enhance Oxalis invasion.
Key words: Oxalis pes-caprae, invasive species, competition, nutrients, Lolium rigidum, asexual reproduction, Mediterranean Islands
Present address: Estación Biológica de Doñana (EBD-CSIC), Avd/ Parque de María Luisa s/n, Pabellón del Perú, 41013 Sevilla, Spain