Does release from natural belowground enemies help

Authors: John C Volin Eric L Kruger Valeria C Volin Michael F Tobin Kaoru Kitajima

Publish Date: 2009/11/21

Volume: 208, Issue: 2, Pages: 223-234

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Abstract

Lygodium microphyllum Cav R Br a climbing fern native to the Pantropics of the Old World is aggressively colonizing natural ecosystems in the Florida Peninsula Here we examined soil factors that might affect the fern’s invasiveness specifically addressing the hypothesis that a release from natural belowground enemies contributes to its vigorous growth in Florida We also investigated phenotypic differences of sporophytes raised from spores collected in Florida and the fern’s native range in Australia hypothesizing that the Florida population would possess traits resulting in faster growth and superior competitive ability than the two Australian populations We tested our hypotheses in parallel greenhouse experiments—one in Australia using soil from the fern’s native habitat and another in Florida USA with soil from a recently colonized ecosystem Fern growth rate and its principal determinants were expressed relative to the optimal growth with a common sand culture in each experiment and compared among treatments in which soil was altered through either sterilization or nutrient amendment or both Contrary to the expectation the optimal growth rates in the sand culture were higher for Australian populations than the Florida population while the comparatively poor growth of all populations in unaltered soil was stimulated by nutrient amendment and sterilization The overall effect of sterilization however was muted under highnutrient conditions suggesting that the effect of soil sterilization may be due to greater nutrient availability in sterilized soils The only exception was the local population from the site where the soil was collected for the experiment in Australia which grew significantly faster in sterilized than in nonsterilized soil and also more rapidly in response to soil insecticide application Our results indicate that the invasiveness of L microphyllum in Florida is not a simple phenotypic difference in inherent growth rate as predicted by the evolution of increased competitive ability hypothesis but it may be mediated in part by release from soilborne enemies that vary in their effectiveness even within the native geographical range of the fernThe research was funded by competitive grants from the Florida Department of Environmental Protection and the South Florida Water Management District A special note of acknowledgment goes to Dr Susanne Schmidt her post docs and students as well as her colleagues Drs Liz Aitken and Gimme Walter at the University of Queensland who provided space and stimulating discussions during the Australian portion of the study Special thanks go to Matthew Purcell Tony Wright and colleagues at the Commonwealth Scientific and Industrial Research Organization’s Australian Biological Control Laboratory without their substantial assistance in the field access to their growth facilities and introduction to a proper Australian pie the Australia study could not have been accomplished Finally we would like to thank many students especially Andrew Ridley on both sides of the World who helped with the harvests The experiments comply with the current laws of both countries where they were performed

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