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United States Department of Agriculture

Agricultural Research Service

Research Project: ECOLOGY, MANAGEMENT AND ENVIRONMENTAL IMPACT OF WEEDY AND INVASIVE PLANT SPECIES IN A CHANGING CLIMATE

Location: Global Change and Photosynthesis Research Unit

Title: Investment in seed physical defence is associated with species' light requirement for regeneration and seed persistence: evidence from Macaranga species in Borneo

Authors
item Tiansawat, Pimonrat -
item Davis, Adam
item Berhow, Mark
item Zalamea, P Camilo -
item Dalling, James -

Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 19, 2014
Publication Date: June 18, 2014
Citation: Tiansawat, P., Davis, A.S., Berhow, M.A., Zalamea, P., Dalling, J.W. 2014. Investment in seed physical defence is associated with species' light requirement for regeneration and seed persistence: evidence from Macaranga species in Borneo. PLoS One. 9(6):e99691.

Interpretive Summary: Improved understanding of seed traits related to long-term survival in the soil seedbank will aid the development of weed management tactics aimed at reducing weed population growth rates. Data on seed coat thickness, seed coat fracture resistance, and the abundance and diversity of phenolic compounds were collected for 10 early successional plant species. Defense trait data were used to test whether there is a trade-off in physical versus chemical defense investment, and to determine how investment varies with seed mass, and adult light requirement. Across species there was no correlation between seed coat thickness and phenolic abundance, indicating no trade-off between physical and chemical defense. However, large variation was found among species in investment in physical and chemical defenses. While chemical defense investment was not correlated to other species and seed traits, physical defenses were positively correlated with adult light requirement. For a subset of the species we evaluated the importance of physical and chemical defence to seed persistence in the soil. Species whose seeds remained viable for longer periods in the soil seedbank were relatively more dependent upon physical defenses than chemical defenses. This relationship has been observed in other habitats, suggesting that it may be broadly applicable. This finding suggests that weed management tactics that create physical damage to weed seeds may be especially useful in reducing their persistence in the soil seedbank.

Technical Abstract: The life stage from seed dispersal to seedling emergence is often critical in determining the regeneration success of plants. During this period seeds must survive an array of seed predators and pathogens and germinate under conditions favorable for seedling establishment. To maximise recruitment success plants protect seeds using a diversity of chemical and physical defenses. However to date, the relationship between these defense classes, and their association with other life history traits, is not well understood. Data on seed coat thickness, seed coat fracture resistance, and the abundance and diversity of phenolic compounds were collected for 10 pioneer tree species in the genus Macaranga from Borneo. Defense trait data were used to test whether there is a trade-off in physical versus chemical defense investment, and to determine how investment varies with seed mass, and adult light requirement. Across species there was no correlation between seed coat thickness and phenolic abundance, indicating no trade-off between physical and chemical defense. However, large interspecific variation was found in investment in physical defense (seed coat thickness 94-410 µm) and chemical defenses (1-20 phenols). While chemical defense investment was not correlated to other species and seed traits, physical defenses were positively correlated with adult light requirement. For a subset of five Macaranga species we evaluated the importance of physical and chemical defense to seed persistence in the soil. Seed persistence in the soil was represented as the time to which the viability of seeds was reduced to half of initial viability (seed half-life). The seed half-life was negatively related to the ratio of seed coat thickness to phenolic abundance, suggesting that for Macaranga, physical defenses are more important than chemical defense in determining seed persistence in the soil.

Last Modified: 9/23/2014
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