Interspecific variation in persistence of buried weed seeds follows trade-offs among physiological, chemical and physical seed defenses

Authors: Davis, Adam; FU, XIANHUI - University Of Illinois; SCHUTTE, BRIAN - New Mexico State University; Berhow, Mark; DALLING, JAMES - University Of Illinois

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2016
Publication Date: 10/1/2016
Citation: Davis, A.S., Fu, X., Schutte, B.J., Berhow, M.A., Dalling, J.W. 2016. Interspecific variation in persistence of buried weed seeds follows trade-offs among physiological, chemical and physical seed defenses. Ecology and Evolution. 6(19):6836-6845.

Interpretive Summary: Weed seedbank management is gaining currency with producers as herbicide resistant weeds proliferate and seedbanks become reservoirs of herbicide resistance genes. Making progress in developing novel, effective approaches to weed seedbank management will benefit from improved understanding of how weed traits affect the persistence of weed seeds in the soil seedbank. We studied trade-offs among physiological, chemical and physical traits of weed seeds and their persistence in the soil seedbank in a common garden study. Seeds of eleven seedbank annual weed species were buried in Savoy, IL, from 2007 through 2012. Seedling emergence was measured weekly and seed viability measured annually. Seed physiological (dormancy), chemical (phenolic compound diversity and concentration, invertebrate toxicity) and physical traits (seed coat mass, thickness and rupture resistance) were measured. Seed half-life in the soil seedbank varied strongly among weed species, ranging from 0.25 years (Bassia scoparia) to 2.22 years (Abutilon theophrasti). A quantitative comparison between our results and other published work indicated that weed seed dormancy and seedbank persistence are linked across environments and agroecosystems. Moreover, relative investment in chemical and physical seed defence varies with seedbank persistence. In particular, species with long seed half-lives in the soil seedbank tend to invest less in chemical defences. This makes them highly vulnerable to physical harvest weed seed control strategies, with small amounts of damage resulting in full decay of such seeds.

Technical Abstract: Soil seedbanks drive infestations of annual weeds, yet weed management focuses largely on seedling mortality. As weed seedbanks increasingly become reservoirs of herbicide resistance, species-specific seedbank management approaches will be essential. Limited understanding of interspecific variation in seed traits underlying seedbank persistence currently hinders the development of targeted seedbank management strategies. We quantified interspecific trade-offs among physiological, chemical and physical traits of weed seeds and their persistence in the soil seedbank in a common garden study. Seeds of eleven seedbank annual weed species were buried in Savoy, IL, from 2007 through 2012. Seedling recruitment was measured weekly and seed viability measured annually. Seed physiological (dormancy), chemical (phenolic compound diversity and concentration, invertebrate toxicity) and physical traits (seed coat mass, thickness and rupture resistance) were measured. Seed half-life in the soil seedbank [t(0.5)] showed strong interspecific variation (F(10,30) = 15, P < 0.0001), ranging from 0.25 years (Bassia scoparia) to 2.22 years (Abutilon theophrasti). Modeling covariances among seed traits and seedbank persistence quantified support for two putative defence syndromes (physiological-chemical and physical-chemical) and highlighted the central role of seed dormancy in controlling seed persistence. A quantitative comparison between our results and other published work indicated that weed seed dormancy and seedbank persistence are linked across environments and agroecosystems. Moreover, among seedbank-forming early successional plant species, relative investment in chemical and physical seed defence varies with seedbank persistence. Strong covariance among weed seed traits and persistence in the soil seedbank indicates potential for seedbank management practices tailored to specific weed species. In particular, species with high t(0.5) values tend to invest less in chemical defences. This makes them highly vulnerable to physical harvest weed seed control strategies, with small amounts of damage resulting in full decay of such seeds.