Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2013
Publication Date: 5/17/2013
Citation: Schutte, B.J., Davis, A.S., Wortman, S.E., Lindquist, J.L. 2013. Maternal environment effects on phenolic defenses in Abutilon theophrasti seeds. American Journal of Plant Sciences. 4:1127-1133. Interpretive Summary: Persistent weed problems have their source in persistent populations of weed seeds in the soil seed bank. To survive such hazards as predation and decay, weed seeds manufacture chemical defenses. Better knowledge of factors influencing weed chemical defenses will aid the development of novel weed control techniques targeting seeds. We studied the impact of resource availability to the mother plant on seed defense concentrations in velvetleaf (Abutilon theophrasti), a weed of economic importance in corn and soybean production in the Midwest. Velvetleaf seeds were produced at two locations: Mead, NE (Nebraska) and Havana, IL (Illinois). At each location, twelve distinct seed production environments were established with a full-factorial combination of soil manure amendment, (two levels: + / -), species combination (two levels: velvetleaf monoculture, velvetleaf with corn), and soil nitrogen fertilizer (three levels: 0, 0.5x or 1x local recommendations for corn). Resource availability was directly linked to velvetleaf plant size. Results indicated that as plant size increased, concentrations of seed chemical defenses decreased, but seed protein concentrations remained unchanged. Furthermore, as maternal plant size increased, total number of seeds produced increased. These results suggest that plants in resource rich environments (i.e., larger plants) produce more seeds, with each seed less chemically protected, than plants in resource poor environments (i.e., smaller plants). More generally, maternal environment appears to influence seed traits associated with susceptibility to predation and decay. Implications for intentional manipulation of weed seed fate through agronomic management require further testing under field conditions.
Technical Abstract: The maternal plant may have considerable influence on a class of phenolic compounds implicated with seed survival, ortho-dihydroxyphenols (hereafter “o-DHP”), because seed phenolic compounds primarily occur in structures derived entirely from the maternal plant (e.g., seed coats). Based on reports of phenolic concentrations in vegetative structures, we hypothesized that seed o-DHP concentrations decrease as resource availability in the maternal environment increases. We tested this hypothesis with Abutilon theophrasti., an agricultural weed of economic importance in the U.S. Corn Belt. Seeds were produced at two locations: Mead, NE (Nebraska) and Havana, IL (Illinois). At each location, twelve distinct seed production environments were established with a full-factorial combination of soil manure amendment, (two levels: + / -), species combination (two levels: A. theophrasti monoculture, A. theophrasti with maize), and soil nitrogen fertilizer (three levels: 0, 0.5x or 1x local recommendations for maize). Resource availability with respect to A. theophrasti was summarized by biomass at seed harvest (maternal environment biomass; MEB), with vegetative and reproductive biomasses measured separately. Seed o-DHP and protein concentrations were determined with spectrophotometric assays. Across seed lots, MEB ranged from 38.7 to 900.6 g/m^2, o-DHP concentrations ranged from 1.1 to 2.2 µmol/seed and protein concentrations ranged from 1.7 to 2.6 mg/seed. As MEB increased, seed o-DHP concentrations decreased exponentially but seed protein concentrations were static. Larger plants produced more seed than smaller plants as vegetative biomass was strongly correlated with reproductive biomass (r = 0.97, p < 0.001). Results support the initial hypothesis and suggest a tradeoff between seed output and levels of chemical protection for individual seeds that is driven by resource availability in the maternal environment.