Maternal Environment Effects on Phenolic Defenses in <i>Abutilon theophrasti</i> Seeds

Abstract

A class of phenolic compounds, ortho- dihydroxyphenols (hereafter “ o- DHP”), has been implicated with seed survival. Based on expectations of the growth-differentiation balance hypothesis, we predicted that seed o- DHP concentration exhibits a curvilinear response to increasing resource availability in the maternal environment, with maximum o- DHP occurring at moderate resource levels. To test this hypothesis, Abutilon theophrasti seeds were produced under field conditions at two locations. Each location included twelve maternal environments established through factorial combinations of soil compost (+/- ), species assemblage ( A. theophrasti with and without maize), and soil nitrogen fertilizer (0, 0.5 × or 1 × local recommendations for maize). Resource availability with respect to A. theophrasti growth was summarized by above-ground biomass at seed harvest (maternal biomass). Results indicated that seed o- DHP concentrations increased then decreased in response to increasing maternal biomass. This relationship was modeled with a unimodal function specific to location (Location 1, y = 1.18 + 0.03 x e - 0.02 x , pseudo -R 2 = 0.59, p = 0.003; Location 2, y = 1.40 + 0.006 x e - 0.005 x ; pseudo- R 2 = 0.34, p = 0.05) . Seed protein concentrations remained constant across maternal biomass levels. Because inherent vulnerability to predation and decay is considered a consequence of chemical protection relative to nutritional offering, our results suggest that A. theophrasti seed susceptibility to lethal attack is influenced by resource levels in the maternal environment. More broadly, our results suggest that the growth- differentiation balance hypothesis can be extended to maternal effects on seed phenolics.