Influence of perennial forage communities on weed seed mortality and seed microbial associations

Understanding how crop species or communities influence weed seed mortality could effectively build ecological weed management systems. Therefore, we examined whether perennial forage monocultures or mixtures can accelerate weed seed mortality and affect the microbial composition of seeds. We buried mesh bags containing weed seeds of either Powell amaranth (Amaranthus powellii S. Watson) or velvetleaf (Abutilon theophrasti Medik.) in perennial forage treatments consisting of monocultures and mixtures of alfalfa (Medicago sativa L.), forage chicory (Cichorium intybus L.), and orchardgrass (Dactylis glomerata L.). Throughout a 2.5-yr duration, we evaluated seed mortality of both weed species and used 16S rRNA and internal transcribed spacer (ITS) amplicon sequencing to characterize A. powellii seed bacterial and fungal composition, respectively. We found limited effects of perennial forage treatment on A. theophrasti seed mortality, as the alfalfa-chicory biculture resulted in greater seed mortality compared with the orchardgrass monoculture. However, we found no other effects of perennial forage treatment on A. theophrasti or A. powellii seed mortality, nor did forage treatment affect the composition of bacteria or fungi associated with A. powellii seeds. We also found no effect of perennial forage richness on seed mortality of either weed species. Interestingly, soil cations (Ca, Mg, and K) tended to be negatively associated with weed seed mortality. Our research provided limited evidence that perennial forage communities can vary in their ability to accelerate weed seed mortality in the soil. However, we did uncover insights into microbial communities associated with weed seeds that could be promising for further research.