Maternal and Burial Environment Effects on Seed Mortality of Velvetleaf (Abutilon theophrasti) and Giant Foxtail (Setaria faberi)

The primary defense against seed mortality, the seed coat, is maternally derived. Hence, weed seed mortality in the soil seedbank is likely to be influenced by the maternal environment and genetics. We hypothesized that seed accessions from contrasting maternal environments (seed lots) exhibit different rates of seed mortality and that the relative differences among seed lots remain consistent across burial environments. Velvetleaf and giant foxtail annual seed mortality rates were Studied in field experiments in Hickory Corners, MI, and Wooster, OH, using seed lots collected from the same locations. Seeds enclosed within mesh bags and unenclosed seeds (seeded cores) exhibited similar levels of seedbank persistence (r = 0.90, P < 0.001) and seed mortality (r = 0.65, P = 0.006). Annual seed mortality rates ranged from 16 to 56% and 27 to 91% for seed lots of velvetleaf and giant foxtail, respectively. Relative differences among velvetleaf seed lots were consistent across burial environments in both years, whereas giant foxtail differences were consistent in only 1 of 2 yr. The relative ranks among velvetleaf seed lots varied between years, indicating that maternal environment may have influenced seed persistence more than seed-lot genetics. Within years, variation in seed mortality was predicted by changes in soil moisture in the burial environment (R-2 = 0.47, P < 0.001 for velvetleaf; R-2 = 0.34, P = 0.007 for giant foxtail). Accelerated seed mortality was associated with moist soils (soil water potential = -6 kPa for velvetleaf, -7 kPa for giant foxtail). These results suggest that agronomic practices affecting the maternal environment and moisture levels in the soil seedbank may promote weed seed mortality in the soil seedbank.