Seed size in lacustrine and riverine populations of wild rice (Zizania palustris)

To study the effects of the hydrological regimes of lakes and rivers on seed size of wild rice (Zizania palustris), four lakes and four rivers were sampled to measure and model the factors affecting seed size. Based on casual observation by harvesters and biologists it has been hypothesized that seeds produced in riverine habitats are smaller than those produced in lacustrine habitats. We found mean seed mass in lake populations was 15.4 mg (41%) larger than in river populations. When seed mass was partitioned between water body type, regional population pair, and individual population, water body type accounted for 71.3% of the variance. Data collected on seed mass, panicle density, seed scars, root mass, sediment characteristics, and water depths were used to create a statistical model to quantify the effects of each factor on seed size. The two mostmimportant environmental factors contributing to seed size were sediment bulk density and water depth at seed collection. Important biological components were seed scar density, proportion of filled seed, and root dry mass.