Tumbleweeds in the Western Australian cropping system:: seed dispersal characteristics of Salsola australis

Salsola australis, like other agricultural weed species of the Salsola genus, produces a mobile seedbank. Aspects of this mobile seedbank were investigated in three field trials, including total seed production, rate of seed shedding, rate at which seeds lose germinability and the distance and directionality of plant movement. Total seed production was highly variable (ranging from 138 to 7734 seeds per plant), but was directly related to aboveground plant biomass at maturity. Following senescence, mature plants broke free of their root system and the wind driven plants moved considerable distances (1.6-1247.2 m). Half of the mobile plants moved < 100 m, as they became entangled with other S. australis plants within the stand. Seed shedding commenced before the plants became mobile and increased with movement, but was also related to the aging and weathering processes experienced by stationary or mobile plants. All plants retained a proportion of their seed in spite of movement, weathering and ageing of the plants, although germinability of retained seed dropped to < 2% after 2 months. Salsola australis engages in broad scale seed dispersal similar to that observed in other species of the Salsola genus, allowing this species to maintain a high rate of invasion and range expansion.