Effects of diaspore position on compound spike, seed position in diaspore, emergence season and watering regimes on life history of the invasive annual grass Tausch’s goatgrass ( Aegilops tauschii )

Seed position on the mother plant, time of seed germination and soil moisture can affect life history characteristics of annual plants. However, most studies considered only one level of seed position, and how seed position combined with emergence season and watering regime affect life history traits of annual invasive plants is not clear. In this study, seeds in different positions within and between diaspores at different positions in compound spikes of the invasive diaspore heteromorphic annual grass Tausch’s goatgrass ( Aegilops tauschii Coss.) sown under different watering conditions and life history traits were monitored. Seeds of A. tauschii germinated in autumn and in spring under both natural and increased soil moisture. Autumn germinated plants were larger but allocated lower proportions of resources to reproductive organs than spring germinated plants. Regardless of emergence season and soil watering regime, A. tauschii exhibited two levels of seed position effects on life history traits. For distal diaspores/seeds, vegetative growth stage was longer and seedling emergence percentages, plant height, number of diaspores per tiller and vegetative allocation were higher, while reproductive growth stage was shorter and seedling survival percentages, number of tillers per plant, number of seeds per diaspore and reproductive allocation were lower than basal diaspores/seeds. Thus, in A. tauschii , distal diaspores/seeds represent a ‘high-risk’ strategy and basal ones a ‘low-risk’ strategy. This apparent ‘bet-hedging’ strategy likely increases survival and geographical/habitat expansion of A. tauschii and also may contribute to its invasiveness.