An experimental investigation of life history and plasticity in two cytotypes of Polygonum aviculare L. subsp. aviculare that coexist in an abandoned arable field.

Polygonum aviculare subsp. aviculare is an annual selfing weed common in abandoned arable fields where it occurs as a widespread hexaploid cytotype (6x=60) and a rarer tetraploid cytotype (4x=40). The basis of phenological differentiation between the two cytotypes observed in a natural population where they coexist was examined in a greenhouse experiment comprising six soil conditions consisting of factorial combinations of two levels of fertility and three pot sizes. The environmental and genetic component of variation in 11 life history and morphological traits was quantified. Even though all traits except life span were plastic the two cytotypes appear to have evolved contrasting life history strategies and it is inferred that this can account for the temporal niche differentiation observed in the abandoned field during the first year of dereliction. Tetraploids are short-lived plants allocating a high proportion of their biomass to reproduction and completing their life cycle before July when the plant cover is sparse. Hexaploids are larger, later flowering, longer lived, plants with a lower reproductive effort and a higher final seed yield; it is inferred that these traits enable the hexaploids to compete successfully with the dense herbaceous layer of summer annuals that develops in the course of the first year of secondary succession. Differentiation in phenotypic plasticity between the two cytotypes was interpreted as indicative of higher opportunism and lower tolerance of poor soils and restricted rooting space in the hexaploid compared to the tetraploid cytotype.