Seed mass and emergence time effects on performance of Panicum dichotomiflorum Michx. across environments

Abstract

The effects of seed mass and emergence time on growth and reproduction of the annual, C grass, Panicum dichotomiflorum Michx., were investigated in an experimental field study. Individual seeds of P. dichotomiflorum of known mass were sown into marked plots in four newly-abandoned fields that differed in soil nutrient availability, soil moisture and the time of the year in which they were abandoned. Seedling emergence was monitored daily for four weeks following sowing. In none of these fields was there any relationship between seed mass and emergence time. Analyses of covariance indicated that the effects of seed mass and emergence date on plant performance varied among fields. Seed mass affected performance in one field (SOUTH EARLY) where abiotic stress after emergence was high. In contrast, later emergence significantly reduced performance in all four fields. We used a path analysis to decompose the direct and indirect effects of seed mass and emergence time on plant performance in each field. The path analysis revealed that in all four fields, final weight had a significant positive effect on seed production. The effect of seed mass and emergence time had variable (and often opposite effects) on these traits. Seed mass only had a significant positive, direct effect on seed production in the most abiotically stressful field (SOUTH LATE). In the other fields, the effects of seed mass on fecundity were mediated by the effect on final weight. Thus, the effects of seed mass and emergence time on growth and reproduction in P. dichotomiflorum vary across environments.

Interference of Pteridium arachnoideum (Kaulf.) Maxon. (Dennstaedtiaceae) on the establishment of rainforest trees

“…As high and rapid seed germination, along with vigorous seedling growth, are factors that affect the fitness of plants (Gross and Smith, 1991; …”

The Evolutionary Ecology of Seed Germination of Arabidopsis Thaliana: Variable Natural Selection on Germination Timing

“…In KY, germination timing alone accounted for 72% of the variation in fitness among genotypes. Many studies have demonstrated strong natural selection on naturally segregating germination variants (Miller 1987;Kalisz 1989;Biere 1991;Gross and Smith 1991;Masuda and Washitani 1992;Donohue 2002;Griffith et al 2004). This study shows just how strong natural selection on germination timing can be on a range of potential segregants derived from natural genotypes.…”

“…The conditions that elicit germination are the same conditions with which the young seedlings must contend, and those conditions can determine or predict conditions experienced throughout the life of a plant. Germination timing strongly influences seedling survivorship (Biere 1991;Gross and Smith 1991), total lifetime fitness (Miller 1987;Kalisz 1989;Masuda and Washitani 1992), life-history expression (Chouard 1960;Venable 1985;Kalisz 1989;Kalisz and Wardle 1994;Nordborg and Bergelson 1999;Galloway 2001Galloway , 2002, and selection on postgermination characters (Evans and Cabin 1995;Weinig 2000;Donohue 2002). An appropriate germination response to environmental cues is thereby the first requirement for establishment of plants in a location; before plants can display adaptive phenotypes for any adult character, they must first survive through germination.…”

Seed mass versus seedling performance in Scots pine: a maternally dependent trait

“…For example, the effect of seed size might change markedly if experiments are performed in a glasshouse or under field conditions (Stanton, 1984 ;Marshall, 1986). Similarly, in natural populations the consequences of variation in seed size depend on the environmental conditions undergone by the progeny (such as competitive environment or water stress), with performance differences between large and small seeds generally being greatest under adverse conditions and lower or even null in more favourable environments (Dolan, 1984 ;Gross, 1984 ;Wulff 1986a,b ;Gross & Smith, 1991).…”

“…This situation might have discouraged seedling emergence and therefore might be regarded as a more stressful environment for emerging seedlings. In fact, under higher environmental stress, larger seed size might favour germination or development even when any relationship is absent under less extreme conditions (Dolan, 1984 ;Gross, 1984 ;Wulff, 1986a,b ;Gross & Smith, 1991 ;Houssard & Escarre! , 1991).…”