Phenotypic plasticity in relation to ploidy level and corm production in the perennial grass Arrhenatherum elatius

Phenotypic plasticity may play a critical role in the response of natural populations to selective pressures in variable environments and may help explain differences in the ecological and geographical distribution of closely related taxa. In this study we quantify phenotypic plasticity in three subspecies of the European grass polyploid complex Arrhenatherum elatius, ssp. sardoum, elatius, and bulbosum, to test two hypotheses: (i) Does the widespread tetraploid ssp. elatius show greater phenotypic homeostasis in fitness related traits than its Mediterranean endemic related diploid ssp. sardoum? (ii) Does the corm-forming tetraploid ssp. bulbosum (which is widespread throughout northwest Europe) differ from ssp. elatius (which does not have corms) in patterns of resource allocation across environments? Eight genotypes from each of two populations of each subspecies were cloned and grown in four replicated garden environments (a combination of two light and nutrient levels). Mean reaction norms for each subspecies showed no consistent variation between tetraploids and diploids in the plasticity of fitness-related traits over the range of the studied environments. Tetraploid genotypes showed consistently greater values than diploids across all environments, which may partly explain the more widespread distribution of tetraploids. The two tetraploids differed in patterns of resource allocation across environments, with ssp. bulbosum maintaining a relatively more constant vegetative to floral biomass ratio across three of the four environments.