Plasticity of growth characteristics in wild barley (Hordeum spontaneum) in response to nutrient limitation

1 The genetic basis of phenotypic plasticity in relative growth rate (RGR) and its components was studied in Hordeum spontaneum (wild barley). Four accessions from each of nine natural populations from Israel and Iran were grown at four nutrient levels. Genetic variation in RGR and its components, differences in phenotypic plasticity, and interactions among growth and relevant morphological characteristics were studied. 2 RGR was reduced by up to 60% at decreased nutrient levels, with contributions from all components (net assimilation rate (NAR), leaf area ratio (LAR), specific leaf area (SLA) and leaf mass fraction (LMF)). NAR and LAR (due mainly to LMF) were both reduced by 35% at the lowest nutrient level. 3 For growth-related traits, most genetic variation was found in LMF and LAR. Differences in RGR among populations could be largely explained by smaller seeds resulting in faster growing plants. Although mean population seed weight correlated negatively with humidity at the sampling site, multivariate analyses showed that differences in growth and morphology among populations were not significantly correlated with differences in environmental conditions in their natural habitats. 4 The level of plasticity in RGR did not differ among populations or accessions-within-populations. By contrast, the RGR components LMF and LAR differed in plasticity, both among populations and among accessions-within-populations. RGR seems to be buffered from changes in plasticity by a trade-off in degree of plasticity between the underlying components (NAR and LAR). 5 Path analysis based on accession means showed that some of the interrelationships among RGR components changed with nutrient level. NAR had the highest influence on RGR. LMF was the connecting factor among morphological and growth traits. At the two lowest nutrient levels trade-offs appeared between LAR (mainly via LMF) and NAR. A trade-off between LMF and SLA appeared at the two intermediate nutrient levels.