Plasticity in fitness and fitness-related traits at ramet and genet levels in a tillering grass Panicum miliaceum under patchy soil nutrients

Abstract

Plasticity in fitness components including seed weight and seed number and fitness-related traits including biomass, plant height, leaf area, and reproductive allocation at various organization levels in response to low- and high-nutrient patches was examined in the tillering grass Panicum miliaceum. Plants were planted in boxes consisting of two patches, the central patch (CP) and surrounding patch (SP), with each containing soil with either low or high nutrients. Nutrient status of the CP and contrast between the CP and SP significantly affected root performance, leaf photosynthesis and turnover, and growth and allocation. The effects of nutrient status of the CP and contrast between the CP and SP on the fitness and fitness-related traits differed between the ortet (the original organism from which a clone was derived), tiller, and genet, suggesting that patchy soil nutrients might have different effects on plasticity in the fitness and fitness-related traits at various levels, or even at the same level. Seed weight and seed number of a genet increased with increasing leaf mortality and leaf natality, respectively. Individual seed weight of the genet was restricted by that of the ortet and tiller together, whereas the number of seeds of the genet was determined mainly by the total number of seeds of the tillers. It is inferred that reallocation of genet-leveled fitness to the ortet and tillers may be beneficial to lower and spread risk of whole genet, and that plasticity in the fitness may help whole genet better adapt to variable environments.