Phenotypic plasticity of alternanthera philoxeroides in response to root neighbors of kin: Introduced vs. native genotypes

Abstract

Plant root neighbors can induce plastic responses, thereby altering root biomass allocation and other functional traits even while available resources remain constant. The evolution of plasticity hypothesis demonstrates that populations in the introduced range of an invasive species have evolved greater plasticity than populations in the native range. Most studies focus on plastic responses of alien plants to light, water, nutrition and nature enemies. However, plastic responses to root neighbors in alien plants has not been studied. We conducted a common garden experiment using five introduced (the United States of America, USA) and five native (Argentina) genotypes of Alternanthera philoxeroides (alligator weed) to compare fitness and functional traits responses to root neighbors of the same genotype plants (kin). We found that introduced genotypes had an increased root to shoot ratio (RSR) and specific leaf area (SLA) when root neighbors were present while the native genotypes showed the opposite responses. However, introduced and native genotypes showed no difference in total biomass, storage root biomass, specific stem length (SSL) and branching intensity (BI). In addition, when root neighbors were present, A. philoxeroides increased in total biomass (+9.9%) and storage root biomass (+13.9%) and decreased in SSL (-9.5%) than when grown without root neighbors. Introduced genotypes showed an increase in total biomass (+62.0%), storage root biomass (+58.9%), and reduction of SSL (-28.5%) and BI (-42.8%) than native genotypes. Our results suggest that functional trait plasticity responses related to resource utilization (i.e. RSR and SLA) showed opposite patterns between introduced and native genotypes, but fitness and functional trait plasticity responses related to plant type (i.e. SSL and BI) showed no difference among introduced and native genotypes.