Biomass allocation and phenotypic plasticity are key elements of successful invasion of Parthenium hysterophorus at high elevation

Abstract

In invasion ecology, hypothesis of an invasive species exhibiting enhanced performance in the introduced range has been widely acknowledged. Examining the role of phenotypic plasticity in improving plants’ performance is essential to understand adaptive responses of an exotic invasive species to environmental variations. As Parthenium hysterophorus L. (Asteraceae) is one of the most widespread subtropical invader globally, we selected it as a model plant for studying its adaptive responses along the elevation gradient. Sites at an elevation of 700 m, 900 m, 1100 m and 1500 m were selected in the lower Himalayas for analysing plant functional traits of the weed and assessing variations in biomass allocation along elevation. Non-reproductive traits, i.e. above-ground plant height (AGPH) and below-ground biomass (BGB), and reproductive traits, i.e. capitula count per plant (CC), seed size, seed thickness and seed mass varied significantly with the elevational gradient. Soil properties also exhibited significant variations along elevation, except pH and total nitrogen (TN). Production of large number of heavier seeds, with smaller size at higher elevations showed enhanced reproductive fitness (adaptation) of P. hysterophorus. The study concluded that alteration in reproductive traits aids the successful invasion and expansion of P. hysterophorus in mountain ecosystems.