EARLY GROWTH OF PARTHENIUM WEED (Parthenium hysterophorus L.) AND CLIMATE CHANGE

Parthenium weed (Parthenium hysterophorus L.; Asteraceae), native to the tropical and subtropical Americas, is an aggressive herbaceous weed of tropical and subtropical environments. In Australia, parthenium weed occurs mainly in Queensland, where two distinct populations of the weed occur. This includes the more widespread ‘Clermont’ population and a less-aggressive ‘Toogoolawah’ population. Potential impacts of climate change on these two populations are not known. This study examined the early growth of the two Australian populations (Clermont or Toogoolawah) of parthenium weed in environmental chambers under two concentration of CO2 (390 ppmv; ambient or 550 ppmv; elevated), two temperature (35/20°C; Warm or 30/15°C; Cool) and two soil moisture (field capacity; Wet or half of field capacity; Dry) regimes. The early growth (as measured by leaf production, the length of the longest leaf, the total leaf area and the plant dry weight) of both biotypes under the elevated CO2, cool temperature, and wet or dry soil moisture conditions was higher from ca. 6% to ca. 305% (than the growth under ambient concentration of CO2 and the same conditions of temperature and soil moisture. However, the growth rates were not significantly different when the young plants were grown under warm temperature and the same conditions of CO2 concentration, soil moisture levels.