Early growth, development and allometry of glyphosate-resistant and susceptible Amaranthus palmeri in response to current and elevated temperature and CO2

This study aimed to evaluate the influence of CO 2 and temperature on glyphosate-resistant and susceptible biotypes of Amaranthus palmeri (Palmer amaranth) in terms of morphological development. Height (cm), stem diameter (cm), leaf area (cm 2 ), number of leaves, leaf, stem, and root dry matter, plant volume (m 3 ), as well as shoot-to-root allometry were evaluated. The Palmer amaranth biotypes were grown under four different scenarios: 1—low temperature (23/33 °C) and CO 2 (410 ± 25 ppm); 2—low temperature (23/33 °C) and high CO 2 (750 ± 25 ppm); 3—high temperature (26/36 °C) and low CO 2 (410 ± 25 ppm); and 4—high temperature (26/36 °C) and CO 2 (750 ± 25 ppm). Between CO 2 and temperature, the majority of differences observed were driven by CO 2 levels. Palmer amaranth grown under 750 ppm of CO 2 was 15.5% taller, displayed 10% more leaf area (cm 2 ), 18% more stem dry matter, and had a 28.4% increase in volume (m 3 ) compared to 410 ppm of CO 2 . GA2017 and GA2020 were 18% and 15.5% shorter, respectively. The number of leaves was 27% greater for GA2005. Plant volume decreased in GA2017 (35.6%) and GA2020 (23.8%). The shoot-to-root ratio was isomeric, except at 14 and 21 DAT, where an allometric growth towards shoot development was significant. Palmer amaranth biotypes responded differently to elevated CO 2 , and the impacts of temperature need further investigation on weed physiology. Thus, environmental and genetic background may affect the response of glyphosate-resistant and susceptible populations to climate change scenarios.