When plants are subjected to competition, their physiological behavior changes. To understand the developmental physiology of weeds will subsidize the development of cropping systems which favor the crops plants in detriment of weeds. The objective of this work was to evaluate the physiological behavior of different weed species, growing under intraspecific competition. Greenhouse experiment was conducted in randomized complete block design arranged in factorial scheme 4 × 5 with four replications. Factor A was the weed species [Urochloa plantaginea (Alexandrergrass), Bidens pilosa (hairy beggarticks), Ipomoea indivisa (morningglory) and Conyza bonariensis (hairy fleabane)], and factor B was the plant density of these species (20, 40, 60, 80 or 100 plants m-2). The following variables were evaluated: sub-stomatal CO2 concentration, photosynthesis rate, consumed CO2, stomatal conductance, transpiration rate, water use efficiency, plant height, shoot diameter, leaf area, and shoot dry biomass. Alexandergrass relies on the superior control of stomatal opening and high water use efficiency. Hairy beggarticks efficiency in competition lies on its ability to remove water from soil to levels when the other surrounding plant species would undergo stress. Morning glory and hairy fleabane did not present detectable particular features in the study, and their importance as weeds is probably tied to other survival abilities but superior competition. In conclusion, the weed species studied present distinct competitive strategies.
Physiology of Weeds in Intraspecific Competition