Respostas da cultura da soja (Glycine max L.) e de plantas daninhas C3 e C4 quando em competição e submetidas a estresses abióticos

Abstract

Stress due to high temperatures, water deficit and competition for resources (light and CO2) are factors that limit crop growth and productivity, can modify interactions between plants, generating morphophysiological, metabolic and molecular responses. The objectives of research were to evaluate the competitive ability of beggarticks and slender amaranth with soybean; to verify isolated responses of soybean, beggarticks, slender amaranth and, crop in competition with slender amaranth under high temperature; to verify the effect of thermal stress, water deficit and plant recovery on soybean and slender amaranth interaction; to verify the impact of temperature and water regime on the interaction between soybean and slender amaranth; and, analyze the responses to CO2 and light in slender amaranth, beggarticks and soybean. Studies were performed simulating competition conditions, water deficit, high temperature, CO2 concentrations, different levels and light quality between soybean, beggarticks and slender amaranth. The results allow to infer that, soybean with C3 photosynthetic route, has higher competitiveness to beggarticks and lower to slender amaranth, and interspecific competition is harmful for C3 species and intraspecific to C4. Regardless of thermal amplitude and water regime, slender amaranth has higher and similar competitiveness to soybean, respectively. High temperature causes oxidative stress in beggarticks and elevates enzymatic activity in slender amaranth, not influencing soybean. In competition, high temperature reduces photosynthetic parameters of culture and increases oxidative stress in slender amaranth. Slender amaranth has higher competitiveness to soybean in the combinations of water regimes and temperatures, being that the water deficit and competition influence more negatively the morphological and photosynthetic parameters of species, compared to elevated temperature. The C3 species have CO2 compensation point, quantum efficiency, photosynthetic and morphological parameters higher to C4, and this has CO2 saturation point, saturation point and light compensation, and carboxylation efficiency higher to beggarticks and soybean.