Crescimento de plantas C3 e C4 em resposta a diferentes concentrações de CO2 e arranjos competitivos

Abstract

Climate projections are based on the emission of greenhouse gases and suggest an increase in the concentration of atmospheric carbon dioxide. Plants with C3 metabolism tend to increase their photosynthetic rate and accumulate more photoassimilates than plants with C4 metabolism when subjected to high concentrations of CO2. Parallel to this scenario, the interaction with other species can alter the productivity of the crops. For this, it sought to evaluate the development of C3 and C4 plants under different concentrations of ambient CO2 in consortium with weeds. To evaluate the C4 plants, two experiments in growth chambers were conducted in a completely randomized design: one with brachiaria decumbens and one with corn cv. Double Hybrid. For brachiaria, a 3 x 4 factorial scheme was set up, the first factor being three concentrations of CO2 in the growth chambers (420; 840 and 1680 µmol mol-1), and the second factor, plant arrangements under competition conditions (brachiaria cultivated in isolation; brachiaria + black picão (Bidens pilosa); brachiaria + corn (cv. Double Hybrid) and brachiaria + Rio beans BRS Perola. With regard to corn plants, the factorial scheme was 3 x 3, being the first factor, three levels of CO2 mentioned and the second factor, the different arrangements of plants in competition with weeds (maize cultivated separately maize + black pepper and maize + brachiaria decumbens). To evaluate the C3 plants, two experiments were carried out in DIC: one with black pepper and one with beans. A 3 x 4 factorial scheme was set up for the black prick, the first factor being three concentrations of CO2 in the growth chambers (420; 840 and 1,680 µmol-1), and the second factor, the plant arrangements in competition (black picão cultivated in isolation, black picao + Brachiaria decumbens, black picão + corn (cv. Hybrid Double) and black pic + bean (carioca BRS Perola). Regarding the evaluation of bean plants, the factorial scheme was 3 x 3, with the first factor represented by the three levels of CO2 mentioned and the second factor, the different arrangements of plants in competition with weeds (beans cultivated alone (carioca BRS Perola), beans + picao-preto and feijoeiro + Brachiaria decumbens. For all experiments, the photochemical efficiency of photosystem II, the ratio between variable fluorescence and maximum fluorescence, chlorophyll contents and chlorophyll fluorescence were evaluated. At 50 days after the emergence of the plants, height was measured and the number of leaves, the dry matter of the roots, the dry matter of the stem, the dry matter of the leaves and the total dry matter were counted. The data were submitted to the Sisvar statistical program for analysis of variance and comparison of means by the Tukey test at 5% probability of error. In general, the increase in gas favored the development of the species through CO2 fertilization, increasing the height, the number of leaves, the total chlorophyll content and the dry mass of the crops, however, the limitation in the interaction with the species competing species is directly related to the species evaluated.