In semi-arid environments, the distribution of rainfall over time is decisive in emergence in a soil seed bank. The objective of this work was to evaluate the effect of rainfall events on the soil seed bank emergence of Caatinga species under high CO2 concentration. The experiment was carried out in an experimental area of Embrapa Semi-arid in a randomized complete block design, with subdivided plots. Each plot consisted of different environmental conditions (open top greenhouse with injection of 550 ppm CO2; open top greenhouse and environmental CO2; natural environment). The subplots consisted of the depth at which the seeds of Poincianella pyramidalis and Myracrodruon urundeuva were sown (superficially and buried at 0.02 m and 0.06 m depth). Seedling emergence was monitored daily after the first rains. During the experiment, weather data showed a rainfall volume of 83 mm, an average air temperature of 28.7 oC, average soil temperature of 35.4 e 34.9 oC, at depths of 0.02 and 0.06 m, respectively. Seedling emergence started 56 days after sowing and 4 days after the first rains. After 154 days of the start of the experiment, drip irrigation was performed. The greenhouse environment, regardless of the addition of CO2 or not, allowed higher emergence percentage of P. pyramidalis. The seeds of this species sowed on the soil surface only emerged when irrigation started. M. urundeuva seeds showed low germination even after irrigation.
