The paper presents the results of studies about photosynthesis at the leaf level in-situ of seedlings of Rhizophora apiculata of natural and artificial origin. The obtained values of photosynthesis are distributed in three zones, corresponding to its values obtained in the pre-afternoon, afternoon and afternoon. The main inhibitory factor affecting photosynthesis (if we do not take into account PAR) is a disturbance in the water balance of leaves. The dependence of photosynthesis on temperature and CO2 concentration has been determined.