Investigation on the influence of fertilization on enlargement of leaf dimensions and seed production of Moehringia trinervia was carried out in July 2006 on Vistula spit, within the largest European breeding colony of cormorant Phalacrocorax carbo, where multiple enhancement of NPK in the soil due to deposition of guano was noted. The control sample was taken from place located ca. 500 m away from the colony, where cormorants never nested. Leaves from the area within the colony were significantly larger and more rounded than leaves of plants growing outside the colony. Enlargement of leaf blade area allows plant to develop assimilation apparatus, which in turn affects on improvement of ability to absorb and transform greater amounts of nitrogen into organic compounds. It had probably an influence on extension of seed number, because plants within the colony area produced significantly more seeds than plants outside the colony. However seeds from the colony were twice lighter seed from the control sample, which may facilitate their dispersal and occupancy on larger area. Probably in this way Moehringia trinervia adapts to the unlimited availability of nutrients coming from bird excrements.