XVI International Botanical Congess

We investigated the potential role of nitrogen fixers in facilitating alien Pennisetum setaceum invasion into native Heteropogon contortus grasslands. Pennisetum stands associated with the alien nitrogen-fixer Chamaechrista nictitans had higher soil nitrogen than adjacent Heteropogon stands. In greenhouse pots, increased nitrogen allowed Pennisetum seedlings to invade established Heteropogon. We also compared seedling competition with and without Chamaechrista nictitans. Under interspecific competition without Chamaechrista, Pennisetum suppressed Heteropogon growth. Pennisetum growth was not facilitated by live Chamaechrista, but Chamaechrista did not increase soil nitrogen until after it had died. Increased nitrogen or the presence of openings can facilitate Pennisetum invasion into Heteropogon grasslands.