Causes of differences in the distribution of the invasive plants Ambrosia artemisiifolia and Ambrosia trifida in Yili Valley, China

Ambrosia artemisiifolia and Ambrosia trifida are two species of very
harmful and invasive plants of the same genus. However, it remains unclear
why A. artemisiifolia is more widely distributed than A. trifida
worldwide. Distribution and abundance of these two species were surveyed
and measured from 2010 to 2017 in the Yili Valley, Xinjiang, China. Soil
temperature and humidity, main companion species, the biological
characteristics in farmland ecotone, residential area, roadside and
grassland, and water demand of the two species were determined and studied
from 2017 to 2018. The area occupied by A. artemisiifolia in the Yili
Valley was more extensive than that of A. trifida, while the abundance of
A. artemisiifolia in grassland was less than that of A. trifida at eight
years after invasion. The interspecific competitive ability of two species
were stronger than those of companion species in farmland ecotone,
residential, and roadside. In addition, A. trifida had greater
interspecific competitive ability than other plant species in grassland.
The seed size and seed weight of A. trifida were five times or eight times
those of A.artemisiifolia. When comparing the changes under simulated
annual precipitation of 840 mm versus 280 mm, the seed yield per m2 of A.
trifida decreased from 50,185 to 19, while that of A. artemisiifolia
decreased from 15,579 to 530. The differences in the distribution of the
two species are mainly due to differences in interspecific competitive
ability, seed size, and water dependence. The two species have stronger
interspecific competitive ability than that of companion species, but A.
artemisiifolia has a smaller seed size and stronger drought tolerance,
which allows A. artemisiifolia to spread farther than A. trifida. The
reason for wider distribution of A. trifida in grassland is that A.
trifida has stronger interspecific competitive ability than A.
artemisiifolia under sufficient water.