The research team found little differences between the spring emergence of leaves in native and their non-native cousins, the timing of which for both groups varied in response to spring temperatures. They also found little differences in spring food production between the groups.
Most significantly, the researchers found that the invaders retained their leaves and continued to photosynthesize almost four weeks longer into the fall than their native cousins, which begin shutting down between late August and mid-September. "The extended leaf activity we found in the invaders is rarely seen in native species that inhabit deciduous forests," Fridley says. "However, the data don't tell us whether this is the primary strategy invasive plants use to compete with native species."
The plants in the study have had separate evolutionary histories since at least the Pleistocene Age (11,400 to 2 million years ago). Climate conditions over the North American continent were colder with more ice coverage than Asia, Fridley says. Native species responded to the shorter growing seasons by pulling nitrogen from their leaves to store in the stems, causing the leaves to turn brown and fall off. "Invaders don't appear to store as much nitrogen," Fridley says. "Their leaves fall off with a higher nitrogen content. It may be that the invasive species are better suited a warming climate."
Which begs the question of how the invaders gain back in the spring the nitrogen that falls to the forest floor in the fall. "One hypothesis," Fridley says, "is that invaders evolved by depending on earthworms to decompose the leaves, making nitrogen available in the spring for the plants." Na
|Contact: Judy Holmes|