Jeff Dukes is studying the effects of a changing climate on plants and soils. Photo: Purdue Agricultural Communication photo/Tom Campbell
Chemical changes in tree leaves subjected to warmer, drier
conditions that could result from climate change may reduce the availability of
soil nutrients, according to a Purdue
Jeff Dukes, an associate professor of forestry and natural
resources, found that red maple leaves accumulate about twice as much tannin
when exposed to hot, drought-like conditions. Those tannins, which defend
leaves from herbivores and pathogens, were shown to interfere with the function
of common enzymes in soil.
“When the leaves are particularly water-stressed by
drought or drought with higher temperatures, we see more protective compounds,
more tannins and a change in the chemistry of the tannins,” said Dukes,
whose findings were published in New
Phytologist. “This suggests that when these leaves fall, they may slow
down soil processes such as decomposition and nutrient cycling. This could, in
turn, affect plant growth and nutrient uptake.”
The findings are the first for the Boston Area Climate
Experiment, a National Science Foundation-funded project that Dukes directs.
Plants on several field plots are exposed to various future climate scenarios
using heaters and other means to control conditions.
“We’ve basically built a big time machine that moves
different plots of land into different possible futures by changing
temperatures and precipitation levels,” Dukes said.
The increase in leaf tannins observed in this experiment
could cause leaves to decompose more slowly and also interfere with critical
soil enzymes, leaving fewer nutrients for plants. The tannins in the red maple
leaves also were chemically different, making them interact more strongly with
the soil enzymes.
Dukes said the tannin issue could effect a sort of tug-of-war
in the carbon cycle. With fewer nutrients, plants would take carbon dioxide out
of the air more slowly. But if fallen leaves are decomposing slower, then the
carbon would be released back to the atmosphere more slowly.
“This is an issue that could affect many natural
processes,” Dukes said. “We just don’t know what the net result will
In this experiment, leaves were removed from the
experiment plots and tested in laboratories. Dukes said he would next test
other plants’ leaves exposed to similar conditions to see how their tannins are
affected. He also will test his findings in the field to see how an increase in
tannins affects soil in a natural setting.
The work was carried out in collaboration Nishanth
Tharayil at Clemson Univ., as well as researchers at Purdue, Clemson Univ., the Univ.
of Massachusetts-Boston, and Natural Resources Canada.