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Can coastal marshes withstand future sea level rise?

In the Chesapeake Bay wetlands, evolution has occurred faster than previously thought. This may be minimizing the chance that coastal marshes can withstand future sea level rise.

Researchers at the University of Notre Dame evaluated the role evolution plays in the Chesapeake Bay by studying a type of grass-like plant called chairmaker’s bulrush. 

The research team used historical seeds, modern plants, and computational models to demonstrate that “resurrected” plants were allocating more resources in their roots below ground, allowing them to store carbon more quickly than modern plants. This provides evidence that supports assumptions about evolutionary change.

“We think this surprising reduction in below-ground growth might be a response to increased pollution in Chesapeake Bay,” said Professor Jason McLachlan.

“Decades of pollution have resulted in higher levels of nitrogen and phosphorus in the waters, and since these are plant nutrients, evolution might now favor plants that ‘invest’ less in expensive roots.”  

The seeds from the historical plants had remained underground since the mid-1900s. Using resurrection ecology, the historical plants were collected to germinate and grow. 

While modern plants and samples from the mid-1900s grew above ground, they invested less into rooting deeper below ground. This created less biomass below ground and could reduce the capacity of wetlands to withstand flooding.

Using computational models, the researchers showed that the modern plants store carbon in soils 15 percent slower than the plants did in the mid-1900s.

“The research shows the role evolution plays as ecosystems are increasingly stressed by the impacts of human society,” said Professor McLachlan. 

It can’t be said with certainty that plants are investing more of their energy above ground because of pollution. However, the experts believe that the combination of their research techniques can support novel predictions of the impact of evolution. This could motivate others to further study the causes that drive evolutionary change.

“For reasons of inconvenience, science has often ignored what happens below ground. But we have learned so much in this study; there are so many secrets happening below ground,” said study first author Megan Vahsen.

According to Professor McLachlan, the research further demonstrates the role evolution plays as ecosystems are increasingly stressed by the impacts of human society. 

“Evolutionary change over almost a century played a destabilizing role for coastal ecosystems. Other species in other ecosystems might have responded differently to human environmental impact, perhaps providing more resilience to ecosystems, or perhaps having no impact at all.”

The researchers hope that others will consider how evolutionary change can affect ecosystem resilience during future studies on the biological response to environmental change. 

By Katherine Bucko, Staff Writer

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