Even as President-elect Donald Trump continues to question China and its policies, his selection of Iowa Governor Terry Branstad to be US ambassador to China may signal a more conciliatory approach to trade, a key part of the Sino-US relationship.

Branstad has accepted Trump's offer, Trump spokesman Jason Miller said on Wednesday.

"The man I've chosen as our ambassador to China is the man who knows and likes China," Trump said of Branstad on his thank you tour stop in Des Moines, Iowa on Thursday evening.

"One of the most important relations we must improve, and we have to improve, is our relationship with China," Trump said.

Branstad has a well-established personal connection with President Xi Jinping, according to Dermot Hayes, a professor at Iowa State University in Ames, Iowa.

"President Xi visited Iowa 30 years ago and met the governor then. They have remained in contact, and President Xi came back to Iowa on his first trip to the US as president," Hayes said in an email.

Branstad may help to soothe a relationship that is defined largely through bilateral trade. Trump has threatened to impose punitive tariffs on Chinese goods coming into the US and last week strained the tie-up further when he accepted a telephone call from Taiwan's president.

China is Iowa's second-largest export market, behind Canada. Figures from the U.S.-China Business Council show Iowa exported $2.3 billion in goods and $273 million in services to China in 2015. Crop production accounted for some $1.4 billion of the exports.

Holly Wang, a professor of agricultural economics at Purdue University in West Lafayette, Indiana, said Iowa is an agricultural giant in the US.

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