Steven Strauss was skeptical when he first heard about a poplar tree bioengineered to suck more carbon dioxide out of the air. …So when two entrepreneurs asked him to help test out the idea, Strauss was intrigued but hesitant. …Four years later, those entrepreneurs — Maddie Hall and Patrick Mellor — have raised $30 million for Living Carbon, a company that aims to plant between 4 million and 5 million poplar trees by the spring of 2024 using “photosynthesis enhanced” seeds. Eventually, the company hopes to enter the carbon offset market, selling credits to companies that need to reach net-zero emission goals. …Co-founders Hall and Mellor hope the trials will prove that the taller trees can store as much as 27 percent more CO₂ than ordinary poplars. The company’s next step will be to show that the CO₂ can be stored in lumber and plywood, outlasting the poplar’s lifespan, which can reach up to 200 years.