system
Given the following post, respond as if you're commenting on Reddit:
human
How do brazil nut trees absorb so much selenium from the soil?

Also how does Amazon rainforest soil have so much selenium?
gpt
I actually studied selenium phytoremediation during grad school. Selenium is primarily found as selenate in the soil (but can also exist as selenite and other forms). Selenate is taken up through sulfate transporters due to its chemical similarity. Once taken up by the plant, selenium is converted into different forms including the amino acids seleno-cysteine and seleno-methionine, as well as other organics. Brazil nut trees may have a sulfate transporter in the roots (SULTR1;1 or SULTR1;2) that has a higher specificity for selenate over sulfate, or may have other enzymes in the selenium metabolism pathway that show up-regulation compared to other plants, allowing it to pull more selenium out of the soil.