Complex sentence: One unanswered question about this symbiotic relationship asks how the endosymbionts receive a sufficient amount nitrogen, due to the dilute and nutrient-poor character of xylem.
Split into simpler sentences: One unanswered question about this symbiotic relationship asks how the endosymbionts receive a sufficient amount nitrogen. This speculation arises due to the dilute and nutrient-poor character of xylem.