which of the following best helps to explain why phosphorus is often a limiting factor in many ecosystems?

Phosphorus is often a limiting factor in many ecosystems primarily because it does not have a gaseous phase in its cycle and is not very mobile. It exists mostly in solid forms, such as phosphate minerals in rocks and soil, and is only slowly released through weathering. This slow release and strong binding to soil particles limit the availability of phosphorus in a form that plants and aquatic organisms can use. Additionally, phosphorus is typically found in low concentrations in the environment, making its availability a bottleneck for biological growth and productivity in ecosystems. This scarcity controls the growth of plants, algae, and other organisms, thereby limiting overall ecosystem productivity until more phosphorus becomes available. In short, phosphorus is limiting because it cycles slowly, is largely immobile, and is scarce as a bioavailable nutrient in most ecosystems.