An ecosystem is defined as a place where organisms interact with one another and with their physical surroundings. The most common phosphorus reservoir in the ecosystem is the sedimentary rock. Add to that, it is believed that phosphorus cycle actually starts in these types of rocks. Through the process of weathering, phosphates are being carried by the rain or water and are dispersed to the soil and different bodies of water. Plants become reservoirs, as well, because they latch on the phosphate ions from the soil.