How to Keep Your P out of the Water

The phosphorus cycle may not be the first nutrient cycle we learn about when the content is first introduced to us in middle-school science class, but it is becoming more and more relevant in our lives. Phosphorus moves through the air, soil, and water; it is eroded out of rocks and released into the atmosphere by factories. Perhaps one of the biggest issues caused by phosphorus is runoff from fertilizer used on farms, which is not healthy if it gets in our water supply. However, this problem in the phosphorus cycle has a potential solution: another stage of the phosphorus cycle! Plants absorb phosphorus form the soil and use it to grow, so why can’t we use this as a natural way to get rid of phosphorus we don’t want just rolling around out there. Further, what kinds of plants can help with this and what kind of plants don’t really need that much phosphorus at all?

Depiction of the Phosphorus cycle. Could C3 plants be more effective at taking
up Phosphorus? Retrieved from http://swroc.cfans.umn.edu/

                I looked at an article by Halsted and Lynch that focused on how plants respond to different levels phosphorus in the soil; in particular, comparing the plants of the C3 and C4 photosystems. The authors grew a number of different species - including C3 and C4 plants as well as monocots and dicots – and grew them in a sand/alumina medium at varying phosphorus treatment levels from stable to phosphorus stress (low levels). They measured each plant’s height, stem width, and carbon dioxide exchange rate (CER), as well as number of branches (for dicots only) and height of highest tiller (for monocots).

                As we would expect, all species grew less under phosphorus stress. However, it turns out that C4 plants’ CER was less effected in situations with low phosphorus, meaning that they are not as reliant on phosphorus availability in soil as C3. This could mean that C3 plants have to take up more phosphorus out of the soil to survive.

                So how can we use this research for our own good? Well, conservation societies have already started working on a solution known as “buffer strips”. These patches of land filled with native plant species are positioned along rivers between main farming sites to absorb the phosphorus before it gets into the water supply. Thanks to the Halsted and Lynch paper, we now know that C3 plants are more phosphorus dependent. This could spark further research to see if C3 plants can actually make buffer strips more effective by absorbing more phosphorus. Research like this can help protect our water supply from dangerous algal blooms; thus, keeping water potable and protecting native fish populations. It can give us good, clean water. And it is a solution we need because we need agriculture, but we need water more.

This is what will happen if you P in the Pool! Algal blooms kill fish and make the water unsafe and they occur if you let too much phosphorus get in the water. Also, it looks and smells gross. Retrieved from http://www.circleofblue.org/

References:

Halsted, M. and J. Lynch. 1995. Phosphorus responses of C3 and C4 species. Journal of Experimental Botany 47: 497-505.