Potassium as a game-changer in prairie food webs

We all know how sports drinks full of sodium (Na) and potassium (K) can rescue your performance on a hot day. But what if you’re a plant? Let me tell you about an experiment with Dr. Ellen Welti that shows the super-powers K gifts to plants. Plants use K as their primary way of keeping cells hydrated, plump, and working. But K is slippery—it’s so soluble that it leaks out of plants and must be constantly resupplied. K today, gone tomorrow. PDF: https://bit.ly/3G9SKwO

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Plants often get their K pre-packaged with Na in urine. But plants don’t need the Na, and we’ve shown it attracts herbivores who, like us, eat plants and need both. What gives? So, we set up an experiment at @KonzaLTER to find out. #NSFFunded

We monthly fertilized 7×7 m plots w the Na and K you’d find from a herd of bison —or just the Na or K—vs controls. We watched what happened to the chemistry of the plants, and numbers of bugs on the plots. @OUBiology

Dr. Ellen Welti, now with the Smithsonian Institution, fertilizing a plot on Konza Prairie LTER.

On control plots, we see the natural course from May through September. Plants get bigger and drier, and a mouthful of May grass is much more nutritious than that in Aug/Sept. Nutrients are diluted in time. PDF: https://bit.ly/3yc5Y6s

But look what happens to all those elements on plots fertilized with K, Na, NK! With repeated fertilization, the net effect sizes become strongly positive by July. The grasses seem to be using the K to help pump nutrients into foliage. By September those same treatments have *lower* nutrients than control plots. NaK is a ‘sports drink’ for prairie plants, allowing them to mobilize nutrients up to leaves when they need them, and down to roots when they need to store them.

Now look at the bug densities: almost the opposite pattern. When the nutrients are high on +KNa plots, the bugs are suppressed. As they decline, the bugs rally, until they are sequestered below round, when they decline again.

One more thing. Perhaps the reason one-time applications of K rarely show an effect in big experiments like #NutNet is that they are applied, w N and P, in May. K is so soluble that it doesn’t stick around. But areas with repeated urine applications—like Bison Lawns and Vole latrines— may be the place to find plants that are true masters of their ionomic domain. But areas with repeated urine applications—like Bison Lawns and Vole latrines— may be the place to find plants that are true masters of their ionomic domain.