Tissue elements in co-occurring herbs scale mostly isometrically, but do different plant strategies play the same game?

Nutrient allocation and scaling affect plant strategy and metabolism but this information is rarely incorporated into fundamental ecological frameworks. One important question is whether plants with a different ecological strategy share the same nutrient allocation patterns.

Here, we tested scaling between nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) concentrations in aboveground tissues of 130 co-occurring Central European grassland species, and examined whether scaling is consistent within the competitor, stress-tolerator, ruderal (CSR) framework.

Tissue element-element relationships were typically isometric (1:1 ratio). However, we observed a few anisometries: K accelerated with N (5:4 ratio), and the scaling of the combined suites of elements (N x P and K x Ca x Mg) deviated from isometry with a 3:4 ratio. We observed no N-Ca and P-Ca relationship. Scaling coefficients and normalisation constants were mostly consistent regardless of plant height or CSR strategy. However, N-Ca and Ca-Mg scaling was apparent only in less competitive species (C scores below median) and for P-K scaling, the normalisation constant was almost twice as high in ruderals than in less ruderal species.

Consistent and proportional nutrient allocation patterns in co-occurring species with different CSR strategies suggest dominant influence of common rules governing nutrient uptake and utilisation in temperate herbs. Tissue Ca could be an exception because its allocation with respect to N and Mg changes along the competitive spectrum, possibly reflecting the role of Ca in cell wall stability and integrity.