Nutrient-use efficiency

All plants require the same macro- and micronutrients, but the concentrations of all these elements vary greatly among plant species. In addition, some plants in specific taxa contain significant concentrations of elements that are not essential or even beneficial at those higher concentrations. In this chapter, I explore the variation among taxa and what the significance of that variation is. Monocots and dicots differ in their requirement for calcium (Ca) and boron (B), which reflects the composition of their cell walls. Monocots have smaller amounts of cell wall components that bind Ca and B. A particularly low leaf phosphorus (P) concentration is common in species that evolved in ancient landscapes, where P is a major limiting nutrient for primary productivity. Despite these low leaf P concentrations, these plants exhibit relatively rapid rates of photosynthesis because they invest little in major leaf P fractions such as nucleic acids and phospholipids and preferentially allocate P to photosynthetically active cells. The high rate of photosynthesis per unit leaf N (PNUE) of C4 plants compared with C3 species can be explained by a low investment in Rubisco, whose oxygenation reaction is suppressed by a high CO2 concentration in its vicinity. In addition, C4 plants have a Rubisco with high catalytic activity. Plant species also vary in their concentrations of elements that are not essential nutrients, for example leaf fluoride (which they accumulate as highly toxic fluoroacetate), selenium and silicon (Si). These elements play a role in defense against herbivores. Silicon plays an additional role in defense against diseases and abiotic stresses. Leaf Si concentrations are particularly high in plants on severely P-impoverished soils because Si is mobilized by carboxylates released by plants that depend on a carboxylate-based P-acquisition strategy.