The dose makes the poison – why we study mineral nutrition

Mineral nutrients are substances that must be taken up by both plants and humans in sufficient amounts to fulfil a variety of vital functions. These essential elements are divided in macro- (e.g. sulfur and phosphorus) and micronutrients (e.g. iron and zinc) based on their amount required by the organism. Both, deficiency and overabundance (toxicity), affect the plants growth negatively. In that sense they are like humans: without coffee nothing works but too much is also not good.

Plants are sessile and therefore cannot run away from their problems (e.g. mineral deficiency). They have to instead adapt to their environment, according to their location and individual needs. Therefore, they use a variety of often complex strategies. Some plants increase the efficiency of their nutrient uptake through a mutually beneficial relationship with bacteria or other microorganisms. But there is no master plan that works for all of them. A variety of abilities are necessary since the availability of the various nutrients are interconnected and, in some cases, negatively correlated.

Global climate change adds another layer to this problem as agriculture is highly vulnerable to changes in temperature, precipitation, and rising atmospheric CO₂ concentration. Many crops show an increase in yield, but a decrease in mineral nutrient content when grown under these predicted elevated CO₂ concentrations. This phenomenon is called “carbon dilution effect”. This is because plants grow faster and produce more biomass but do not take up correspondingly more mineral nutrients. To stay with the coffee analogy: We brew our 500 ml morning coffee using 50 g coffee powder. If we use the same amount of ground coffee to brew 1 l coffee it will be watery and flavourless and will hardly help with waking up.

Therefore, my research aims to study the interplay between the uptake and conversion of various macronutrients. An improved understanding of these processes can help to optimize the plants nutritional performance. This will then allow a more target approach towards increasing the yield of crops such as rice while simultaneously reducing fertilizer usage.

The dimensions of this effect are immense: In an experiment, scientists showed that e.g. rice grown under the atmospheric CO₂ predicted for 2050 contains 7,8 % less protein.

The reduced nutrient content of these plants leads to a potential nutrient deficiency of the consumer. But the experiment also showed that this effect is less pronounced in some plant species. This group, the so-called C₄ plants, includes e.g. maize. They differ from other plants in their special photosynthesis mechanism (You find further information on C₄ photosynthesis in a previous planter’s punch by Sebastian Triesch). C₄plants evolved from C₃ plants and there are also intermediate species, the so-called C₃-C₄ plants. The photosynthesis performance and mineral nutrition traits of these intermediates are between those of C₃ and C₄ species and therefore represent an intermediate evolutionary step.

So far it is not fully resolved how the uptake and processing of mineral nutrients has changed during the C₄ photosynthetic evolution and whether these changes are possible even a prerequisite for the former. With my work I therefore study the connections between the uptake and processing of the macro nutrients nitrogen, sulphur and phosphorus in C₄ plants, which are as important to the plants as our morning coffee is to us. A better understanding of processes can help us to optimize plant nutritional performance and increase the yield of crop plants like rice in a more targeted fashion while simultaneously reducing fertilizer usage.