Max Planck Gesellschaft

Peppermint and carbon limitation

Objectives

Under carbon limiting conditions plants face the dilemma of whether to allocate resources to ongoing metabolism, growth, storage or defense (Herms & Mattson, 1992; McDowell, 2011). Drought can be understood as a cause of plant carbon limitation. Drought constrains plants to live on smaller amount of carbon as stomata are closed preventing water loss through transpiration. Chemical defenses used against herbivores and pathogens as antimicrobial active compounds, detterents, antifeedants and attractants for herbivore predators are represented by secondary metabolites such as terpenoids. Terpenoids production means high carbon cost for a plant.

We want to study carbon allocation preferences under drought with special focus on chemical plant defense. As counterpart treatment to drought we use low [CO2], plants are exposed to atmosphere of low [CO2] (minimum 20 ppm) while being well watered. Combination of low [CO2] treatment and continuous 13CO2 labelling helps us to track carbon into the following carbon pools: ongoing metabolism, growth, storage or defense. This great experiment setup helps us to interpret changes in carbon metabolism caused by drought and so potentially predict development trends in plant chemical defences under climate change.

Methods

"Plant"

In order to meet our objectives we choose peppermint (Mentha x piperita var. Multimentha; cultivar used in Thuringia, Germany) as our model plant. Peppermint is a perennial sterile natural hybrid of water mint (Mentha aquatic L.) and spearmint (Mentha spicata L.) belonging to the Lamiaceae family. It was first cultivated in England and is an economically important species in pharmacy, food and cosmetic industries (Lawrence, 2007).

"Growth chambers"

Fig. 1 Schematic view of one of the 12 growth chambers showing the ventilation system and the set of sensors: photosynthetic active radiation (PAR) sensor and frequency domain reflectometry (FDR) probe. Chambers dimensions are 75 cm x 45 cm x 80 cm (length x width x height) (drawn by Martin Strube).

Fig. 2 Growth chamber system in the greenhouse of the Max Planck Institute for Biogeochemistry (photo by Silvana Schott).

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