Photosynthetic opportunity cost and energetic cost of a rapid leaf closure behavior in Mimosa pudica

Premise of the Study The rapid leaf movement of Mimosa pudica is expected to be costly because of energetic trade‐offs with other processes such as growth and reproduction. Here, we assess the photosynthetic opportunity cost and energetic cost of the unique leaf closing behavior of M. pudica . Methods In the greenhouse, we employed novel touch‐stimulation machines to expose plants to one of three treatments: (1) untouched control plants; (2) plants touch‐stimulated to close their leaves during the day to incur energetic costs associated with leaf movement and reduced photosynthesis; (3) plants touched at night to assess the effects of touch alone. M. pudica is nyctinastic and closes its leaves at night; thus, touching at night does not impart additional costs. We directly assessed costs by comparing physical traits. Leaf re‐opening response was measured to assess the potential for plant behavioral plasticity to impact photosynthetic opportunity costs. Key Results The cost of rapid leaf closure behavior was expressed as a 47% reduction in reproductive biomass accounting for the effect of touch. Touch itself changed physical traits such as biomass, with touched plants being generally bigger. Plants touched at night re‐opened their leaflets 26% quicker than plants touched during the day. Conclusions We reason that the reproductive allocation costs incurred by M. pudica can be attributed to a combination of photosynthetic opportunity cost and the energetic cost associated with increased stimulation of leaf movement and that behavioral plasticity has the potential to alter photosynthetic opportunity costs.