Sinapis arvensis L. (Common Charlock, Brassicaceae) is a wide-spread annual self-incompatible plant. It is native to Southern and Middle Europe, occurs mainly on fields, field margin and ruderal areas and is visited by a broad range of flower visitors; mostly hoverflies, bees and bumble bees (Kunin 1993; Hoffmeister et al. 2016). Its ecological indicator values for moisture is 3, i.e. relatively moist (range: 1 = very dry to 5 = standing in water), according to Landolt et al. (2010) and indifferent according to Ellenberg et al. (1992). Its turgor loss point or ‘wilting point’ is −1.74 ± 0.031 MPa following the method of Sun et al. (2020) and thus exhibits approximately the mean value of the 41 temperate perennial grassland species (Sun et al. 2020). In general, the turgor loss point is a key drought tolerance trait that characterizes the constitutive drought tolerance of most species (Bartlett et al. 2014). It is mostly used for woody species but recently has also been applied to herbaceous species (Sun et al. 2020).

Our experimental plants were grown in a climate chamber (Phytotron, Vötsch Industrietechnik GmbH, Balingen-Frommern, Germany) in the Botanical Garden of Ulm University, Germany. Seeds from a natural population in Southern Germany (Rieger-Hoffman GmbH, Blaufelden-Raboldshausen, Germany) were placed on filter paper soaked with aqueous gibberelic acid solution (1000 ppm; Roth, Karlsruhe, Germany) and maintained under complete darkness at room temperature until germination. Seedlings were transferred to pots (10 × 10.5 × 10.5 cm) filled with a soil mixture of 3:2:1 TKS2:compost:sand (TKS2, Floragard Vertriebs-GmbH, Oldenburg, Germany). After 1 week in a greenhouse, the pots were moved to a climate chamber (12-h photoperiod with 500 μmol m−2, 21 °C, 60 % relative humidity). Each week, 30 plants were placed in the climate chamber in order to obtain a succession of flowering individuals.

At the on-set of floral buds, half of these plants (N = 15) were randomly placed under a pulsed water treatment to induce intermittent drought stress (Huberty and Denno 2004), as continuous stress might impede flower development (Burkle and Runyon 2016). Individuals in the control group (= watered treatment) were watered daily with 75 mL water, whereas individuals within the drought treatment were watered every third day with the same amount of water; the start of wilting usually occurred on the third day without water. Each plant was treated for at least 10 days before being used in the flight cage experiment. Soil moisture was controlled using a custom-made soil moisture sensor with the Arduino system (Iduino ME110, Arduino software version 1.8.8, board: Genuino Uno; ElectroPeak 2019) calibrated with a soil moisture sensor (Hydrosense 2, Campbell Instruments, Bremen, Germany).

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