Impact of an extreme drought event on clonal reproduction and the acclimation capacity of the succulent plant Sempervivum tectorum L.

Functional traits have been defined as those that affect organismal performance, that is growth and development, reproduction and survival, so they have been generally associated with acclimation and adaptation. Here, we aimed to study the impact of an extreme drought event on clonal reproduction and hormonal mechanisms underlying acclimation of houseleek (Sempervivum tectorum L.), a plant adapted to survive harsh environments. We also explored the validity of growth- and stress-related phytohormones as functional traits to evaluate stress acclimation responses in the field. We compared the response of plants, considering both mother rosettes and newly produced clones, to a very extreme summer drought event occurring in small cliffs in Les Guilleries mountains (NE Spain). We measured various stress makers in the field together with hormonal profiling through a metabolomic approach using liquid chromatography coupled to tandem mass spectrometry. Results showed that clonal propagation was arrested during the study period and revealed a 100-fold increase in abscisic acid content from spring to summer both in mothers and new clones, concomitantly with reductions in relative water content, which decreased by 20% only. The stress-related bioactive jasmonate, jasmonoyl-isoleucine increased simultaneously with abscisic acid, while growth-related hormones, including bioactive cytokinins (2-isopentenyl adenine and trans-zeatin) decreased from spring to summer, which was consistent with growth arrest. It is concluded that S. tectorum adjusts recruitment of new clones during periods of low water availability and withstands extreme drought events during the summer (preventing severe cell turgor loss at soil water contents below 2% and temperatures above 43 ºC) by successfully activating a complex hormonal response that underlies the great capacity of this species to survive extreme climatic events.