Freezing avoidance mechanisms in juveniles of giant rosette plants of the genus Espeletia

Abstract

Along soil–air gradients in tropical high mountains, plants growing at soil level tolerate frost while those growing well above ground, including all species in the genus Espeletia, use freezing avoidance mechanisms to survive low nighttime temperatures. The question that arises and the objective of this work were: What are the low temperature resistance mechanisms in giant rosettes when they are within the juvenile stages, i.e. closer to the ground? Juveniles of Espeletia spicata and Espeletia timotensis, dominant plants of the high Venezuelan Andes, were chosen for this study. To determine resistance mechanisms for these species, air and leaf temperatures were recorded in the field in 24 h cycles, while thermal analysis and injury temperature were determined in the laboratory. Both E. spicata and E. timotensis juveniles depend on avoidance mechanisms through a high supercooling capacity, permitting leaves to resist low nighttime temperatures. Minimum leaf temperatures were –4.9 and –5.1 °C, for E. spicata and E. timotensis, respectively, occurring during the dry season. Ice formation occurred at –14.3 and –15.3 °C for E. spicata and E. timotensis, respectively. Injury occurred at approximately –15 °C in both species. Low temperature resistance mechanisms in juveniles are similar to those in adult plants.