Low‐temperature resistance in Polylepis tarapacana, a tree growing at the highest altitudes in the world

Abstract

The Polylepis tarapacana forests found in Bolivia are unique with respect to their altitudinal distribution (4200-5200 m). Given the extreme environmental conditions that characterize these altitudes, this species has to rely on distinct mechanisms to survive stressful temperatures. The purpose of this study was to determine lowtemperature resistance mechanisms in P. tarapacana. Tissue was sampled for carbohydrate and proline contents and micro-climatic measurements were made at two altitudes, 4300 and 4850 m, during both the dry cold and wet warm seasons. Supercooling capacity (-3 to -6°C for the cold dry and -7 to -9°C for the wet warm season) and injury temperatures (-18 to -23°C for both seasons), determined in the laboratory, indicate that P. tarapacana is a frost-tolerant species. On the other hand, an increase in supercooling capacity, as the result of significant increase in total soluble sugar and proline contents, occurs during the wet warm season as a consequence of higher metabolic activity. Hence, P. tarapacana, a frost-tolerant species during the colder unfavourable season, is able to avoid freezing during the more favourable season when minimum night-time temperatures are not as extreme.

Frost resistance of the New Zealand narrow‐leaved snow tussock grass,Chionochloa rigida

“…The alpine floras of New Zealand and tropical mountains also show similar levels of frost resistance (Bannister et al in press). For example, Polylepis tarapacana grows in Bolivia at the highest altitudes for any tree in the world (Rada et al 2001) and has a frost resistance of-18 to -23°C, similar that of Chionochloa rigida and New Zealand sub-alpine shrubs in winter (Sakai & Wardle 1978;Reitsma 1994).…”

Leaf Gas Exchange and Water Relations in Polylepis tarapacana at Extreme Altitudes in the Bolivian Andes

“…In spite of the occurrence of extra-cellular freezing during the dry-cold season (Rada et al 2001), P. tarapacana leaves showed a rapid transition from frozen state to a photosynthetically active state. P N close to the compensation at low Ψ L and g s were registered early in the morning.…”

“…These trees have a mean height of 3 m whereas exceptional individuals may reach 6 m or more in height (Liberman-Cruz et al 1997). Low temperature resistance in this species is constituted by freezing tolerance during the dry season while during the wet season super-cooling capacity increases significantly so that, for most of the nights, tissue freezing does not occur (Rada et al 2001).…”

Mass Elevation Effect and Its Contribution to the Altitude of Snowline in the Tibetan Plateau and Surrounding Areas

“…Polylepis tarapacana, the dominant species at the highest treeline in the central Andes, is considered frost tolerant (Rada et al 2001).…”