How endangered is sexual reproduction of high-mountain plants by summer frosts? Frost resistance, frequency of frost events and risk assessment

• Published in: Oecologia Vol. 171; no. 3; pp. 743 - 760
• Main Authors: Ladinig, Ursula, Hacker, Jürgen, Neuner, Gilbert, Wagner, Johanna
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer 01.03.2013; Springer-Verlag; Springer Nature B.V
• Subjects: Adaptation, Physiological; Alpine environments; Alpine glaciers; Biomedical and Life Sciences; Cerastium; Cold weather; Ecology; Endangered plants; Endangered species; Europe; Flower buds; Flowering; Freezing; Frost; Frost damage; Frost resistance; Fruits; Glaciers; Hydrology/Water Resources; Ice; Life Sciences; Loiseleuria procumbens; Mountains; Plant Physiological Phenomena; Plant Sciences; Plant species; Plants; Ranunculus glacialis; Reproduction; Reproduction - physiology; Rhododendron ferrugineum; Risk assessment; Saxifraga; Seasons; Seed germination; Shoots; Snow; SPECIAL TOPIC: IN HONOR OF CHRISTIAN KÖRNER; Europe; Ice nucleation; Reproductive success; Alpine plants; Reproductive development; Frost resistance
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-012-2581-8

In temperate-zone mountains, summer frosts usually occur during unpredictable cold spells with snowfalls. Earlier studies have shown that vegetative aboveground organs of most high-mountain plants tolerate extracellular ice in the active state. However, little is known about the impact of frost on reproductive development and reproductive success. In common plant species from the European Alps (Cerastium uniflorum, Loiseleuria procumbens, Ranunculus glacialis, Rhododendron ferrugineum, Saxifraga bryoides, S. moschata, S. caesia), differing in growth form, altitudinal distribution and phenology, frost resistance of reproductive and vegetative shoots was assessed in different reproductive stages. Intact plants were exposed to simulated night frosts between -2 and -14 °C in temperature-controlled freezers. Nucleation temperatures, freezing damage and subsequent reproductive success (fruit and seed set, seed germination) were determined. During all reproductive stages, reproductive shoots were significantly less frost resistant than vegetative shoots (mean difference for LT 50 -4.2 ± 2.7 K). In most species, reproductive shoots were ice tolerant before bolting and during fruiting (mean LT 50 -7 and -5.7 °C), but were ice sensitive during bolting and anthesis (mean LT 50 around -4 °C). Only R. glacialis remained ice tolerant during all reproductive stages. Frost injury in reproductive shoots usually led to full fruit loss. Reproductive success of frost-treated but undamaged shoots did not differ significantly from control values. Assessing the frost damage risk on the basis of summer frost frequency and frost resistance shows that, in the alpine zone, low-statured species are rarely endangered as long as they are protected by snow. The situation is different in the subnival and nival zone, where frost-sensitive reproductive shoots may become frost damaged even when covered by snow. Unprotected individuals are at high risk of suffering from frost damage, particularly at higher elevations. It appears that ice tolerance in reproductive structures is an advantage but not an absolute precondition for colonizing high altitudes with frequent frost events.