Is sexual reproduction of high-mountain plants endangered by heat?

Abstract

Strong solar irradiation in combination with still air and dry soil can cause prostrate high-mountain plants to heat up considerably and ultimately suffer heat damage. Such heat damage has been repeatedly shown for vegetative structures, but not for reproductive structures, which we expected to be particularly vulnerable to heat. Heat effects on cold-adapted plants may increase with rising global temperatures and the predicted increase in heat waves. We have tested the heat tolerance of reproductive versus vegetative shoots at different reproductive stages, comparing ten common plant species from different elevation belts in the European Alps. Plant samples were exposed to temperatures in 2-K steps of 30 min each between 42 and 56 °C. Heat damage was assessed by visual rating and vital staining. Reproductive shoots were on average 2.5 K less heat tolerant (LT50, i.e. the mean temperature causing 50 % heat damage, 47.2 °C) than vegetative shoots (mean LT50 49.7 °C). Initial heat injuries (mean LT10) were observed at 43–45 °C in heat-susceptible species and at 45–47 °C in more heat-tolerant species, in at least one reproductive stage. Generally, heat tolerance was significantly higher during fruiting than during the bud stages and anthesis. Prostrate species with acaulescent buds and flowers tolerated heat better than those with caulescent buds and flowers. Petals were the most heat-susceptible plant structure and mature pollen the most heat tolerant. Based on these data, heat tolerance of reproductive structures appears to be adapted to the prevailing maximum temperatures which the plants experience during different reproductive stages in their environment. During hot spells, however, heat tolerance thresholds may be exceeded. More frequent heat waves would decrease the reproductive output and, consequently, the competitiveness of heat-susceptible species.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-015-3247-0) contains supplementary material, which is available to authorized users.

Solar irradiation levels during simulated long‐ and short‐term heat waves significantly influence heat survival, pigment and ascorbate composition, and free radical scavenging activity in alpine Vaccinium gaultherioides

“…We also show that different light intensities affect the hardening process in different ways, not only during long‐term heat exposure, but also during short‐term heat exposure. In untreated leaves temperatures reached 46.4°C (HHM) and heat damage due to natural overheating was observed on several individuals leaves (Appendix S5), supporting earlier assumptions that (sub)alpine plants are at high risk of experiencing critically high temperatures (Ladinig et al ). This does not necessarily mean that V. gaultherioides will become extinct as alpine habitats are characterized by dense thermal microhabitat mosaics where plants are able to ‘escape’ (described by Scherrer and Körner ).…”

“…Predictions for further increases in global temperature range from 0.3 to 4.8 K for the time period from 1998-2012 to 2100 (IPCC 2013), with recurrent short-term heat spells as well as long-term heat waves. As a consequence, changes in species composition and plant migration toward higher altitudes have been reported for almost all major mountain ranges in Europe (Grabherr et al 1994, Pauli et al 2003, Erschbamer 2007, Kudernatsch et al 2008, Lenoir et al 2008, Steinacher and Wagner 2012, Ladinig et al 2015, and this trend is expected to continue.…”

“…In this study Vaccinium gaultherioides Bigelow, a woody dwarf shrub commonly found in the lower alpine zones, which have been associated with an increased risk of heat‐damage (Ladinig et al ), was selected as the study species. Under field conditions, we tested the effects of light in combination with simulated short‐ and long‐term heat exposure on heat hardening.…”

The diversity of floral temperature patterns, and their use by pollinators

“…As well as being sensitive to differences between the flower and its environment ( Whitney et al, 2008 ; Hammer et al, 2009 ), insects should also be sensitive to differences within a floral display. When flowers are observed using infrared thermography (thermal imaging), it is apparent that floral temperature is not necessarily distributed uniformly across the flower surface ( Rejšková et al, 2010 ; Dietrich and Körner, 2014 ; Ladinig et al, 2015 ; Atamian et al, 2016 ). It has not been investigated whether any pollinators can learn to recognise flowers based on which parts of the flower are hotter or colder, which will determine the flower’s temperature pattern.…”

Pollination in a new climate: Assessing the potential influence of flower temperature variation on insect pollinator behaviour

“…For example, [ 64 ] experimentally showed that long exposure of a floral organ at constant ambient temperature may damage the petal, pollen and gynoecium. Recently, [ 95 ] also suggested that frequent heat waves would decrease the reproductive output of flowering plants. Our study shows that flowering plants in Australia may use a range of mechanisms to modulate temperature with implications for changing environmental conditions (Figs 4 – 9 ), however we did not find any simple relationship between flower shape and its response to ambient temperature ( Table 1 ).…”