Thermal Decoupling May Promote Cooling and Avoid Heat Stress in Alpine Plants

Abstract

In alpine ecosystems, where low temperatures predominate, prostrate growth forms play a crucial role in thermal resistance by enabling thermal decoupling from ambient conditions, thereby creating a warmer microclimate. However, this strategy may be maladaptive during frequent heatwaves driven by climate change. This study combined microclimatic and plant characterization, infrared thermal imaging, and leaf photoinactivation to evaluate how thermal decoupling (TD) affects heat resistance (LT₅₀) in six alpine species from the Nevados de Chillán volcano complex in the Andes of south-central Chile. Results showed that plants' temperatures increased with solar radiation, air, and soil temperatures, but decreased with increasing humidity. Most species exhibited negative TD, remaining 6.7 K cooler than the air temperature, with variation across species, time of day, and growth form; shorter, rounded plants showed stronger negative TD. Notably, despite negative TD, all species exhibited high heat resistance (Mean LT₅₀ = 46 °C), with LT₅₀ positively correlated with TD in shrubs. These findings highlight the intricate relationships between thermal decoupling, environmental factors, and plant traits in shaping heat resistance. This study provides insights into how alpine plants may respond to the increasing heat stress associated with climate change, emphasizing the adaptive significance of thermal decoupling in these environments.

Keywords: alpine; heat resistance; microclimate; short plants; thermal decoupling.

Figure 1

Principal component analysis (PCA) of environmental variables influencing plant temperature. (A) Biplot of the first two principal components (PC1 and PC2), derived from five environmental variables: air temperature (AT), photosynthetically active radiation (PAR), relative humidity (RH), soil temperature (ST), and wind speed (WS). The percentage of variance explained by each component is indicated in brackets. (B) Bar plots showing the contribution (%) of each environmental variable to the formation of PC1 and PC2. The red dashed line represents the expected average contribution if all variables contributed equally. Variables with contributions above this threshold are considered the most influential in defining each principal component.

Figure 2

Infrared (IR) images of the six alpine study species. Images were taken between 14:00 and 15:00 (P2) on a north-facing slope during three sampling days (7, 8 March, and 12 April 2023). Rosette species are shown in the upper row, and dwarf shrubs in the lower row. Air temperature (AT, °C) and plant temperature (PT, °C) at the time of capture are shown in the upper left corner of each image, while the exact capture time is displayed in the upper right. Species names are indicated in the lower left corner of each panel.

Figure 3

Air (blue) and plant (green) temperatures measured across three time periods: P1 (10:00–12:00), P2 (13:00–15:00), and P3 (16:00–18:00). For Berberis empetrifolia, P1 corresponds to 12:00–13:00. Species abbreviations: rosettes—Ht (Hypochaeris tenuifolia), Ps (Phacelia secunda), Va (Viola aizoon); dwarf shrubs—Ap (Azorella prolifera), Be (Berberis empetrifolia), Sp (Senecio pachyphyllos). Circles represent mean temperatures; whiskers are the standard deviation (SD). Blue bars represent mean thermal decoupling (TD = PT − AT), shown with SD. Statistical significance of TD is indicated as follows: *** p < 0.001, * p < 0.05, and n.s. = not significant.

Figure 4

Leaf heat resistance (LT₅₀, °C) in six alpine species. LT₅₀, defined as the lethal temperature at which 50% of tissue damage occurs, was estimated for rosette species Ht (Hypochaeris tenuifolia), Ps (Phacelia secunda), Va (Viola aizoon) and dwarf shrub species Ap (Azorella prolifera), Be (Berberis empetrifolia), Sp (Senecio pachyphyllos). Box plots show the median (line inside the box), interquartile range (IQR; box limits), and whiskers extending to 1.5 × IQR. Circles indicate mean values. Different superscript letters denote statistically significant differences in LT₅₀ among species (p < 0.05).

Figure 5

Relationship between thermal decoupling (TD) and heat resistance (LT₅₀) across alpine species. (A) Correlation between TD and LT₅₀ for all species combined; (B) rosette species (triangles); and (C) dwarf shrub species (circles) analyzed separately. Thermal decoupling (TD) corresponds to the mean difference between plant and air temperature, averaged per individual across three daytime measurement periods (between 10:00–18:00). LT₅₀ refers to the lethal temperature at which 50% tissue damage occurred. Different colors represent different species. Spearman’s rank correlation coefficient (ρ) and corresponding p-value are shown at the bottom of each plot.

Figure 6

Plant species studied in the alpine belt of the Nevados de Chillán Volcano complex. In the upper section, the rosette species are (A) Hypochaeris tenuifolia, (B) Phacelia secunda, and (C) Viola aizoon. In the lower section, the dwarf shrub species are (D) Azorella prolifera, (E) Berberis empetrifolia, and (F) Senecio pachyphyllos.