High-temperature tolerance of a tropical tree, Ficus insipida: methodological reassessment and climate change considerations

Abstract

In view of anthropogenic global warming, heat tolerance of a neotropical pioneer tree, Ficus insipida Willd., was determined. Sections of sun leaves from a mature tree and from seedlings cultivated at ambient and elevated temperatures were heated to 42–53°C. Leaves from a late-successional tree species, Virola sebifera Aubl., were also studied. Widely used chlorophyll a fluorescence methods based on heat-induced rise of initial fluorescence emission, Fo, and decrease in the ratio of variable to maximum fluorescence, Fv/Fm, were reassessed. Fv/Fm determined 24 h after heat treatment was the fluorescence parameter most suitable to assess the lethal temperature causing permanent tissue damage. Thermo-tolerance was underestimated when Fo and Fv/Fm were recorded immediately after the heat treatment. The limit of thermo-tolerance was between 50 and 53°C, only a few °C above peak leaf temperatures measured in situ. The absence of seasonal changes in thermo-tolerance and only marginal increases in thermo-tolerance of plants grown under elevated temperatures suggest little capacity for further heat acclimation. Heat-stress experiments with intact potted seedlings also revealed irreversible leaf damage at 51–53°C, but plants survived and developed new leaves during post-culture.

Light-stimulated heat tolerance in leaves of two neotropical tree species, Ficus insipida and Calophyllum longifolium

“…As a consequence, leaf temperatures may rise considerably above air temperature (Hamerlynck and Knapp 1994;Krause et al 2006). For example, under full solar radiation with little air movement, sun-exposed outer canopy leaves of F. insipida reached temperatures in situ up to 46À48 C, only a few degrees below T 50 (Krause et al 2010). In contrast to temperate species (e.g.…”

“…In contrast to temperate species (e.g. Havaux and Tardy 1996), leaves of trees in the humid tropics appear to possess only a low capacity of acclimation to increased heat stress (Cunningham and Read 2003;Krause et al 2010Krause et al , 2013. Nonetheless, at elevated temperatures below T 50 , high-temperature acclimation of physiological processes such as photosynthetic CO 2 uptake and dark respiration has been reported for tropical plants Winter 2013a, 2013b;Krause et al 2013;Slot et al 2014) The lack of an increase in T 50 in response to rising temperature may be related to the low seasonal temperature variation in the tropics.…”

“…Reported limits of heat tolerance of tropical agricultural (e.g. Smillie and Nott 1979;Weng and Lai 2005) and rainforest species (Königer et al 1998;Kitao et al 2000;Cunningham and Read 2006;Krause et al 2010Krause et al , 2013) vary between~35 C and 54 C, depending on the species tested, the growth regime and test method. Presumably, when F 0 alone is examined, very low T c values reflect reversible heat-induced fluorescence changes rather than irreversible leaf damage.…”

“…It has been shown for leaves of Ficus insipida Willd. that the temperature leading to a 50% decline in F v /F m (T 50 ) after 24 h of 'recovery' provides a reliable indicator of the temperature leading to irreversible visible tissue damage (necrosis) observed after long-term (11 days) storage of leaf sections (Krause et al 2010). Reported limits of heat tolerance of tropical agricultural (e.g.…”

“…(a late-successional species) were studied. The response of PSII to heat stress was assessed by means of chl a fluorescence recording (Krause et al 2010). Heat-induced tissue damage was estimated from the extent of necrosis occurring during longterm storage of heat-treated leaf sections.…”