In situ temperature relationships of biochemical and stomatal controls of photosynthesis in four lowland tropical tree species

Abstract

Net photosynthetic carbon uptake of Panamanian lowland tropical forest species is typically optimal at 30-32 °C. The processes responsible for the decrease in photosynthesis at higher temperatures are not fully understood for tropical trees. We determined temperature responses of maximum rates of RuBP-carboxylation (V ) and RuBP-regeneration (J ), stomatal conductance (G ), and respiration in the light (R ) in situ for 4 lowland tropical tree species in Panama. G had the lowest temperature optimum (T ), similar to that of net photosynthesis, and photosynthesis became increasingly limited by stomatal conductance as temperature increased. J peaked at 34-37 °C and V ~2 °C above that, except in the late-successional species Calophyllum longifolium, in which both peaked at ~33 °C. R significantly increased with increasing temperature, but simulations with a photosynthesis model indicated that this had only a small effect on net photosynthesis. We found no evidence for Rubisco-activase limitation of photosynthesis. T of V and J fell within the observed in situ leaf temperature range, but our study nonetheless suggests that net photosynthesis of tropical trees is more strongly influenced by the indirect effects of high temperature-for example, through elevated vapour pressure deficit and resulting decreases in stomatal conductance-than by direct temperature effects on photosynthetic biochemistry and respiration.

Tropical forest temperature thresholds for gross primary productivity

“…S1). Measures of T leaf from Panamanian tree species using thermocouple wires also noted the bimodal distribution of daytime temperatures (Rey-S anchez et al 2016, Slot andWinter 2017b). Thus, mean values do not accurately capture canopy temperatures, with maximum temperatures in the afternoon driving temperatures away from the mean most frequently.…”

Causes of reduced leaf‐level photosynthesis during strong El Niño drought in a Central Amazon forest

“…While we could use a model to adjust our measurements to the 25°C convention, we prefer to report the standard temperature that was in fact used. All measurements were made at a leaf temperature of 31°C, which is close to optimal for net photosynthesis (Lloyd & Farquhar, ; Slot & Winter, ; Tan et al., ; Tribuzy, ). We report both photosynthesis and dark respiration at this leaf temperature.…”

“…The mechanism of leaf-level photosynthesis reduction during drought stress might be stomatal closure (which limits CO 2 assimilation), nonstomatal limitations to photosynthetic function, or a combination of the two (Flexas & Medrano, 2002;Lloyd & Farquhar, 2008). Under increased vapor pressure deficit from low humidity and/or high temperature, plants close their stomata (Cunningham, 2004;Slot & Winter, 2017). This maintains leaf turgor and water column integrity in xylem vessels-at least up to a critical leaf water potential-despite low availability of soil water and high atmospheric evaporative demand (Bonal, Barigah, Granier, & Guehl, 2000;Chastain et al, 2014;Flexas & Medrano, 2002;Sperlich, Chang, Peñuelas, Gracia, & Sabat e, 2015).…”

Acclimation and adaptation components of the temperature dependence of plant photosynthesis at the global scale

“…The peaked Arrhenius model can also be used to calculate the optimum temperatures of V cmax ( T optV ) and J max ( T optJ ). These parameters have now been documented for a wide range of species from different biomes and PFTs (Onoda et al ., ; Rogers et al ., ; Slot & Winter, ). Evidence suggests that the Arrhenius model parameters vary significantly across plant taxa but also that these parameters have the capacity to acclimate to the growth temperature (Crous et al ., , ).…”