Complete or overcompensatory thermal acclimation of leaf dark respiration in African tropical trees

Abstract

• Tropical climates are getting warmer, with pronounced dry periods in large areas. The productivity and climate feedbacks of future tropical forests depend on the ability of trees to acclimate their physiological processes, such as leaf dark respiration (R d), to these new conditions. However, knowledge on this is currently limited due to data scarcity. • We studied the impact of growth temperature on R d and its dependency on net photosynthesis (A n), leaf nitrogen (N) and phosphorus (P) contents, and leaf mass per unit area (LMA) in 16 early-(ES) and late-successional (LS) tropical tree species in multi-species plantations along an elevation gradient. Moreover, we explored the effect of drought on R d in one ES and one LS species. • Leaf R d at 20 °C decreased at warmer sites, regardless if it was expressed per unit leaf area, mass, N or P. This acclimation resulted in 8% and 28% decrease in R d at prevailing nighttime temperatures in trees at the intermediate and warmest sites, respectively. Moreover, drought reduced R d , particularly in the ES species and at the coolest site. • Thermal acclimation of R d is complete or over-compensatory and independent of changes in leaf nutrients or LMA in African tropical trees.

Warming induces divergent stomatal dynamics in co‐occurring boreal trees

“…Several earlier studies, including those with boreal tree species, have reported strong acclimation of leaf dark respiration to warming (e.gDusenge et al, 2020;Mujawamariya et al, 2020;Reich et al, 2016;Slot & Kitajima, 2015;Smith & Dukes, 2017). Thermal acclimation of R results in reduced leaf respiratory rates in warm-grown trees when measured at a common leaf temperature, leading to near-(and sometimes complete) homeostatic respiration rates measured at the respective growth temperatures (Mujawamariya et al, 2020;Reich et al, 2016;Slot & Kitajima, 2015).…”

“…Thermal acclimation of leaf respiration is common in tree species from different biomes and plant functional types (Kroner & Way, 2016;Mujawamariya et al, 2020;Reich et al, 2016;Slot & Kitajima, 2015;Smith & Dukes, 2017;Zhu et al, 2020). In some studies, this thermal acclimation was shown to be driven by concomitant reductions in A with warming, since leaf respiration is strongly correlated with photosynthesis (Dusenge et al, 2019;O'Leary et al, 2019;Wang et al, 2020;Way & Sage, 2008b).…”

Limited thermal acclimation of photosynthesis in tropical montane tree species

“…HE is considered as the control site as most species used in this experiment naturally grow in the neighbouring montane rainforest, named Nyungwe National Park. Further details of the experiment can be found in Mujawamariya et al (2020). In this study, we report findings from a parallel study using the same sites and plant material as in the main experiment, but in which eight species were grown in 11‐litre pots using the soil from the Sigira site at all three sites, to eliminate soil as a possible confounding factor.…”

“…This thermal acclimation of respiration has also been observed in trees from the tropics (Cheesman & Winter, 2013a, 2013b; Drake et al, 2015; Scafaro et al, 2017; Slot et al, 2014; Slot & Winter, 2017b, 2018; Smith & Dukes, 2017). A recent study from the same elevation gradient experiment used in this study (Rwanda‐TREE), but with 16 montane tropical tree species freely rooted in the soil, reported that thermal acclimation of leaf respiration at the warmer, lower‐elevation sites led to complete or even over‐compensation of respiration (Mujawamariya et al, 2020). Altogether, these findings suggest that foliar respiration readily acclimates to warming, and may have little constraint on carbon availability for tropical tree growth in future climates.…”

Respiratory temperature responses of tropical conifers differ with leaf morphology

“…The short timeframes over which these fluctuations occur may preclude acclimation of respiration to these new temperatures (Zhu et al., 2021), raising the important question of how expected future increases in temperature (Ho et al., 2011) as well as increases in the frequency of extreme events (Diffenbaugh & Scherer, 2011; Ho et al., 2011) might affect the carbon balance of these unique conifer species. Future studies examining the magnitude of the long‐term acclimation of R to T as well as the photosynthetic temperature response of conifers and tropical montane species from across a breadth of biogeographical regions are urgently needed (but see Mujawamariya et al., 2021). Such studies, in addition to our own study of the short‐term RT response, will provide a clearer understanding of the effects of future temperature regimes on the continued presence of the gymnosperms in this forest, and illuminate the effects of rising temperatures on tropical montane forest composition and carbon storage.…”