Photosynthetic temperature responses of tree species in Rwanda: evidence of pronounced negative effects of high temperature in montane rainforest climax species

Abstract

, maximum rate of electron transport (J max ), optimum temperature (T opt ), stomatal conductance (g s ), the maximum carboxylation rate of oxygenase (V cmax ), tropical montane rainforest. SummaryThe sensitivity of photosynthetic metabolism to temperature has been identified as a key uncertainty for projecting the magnitude of the terrestrial feedback on future climate change. While temperature responses of photosynthetic capacities have been comparatively well investigated in temperate species, the responses of tropical tree species remain unexplored.We compared the responses of seedlings of native cold-adapted tropical montane rainforest tree species with those of exotic warm-adapted plantation species, all growing in an intermediate temperature common garden in Rwanda. Leaf gas exchange responses to carbon dioxide (CO 2 ) at different temperatures (20-40°C) were used to assess the temperature responses of biochemical photosynthetic capacities.Analyses revealed a lower optimum temperature for photosynthetic electron transport rates than for Rubisco carboxylation rates, along with lower electron transport optima in the native cold-adapted than in the exotic warm-adapted species. The photosynthetic optimum temperatures were generally exceeded by daytime peak leaf temperatures, in particular in the native montane rainforest climax species.This study thus provides evidence of pronounced negative effects of high temperature in tropical trees and indicates high susceptibility of montane rainforest climax species to future global warming.

Photosynthetic acclimation to warming in tropical forest tree seedlings

“…The J Max : V CMax ratio correlated strongly and negatively with T Opt , suggesting that the acclimation of T Opt was a result of J Max exerting greater control over light-saturated photosynthesis than in plants grown at lower temperatures – and that RuBP-regeneration-limited photosynthesis had a higher temperature optimum than RuBP-carboxylation-limited photosynthesis, V CMax , consistent with the mechanism proposed by Hikosaka et al (2006). Recent observations for montane tropical tree species, however, found a lower T Opt of J Max than of V CMax and electron-transport limitation of photosynthesis at high measurement temperatures (Vårhammar et al , 2015). Clearly, more detailed measurements of A - c i curves across a wide temperature range are needed for lowland tropical forest trees to better understand the biochemical adjustments underlying the observed acclimation response.…”

Stomatal CO2 responsiveness and photosynthetic capacity of tropical woody species in relation to taxonomy and functional traits

“…Precipitation exhibits some seasonal variation, with the highest and lowest amounts occurring in March–May and June–August, respectively. Additional meteorological information can be found in Nsabimana et al (2009) and Vårhammar et al (2015). …”

Temperate and Tropical Forest Canopies are Already Functioning beyond Their Thermal Thresholds for Photosynthesis

“…Dacryodes excelsa has historically shown relatively low light saturated photosynthesis, about 2.7 µmol CO 2 m −2 s −1 [84]. Leaves were sampled from seven heights (8,11,15,18,20,23, and 25 m).…”

“…Many global vegetation models are based on Farquhar's model of photosynthesis [7], but our ability to accurately parameterize these models is hampered by a lack of mechanistic data on Many global vegetation models are based on Farquhar's model of photosynthesis [7], but our ability to accurately parameterize these models is hampered by a lack of mechanistic data on physiological responses to warming and thermal acclimation potential of canopy photosynthesis and respiration, especially for tropical forests [8][9][10][11][12][13][14][15][16]. Models analyzing the responses of tropical carbon storage to elevated temperature have produced inconsistent predictions on whether these forests will remain sinks or become sources [14,17].…”