Limited thermal acclimation of photosynthesis in tropical montane tree species. (16th July 2021)

• Record Type: Journal Article
• Authors: Dusenge, Mirindi Eric; Wittemann, Maria; Mujawamariya, Myriam; Ntawuhiganayo, Elisée B.; Zibera, Etienne; Ntirugulirwa, Bonaventure; Way, Danielle A.; Nsabimana, Donat; Uddling, Johan; Wallin, Göran
• Is Part Of: Global change biology. Volume 27:Number 19(2021)
• Page Start: 4860
• Page End: 4878
• Publication Date: 2021-07-16
• Subjects: Africa -- biomass -- climate change -- leaf dark respiration -- Vcmax and Jmax -- warming; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.15790
• Languages: English
• ISSNs: 1354-1013

Abstract

Abstract: The temperature sensitivity of physiological processes and growth of tropical trees remains a key uncertainty in predicting how tropical forests will adjust to future climates. In particular, our knowledge regarding warming responses of photosynthesis, and its underlying biochemical mechanisms, is very limited. We grew seedlings of two tropical montane rainforest tree species, the early‐successional species Harungana montana and the late‐successional species Syzygium guineense, at three different sites along an elevation gradient, differing by 6.8℃ in daytime ambient air temperature. Their physiological and growth performance was investigated at each site. The optimum temperature of net photosynthesis ( T optA ) did not significantly increase in warm‐grown trees in either species. Similarly, the thermal optima ( T optV and T optJ ) and activation energies ( E aV and E aJ ) of maximum Rubisco carboxylation capacity ( V cmax ) and maximum electron transport rate ( J max ) were largely unaffected by warming. However, V cmax, J max and foliar dark respiration ( R d ) at 25℃ were significantly reduced by warming in both species, and this decline was partly associated with concomitant reduction in total leaf nitrogen content. The ratio of J max / V cmax decreased with increasing leaf temperature for both species, but the ratio at 25℃ was constant across sites. Furthermore, in H . montana, stomatal conductance at 25℃ remained constant across the different temperature treatments, while in S . guineense it increased with warming. Total dry biomass increased with warming in H . montana but remained constant in S . guineense . The biomass allocated to roots, stem and leaves was not affected by warming in H . montana, whereas the biomass allocated to roots significantly increased in S . guineense . Overall, our findings show that in these two tropical montane rainforest tree species, the capacity to acclimate the thermal optimum of photosynthesis is limited while warming‐induced reductions in respiration and photosynthetic capacity rates are tightly coupled and linked to responses of leaf nitrogen. Abstract : We report findings from a field study investigating the instantaneous temperature responses of photosynthesis and how they acclimate to long‐term warming in tropical tree species. Trees of two montane species with contrasting successional strategies were grown in the field in 11 liters‐pots with similar soil, along an elevation gradient in the Rwanda‐TREE project. Surprisingly, the optimal temperature of net photosynthesis and underlying biochemical processes ( V cmax, J max ) did not significantly increase with warming in any species. However, both V cmax, J max, and leaf respiration ( R d ) significantly decreased in a coordinated manner at warmer sites and were linked to responses of leaf nitrogen.