Mirindi Eric Dusenge

Acclimation of photosynthetic capacity and foliar respiration in Andean tree species to temperature change

Publisher: Wiley

Date: 12-04-2023

DOI: 10.1111/NPH.18900

Abstract: Climate warming is causing compositional changes in Andean tropical montane forests (TMFs). These shifts are hypothesised to result from differential responses to warming of cold‐ and warm‐affiliated species, with the former experiencing mortality and the latter migrating upslope. The thermal acclimation potential of Andean TMFs remains unknown. Along a 2000 m Andean altitudinal gradient, we planted in iduals of cold‐ and warm‐affiliated species (under common soil and irrigation), exposing them to the hot and cold extremes of their thermal niches, respectively. We measured the response of net photosynthesis ( A net ), photosynthetic capacity and leaf dark respiration ( R dark ) to warming/cooling, 5 months after planting. In all species, A net and photosynthetic capacity at 25°C were highest when growing at growth temperatures ( T g ) closest to their thermal means, declining with warming and cooling in cold‐affiliated and warm‐affiliated species, respectively. When expressed at T g , photosynthetic capacity and R dark remained unchanged in cold‐affiliated species, but the latter decreased in warm‐affiliated counterparts. R dark at 25°C increased with temperature in all species, but remained unchanged when expressed at T g . Both species groups acclimated to temperature, but only warm‐affiliated species decreased R dark to photosynthetic capacity ratio at T g as temperature increased. This could confer them a competitive advantage under future warming.

Optimal stomatal theory predicts CO₂ responses of stomatal conductance in both gymnosperm and angiosperm trees

Publisher: Wiley

Date: 15-12-2022

DOI: 10.1111/NPH.18618

Abstract: Optimal stomatal theory predicts that stomata operate to maximise photosynthesis ( A net ) and minimise transpirational water loss to achieve optimal intrinsic water‐use efficiency (iWUE). We tested whether this theory can predict stomatal responses to elevated atmospheric CO 2 (eCO 2 ), and whether it can capture differences in responsiveness among woody plant functional types (PFTs). We conducted a meta‐analysis of tree studies of the effect of eCO 2 on iWUE and its components A net and stomatal conductance ( g s ). We compared three PFTs, using the unified stomatal optimisation (USO) model to account for confounding effects of leaf–air vapour pressure difference ( D ). We expected smaller g s , but greater A net , responses to eCO 2 in gymnosperms compared with angiosperm PFTs. We found that iWUE increased in proportion to increasing eCO 2 in all PFTs, and that increases in A net had stronger effects than reductions in g s . The USO model correctly captured stomatal behaviour with eCO 2 across most datasets. The chief difference among PFTs was a lower stomatal slope parameter ( g 1 ) for the gymnosperm, compared with angiosperm, species. Land surface models can use the USO model to describe stomatal behaviour under changing atmospheric CO 2 conditions.

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

Publisher: Wiley

Date: 05-02-2015

DOI: 10.1111/NPH.13291

Abstract: The 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.

A reporting format for leaf-level gas exchange data and metadata

Publisher: Elsevier BV

Date: 03-2021

DOI: 10.1016/J.ECOINF.2021.101232

Convergence in phosphorus constraints to photosynthesis in forests around the world

Publisher: Springer Science and Business Media LLC

Date: 25-08-2022

DOI: 10.1038/S41467-022-32545-0

Abstract: Tropical forests take up more carbon (C) from the atmosphere per annum by photosynthesis than any other type of vegetation. Phosphorus (P) limitations to C uptake are paramount for tropical and subtropical forests around the globe. Yet the generality of photosynthesis-P relationships underlying these limitations are in question, and hence are not represented well in terrestrial biosphere models. Here we demonstrate the dependence of photosynthesis and underlying processes on both leaf N and P concentrations. The regulation of photosynthetic capacity by P was similar across four continents. Implementing P constraints in the ORCHIDEE-CNP model, gross photosynthesis was reduced by 36% across the tropics and subtropics relative to traditional N constraints and unlimiting leaf P. Our results provide a quantitative relationship for the P dependence for photosynthesis for the front-end of global terrestrial C models that is consistent with canopy leaf measurements.

Mount Allison University

Location: Canada

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University Of Gothenburg

Location: Sweden

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Western University

Location: Canada

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University Of Exeter

Location: United Kingdom of Great Britain and Northern Ireland

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Discovery Early Career Researcher Award - Grant ID: DE240100301

Start Date: 2024

End Date: 12-2026

Amount: $440,000.00

Funder: Australian Research Council