Acclimation of leaf respiration temperature responses across thermally contrasting biomes.

Short-term temperature response curves of leaf dark respiration (R-T) provide insights into a critical process that influences plant net carbon exchange. This includes how respiratory traits acclimate to sustained changes in the environment. Our study analysed 860 high-resolution R-T (10-70°C range) curves for: (a) 62 evergreen species measured in two contrasting seasons across several field sites/biomes; and (b) 21 species (subset of those sampled in the field) grown in glasshouses at 20°C : 15°C, 25°C : 20°C and 30°C : 25°C, day : night.

Global photosynthetic capacity is optimized to the environment.

Earth system models (ESMs) use photosynthetic capacity, indexed by the maximum Rubisco carboxylation rate (V ), to simulate carbon assimilation and typically rely on empirical estimates, including an assumed dependence on leaf nitrogen determined from soil fertility. In contrast, new theory, based on biochemical coordination and co-optimization of carboxylation and water costs for photosynthesis, suggests that optimal V can be predicted from climate alone, irrespective of soil fertility. Here, we develop this theory and find it captures 64% of observed variability in a global, field-measured V dataset for C plants.

Plasticity of photosynthetic heat tolerance in plants adapted to thermally contrasting biomes.

In many biomes, plants are subject to heatwaves, potentially causing irreversible damage to the photosynthetic apparatus. Field surveys have documented global, temperature-dependent patterns in photosynthetic heat tolerance (P ); however, it remains unclear if these patterns reflect acclimation in P or inherent differences among species adapted to contrasting habitats. To address these unknowns, we quantified seasonal variations in T (high temperature where minimal chlorophyll-a fluorescence rises rapidly, reflecting disruption to photosystem II) in 62 species native to 6 sites from 5 thermally contrasting biomes across Australia.

Macromolecular rate theory (MMRT) provides a thermodynamics rationale to underpin the convergent temperature response in plant leaf respiration.

Temperature is a crucial factor in determining the rates of ecosystem processes, for example, leaf respiration (R) - the flux of plant respired CO from leaves to the atmosphere. Generally, R increases exponentially with temperature and formulations such as the Arrhenius equation are widely used in earth system models. However, experimental observations have shown a consequential and consistent departure from an exponential increase in R.

Solar radiation and functional traits explain the decline of forest primary productivity along a tropical elevation gradient.

One of the major challenges in ecology is to understand how ecosystems respond to changes in environmental conditions, and how taxonomic and functional diversity mediate these changes. In this study, we use a trait-spectra and individual-based model, to analyse variation in forest primary productivity along a 3.3 km elevation gradient in the Amazon-Andes.

Strong thermal acclimation of photosynthesis in tropical and temperate wet-forest tree species: the importance of altered Rubisco content.

Understanding of the extent of acclimation of light-saturated net photosynthesis (A ) to temperature (T), and associated underlying mechanisms, remains limited. This is a key knowledge gap given the importance of thermal acclimation for plant functioning, both under current and future higher temperatures, limiting the accuracy and realism of Earth system model (ESM) predictions. Given this, we analysed and modelled T-dependent changes in photosynthetic capacity in 10 wet-forest tree species: six from temperate forests and four from tropical forests.

Thermal limits of leaf metabolism across biomes.

High-temperature tolerance in plants is important in a warming world, with extreme heat waves predicted to increase in frequency and duration, potentially leading to lethal heating of leaves. Global patterns of high-temperature tolerance are documented in animals, but generally not in plants, limiting our ability to assess risks associated with climate warming. To assess whether there are global patterns in high-temperature tolerance of leaf metabolism, we quantified T (high temperature where minimal chlorophyll a fluorescence rises rapidly and thus photosystem II is disrupted) and T (temperature where leaf respiration in darkness is maximal, beyond which respiratory function rapidly declines) in upper canopy leaves of 218 plant species spanning seven biomes.

Leaf-level photosynthetic capacity in lowland Amazonian and high-elevation Andean tropical moist forests of Peru.

We examined whether variations in photosynthetic capacity are linked to variations in the environment and/or associated leaf traits for tropical moist forests (TMFs) in the Andes/western Amazon regions of Peru. We compared photosynthetic capacity (maximal rate of carboxylation of Rubisco (V ), and the maximum rate of electron transport (J )), leaf mass, nitrogen (N) and phosphorus (P) per unit leaf area (M , N and P , respectively), and chlorophyll from 210 species at 18 field sites along a 3300-m elevation gradient. Western blots were used to quantify the abundance of the CO -fixing enzyme Rubisco.

Convergence in the temperature response of leaf respiration across biomes and plant functional types.

Plant respiration constitutes a massive carbon flux to the atmosphere, and a major control on the evolution of the global carbon cycle. It therefore has the potential to modulate levels of climate change due to the human burning of fossil fuels. Neither current physiological nor terrestrial biosphere models adequately describe its short-term temperature response, and even minor differences in the shape of the response curve can significantly impact estimates of ecosystem carbon release and/or storage.

A test of the 'one-point method' for estimating maximum carboxylation capacity from field-measured, light-saturated photosynthesis.

Simulations of photosynthesis by terrestrial biosphere models typically need a specification of the maximum carboxylation rate (Vcmax ). Estimating this parameter using A-Ci curves (net photosynthesis, A, vs intercellular CO2 concentration, Ci ) is laborious, which limits availability of Vcmax data. However, many multispecies field datasets include net photosynthetic rate at saturating irradiance and at ambient atmospheric CO2 concentration (Asat ) measurements, from which Vcmax can be extracted using a 'one-point method'.

Non-structural carbohydrates in woody plants compared among laboratories.

Non-structural carbohydrates (NSC) in plant tissue are frequently quantified to make inferences about plant responses to environmental conditions. Laboratories publishing estimates of NSC of woody plants use many different methods to evaluate NSC. We asked whether NSC estimates in the recent literature could be quantitatively compared among studies.

Global variability in leaf respiration in relation to climate, plant functional types and leaf traits.

Leaf dark respiration (Rdark ) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of Rdark and associated leaf traits. Data for 899 species were compiled from 100 sites (from the Arctic to the tropics).

Drought increases heat tolerance of leaf respiration in Eucalyptus globulus saplings grown under both ambient and elevated atmospheric [CO2] and temperature.

Climate change is resulting in increasing atmospheric [CO2], rising growth temperature (T), and greater frequency/severity of drought, with each factor having the potential to alter the respiratory metabolism of leaves. Here, the effects of elevated atmospheric [CO2], sustained warming, and drought on leaf dark respiration (R(dark)), and the short-term T response of R(dark) were examined in Eucalyptus globulus. Comparisons were made using seedlings grown under different [CO2], T, and drought treatments.

Canopy position affects the relationships between leaf respiration and associated traits in a tropical rainforest in Far North Queensland.

We explored the impact of canopy position on leaf respiration (R) and associated traits in tree and shrub species growing in a lowland tropical rainforest in Far North Queensland, Australia. The range of traits quantified included: leaf R in darkness (RD) and in the light (RL; estimated using the Kok method); the temperature (T)-sensitivity of RD; light-saturated photosynthesis (Asat); leaf dry mass per unit area (LMA); and concentrations of leaf nitrogen (N), phosphorus (P), soluble sugars and starch. We found that LMA, and area-based N, P, sugars and starch concentrations were all higher in sun-exposed/upper canopy leaves, compared with their shaded/lower canopy and deep-shade/understory counterparts; similarly, area-based rates of RD, RL and Asat (at 28 °C) were all higher in the upper canopy leaves, indicating higher metabolic capacity in the upper canopy.