Mesophyll conductance does not contribute to greater photosynthetic rate per unit nitrogen in temperate compared with tropical evergreen wet‐forest tree leaves

Bahar, Nur H. A.; Hayes, Lucy; Scafaro, Andrew P.; Atkin, Owen K.; Evans, John R.

doi:10.1111/nph.15031

Cited by 31 publications

(29 citation statements)

References 71 publications

(178 reference statements)

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“…The adjustment from apparent to true values resulted in changes to the key parameters V cmax25 and J max25 that are qualitatively comparable to the results of previous adjustments (Sun, Gu, Dickinson, Pallardy et al, ), and that compare well with independently adjusted parameters by Bahar, Hayes, Scafaro, Atkin, and Evans () (results not shown). The adjustment again underlines the asymmetrical effects that g m has on V cmax25 and J max25 .…”

Section: Discussionsupporting

confidence: 83%

Effects of mesophyll conductance on vegetation responses to elevated CO₂concentrations in a land surface model

Knauer

Zaehle

Kauwe

et al. 2019

Global Change Biology

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Mesophyll conductance ( g m ) is known to affect plant photosynthesis. However, g m is rarely explicitly considered in land surface models (LSMs), with the consequence that its role in ecosystem and large‐scale carbon and water fluxes is poorly understood. In particular, the different magnitudes of g m across plant functional types (PFTs) are expected to cause spatially divergent vegetation responses to elevated CO 2 concentrations. Here, an extensive literature compilation of g m across major vegetation types is used to parameterize an empirical model of g m in the LSM JSBACH and to adjust photosynthetic parameters based on simulated A n − C i curves. We demonstrate that an explicit representation of g m changes the response of photosynthesis to environmental factors, which cannot be entirely compensated by adjusting photosynthetic parameters. These altered responses lead to changes in the photosynthetic sensitivity to atmospheric CO 2 concentrations which depend both on the magnitude of g m and the climatic conditions, particularly temperature. We then conducted simulations under ambient and elevated (ambient + 200 μmol/mol) CO 2 concentrations for contrasting ecosystems and for historical and anticipated future climate conditions (representative concentration pathways; RCPs) globally. The g m ‐explicit simulations using the RCP8.5 scenario resulted in significantly higher increases in gross primary productivity (GPP) in high latitudes (+10% to + 25%), intermediate increases in temperate regions (+5% to + 15%), and slightly lower to moderately higher responses in tropical regions (−2% to +5%), which summed up to moderate GPP increases globally. Similar patterns were found for transpiration, but with a lower magnitude. Our results suggest that the effect of an explicit representation of g m is most important for simulated carbon and water fluxes in the boreal zone, where a cold climate coincides with evergreen vegetation.

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Section: Discussionsupporting

confidence: 83%

Effects of mesophyll conductance on vegetation responses to elevated CO₂concentrations in a land surface model

Knauer

Zaehle

Kauwe

et al. 2019

Global Change Biology

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“…This is an important area for future research, both empirical and theoretical, on the control of photosynthetic traits, although debate remains as to the necessity of incorporating g m estimates into wider models (e.g. Bahar et al ., ).…”

Section: Discussionmentioning

confidence: 97%

The validity of optimal leaf traits modelled on environmental conditions

et al. 2018

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The ratio of leaf intercellular to ambient CO 2 (v) is modulated by stomatal conductance (g s ). These quantities link carbon (C) assimilation with transpiration, and along with photosynthetic capacities (V cmax and J max ) are required to model terrestrial C uptake. We use optimization criteria based on the growth environment to generate predicted values of photosynthetic and water-use efficiency traits and test these against a unique dataset.Leaf gas-exchange parameters and carbon isotope discrimination were analysed in relation to local climate across a continental network of study sites. Sun-exposed leaves of 50 species at seven sites were measured in contrasting seasons.Values of v predicted from growth temperature and vapour pressure deficit were closely correlated to ratios derived from C isotope (d 13 C) measurements. Correlations were stronger in the growing season. Predicted values of photosynthetic traits, including carboxylation capacity (V cmax ), derived from d 13 C, growth temperature and solar radiation, showed meaningful agreement with inferred values derived from gas-exchange measurements. Betweensite differences in water-use efficiency were, however, only weakly linked to the plant's growth environment and did not show seasonal variation.These results support the general hypothesis that many key parameters required by Earth system models are adaptive and predictable from plants' growth environments.

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“…In our A / C i curve fitting method, we did not account for the variations in mesophyll conductance ( g m ) as g m is not separately identifiable from V cmax when fitting an A / C i curve. Therefore, the estimated parameters, V cmax and J max , are considered apparent values (Bahar, Hayes, Scafaro, Atkin, & Evans, ). This approach is appropriate for this analysis because almost all current TBMs ignore g m and use apparent V cmax and J max values.…”

Section: Methodsmentioning

confidence: 99%

No evidence for triose phosphate limitation of light‐saturated leaf photosynthesis under current atmospheric CO₂ concentration

Kumarathunge

Medlyn

Drake

et al. 2019

Plant Cell & Environment

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The triose phosphate utilization (TPU) rate has been identified as one of the processes that can limit terrestrial plant photosynthesis. However, we lack a robust quantitative assessment of TPU limitation of photosynthesis at the global scale. As a result, TPU, and its potential limitation of photosynthesis, is poorly represented in terrestrial biosphere models (TBMs). In this study, we utilized a global data set of photosynthetic CO 2 response curves representing 141 species from tropical rainforests to Arctic tundra. We quantified TPU by fitting the standard biochemical model of C 3 photosynthesis to measured photosynthetic CO 2 response curves and characterized its instantaneous temperature response. Our results demonstrate that TPU does not limit leaf photosynthesis at the current ambient atmospheric CO 2 concentration. Furthermore, our results showed that the light-saturated photosynthetic rates of plants growing in cold environments are not more often limited by TPU than those of plants growing in warmer environments. In addition, our study showed that the instantaneous temperature response of TPU is distinct from temperature response of the maximum rate of Rubisco carboxylation. The new formulations of the temperature response of TPU derived in this study may prove useful in quantifying the biochemical limits to terrestrial plant photosynthesis and improve the representation of plant photosynthesis in TBMs. KEYWORDSA/C i curves, C 3 photosynthesis, maximum carboxylation capacity, potential electron transport rate, temperature, terrestrial biosphere models

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Mesophyll conductance does not contribute to greater photosynthetic rate per unit nitrogen in temperate compared with tropical evergreen wet‐forest tree leaves

Cited by 31 publications

References 71 publications

Effects of mesophyll conductance on vegetation responses to elevated CO₂concentrations in a land surface model

Effects of mesophyll conductance on vegetation responses to elevated CO₂concentrations in a land surface model

The validity of optimal leaf traits modelled on environmental conditions

No evidence for triose phosphate limitation of light‐saturated leaf photosynthesis under current atmospheric CO₂ concentration

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Mesophyll conductance does not contribute to greater photosynthetic rate per unit nitrogen in temperate compared with tropical evergreen wet‐forest tree leaves

Cited by 31 publications

References 71 publications

Effects of mesophyll conductance on vegetation responses to elevated CO2concentrations in a land surface model

Effects of mesophyll conductance on vegetation responses to elevated CO2concentrations in a land surface model

The validity of optimal leaf traits modelled on environmental conditions

No evidence for triose phosphate limitation of light‐saturated leaf photosynthesis under current atmospheric CO2 concentration

Contact Info

Product

Resources

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Effects of mesophyll conductance on vegetation responses to elevated CO₂concentrations in a land surface model

Effects of mesophyll conductance on vegetation responses to elevated CO₂concentrations in a land surface model

No evidence for triose phosphate limitation of light‐saturated leaf photosynthesis under current atmospheric CO₂ concentration