The strategies of water–carbon regulation of plants in a subtropical primary forest on karst soils in China

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Abstract

Abstract. Coexisting plant species in a karst ecosystem may use diverse strategies of trade off between carbon gain and water loss to adopt to the low soil nutrient and low water availability conditions. An understanding of the impact of CO2 diffusion and maximum carboxylase activity of Rubisco (Vcmax) on the light-saturated net photosynthesis (A) and intrinsic water use efficiency (iWUE) can provide insight into physiological strategies of the water–carbon regulation of coexisting plant species used in adaptation to karst environments at the leaf scale. We selected 63 dominant species (across 6 life forms) in a subtropical karst primary forest in southwestern China, measured their CO2 response curves, and calculated the corresponding stomatal conductance to CO2 (gs), mesophyll conductance to CO2 (gm), and Vcmax. The results showed that gs and gm varied about 7.6- and 34.5-fold, respectively, and that gs was positively related to gm. The contribution of gm to the leaf CO2 gradient was similar to that of gs. gs∕A, gm∕A and gt∕A was negatively related to Vcmax∕A. The relative limitations of gs (ls), gm (lm), and Vcmax (lb) to A for the whole group (combined six life forms) were significantly different from each other (P&lt;0.05). lm was the largest (0.38±0.12), followed by lb (0.34±0.14), and ls (0.28±0.07). No significant difference was found between ls, lm, and lb for trees and tree/shrubs, while lm was the largest, followed by lb and ls for shrubs, grasses, vines and ferns (P&lt;0.05). iWUE varied about 3-fold (from 29.52 to 88.92µmolCO2mol−1H2O) across all species, and was significantly correlated with gs, Vcmax, gm∕gs, and Vcmax∕gs. These results indicated that karst plants maintained relatively high A and low iWUE through the covariation of gs, gm, and Vcmax as an adaptation to a karst environment.

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Fitting photosynthetic carbon dioxide response curves for C(3) leaves.

Thomas D. Sharkey, Carl J Bernacchi, Graham Farquhar … (2007)

Photosynthetic responses to carbon dioxide concentration can provide data on a number of important parameters related to leaf physiology. Methods for fitting a model to such data are briefly described. The method will fit the following parameters: V(cmax), J, TPU, R(d) and g(m)[maximum carboxylation rate allowed by ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco), rate of photosynthetic electron transport (based on NADPH requirement), triose phosphate use, day respiration and mesophyll conductance, respectively]. The method requires at least five data pairs of net CO(2) assimilation (A) and [CO(2)] in the intercellular airspaces of the leaf (C(i)) and requires users to indicate the presumed limiting factor. The output is (1) calculated CO(2) partial pressure at the sites of carboxylation, C(c), (2) values for the five parameters at the measurement temperature and (3) values adjusted to 25 degrees C to facilitate comparisons. Fitting this model is a way of exploring leaf level photosynthesis. However, interpreting leaf level photosynthesis in terms of underlying biochemistry and biophysics is subject to assumptions that hold to a greater or lesser degree, a major assumption being that all parts of the leaf are behaving in the same way at each instant.

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Gas exchange measurements, what can they tell us about the underlying limitations to photosynthesis? Procedures and sources of error.

S. LONG, C. J. Bernacchi (2003)

The principles, equipment and procedures for measuring leaf and canopy gas exchange have been described previously as has chlorophyll fluorescence. Simultaneous measurement of the responses of leaf gas exchange and modulated chlorophyll fluorescence to light and CO2 concentration now provide a means to determine a wide range of key biochemical and biophysical limitations on photo synthesis in vivo. Here the mathematical frameworks and practical procedures for determining these parameters in vivo are consolidated. Leaf CO2 uptake (A) versus intercellular CO2 concentration (Ci) curves may now be routinely obtained from commercial gas exchange systems. The potential pitfalls, and means to avoid these, are examined. Calculation of in vivo maximum rates of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) carboxylation (Vc,max), electron transport driving regeneration of RuBP (Jmax), and triose-phosphate utilization (VTPU) are explained; these three parameters are now widely assumed to represent the major limitations to light-saturated photosynthesis. Precision in determining these in intact leaves is improved by the simultaneous measurement of electron transport via modulated chlorophyll fluorescence. The A/Ci response also provides a simple practical method for quantifying the limitation that stomata impose on CO2 assimilation. Determining the rate of photorespiratory release of oxygen (Rl) has previously only been possible by isotopic methods, now, by combining gas exchange and fluorescence measurements, Rl may be determined simply and routinely in the field. The physical diffusion of CO2 from the intercellular air space to the site of Rubisco in C3 leaves has long been suspected of being a limitation on photosynthesis, but it has commonly been ignored because of the lack of a practical method for its determination. Again combining gas exchange and fluorescence provides a means to determine mesophyll conductance. This method is described and provides insights into the magnitude and basis of this limitation.

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Stomatal size, speed, and responsiveness impact on photosynthesis and water use efficiency.

Tracy Lawson, Michael R Blatt (2014)

The control of gaseous exchange between the leaf and bulk atmosphere by stomata governs CO₂ uptake for photosynthesis and transpiration, determining plant productivity and water use efficiency. The balance between these two processes depends on stomatal responses to environmental and internal cues and the synchrony of stomatal behavior relative to mesophyll demands for CO₂. Here we examine the rapidity of stomatal responses with attention to their relationship to photosynthetic CO₂ uptake and the consequences for water use. We discuss the influence of anatomical characteristics on the velocity of changes in stomatal conductance and explore the potential for manipulating the physical as well as physiological characteristics of stomatal guard cells in order to accelerate stomatal movements in synchrony with mesophyll CO₂ demand and to improve water use efficiency without substantial cost to photosynthetic carbon fixation. We conclude that manipulating guard cell transport and metabolism is just as, if not more likely to yield useful benefits as manipulations of their physical and anatomical characteristics. Achieving these benefits should be greatly facilitated by quantitative systems analysis that connects directly the molecular properties of the guard cells to their function in the field.

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Author and article information

Journal

Title: Biogeosciences

Abbreviated Title: Biogeosciences

Publisher: Copernicus GmbH

ISSN (Electronic): 1726-4189

Publication date Created: 2018

Publication date (Electronic): July 11 2018

Volume: 15

Issue: 13

Pages: 4193-4203

Article

DOI: 10.5194/bg-15-4193-2018

SO-VID: 6d5f1df8-34f4-4b23-95fc-7c6311e8b058

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https://creativecommons.org/licenses/by/4.0/

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The strategies of water–carbon regulation of plants in a subtropical primary forest on karst soils in China

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Most cited references 56

Fitting photosynthetic carbon dioxide response curves for C(3) leaves.

Gas exchange measurements, what can they tell us about the underlying limitations to photosynthesis? Procedures and sources of error.

Stomatal size, speed, and responsiveness impact on photosynthesis and water use efficiency.

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Cited by 3

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