Fitting photosynthetic carbon dioxide response curves for C₃ leaves

Abstract

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: Vcmax, J, TPU, Rd and gm [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 CO2 assimilation (A) and [CO2] in the intercellular airspaces of the leaf (Ci) and requires users to indicate the presumed limiting factor. The output is (1) calculated CO2 partial pressure at the sites of carboxylation, Cc, (2) values for the five parameters at the measurement temperature and (3) values adjusted to 25°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.

Leaf Growth, Gas Exchange and Chlorophyll Fluorescence Parameters in Response to Different Water Deficits in Wheat Cultivars

“…1J). This was mainly due to the rapid adjustment of water loss through transpiration and absorption of CO 2 through stomatal regulation (Sharkey et al, 2007;Wu et al, 2008). The increase in instantaneous water use effi ciency under water defi cit conditions was less in CY17 than in XN889, further indicating that CY17 was more drought-sensitive.…”

Thermal acclimation of leaf photosynthetic traits in an evergreen woodland, consistent with the coordination hypothesis

“…Following Domingues et al (2010), we discarded 23 A-c i curves in which stomatal conductance declined to very low levels, resulting in 86 curves being used in further analyses. TPU (triose phosphate utilization) limitation (Sharkey et al, 2007) was not considered, as it would be unlikely to occur at our field temperatures of above 17 • C.…”

Water relations and photosynthesis along an elevation gradient for Artemisia tridentata during an historic drought

“…We measured photosynthetic gas exchange responses to CO 2 and light (A-C i and A-Q curves; Sharkey et al 2007) for each study plant using an open-mode portable photosynthesis system (model LI-6400; LI-COR, Lincoln, NE, USA). Leaf area was determined by estimation compared to area standards, and leaves were spread out to minimize overlap.…”

“…From the A-C i data, curve parameters were determined using Sharkey et al (2007), and included maximum rate of carboxylation (V cmax ), and maximum rate of electron transport (J max ), both of which were evaluated at a standard temperature of 25 °C. From the A-Q data, curve parameters were determined using Marshall and Biscoe (1980), Thornley and Johnson (1990), and http://landflux.org, and included maximal photosynthetic rate (A max ), dark respiration (R dark ), quantum yield (Φ), and light compensation point (LCP).…”