Investigating C3/C4 plants competition using carbon isotopes and optimality principles
crossref(2022)
Abstract
<p>Understanding the mechanisms underlying changes in carbon isotope discrimination (Δ<sup>13</sup>C) in C<sub>3</sub> and C<sub>4</sub> plants is critical for predicting the C<sub>3</sub>/C<sub>4</sub> fraction in mixed ecosystems. Variations in Δ<sup>13</sup>C are closely related to changes in the stomatal limitation of photosynthesis (i.e. the ratio of leaf internal to ambient partial pressure of CO<sub>2</sub>, <em>c</em><sub>i</sub>/<em>c</em><sub>a</sub>), which are in turn determined by environmental variables, but also depend on the pathway of carbon assimilation. For instance, isotopic fractionation during the diffusion of CO<sub>2</sub> through the stomata primarily influences Δ<sup>13</sup>C in C<sub>4</sub> plants, while fractionation during Rubisco carboxylation has a stronger imprint on Δ<sup>13</sup>C in C<sub>3</sub> plants. As a result, C<sub>3</sub> plants are depleted in <sup>13</sup>C compared to C<sub>4</sub> plants. Isotopic measurements can thus be used as tracers of physiological processes in plants.</p><p>Here we implement Δ<sup>13</sup>C formulations for C<sub>3</sub> and C<sub>4</sub> plants in the optimal P model to investigate the abundance of C<sub>3</sub> and C<sub>4</sub> plants at different locations across the globe. We first test model predictions of Δ<sup>13</sup>C (and hence <em>c</em><sub>i</sub>/<em>c</em><sub>a</sub>) for the two carbon pathways against a large network of isotopic measurements from leaves. We then predict the expected mean Δ<sup>13</sup>C in soil organic materials after plants decomposition using maps of C<sub>3</sub>/C<sub>4</sub> plants distribution and assess model predictions with real isotopic measurements. Based on our results, we propose a model to predict the competition of C<sub>3</sub>/C<sub>4</sub> plants as a response to environmental variations in different ecosystems.</p>
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