Physiological advantages of C4 grasses in the field: a comparative experiment demonstrating the importance of drought. (28th March 2014)

• Record Type: Journal Article
• Authors: Taylor, Samuel H.; Ripley, Brad S.; Martin, Tarryn; De‐Wet, Leigh‐Ann; Woodward, F. Ian; Osborne, Colin P.
• Is Part Of: Global change biology. Volume 20:Number 6(2014:Jun.)
• Page Start: 1992
• Page End: 2003
• Publication Date: 2014-03-28
• Subjects: Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.12498
• Languages: English
• ISSNs: 1354-1013

Abstract

<abstract abstract-type="main" id="gcb12498-abs-0001"> <title>Abstract</title> <p>Global climate change is expected to shift regional rainfall patterns, influencing species distributions where they depend on water availability. Comparative studies have demonstrated that C<sub>4</sub> grasses inhabit drier habitats than C<sub>3</sub> relatives, but that both C<sub>3</sub> and C<sub>4</sub> photosynthesis are susceptible to drought. However, C<sub>4</sub> plants may show advantages in hydraulic performance in dry environments. We investigated the effects of seasonal variation in water availability on leaf physiology, using a common garden experiment in the Eastern Cape of South Africa to compare 12 locally occurring grass species from C<sub>4</sub> and C<sub>3</sub> sister lineages. Photosynthesis was always higher in the C<sub>4</sub> than C<sub>3</sub> grasses across every month, but the difference was not statistically significant during the wettest months. Surprisingly, stomatal conductance was typically lower in the C<sub>3</sub> than C<sub>4</sub> grasses, with the peak monthly average for C<sub>3</sub> species being similar to that of C<sub>4</sub> leaves. In water‐limited, rain‐fed plots, the photosynthesis of C<sub>4</sub> leaves was between 2.0 and 7.4 <italic>μ</italic>mol m<sup>−2</sup> s<sup>−1</sup> higher, stomatal conductance almost double, and transpiration 60% higher than for C<sub>3</sub> plants. Although C<sub>4</sub> average instantaneous water‐use efficiencies were higher (2.4–8.1 mmol mol<sup>−1</sup>) than C<sub>3</sub> averages (0.7–6.8 mmol mol<sup>−1</sup>), differences were not as great as we expected and were statistically significant only as drought became established. Photosynthesis declined earlier during drought among C<sub>3</sub> than C<sub>4</sub> species, coincident with decreases in stomatal conductance and transpiration. Eventual decreases in photosynthesis among C<sub>4</sub> plants were linked with declining midday leaf water potentials. However, during the same phase of drought, C<sub>3</sub> species showed significant decreases in hydrodynamic gradients that suggested hydraulic failure. Thus, our results indicate that stomatal and hydraulic behaviour during drought enhances the differences in photosynthesis between C<sub>4</sub> and C<sub>3</sub> species. We suggest that these drought responses are important for understanding the advantages of C<sub>4</sub> photosynthesis under field conditions.</p> </abstract>