JXB Advance Access originally published online on April 9, 2008
Journal of Experimental Botany 2008 59(7):1743-1754; doi:10.1093/jxb/ern062
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RESEARCH PAPER |
Low temperature effects on leaf physiology and survivorship in the C3 and C4 subspecies of Alloteropsis semialata
1Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
2Botany Department, Rhodes University, PO Box 94, Grahamstown 6140, South Africa
* To whom correspondence should be addressed. E-mail: c.p.osborne{at}sheffield.ac.uk
The species richness of C4 grasses is strongly correlated with temperature, with C4 species dominating subtropical ecosystems and C3 types predominating in cooler climates. Here, the effects of low temperatures on C4 and C3 grasses are compared, controlling for phylogenetic effects by using Alloteropsis semialata, a unique species with C4 and C3 subspecies. Controlled environment and common garden experiments tested the hypotheses that: (i) photosynthesis and growth are greater in the C4 than the C3 subspecies at high temperatures, but this advantage is reversed below 20 °C; and (ii) chilling-induced photoinhibition and light-mediated freezing injury of leaves occur at higher temperature thresholds in the C4 than the C3 plants. Measurements of leaf growth and photosynthesis showed the expected advantages of the C4 pathway over the C3 type at high temperatures. These declined with temperature, but were not completely lost until 15 °C, and there was no evidence of a reversal to give a C3 advantage. Chronic chilling (5–15 °C) or acute freezing events induced a comparable degree of photodamage in illuminated leaves of both subspecies. Similarly, freezing caused high rates of mortality in the unhardened leaves of both subtypes. However, a 2-week chilling treatment prior to these freezing events halved injury in the C3 but not the C4 subspecies, suggesting that C4 leaves lacked the capacity for cold acclimation. These results therefore suggest that C3 members of this subtropical species may gain an advantage over their C4 counterparts at low temperatures via protection from freezing injury rather than higher photosynthetic rates.
Key words: Alloteropsis semialata, C3 photosynthesis, C4 photosynthesis, chilling, cold acclimation, freezing, photodamage, quantum yield, temperature
Received 9 December 2007; Revised 28 January 2008 Accepted 12 February 2008