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The Impacts of Warming on an Important Tropical Forage Legume
Martinez, C.A., Bianconi, M., Silva, L., Approbato, A., Lemos, M., Santos, L., Curtarelli, L., Rodrigues, A., Mello, T. and Manchon, F. 2014. Moderate warming increases PSII performance, antioxidant scavenging systems and biomass production in Stylosanthes capitata Vogel. Environmental and Experimental Botany 102: 58-67.

For plants growing in warm-to-hot tropical regions, one might expect that additional warming would be disastrous for them. But first impressions can often be deceiving, as in the case of Stylosanthes capitata - an important forage legume of tropical and subtropical regions - which was recently examined within this context by Martinez et al.

What was done
The ten Brazilian researchers planted S. capitata seeds in fertilized soil in 12-m x 12-m plots under normal field conditions, following the recommendations of Embrapa (2007), after which a warming treatment was applied at the plants' vegetative stage via a T-FACE system of the type described by Kimball et al. (2008), whereby an approximate canopy temperature differential of 2°C was maintained between the heated and ambient-temperature plots.

What was learned
Martinez et al. report that the warmed plants showed "good photochemical performance and photosynthetic adjustment under warming conditions," which led to "higher growth and biomass production than control plants," likely due to "adjustments in both the photosynthetic thermal optimum and the photosynthetic rates at the growth temperature," a combination that they say "may be a constructive adjustment," citing the supportive studies of Zhang and Dang (2013) and Way and Yamori (2014). And they also report that the S. capitata plants they studied "increased their chlorophyll content and antioxidative enzyme activity."

What it means
Quoting the ten scientists, "our results suggest that the higher antioxidant defense system levels induced by warming may protect photosynthesis against oxidative damage, thus alleviating the harmful effects of superoxide anion radicals and hydrogen peroxide." And that this is likely a general characteristic of plants, they write that "according to Sage and Kubien (2007), most plant species can acclimate to alterations in growth temperature by acclimatizing the photosynthesis system in a way that improves performance in the new temperature environment," while noting as an example that Ribeiro et al. (2012) found that sweet orange trees respond "positively to moderate warming conditions by improving photosynthesis and vegetative growth." And in light of these several findings of their own and others, they thus arrived at their ultimate conclusion, i.e., that "lower levels of warming would be advantageous for the growth of tropical plants."

Embrapa. 2007. Cropping and use of Stylosanthes campo grande. Technical Bulletin 105.

Kimball, B.A., Conley, M.M., Wang, S., Lin, X., Luo, C., Morgan, J. and Smith, D. 2008. Infrared heater arrays for warming ecosystem field plots. Global Change Biology 14: 309-320.

Ribeiro, R., Machado, E.C., Nunez, E., Ramos, R. and Machado, D. 2012. Moderate warm temperature improves shoot growth, affects carbohydrate status and stimulates photosynthesis of sweet orange plants. Brazilian Journal of Plant Physiology 24: 37-46.

Sage, R. and Kubien, D.S. 2007. The temperature response of C3 and C4 photosynthesis. Plant, Cell and Environment 30: 1086-1106.

Way, D.A. and Yamori, W. 2014. Thermal acclimation of photosynthesis: on the importance of adjusting our definitions and accounting for thermal acclimation of respiration. Photosynthesis Research 119: 89-100.

Zhang, S. and Dang, Q.L. 2013. CO2 elevation improves photosynthetic performance in progressive warming environment in white birch seedlings. F1000Res: 10.12688/f1000research.2-13.v1.

Reviewed 13 August 2014