Background
The authors write that "contemporary global warming has been accompanied by the narrowing of the diel (24 hour) temperature range by the asymmetric rise in night-time and daytime temperatures (Kukla and Karl, 1993; Easterling et al., 1997)," and they say that "it is likely that the emergence of novel temperature regimes in the tropics (Diffenbaugh and Scherer, 2011) will include the continued asymmetric rise of night-time temperatures (IPCC, 2007), with potentially profound implications upon plant growth in an already compromised ecosystem (Wright, 2010)."

What was done
After collecting seeds of two fast-growing tropical pioneer tree species - Ficus insipida and Ochroma pyramidale - from forests surrounding Panama City, Cheesman and Winter grew the seedlings the seeds produced in controlled-environment chambers at a constant daytime temperature (33°C) and a range of increasing night-time temperatures (22, 25, 28 and 31°C) for 38 days in the case of O. pyramidale and for 54 days in the case of F. insipida, after which they harvested the young trees and determined their total biomass production.

What was learned
In going from the coldest to the warmest night-time temperature treatment, total tree biomass accumulation rose from a mean of 0.85 g per seedling to a mean of 2.23 g per seedling in F. insipida; while in O. pyramidale, corresponding biomass accumulation values were 1.21 g and 2.65 g. And these enhancements in growth rates in response to rising night-time temperatures even occurred in spite of warming-induced increases in leaf-level dark respiration rates!

What it means
The two researchers state that "contrary to the notion of adverse effects of increasing night-time temperatures on tropical tree performance (Clark et al., 2003, 2010), our results demonstrate that under well-watered conditions elevated night-time temperature promotes growth in seedlings of two neotropical pioneer tree species ... even at 31°C, far in excess of night-time temperatures currently seen in lowland Panama."

References
Clark, D.B., Clark, D.A. and Oberbauer, S.F. 2010. Annual wood production in a tropical rain forest in NE Costa Rica linked to climatic variation but not to increasing CO2. Global Change Biology 16: 747-759.

Clark, D.A., Piper, S.C., Keeling, C.D. and Clark, D.B. 2003. Tropical rain forest tree growth and atmospheric carbon dynamics linked to interannual temperature variation during 1984-2000. Proceedings of the National Academy of Sciences, USA 100: 5852-5857.

Diffenbaugh, N.S. and Scherer, M. 2011. Observational and model evidence of global emergence of permanent, unprecedented heat in the 20th and 21st centuries. Climatic Change 197: 615-624.

Easterling, D.R., Horton, B., Jones, P.D., Peterson, T.C., Karl, T.R., Parker, D.E., Salinger, M.J., Razuvayev, V., Plummer, N., Jamason, P. and Folland, C.K. 1997. Maximum and minimum temperature trends for the globe. Science 277: 364-367.

Kukla, G. and Karl, T.R. 1993. Nighttime warming and the greenhouse effect. Environmental Science and Technology 27: 1468-1474.

Wright, S.J. 2010. The future of tropical forests. In: Ostfeld, R.S. and Schlesinger, W.H. (Eds.). The Year in Ecology and Conservation Biology 2010. Wiley-Blackwell, Malden, Massachusetts, USA, pp. 1-27.