The Thermal Optimality of Entire Ecosystems
Niu, S., Luo, Y., Fei, S., Yuan, W., Schimel, D., Law, B.E., Ammann, C., Arain, M.A., Arneth, A., Aubinet, M., Barr, A., Beringer, J., Bernhofer, C., Black, T.A., Buchmann, N., Cescatti, A., Chen, J., Davis, K.J., Dellwik, E., Desai, A.R., Etzold, S., Francois, L., Gianelle, D., Gielen, B., Goldstein, A., Groenendijk, M., Gu, L., Hanan, N., Helfter, C., Hirano, T., Hollinger, D.Y., Jones, M.B., Kiely, G., Kolb, T.E., Kutsch, W.L., Lafleur, P., Lawrence, D.M., Li, L., Lindroth, A., Litvak, M., Loustau, D., Lund, M., Marek, M., Martin, T.A. Matteucci, G., Migliavacca, M., Montagnani, L., Moors, E., Munger, J.W., Noormets, A., Oechel, W., Olejnik, J., Paw U., K.T., Pilegaard, K., Rambal, S., Raschi, A., Scott, R.L., Seufert, G., Spano, D., Stoy, P., Sutton, M.A., Varlagin, A., Vesala, T., Weng, E., Wohlfahrt, G., Yang, B., Zhang, Z. and Zhou, X. 2012. Thermal optimality of net ecosystem exchange of carbon dioxide and underlying mechanisms. New Phytologist 194: 775-783.
In a study designed to test the merits of their hypothesis, Niu et al. "compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of net ecosystem exchange (NEE), an ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms." And what did they find?
The international team of researchers - hailing from Australia, Austria, Belgium, Canada, China, the Czech Republic, Denmark, Finland, France, Germany, Ireland, Italy, Japan, the Netherlands, Russia, Sweden, Switzerland, the United Kingdom and the United States - say they found that "the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites," and they say that "shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of ecosystem respiration." In addition, however, they indicate that "extended growing seasons, increased nitrogen mineralization, and enhanced root growth (Penuelas and Filella, 2001; Churkina et al., 2005; Luo et al., 2009) may also have contributed to the increased CO2 uptake under higher temperatures, leading to the upward shift in the optimum temperature of gross primary productivity in warmer years." Thus, if the world begins to warm again, for whatever reason, we can probably expect the bulk of the planet's vast array of ecosystems to become even more productive than they are today.
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