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Elevated CO2 Increases the Nitrogen Productivity of 12 Tree Species

Paper Reviewed
Ågren, G.I. and Kattge, J. 2017. Nitrogen productivity and allocation responses of 12 important tree species to increased CO2. Trees 31: 617-621.

Introducing their study, Ågren and Kattge (2017) note that CO2 and nitrogen interact at multiple temporal and spatial scales, which makes predictions of future plant responses to these two factors somewhat difficult. Therefore, they say that "it is of interest to find ways of expressing the interaction between CO2 and nitrogen that simplify the description of this interaction." And in this regard, they introduce the concept of nitrogen productivity, which they define as "the growth rate of plant biomass per unit of nitrogen in the plant," which they say "is directly designed to handle plant growth under dynamic nitrogen conditions." Thus, they set out to determine the effects of elevated CO2 on this parameter.

To accomplish their objective, the two scientists grew nine deciduous and three conifer tree species under controlled laboratory conditions at the Justus Liebig University of Giessen in Rauischholzhausen, Germany, where they subjected the trees to one of two CO2 concentrations (either 360 or 1000 ppm) and one of four nitrogen regimes (N0, no nitrogen added, N1, 1 mmol L-1 nitrogen added, N5, 5 mmol L-1 nitrogen added and N25, 25 mmol L-1 nitrogen added) for approximately 3 months.

In discussing their findings, Ågren and Kattge report that all but two species increased their nitrogen productivity under elevated CO2 and that, averaged over all species and all nitrogen levels, elevated CO2 stimulated nitrogen productivity by 28%. However, the strongest response was noted in deciduous tree species (average increase of 34%) and the weakest in conifers (average increase of 8%). Two other observations of note include the findings that elevated CO2 had "no clear effects on biomass allocation" of plant organs (i.e. stem, leaves, coarse and fine roots), nor was there any statistical difference in whole-plant nitrogen concentration among the trees growing in the different CO2 and nitrogen regimes.

Posted 20 October 2017