Paper Reviewed
Hasegawa, S., MacDonald, C.A. and Power, S.A. 2016. Elevated carbon dioxide increases soil nitrogen and phosphorus availability in a phosphorus-limited Eucalyptus woodland. Global Change Biology 22: 1628-1643.

Under present conditions, plant growth and development are typically carbon-limited, which is why plants generally exhibit increased growth and biomass production in response to atmospheric CO2 enrichment. After carbon, nitrogen (N) is usually the second most limiting nutrient to plant growth, followed by phosphorus (P). Thus, although it is a less significant component of plant tissues than carbon and nitrogen, phosphorus is still required for successful life-cycle completion in many plant species; and, therefore, it is prudent to investigate aspects of plant phosphorus acquisition in response to atmospheric CO2 enrichment when phosphorus concentrations in soils are less than optimal.

The latest research team to perform such an investigation is Hasegawa et al. (2016), who examined the effects of elevated atmospheric CO2 on a phosphorus (P)-limited Eucalyptus woodland (Cumberland Plain Woodland) located near Richmond, New South Wales, Australia. There, using free-air CO2 enrichment technology, the three researchers subjected portions of the mature woodland ecosystem to ambient and ambient +150 ppm CO2 over a period of 18 months, during which time they made repeated measurements to assess pools and fluxes of inorganic N and P. And what did those measurements reveal?

Elevated CO2 increased levels of plant accessible nutrients in the Eucalyptus woodland for nitrate (+93%), ammonium (+12%) and phosphate (+54%). This finding, coupled with other measurements, led the authors to ultimately conclude that "CO2 fertilization increases nutrient availability -- particularly for phosphate -- in P-limited soils." With respect to how this happens, Hasegawa et al. write it is likely due to "increased plant belowground investment in labile carbon and associated enhancement of microbial turnover of organic matter and mobilization of chemically bound P."

The results of this analysis are significant in that the authors say "this is the first study to investigate ecosystem responses to elevated CO2 in a mature, P-limited woodland and, as such, provides novel insight into soil nutrient dynamics in a higher CO2 world." And that insight reveals "there is at least the potential for CO2-driven increases in soil P availability to support increased carbon accumulation in nutrient-poor, P-limited ecosystems as CO2 concentrations continue to rise." And that is more good news for the biosphere!