How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

A CO2-induced Mechanism for Alleviating Growth Restrictions in Phosphorus-limited Ecosystems

Paper Reviewed
Keane, J.B., Hoosbeek, M.R., Taylor, C.R., Miglietta, F., Phoenix, G.K. and Hartley, I.P. 2020. Soil C, N and P cycling enzyme responses to nutrient limitation under elevated CO2. Biogeochemistry,

Numerous studies conducted over the past several years have revealed large and significant CO2-induced increases in global net primary productivity as ecosystems around the world have positively responded to rising atmospheric CO2 concentrations. However, rather than rejoicing in such good news, climate alarmists exude pessimism that the observed productivity enhancements will be short-lived, opining they will be limited by a lack of available soil nutrients necessary to sustain the ongoing CO2-induced enhancements in plant photosynthesis and growth. But is this cynical assessment correct?

A new paper by Keane et al. (2020) provides some insight into this topic. Publishing in the journal Biogeochemistry, the team of six European researchers examined the impact of elevated CO2 on phosphorus (P) cycling in a grassland ecosystem suffering from P limitation. Their work was conducted at the Bradfield Environment Laboratory research station in Peak District National Park, UK. Intact soil-turf monoliths were extracted from a long-term grassland nutrient manipulation experiment and subjected to elevated CO2 concentrations of 600 ppm (compared to ambient at 400 ppm) during daylight hours for a full growing season in a miniFACE experimental design.

Results of the study revealed that "soil microbes increase their relative investment in extra cellular enzymes (their extracellular enzyme stoichiometry) according to changes [in] P limitation." More specifically, they note that under elevated CO2, soil microbes "reduced investment in carbon cycling enzymes in favor of phosphorus or nitrogen cycling enzymes."

In essence, what occurred was a series of events starting with a CO2-induced increase in below-ground carbon, caused by increased grassland root biomass and/or rates of root exudation at higher CO2. Thereafter, soil microbes were able to utilize this additional labile pool of carbon, and possibly some of the nitrogen (N) saved from reduced investment in carbon cycle enzymes, to synthesize P-acquiring enzymes in order to obtain more of this scarce nutrient. Consequently, the increased relative microbial investment in P acquisition enabled increased mineralization in the naturally P-limited grassland ecosystems, thereby providing a mechanism by which elevated CO2 helped to alleviate the plant and ecosystem P limitation.

Commenting on these key findings the authors state "if microbes need to invest less in carbon-cycle enzymes this may allow them to invest more in cycling the P, the element that most strongly limits plant productivity in these grasslands," which "suggests that, in time, under elevated CO2 microbes may alleviate P limitation of plants and help to sustain increased NPP."

And so it is that rising atmospheric CO2 is helping plants escape P limitation via a synergistic relationship, where rising CO2 increase plant carbon cycling in the soil, which in turn stimulates microbial investment in P-cycle enzymes and ultimately increases soil P availability in order to sustain greater ecosystem productivity and growth.

Posted 30 December 2020