PhD Research Project: NERC CENTA - Nutrient limitation in forests: less carbon sequestration, faste

Enhanced plant growth as a result of elevated atmospheric carbon dioxide concentration (eCO2) and nutrient deposition has been estimated to be largely responsible for absorbing more than a quarter of recent anthropogenic CO2 emissions. The present-day global net land sink is located primarily in northern ecosystems, and in particular old-growth forests. Land C responses to eCO2 are potentially the most important, but also the most uncertain C-cycle feedback to climate change. This is primarily because availability of nutrients (macro- and micronutrients) may limit forest C sequestration, with models and empirical data identifying a potentially strong sensitivity of eCO2 response rates to the availability of nitrogen. This would imply that the potential for C uptake by terrestrial ecosystems may have been overestimated, adding tens of ppmv (15 – 150 ppmv) to the predicted 21st-century atmospheric CO2 concentration. If confirmed, a major reduction in allowable emissions of CO2 would be required to achieve the challenging < 2oC target agreed at the UN COP21, which has profound policy and social implications.

Therefore, to predict long-term responses of forest to increase CO2 concentration, it is essential to determine how nutrient cycling processes interact with carbon cycling in forest ecosystems in a high CO2 world. However, this is only possible when the new BIFoR-FACE facility becomes available (2017).

Aim and objectives: The aim of this project is to quantify the nutrient (e.g., P, Mn, Zn, K) cycling processes in a temperate forest under elevated CO2. The specific objectives are:
1) To measure the change in the stocks and fluxes of selected nutrients in soils at BIFoR-FACE site before and after CO2 fumigation.
2) To elucidate the role of nutrients in BIFoR-FACE woodland soil respiration and carbon storage.

Methodology:
Microbially mediated nutrient cycling (P, Mn, Zn, and K) will be assessed by analysis of atmospheric deposition, soil and soil water, soil nutrients (using memberances), leaves, and roots. Samples collected by the student, other BIFoR students, or technicians will be analysed for speciated P, Mn, Zn, and K using nurient analyser, IC and ICP-OES to establish the flux and budget of bioavailable nutrients, and the net products of microbial metabolism in soils and soil waters under elevated CO2.

The student will also work closely with Earth System Modellers at Birmingham, Exeter and elsewhere to test and improve their models.

Funding Notes

In addition to completing an online application form, you will also need to complete and submit the CENTA studentship application form available from www.centa.org.uk.

CENTA studentships are for 3.5 years and are funded by the Natural Environment Research Council (NERC). In addition to the full payment of their tuition fees, successful candidates will receive the following financial support.

Annual stipend, set at £14,296 for 2016/17
Research training support grant (RTSG) of £8,000

CENTA students are required to undertake from 45 days training throughout their PhD including a 10 day placement.
 

References

1) Bernhardt E et al., 2006. Long-term effects of free air CO2 enrichment (FACE) on soil respiration. Biogeochem, 77, 91-116
2) Fernandez-Martinez M et al., 2014. Nutrient availability as the key regulator of global forest carbon balance. Nat Clim Change, 4, 471-476.
3) Hartley IP, 2014. Soil carbon: Resisting climate change. Nat Climate Change, 4, 760-761.
4) Hartley I et al., 2013. A potential loss of carbon associated with greater plant growth in the European Arctic. Nat Climate Change, 2, 875-879.
5) Jackon RB et al., 2009. Increased belowground biomass and soil CO2 fluxes after a decade of carbon dioxide enrichment in a warm-temperate forest. Ecology, 90, 3352-3366.
6) Medlyn B et al., 2015. Using ecosystem experiments to improve vegetation models. Nat Clim Change 5, 528-534.
7) Mildner, M. et al., 2015. Respiratory fluxes and fine root responses in mature Picea abies trees exposed to elevated atmospheric CO2 concentrations. Biogeochem, 124, 95-111.
8) Norby R et al., 2016. Model-data synthesis for the next generation of forest free-air CO2 enrichment (FACE) experiments. New Phytol 209, 1728.
9) Siemens J et al., 2012. Elevated air carbon dioxide concentrations increase dissolved carbon leaching from a cropland soil. Biogeochem,108, 135-148.
10) Van Groenigen KJ et al. 2014. Faster decomposition under increased atmospheric CO2 limits soil carbon storage. Science, 344, 508-509.