Preprints
https://doi.org/10.5194/bg-2020-392
https://doi.org/10.5194/bg-2020-392

  09 Nov 2020

09 Nov 2020

Review status: this preprint is currently under review for the journal BG.

Carbon storage in phosphorus limited grasslands may decline in response to elevated nitrogen deposition: a long-term field manipulation and modelling study

Christopher R. Taylor1, Victoria Janes-Bassett3, Gareth Phoenix1, Ben Keane1, Iain P. Hartley2, and Jessica A. C. Davies3 Christopher R. Taylor et al.
  • 1Department of Animal and Plant Sciences, University of Sheffield, Sheffield, UK
  • 2Geography, College of Life and Environmental Science, University of Exeter, Exeter, UK
  • 3Lancaster Environment Centre, Lancaster University, Lancaster, UK

Abstract. In many temperate ecosystems, nitrogen (N) limits productivity, meaning anthropogenic N deposition can stimulate plant growth and subsequently carbon (C) sequestration. Phosphorus (P) and N-P co-limited grasslands are widespread, yet there is limited understanding of their responses to N deposition, which may transition more ecosystems toward P-limited or N-P co-limited states. Here, we investigate the consequences of enhanced N addition on the C-N-P pools of grasslands in different states of nutrient limitation. We explored the response of a long-term nutrient-manipulation experiment on two N-P co-limited grasslands; an acidic grassland of stronger N-limitation and a calcareous grassland of stronger P-limitation, by combining data with an integrated C-N-P cycling model (N14CP). To explore the role of P-access mechanisms in determining ecosystem state, we allowed P-access to vary, and compared the outputs to plant-soil C-N-P data. Combinations of organic P access and inorganic P availability most closely representing data were used to simulate the grasslands and quantify their temporal response to nutrient manipulation. The model suggested N additions have increased C stocks in the acidic grassland, but decreased them in the calcareous, where N provision exacerbated P-limitation and reduced biomass input to the soil. Furthermore, plant acquisition of organic P may play an important role in reducing P-limitation, as both simulated grasslands increased organic P uptake to meet P demand. We conclude that grasslands of differing limiting nutrients may respond to N deposition in contrasting ways, and stress that as N deposition shifts ecosystems toward P-limitation, a globally important carbon sink risks degradation.

Christopher R. Taylor et al.

 
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

Christopher R. Taylor et al.

Christopher R. Taylor et al.

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Short summary
We used experimental data to model grasslands of contrasting nutrient limitation to investigate their response to nitrogen (N) deposition. We show that when N limits plant growth, deposition stimulated plant carbon (C) input to the soil, but when phosphorus (P) was limiting, we found the reverse; N deposition exacerbated P demand and reduced plant C input. This caused more C to be released into the atmosphere than is taken in, reducing the climate-mitigation capacity of the P-limited grassland.
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