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Major contribution of grass roots to soil carbon pools and CO2 fluxes in a mesic savanna

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Abstract

Aims

There is a trend of increasing woody biomass in tropical savannas. Here we ask what effect this increase may have on soil carbon pools and fluxes.

Methods

Using a field experiment we determine the amount of soil carbon directly under grasses, a juvenile tree among grasses and a juvenile tree with no grasses. We also measure CO2 efflux at the soil surface and use gas wells to extract CO2 from several soil depths.

Results

Our results show that grasses contribute substantially more than trees to both soil carbon and soil respiration. Grasses also make a disproportionate contribution to the δ13C value of SOC in the tree only treatments. The surface gas efflux data show that soil respiration increased with an increase in volumetric soil moisture and temperature and plots with both grasses and trees had higher respiration rates than plots with trees only or with grasses only.

Conclusions

The highest soil respiration is in the top 20 cm of the soil with grasses the primary contributors to both δ13CSOC and δ13CR. Any increase in woody biomass will result in a decline in SOM turnover and nitrogen mineralization rates resulting in higher SOC pools. The associated increases in SOC and above ground biomass will however be associated with negative economic and biodiversity impacts.

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Acknowledgements

The research was funded by the Andrew W. Mellon Foundation (#30600716). We would like to thank SANParks for permission to work in the Kruger National Park. We are grateful to Ben Wigley, Corli Coetsee, Henri Combrinck and Paola Vimercati for help with fieldwork. Thanks to Anna Richards for helpful comments on the manuscript.

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Authors and Affiliations

  1. Department Biological Sciences, University of Cape Town, Private bag, Rondebosch, 7701, South Africa

    Edmund February

  2. Agroecology, University of Bayreuth, Universitätsstr. 30, Bayreuth, 95440, Germany

    Johanna Pausch

  3. Plant Ecology, University of Bayreuth, Universitätsstr. 30, Bayreuth, 95440, Germany

    Steven I. Higgins

Authors
  1. Edmund February
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  2. Johanna Pausch
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  3. Steven I. Higgins
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Contributions

ECF and SH conceived and designed the experiments. ECF performed the experiments. ECF, SH and JP analysed the data. ECF, SH and JP wrote the manuscript.

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Correspondence to Edmund February.

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February, E., Pausch, J. & Higgins, S.I. Major contribution of grass roots to soil carbon pools and CO2 fluxes in a mesic savanna. Plant Soil 454, 207–215 (2020). https://doi.org/10.1007/s11104-020-04649-3

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  • DOI: https://doi.org/10.1007/s11104-020-04649-3

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