Biodiversity, Nitrogen Deposition, and CO2 Affect Grassland Soil Carbon Cycling but not Storage
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Grasslands are globally widespread and capable of storing large amounts of carbon (C) in soils, and are generally experiencing increasing atmospheric CO2, nitrogen (N) deposition, and biodiversity losses. To better understand whether grasslands will act as C sources or sinks in the future we measured microbial respiration in long-term laboratory incubations of soils collected from a grassland field experiment after 9 years of factorial treatment of atmospheric CO2, N deposition, and plant species richness on a deep and uniformly sandy soil. We fit microbial soil respiration rates to three-pool models of soil C cycling to separate treatment effects on decomposition and pool sizes of fast, slow, and resistant C pools. Elevated CO2 decreased the mean residence time (MRT) of slow C pools without affecting their pool size. Decreasing diversity reduced the size and MRT of fast C pools (comparing monocultures to plots planted with 16 species), but increased the slow pool MRT. N additions increased the size of the resistant pool. These effects of CO2, N, and species-richness treatments were largely due to plant biomass differences between the treatments. We found no significant interactions among treatments. These results suggest that C sequestration in sandy grassland soils may not be strongly influenced by elevated CO2 or species losses. However, high N deposition may increase the amount of resistant C in these grasslands, which could contribute to increased C sequestration.
KeywordsC sequestration elevated CO2 FACE experiment soil C cycling biodiversity nitrogen deposition
We thank the undergraduate BioCON interns for field work, Jared Trost and Kally Worm for experimental maintenance and management, and Chris Clark for assistance in the lab. We thank the US National Science Foundation through the Cedar Creek Long Term Ecological Research program (DEB-0080382), LTER (9411972, 0620652), Biocomplexity (0322057), and LTREB (0716587) programs; the US Department of Energy (DE-FG02-96ER62291 and DE-FC02-06ER64158); and the Minnesota Environment and Natural Resources Trust Fund for support of this project. Joseph Reid was supported by NSF IGERT 0504195.
- DeForest JL, Zak DR, Pregitzer KS, Burton AJ. 2004. Atmospheric nitrate deposition, microbial community composition, and enzyme activity in northern hardwood forests. Soil Sci Soc Am J 68(1):132–8.Google Scholar
- Grigal DF, Chamberlain LM, Finney HR, Wroblewski DV, Gross ER. 1974. Soils of the cedar creek natural history area. Agricultural Experiment Station, Miscellaneous Report 123:47–81. University of Minnesota.Google Scholar
- Hansen J, Sato M, Kharecha P, Beerling D, Berner R, Masson-Delmotte V, Pagani M, Raymo M, Royer DL, Zachos JC. 2008. Target atmospheric CO2: where should humanity aim? ArXiv 2:217–31.Google Scholar
- Paul E, Morris S, Böhm S. 2001a. The determination of soil C pool sizes and turnover rates: biophysical fractionation and tracers. In: Lal R, Kimble JM, Follett RF et al., Eds. Assessment methods for soil carbon. Boca Raton (FL): CRC Press. p 193.Google Scholar
- Pregitzer KS, Burton AJ, Zak DR, Talhelm AF. 2008. Simulated chronic nitrogen deposition increases carbon storage in northern temperate forests. Glob Change Biol 14(1):142–53.Google Scholar
- Reich PB, Tilman D, Craine J, Ellsworth D, Tjoelker M, Knops J, Wedin D, Naeem S, Bahauddin D, Goth J et al. 2001a. Do species and functional groups differ in acquisition and use of C, N and water under varying atmospheric CO2 and N availability regimes? A field test with 16 grassland species. New Phytol 150(2):435–48.CrossRefGoogle Scholar
- Schlesinger WH. 1997. Biogeochemistry: an analysis of global change. San Diego (CA): Academic Press. p 588.Google Scholar
- Sollins P, Glassman C, Paul EA, Swanston C, Lajtha K, Heil JW, Elliott ET. 1999. Soil carbon and nitrogen: pools and fractions. In: Robertson GP, Ed. Standard soil methods for long-term ecological research. New York: Oxford University Press. p 89.Google Scholar