Carbon and Nitrogen Decoupling Under an 11-Year Drought in the Shortgrass Steppe
The frequency and magnitude of drought is expected to increase in the US Great Plains under future climate regimes. Although semiarid systems are considered highly resistant to water limitation, novel drought events could alter linkages among biogeochemical processes, and result in new feedbacks that influence the timescale of ecosystem recovery. We examined changes in carbon and nitrogen cycling in the last 2 years of an 11-year drought manipulation in the shortgrass steppe, and under the first 2 years of recovery from drought. We measured plant production, plant tissue chemistry, soil trace gas flux, and soil inorganic nitrogen dynamics to test the extent that this magnitude of drought altered carbon and nitrogen fluxes and how these changes affected post-drought dynamics. We found that soil inorganic nitrogen was up to five times higher under severe drought than under control conditions, but that this nitrogen may not have been accessible to plants and microbial communities during drought due to diffusion limitations. Drought plots had higher N2O flux when they received equal rainfall pulses, showing that this accumulated N may be vulnerable to loss. In addition, plants in drought plots had higher tissue nitrogen for 2 years following drought. These results show that decadal-length droughts that may occur under future precipitation regimes are likely to alter ecosystem properties through interactions among precipitation, vegetation, and N cycling. Shifts in plant N, vulnerability of nitrogen to loss, and rainfall use efficiency that we observed are likely to affect the recovery time of semiarid systems subject to droughts of this magnitude.
Keywordssemiarid grassland shortgrass steppe precipitation climate change coupled biogeochemical cycles ecosystem lags rainfall manipulations N conservation
This work was conducted at the Central Plains Experimental Range (CPER), which is administered by the USDA Agricultural Research Service (ARS) and is a Long Term Ecological Research site (SGS-LTER) funded by the National Science Foundation (NSF DEB 0823405 and NSF DEB 0217631). This work would not have been possible without the 1998–2011 SGS field crews and staff, the SGS-LTER Information Manager Nicole Kaplan, and Kenneth Murphy, who conceived and implemented the rainfall manipulation plots. We also would like to thank Dr. Joe von Fischer for assistance in trace gas analysis, Dr. Phillip Chapman for statistical advising, and two anonymous reviewers and the associate editor for their helpful comments.
- Burke IC, Mosier AR, Hook PB, Milchunas DG, Barrett JE, Vinton MA, McCulley RL, Kaye JP, Gill RA, Epstein HA, Kelly RH, Parton WJ, Yonker CM, Lowe P, Lauenroth WK. 2008. Soil organic matter and nutrient dynamics of shortgrass steppe ecosystems. In: Lauenroth WK, Burke IC, Eds. Ecology of the shortgrass steppe. New York: Oxford University Press. p 84–118.Google Scholar
- CCSP, 2008. Effects of climate change on energy production and use in the United States. In: Research, U.C.C.S.C.a.t.S.o.G.C. (Ed.).Google Scholar
- Dijkstra F, Augustine D, Brewer P, Fischer J. 2012. Nitrogen cycling and water pulses in semiarid grasslands: are microbial and plant processes temporally asynchronous? Oecologia 1–10. doi: 10.1007/s00442-012-2336-6.
- Evans SE, Byrne KM, Burke IC, Lauenroth WK. 2011. Defining the limit to resistance in a drought-tolerant grassland: long-term severe drought significantly reduces the dominant species and increases ruderals. J Ecol 99:1500–07.Google Scholar
- Evans SE, Wallenstein MA. 2012. Does moisture niche partitioning drive shifts in microbial community composition under long-term drought in the shortgrass steppe? International Society for Microbial Ecology (ISME) Journal (submitted).Google Scholar
- Hooper DU, Johnson L. 1999. Nitrogen limitation in dryland ecosystems: responses to geographical and temporal variation in precipitation. Biogeochemistry 46:247–93.Google Scholar
- IPCC. 2007. Climate change 2007: synthesis report. Geneva: Intergovernmental Panel on Climate Change.Google Scholar
- Lauenroth WK. 2008. Vegetation of the shortgrass steppe. In: Lauenroth WK, Burke IC, Eds. Ecology of the shortgrass steppe. New York: Oxford University Press. p 70–83.Google Scholar
- Lauenroth WK, Burke IC, Morgan JA. 2008a. The shortgrass steppe. New York: Oxford University Press.Google Scholar
- Lauenroth WK, Milchunas DG, Sala OE, Burke IC, Morgan JA. 2008b. Net primary production in the shortgrass steppe. In: Lauenroth WK, Burke IC, Eds. Ecology of the shortgrass steppe. New York: Oxford University Press. p 270–305.Google Scholar
- Livingston GP, Hutchinson GL. 1995. Enclosure-based measurement of trace gas exchange: applications and sources of error. In: Matson PA, Harris RC, Eds. Biogenic trace gases: measuring emissions from soil and water. Cambridge: Blackwell Science. p 394.Google Scholar
- Peters DPC, Lauenroth WK, Burke IC. 2008. The role of disturbance in shortgrass steppe community and ecosystem dynamics. In: Lauenroth WK, Burke IC, Eds. Ecology of the shortgrass steppe. New York: Oxford University Press. p 84–118.Google Scholar
- Schlesinger WH. 1997. Biogeochemistry: an analysis of global change. Oxford: Elsevier.Google Scholar
- Tappe W, Laverman A, Bohland M, Braster M, Ritterhaus S, GRoeneweg J, van Verseveld HW. 1999. Maintenance energy demand and starvation recovery dynamics of Nitrosomonas europaea and Nitrobacter winogradskyi cultivated in a retentostat with complete biomass retention. Appl Environ Microbiol 65:2471–7.PubMedGoogle Scholar
- Vogt KA, Persson H. 1991. Root methods. In: Lassoie H, Hinkley TM, Eds. Techniques and approaches in forest tree ecophysiology. Boca Raton: CRC Press. p 477–501.Google Scholar
- von Fischer, JC, Butters, G, Duchateau, PC, Thelwell, RJ, Siller, R, 2009. In situ measures of methanotroph activity in upland soils: A reaction-diffusion model and field observation of water stress. Journal of Geophysical Research-Biogeosciences 114.Google Scholar