title: Nitrogen regulation of the climate-carbon feedback: evidence from a long-term global change experiment.
abstract: Modeling studies have shown that nitrogen (N) strongly regulates ecosystem responses and feedback to climate warming. However, it remains unclear what mechanisms underlie N regulation of ecosystem-climate interactions. To examine N regulation of ecosystem feedback to climate change, we have conducted a warming and clipping experiment since November 1999 in a tallgrass prairie of the Great Plains, USA. Infrared heaters were used to elevate soil temperature by an average of 1.96 degrees C at a depth of 2.5 cm from 2000 to 2008. Yearly biomass clipping mimicked hay or biofuel feedstock harvest. We measured carbon (C) and N concentrations, estimated their content and C:N ratio in plant, root, litter, and soil pools. Warming significantly stimulated C storage in aboveground plant, root, and litter pools by 17%, 38%, and 29%, respectively, averaged over the nine years (all P < 0.05) but did not change soil C content or N content in any pool. Plant C:N ratio and nitrogen use efficiency increased in the warmed plots compared to the control plots, resulting primarily from increased dominance of C4 plants in the community. Clipping significantly decreased C and N storage in plant and litter pools (all P < 0.05) but did not have interactive effects with warming on either C or N pools over the nine years. Our results suggest that increased ecosystem nitrogen use efficiency via a shift in species composition toward C4 dominance rather than plant N uptake is a key mechanism underlying warming stimulation of plant biomass growth.
authors.affiliation: Department of Botany and Microbiology, University of Oklahoma, Norman, Oklahoma 73019, USA. sniu@ou.edu
authors.forename: Shuli
authors.initials: S
authors.lastname: Niu
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Sherry
authors.forename: Xuhui
authors.initials: X
authors.lastname: Zhou
authors.forename: Shiqiang
authors.initials: S
authors.lastname: Wan
authors.forename: Yiqi
authors.initials: Y
authors.lastname: Luo
mesh_terms: D002244:Carbon / Q000378:metabolism*; D017753:Ecosystem; D057232:Global Warming; D009584:Nitrogen / Q000378:metabolism*; D018517:Plant Roots; D010944:Plants / Q000378:metabolism*; D012987:Soil / Q000737:chemistry; D013997:Time Factors
chemical_list: D012987:Soil; D002244:Carbon; D009584:Nitrogen