title: Effects of water and nitrogen addition on ecosystem carbon exchange in a meadow steppe.
abstract: A changing precipitation regime and increasing nitrogen deposition are likely to have profound impacts on arid and semiarid ecosystem C cycling, which is often constrained by the timing and availability of water and nitrogen. However, little is known about the effects of altered precipitation and nitrogen addition on grassland ecosystem C exchange. We conducted a 3-year field experiment to assess the responses of vegetation composition, ecosystem productivity, and ecosystem C exchange to manipulative water and nitrogen addition in a meadow steppe. Nitrogen addition significantly stimulated aboveground biomass and net ecosystem CO2 exchange (NEE), which suggests that nitrogen availability is a primary limiting factor for ecosystem C cycling in the meadow steppe. Water addition had no significant impacts on either ecosystem C exchange or plant biomass, but ecosystem C fluxes showed a strong correlation with early growing season precipitation, rather than whole growing season precipitation, across the 3 experimental years. After we incorporated water addition into the calculation of precipitation regimes, we found that monthly average ecosystem C fluxes correlated more strongly with precipitation frequency than with precipitation amount. These results highlight the importance of precipitation distribution in regulating ecosystem C cycling. Overall, ecosystem C fluxes in the studied ecosystem are highly sensitive to nitrogen deposition, but less sensitive to increased precipitation.
authors.affiliation: Key Laboratory for Vegetation Ecology, Ministry of Education, Institute of Grassland Science, Northeast Normal University, Changchun, Jilin Province, P. R. China.
authors.forename: Yunbo
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Key Laboratory for Vegetation Ecology, Ministry of Education, Institute of Grassland Science, Northeast Normal University, Changchun, Jilin Province, P. R. China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Jiang
authors.affiliation: Key Laboratory for Vegetation Ecology, Ministry of Education, Institute of Grassland Science, Northeast Normal University, Changchun, Jilin Province, P. R. China; Veterinary and Animal Science College of Heilongjiang Bayi Agricultural University, Daqing, Heilongjiang Province, P. R. China.
authors.forename: Zhiming
authors.initials: Z
authors.lastname: Yang
authors.affiliation: Key Laboratory for Vegetation Ecology, Ministry of Education, Institute of Grassland Science, Northeast Normal University, Changchun, Jilin Province, P. R. China.
authors.forename: Wei
authors.initials: W
authors.lastname: Sun
authors.affiliation: Key Laboratory for Vegetation Ecology, Ministry of Education, Institute of Grassland Science, Northeast Normal University, Changchun, Jilin Province, P. R. China.
authors.forename: Deli
authors.initials: D
authors.lastname: Wang
mesh_terms: D002244:Carbon / Q000032:analysis*; D002245:Carbon Dioxide / Q000032:analysis; D017753:Ecosystem; D009584:Nitrogen / Q000032:analysis*; D014867:Water / Q000032:analysis*
chemical_list: D014867:Water; D002245:Carbon Dioxide; D002244:Carbon; D009584:Nitrogen