, Volume 154, Issue 2, pp 349–359 | Cite as

Microbial responses to nitrogen addition in three contrasting grassland ecosystems

  • Lydia H. ZeglinEmail author
  • Martina Stursova
  • Robert L. Sinsabaugh
  • Scott L. Collins
Ecosystem Ecology


The effects of global N enrichment on soil processes in grassland ecosystems have received relatively little study. We assessed microbial community response to experimental increases in N availability by measuring extracellular enzyme activity (EEA) in soils from three grasslands with contrasting edaphic and climatic characteristics: a semiarid grassland at the Sevilleta National Wildlife Refuge, New Mexico, USA (SEV), and mesic grasslands at Konza Prairie, Kansas, USA (KNZ) and Ukulinga Research Farm, KwaZulu-Natal, South Africa (SAF). We hypothesized that, with N enrichment, soil microbial communities would increase C and P acquisition activity, decrease N acquisition activity, and reduce oxidative enzyme production (leading to recalcitrant soil organic matter [SOM] accumulation), and that the magnitude of response would decrease with soil age (due to higher stabilization of enzyme pools and P limitation of response). Cellulolytic activities followed the pattern predicted, increasing 35–52% in the youngest soil (SEV), 10–14% in the intermediate soil (KNZ) and remaining constant in the oldest soil (SAF). The magnitude of phosphatase response did not vary among sites. N acquisition activity response was driven by the enzyme closest to its pH optimum in each soil: i.e., leucine aminopeptidase in alkaline soil, β-N-acetylglucosaminidase in acidic soil. Oxidative enzyme activity varied widely across ecosystems, but did not decrease with N amendment at any site. Likewise, SOM and %C pools did not respond to N enrichment. Between-site variation in both soil properties and EEA exceeded any treatment response, and a large portion of EEA variability (leucine aminopeptidase and oxidative enzymes), 68% as shown by principal components analysis, was strongly related to soil pH (r = 0.91, P < 0.001). In these grassland ecosystems, soil microbial responses appear constrained by a molecular-scale (pH) edaphic factor, making potential breakdown rates of SOM resistant to N enrichment.


Extracellular enzyme activity Soil carbon 



Funding for this work was provided by the National Science Foundation, the Sevilleta Long-Term Ecological Research (LTER) Program, the Konza Prairie LTER Program, the Ukulinga Research Farm (South Africa) and the University of KwaZulu-Natal (South Africa). Support of data collection and analysis was provided by Cliff Dahm, Chris Lauber, Marcy Gallo, John Blair, Alan Knapp, Melinda Smith, Rich Fynn, Chelsea Crenshaw, Nathan Daves-Brody, Kris Mossberg, Kylea Odenbach and John Craig. This article was improved by comments from Dr. Jason Kaye and three anonymous reviewers. The experiments described herein comply with the current laws of the countries in which they were performed.


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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • Lydia H. Zeglin
    • 1
    Email author
  • Martina Stursova
    • 1
  • Robert L. Sinsabaugh
    • 1
  • Scott L. Collins
    • 1
  1. 1.Department of Biology, MSC03 2020University of New MexicoAlbuquerqueUSA

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