The synergistic response of primary production in grasslands to combined nitrogen and phosphorus addition is caused by increased nutrient uptake and retention

Eduardo Vázquez, Elizabeth T. Borer, Miguel N. Bugalho, Maria C. Caldeira, Rebecca L. McCulley, Anita C. Risch, Eric W. Seabloom, George R. Wheeler, Marie Spohn

Research output: Contribution to journalArticlepeer-review


Background and aims: A synergistic response of aboveground plant biomass production to combined nitrogen (N) and phosphorus (P) addition has been observed in many ecosystems, but the underlying mechanisms and their relative importance are not well known. We aimed at evaluating several mechanisms that could potentially cause the synergistic growth response, such as changes in plant biomass allocation, increased N and P uptake by plants, and enhanced ecosystem nutrient retention. Methods: We studied five grasslands located in Europe and the USA that are subjected to an element addition experiment composed of four treatments: control (no element addition), N addition, P addition, combined NP addition. Results: Combined NP addition increased the total plant N stocks by 1.47 times compared to the N treatment, while total plant P stocks were 1.62 times higher in NP than in single P addition. Further, higher N uptake by plants in response to combined NP addition was associated with reduced N losses from the soil (evaluated based on soil δ15N) compared to N addition alone, indicating a higher ecosystem N retention. In contrast, the synergistic growth response was not associated with significant changes in plant resource allocation. Conclusions: Our results demonstrate that the commonly observed synergistic effect of NP addition on aboveground biomass production in grasslands is caused by enhanced N uptake compared to single N addition, and increased P uptake compared to single P addition, which is associated with a higher N and P retention in the ecosystem.

Original languageEnglish
JournalPlant and Soil
StateAccepted/In press - 2023

Bibliographical note

Funding Information:
We thank Renate Krauss for laboratory assistance and the Analytical Chemistry laboratory (CAN) of the Bayreuth Center of Ecological and Environmental Research (BayCEER) for performing parts of the chemical analyses. In addition, we thank the stable isotope laboratory of BayCEER for performing the isotope analyses. EV and MS have been funded by the German Research Foundation through the Emmy Noether-program (grant SP1389/6-1). This work was generated using data from the Nutrient Network ( ) experiment, funded at the site-scale by individual researchers. Coordination and data management have been supported by funding to ETB and EWS from the National Science Foundation Research Coordination Network (NSF-DEB-1042132) and Long-Term Ecological Research (NSF-DEB-1234162 and NSF-DEB-1831944 to Cedar Creek LTER) programs, and the Institute on the Environment (DG-0001-13). We also thank the Minnesota Supercomputer Institute for hosting project data and the Institute of the Environment for hosting Network meetings. Soil analyses were supported, in part, by USDA-ARS grant 58-3098-7-007 to ETB. MCC thanks Portuguese Science Foundation (FCT) for funding the research unit CEF (UIDB/00239/2020). We thank Rui Alves and Companhia das Lezírias for logistic support and for granting access to the study site ( MN Bugalho acknowledges financial support by the Portuguese Science Foundation (FCT) through contract DL57/2016/CP1382/CT0030 and research unit (CEABN-InBIO) funding through projects POCI-01-0145-FEDER-006821 and UID/BIA/50027/2020.

Publisher Copyright:
© 2023, The Author(s).


  • Grasslands
  • N natural abundance
  • Nitrogen addition
  • Nitrogen losses
  • NutNet
  • Phosphorus addition
  • Synergistic growth effect

ASJC Scopus subject areas

  • Soil Science
  • Plant Science


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