Defoliation induces root exudation and triggers positive rhizospheric feedbacks in a temperate grassland

E. William Hamilton, Douglas A. Frank, Paul M. Hinchey, Tanya R. Murray

Research output: Contribution to journalArticlepeer-review

169 Scopus citations


The facilitating effect of the exudation of carbon (C) compounds from roots on rhizospheric processes has been shown in controlled experiments; however, it still remains unclear how important this pathway of C from plants to the soil may be in energy and nutrient processes in grazed grasslands under natural conditions. Root exudation may be a particularly important C pathway in grazed grasslands and help promote positive feedbacks between large herbivores and plants. In this study we performed a 13C pulse-chase experiment on plots that were clipped or left unclipped in a mesic grassland in Yellowstone National Park. The dominant grass species in the plots was Poa pratensis and it was used to measure the effect of defoliation on root C exudation, the rhizospheric microbial community, and feedbacks on plant nutrient uptake over a time period of 24-72 h. Defoliation stimulated C exudation from roots by 1.5-fold, which concomitantly increased rhizospheric microbial biomass by the same factor. The facilitating effects of defoliation on rhizospheric processes resulted in positive feedback on soil inorganic N pools and leaf N content, which increased by 1.2- and 1.5-fold respectively. Changes in soil inorganic N pools during the experiment indicated that the effect of the C flush on the rhizospheric decomposer community of defoliated plants resulted in a 5-fold increase in rhizospheric daily net N mineralization rate. These findings demonstrate that in a natural grassland community defoliation-induced stimulation of C exudation stimulates rhizospheric N-mineralization which ultimately benefits defoliated plants. The results also indicate the important role that short-term root-rhizospheric microbe interactions play in the C and N processes in grazed grasslands.

Original languageEnglish (US)
Pages (from-to)2865-2873
Number of pages9
JournalSoil Biology and Biochemistry
Issue number11
StatePublished - Nov 2008


  • Decomposition
  • Defoliation
  • Organic matter
  • Poa pratensis
  • Rhizosphere

ASJC Scopus subject areas

  • Microbiology
  • Soil Science


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