Effects of herbivores on nitrogen fixation by grass endophytes, legume symbionts and free-living soil surface bacteria in the Serengeti

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Grass roots can harbor abundant endophytic N2-fixing microbes (diazotrophs), but their abundance and activity compared to those on legumes and in soil crusts is still unknown. Here, in a natural ecosystem, the Serengeti of East Africa, we explored whether herbivores and soil nutrients limited grass root endophyte diazotroph abundance and their root mass-specific and area-specific N2-fixation, as they often do for diazotrophs symbiotic with legumes and those free-living in soil. N2-fixation and copy number of the nitrogenase gene nifH was measured with stable isotope and molecular methods, respectively, for the dominant grass Themeda triandra, and legume, Indigofera volkensii, and in the top 5 cm of soil in a 16-year herbivore exclosure experiment across four sites that varied in mean annual rainfall and soil N, P, and moisture. T. triandra nifH gene copy number was highly variable across sites and individuals but often approached or exceeded that of I. volkensii roots and soils. T. triandra roots generally exhibited lower root mass-specific N2-fixation (activity), which was not reduced by herbivores and increased in drier soils. In contrast, I. volkensii activity was only reduced by herbivores and soil diazotrophs were mostly inactive. T. triandra exhibited greater area-specific N2-fixation than I. volkensii, due to its much greater root biomass, but this difference was reduced by herbivores. Grass-associated endophytic diazotrophs may fix far more N2 in natural systems than previously realized, and may be limited by different factors those affecting symbiotic legume and free-living soil diazotrophs.

Original languageEnglish (US)
Pages (from-to)233-241
Number of pages9
JournalPedobiologia
Volume59
Issue number5-6
DOIs
StatePublished - Nov 1 2016

Fingerprint

endophyte
nitrogen fixation
symbiont
endophytes
symbionts
nitrogen-fixing bacteria
herbivore
Themeda triandra
soil surface
herbivores
legumes
grass
grasses
bacterium
bacteria
fixation
soil
Indigofera
gene dosage
soil crusts

Keywords

  • Bacteria
  • Grasses
  • Grasslands
  • Herbivory
  • Legumes
  • microbes
  • nifH gene
  • Nitrogen fixation
  • Roots
  • Stable isotopes

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Soil Science

Cite this

@article{4c53bf9d2f5841b69e8f4f93a3f30d75,
title = "Effects of herbivores on nitrogen fixation by grass endophytes, legume symbionts and free-living soil surface bacteria in the Serengeti",
abstract = "Grass roots can harbor abundant endophytic N2-fixing microbes (diazotrophs), but their abundance and activity compared to those on legumes and in soil crusts is still unknown. Here, in a natural ecosystem, the Serengeti of East Africa, we explored whether herbivores and soil nutrients limited grass root endophyte diazotroph abundance and their root mass-specific and area-specific N2-fixation, as they often do for diazotrophs symbiotic with legumes and those free-living in soil. N2-fixation and copy number of the nitrogenase gene nifH was measured with stable isotope and molecular methods, respectively, for the dominant grass Themeda triandra, and legume, Indigofera volkensii, and in the top 5 cm of soil in a 16-year herbivore exclosure experiment across four sites that varied in mean annual rainfall and soil N, P, and moisture. T. triandra nifH gene copy number was highly variable across sites and individuals but often approached or exceeded that of I. volkensii roots and soils. T. triandra roots generally exhibited lower root mass-specific N2-fixation (activity), which was not reduced by herbivores and increased in drier soils. In contrast, I. volkensii activity was only reduced by herbivores and soil diazotrophs were mostly inactive. T. triandra exhibited greater area-specific N2-fixation than I. volkensii, due to its much greater root biomass, but this difference was reduced by herbivores. Grass-associated endophytic diazotrophs may fix far more N2 in natural systems than previously realized, and may be limited by different factors those affecting symbiotic legume and free-living soil diazotrophs.",
keywords = "Bacteria, Grasses, Grasslands, Herbivory, Legumes, microbes, nifH gene, Nitrogen fixation, Roots, Stable isotopes",
author = "Ritchie, {Mark E} and Ramesh Raina",
year = "2016",
month = "11",
day = "1",
doi = "10.1016/j.pedobi.2016.09.001",
language = "English (US)",
volume = "59",
pages = "233--241",
journal = "Pedobiologia",
issn = "0031-4056",
publisher = "Urban und Fischer Verlag Jena",
number = "5-6",

}

TY - JOUR

T1 - Effects of herbivores on nitrogen fixation by grass endophytes, legume symbionts and free-living soil surface bacteria in the Serengeti

AU - Ritchie, Mark E

AU - Raina, Ramesh

PY - 2016/11/1

Y1 - 2016/11/1

N2 - Grass roots can harbor abundant endophytic N2-fixing microbes (diazotrophs), but their abundance and activity compared to those on legumes and in soil crusts is still unknown. Here, in a natural ecosystem, the Serengeti of East Africa, we explored whether herbivores and soil nutrients limited grass root endophyte diazotroph abundance and their root mass-specific and area-specific N2-fixation, as they often do for diazotrophs symbiotic with legumes and those free-living in soil. N2-fixation and copy number of the nitrogenase gene nifH was measured with stable isotope and molecular methods, respectively, for the dominant grass Themeda triandra, and legume, Indigofera volkensii, and in the top 5 cm of soil in a 16-year herbivore exclosure experiment across four sites that varied in mean annual rainfall and soil N, P, and moisture. T. triandra nifH gene copy number was highly variable across sites and individuals but often approached or exceeded that of I. volkensii roots and soils. T. triandra roots generally exhibited lower root mass-specific N2-fixation (activity), which was not reduced by herbivores and increased in drier soils. In contrast, I. volkensii activity was only reduced by herbivores and soil diazotrophs were mostly inactive. T. triandra exhibited greater area-specific N2-fixation than I. volkensii, due to its much greater root biomass, but this difference was reduced by herbivores. Grass-associated endophytic diazotrophs may fix far more N2 in natural systems than previously realized, and may be limited by different factors those affecting symbiotic legume and free-living soil diazotrophs.

AB - Grass roots can harbor abundant endophytic N2-fixing microbes (diazotrophs), but their abundance and activity compared to those on legumes and in soil crusts is still unknown. Here, in a natural ecosystem, the Serengeti of East Africa, we explored whether herbivores and soil nutrients limited grass root endophyte diazotroph abundance and their root mass-specific and area-specific N2-fixation, as they often do for diazotrophs symbiotic with legumes and those free-living in soil. N2-fixation and copy number of the nitrogenase gene nifH was measured with stable isotope and molecular methods, respectively, for the dominant grass Themeda triandra, and legume, Indigofera volkensii, and in the top 5 cm of soil in a 16-year herbivore exclosure experiment across four sites that varied in mean annual rainfall and soil N, P, and moisture. T. triandra nifH gene copy number was highly variable across sites and individuals but often approached or exceeded that of I. volkensii roots and soils. T. triandra roots generally exhibited lower root mass-specific N2-fixation (activity), which was not reduced by herbivores and increased in drier soils. In contrast, I. volkensii activity was only reduced by herbivores and soil diazotrophs were mostly inactive. T. triandra exhibited greater area-specific N2-fixation than I. volkensii, due to its much greater root biomass, but this difference was reduced by herbivores. Grass-associated endophytic diazotrophs may fix far more N2 in natural systems than previously realized, and may be limited by different factors those affecting symbiotic legume and free-living soil diazotrophs.

KW - Bacteria

KW - Grasses

KW - Grasslands

KW - Herbivory

KW - Legumes

KW - microbes

KW - nifH gene

KW - Nitrogen fixation

KW - Roots

KW - Stable isotopes

UR - http://www.scopus.com/inward/record.url?scp=85028249009&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85028249009&partnerID=8YFLogxK

U2 - 10.1016/j.pedobi.2016.09.001

DO - 10.1016/j.pedobi.2016.09.001

M3 - Article

AN - SCOPUS:85028249009

VL - 59

SP - 233

EP - 241

JO - Pedobiologia

JF - Pedobiologia

SN - 0031-4056

IS - 5-6

ER -