Alvarez-Clare, Silvia

Cleveland, Cory C.

Lekberg, Ylva

Nasto, Megan K.

Sullivan, Benjamin W.

Townsend, Alan R.

English

University of Montana

University of Montana ScholarWorks at University of Montana UM Graduate Student Research Conference (GradCon) Apr 12th, 12:20 PM - 12:40 PM Symbiotic dinitrogen fixation enhances soil phosphorus acquisition strategies in tropical forests Megan K. Nasto The University of Montana, megan.nasto@umontana.edu Silvia Alvarez-Clare The University of Montana, silvia.alvarez.clare@gmail.com Ylva Lekberg MPG Ranch Benjamin W. Sullivan The University Of Montana, benjamin.sullivan@umontana.edu Alan R. Townsend University of Colorado at Boulder, alan.townsend@colorado.edu See next page for additional authors Follow this and additional works at: https://scholarworks.umt.edu/gsrc Let us know how access to this document benefits you. Nasto, Megan K.; Alvarez-Clare, Silvia; Lekberg, Ylva; Sullivan, Benjamin W.; Townsend, Alan R.; and Cleveland, Cory C., "Symbiotic dinitrogen fixation enhances soil phosphorus acquisition strategies in tropical forests" (2014). UM Graduate Student Research Conference (GradCon). 4. https://scholarworks.umt.edu/gsrc/2014/oralpres2a/4 This Oral Presentation is brought to you for free and open access by ScholarWorks at University of Montana. It has been accepted for inclusion in UM Graduate Student Research Conference (GradCon) by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact scholarworks@mso.umt.edu. Authors' Names Megan K. Nasto, Silvia Alvarez-Clare, Ylva Lekberg, Benjamin W. Sullivan, Alan R. Townsend, and Cory C. Cleveland This oral presentation is available at ScholarWorks at University of Montana: https://scholarworks.umt.edu/gsrc/2014/oralpres2a/4 Symbiotic	  dinitrogen	  (N2)	  fixation	  –	  a	  process	  that	  allows	  some	  plants	  to	  overcome	  nitrogen	  (N)	  limitation	  by	  converting	  atmospheric	  N2	  into	  bioavailable	  forms	  –	  is	  an	  energetically	  expensive	  mutualism	  that	  requires	  carbon	  and	  phosphorus	  (P)	  from	  host	  plants	  to	  support	  their	  microbial	  symbionts.	  Ecological	  theory	  suggests	  that	  N2	  fixers	  –	  and	  N2	  fixation	  –	  should	  have	  a	  competitive	  advantage	  in	  low	  N-­‐high	  P	  environments,	  but	  be	  outcompeted	  –	  or	  down-­‐regulated	  –	  in	  high	  N-­‐low	  P	  environments.	  Yet,	  N2	  fixers	  are	  relatively	  rare	  in	  N-­‐poor	  temperate	  forests,	  but	  abundant	  and	  active	  in	  N-­‐rich	  lowland	  tropical	  forests.	  Previous	  research	  addressing	  this	  paradigm	  hypothesized	  that	  N2	  fixers	  have	  the	  capacity	  to	  acquire	  more	  soil	  P	  than	  non-­‐N2	  fixers	  because	  they	  can	  invest	  fixed	  N2	  in	  extracellular	  phosphatase	  enzymes,	  giving	  N2	  fixers	  a	  competitive	  advantage	  in	  acquiring	  this	  often-­‐limiting	  nutrient.	  We	  tested	  this	  hypothesis,	  as	  well	  as	  the	  potential	  ability	  for	  N2	  fixers	  to	  host	  more	  arbuscular	  mycorrhizal	  (AM)	  fungi	  than	  non-­‐N2	  fixers,	  by	  comparing	  enzyme	  activities	  and	  AM	  colonization	  between	  active	  N2	  fixers	  and	  non-­‐N2	  fixers	  in	  two	  lowland	  rainforest	  sites	  that	  compose	  a	  soil	  P	  gradient	  in	  Costa	  Rica.	  At	  both	  lowland	  rainforest	  sites,	  phosphatase	  enzyme	  activity	  and	  AM	  colonization	  were	  significantly	  greater	  on	  the	  roots	  of	  N2	  fixers	  than	  non-­‐N2	  fixers.	  Also,	  AM	  colonization	  was	  strongly	  and	  positively	  related	  to	  both	  N2	  fixation	  rates	  and	  nodule	  biomass,	  and	  the	  nature	  of	  the	  relationships	  was	  similar	  between	  both	  lowland	  rainforest	  sites.	  This	  indicates	  a	  potential	  link	  between	  the	  two	  mutualistic	  strategies	  of	  acquiring	  soil	  N	  and	  P,	  though	  the	  mechanism	  enabling	  N2	  fixers	  to	  host	  more	  AM	  fungi	  than	  non-­‐N2	  fixers	  remains	  unclear.	  Overall,	  our	  results	  show	  a	  consistent	  set	  of	  N	  and	  P	  interactions	  across	  a	  range	  of	  plant	  species	  in	  two	  functional	  groups	  (i.e.,	  N2	  fixers	  and	  non-­‐N2	  fixers),	  and	  across	  a	  large	  gradient	  of	  soil	  total	  and	  extractable	  P	  that	  comprise	  the	  two	  lowland	  rainforest	  sites.	  Our	  results	  also	  suggest	  that	  the	  enhanced	  P	  acquisition	  strategies	  provide	  N2	  fixers	  with	  a	  competitive	  advantage	  in	  nutrient	  acquisition	  across	  a	  wide	  range	  of	  soil	  nutrient	  conditions	  found	  in	  the	  tropics,	  and	  perhaps	  contributing	  to	  their	  relatively	  high	  abundance	  in	  tropical	  forests.	  	  	  

Symbiotic dinitrogen fixation enhances soil phosphorus acquisition strategies in tropical forests

https://scholarworks.umt.edu/cgi/viewcontent.cgi?article=1041&amp;context=gsrc

Symbiotic dinitrogen fixation enhances soil phosphorus acquisition strategies in tropical forests

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