title: Stable-isotope labeling and probing of recent photosynthates into respired CO2, soil microbes and soil mesofauna using a xylem and phloem stem-injection technique on Sitka spruce (Picea sitchensis).
abstract: BACKGROUND
  Here we report on the successful application of a novel stem-injection stable-isotope-labeling and probing technique in mature trees to trace the spatial and temporal distribution of rhizosphere carbon belowground.
  
  
  METHODS
  Three 22-year-old Sitka spruce trees were injected with 6.66 g of (13)C-labeled aspartic acid. Over the succeeding 30 days, soil CO(2) efflux, phospholipid fatty-acid (PLFA) microbial biomarkers and soil invertebrates (mites, collembolans and enchytraeids) were analyzed along a 50 m transect from each tree to determine the temporal and spatial patterns in the translocation of recently fixed photosynthates belowground.
  
  
  RESULTS
  Soil δ(13)CO(2) values peaked 13-23 days after injection, up to 5 m from the base of the injected tree and was, on average, 3.5‰ enriched in (13)C relative to the baseline. Fungal PLFA biomarkers peaked 2-4 days after stem-injection, up to 20 m from the base of the injected tree and were (13)C-enriched by up to 50‰. Significant (13)C enrichment in mites and enchytraeids occurred 4-6 days after injection (by, on average, 1.5‰).
  
  
  CONCLUSIONS
  Stem injection of large trees with (13)C-enriched compounds is a successful tool to trace C-translocation belowground. In particular, the significant (13)C enrichment of CO(2) and enchytraeids near the base of the tree and the significant (13)C enrichment of PLFAs up to 20 m away indicate that mature Sitka spruce (Picea sitchensis) have the capacity to support soil communities over large distances.
authors.affiliation: Belowground Ecosystem Group, Department of Forest Sciences, University of British Columbia, Vancouver, B.C., Canada. carolyn.churchland@gmail.com
authors.forename: Carolyn
authors.initials: C
authors.lastname: Churchland
authors.forename: Andrew
authors.initials: A
authors.lastname: Weatherall
authors.forename: Maria J I
authors.initials: MJ
authors.lastname: Briones
authors.forename: Sue J
authors.initials: SJ
authors.lastname: Grayston
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism*; D002247:Carbon Isotopes / Q000032:analysis / Q000378:metabolism; D017753:Ecosystem; D007553:Isotope Labeling / Q000379:methods*; D052585:Phloem / Q000378:metabolism; D010743:Phospholipids / Q000032:analysis / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology*; D028222:Picea / Q000737:chemistry* / Q000378:metabolism*; D018547:Plant Stems / Q000737:chemistry / Q000378:metabolism; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D052584:Xylem / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D010743:Phospholipids; D012987:Soil; D002245:Carbon Dioxide