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Could co-limitation be caused by different nutrients limiting shoots and roots? Melany Fisk

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Could co-limitation be caused by different nutrients limiting shoots and roots? Melany Fisk

  1. 1. Intro to MELNHE
  2. 2. Elser et al. (2007) Ecology Letters Intro to MELNHE • Co-limitation: adding 2 resources together increases productivity more so than adding either alone • Lots of interest; limited mechanistic understanding • MELNHE study conceived to examine co-limitation in more detail
  3. 3. Thirteen forest stands: • 3 sites: Hubbard Brook (HB), Jeffers Brook (JB), Bartlett (BEF) • 3 ages: young (~30 yrs), mid (~45 yrs), and mature (>100 yrs) • Color-coded General question: • Is forest productivity co-limited by N and P? So far (among many results): • Tree growth limited primarily by P (2011-2015; Goswami et al. 2018) • No obvious co-limitation detected N: 30 kg/ha/yr P: 10 kg/ha/yr N+P Control One forest stand: four 50 x 50 m treatment plots NxP fertilization initiated in 2011
  4. 4. Testing limitation control nutrient addition Limitation is inferred if added nutrient increases growth What about belowground?
  5. 5. Testing limitation of root growth control nutrient addition Limitation is inferred if added nutrient increases growth What about belowground? (1) Direct nutrient limitation of root growth
  6. 6. Testing limitation of root growth control nutrient addition Limitation is inferred if added nutrient increases growth What about belowground? (1) Direct nutrient limitation of root growth (2) Allocation response to aboveground limitation - alleviating aboveground limitation reduces growth
  7. 7. Testing limitation of root growth control nutrient-rich patch (hotspot) Limitation is inferred if added nutrient increases growth What about belowground? (1) Direct nutrient limitation of root growth (2) Allocation response to aboveground limitation - alleviating aboveground limitation reduces growth - foraging response to nutrient heterogeneity
  8. 8. Testing limitation of root growth Question: Is root growth controlled by (1) belowground nutrient limitation, or (2) allocation in response to aboveground limitation? (Shan et al. in review) Used root ingrowth cores in 3 mature forest stands, 2014.
  9. 9. Root growth: 3 mature stands Fine root growth was greater in response to N addition (direct nutrient limitation) No response to P addition (Shan et al. in review) *
  10. 10. Root growth: 3 mature stands Fine roots foraged for P (allocation response to aboveground limitation) Phosphorus hotspot Control soil (Shan et al. in review) Fine root ingrowth length (cm/core)
  11. 11. Conclusions Fine roots forage for P but their growth is limited by N Whole-tree growth may be co-limited by N and P Does N limit P acquisition? Acknowledgements: Funding from LTER, NSF, USDA; support from HBEF, BEF; participation of many students P limitation N limitation

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