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N-P co-limitation in young northern hardwood forest. Tim Fahey

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MELNHE overview 2016
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N-P co-limitation in young northern hardwood forest. Tim Fahey

  1. 1. Nitrogen, phosphorus and fine roots Tim Fahey Cornell University
  2. 2. Functional considerations on fine roots • Lower soil resource supply should require more roots • Evidence: high root:shoot ratio in dry or infertile sites
  3. 3. Simplest hypothesis Increasing soil fertility should cause a reduction in belowground carbon allocation and fine root biomass and production
  4. 4. Complication of nitrogen-phosphorus co-limitation If N and P are co-limiting, then adding only one (N or P) might create greater demand for the other, stimulating increased fine root biomass and production
  5. 5. Response of fine root biomass in three young northern hardwood stands to long-term additions of N and P
  6. 6. Why does adding both N and P cause a big increase in fine root biomass in young northern hardwood stands? Hypothesis: Growth of new fine roots might be nutrient co- limited – i.e. growing new roots requires balanced mineral nutrition
  7. 7. Why does adding both N and P cause a big increase in fine root biomass in young northern hardwood stands? Hypothesis: Growth of new fine roots might be nutrient co- limited – i.e. new roots require balanced mineral nutrition Approach: factorial experiment using ingrowth cores to evaluate whether root production is co-limited by N and P
  8. 8. Microsite NP addition in control plots did not cause increased local root production
  9. 9. Fine root growth increased in response to N plus P addition at the plot level in two young stands
  10. 10. Increased proportional allocation to roots vs. leaves: Ratio of fine root production to fine litter production
  11. 11. Conclusion and Speculation • In young northern hardwood stands, fine root biomass and growth are co-limited by N and P, but this limitation is expressed at the stand level not at the soil microsite level. • This co-limitation is not observed in older stands. • Perhaps in young stands, where fine root systems have not fully exploited soil volume, competition among trees for co-limiting N and P induces greater allocation to root growth
  12. 12. Acknowledgments The shoestring team, especially Shiyi Li and Geoff Wilson. The MELNHE Project is funded by USDA NIFA (2019-67019- 29464) and NSF (DEB-1637685) . For more information, please visit www.esf.edu/melnhe
  13. 13. Evidence of N-P co-limitation in a young northern hardwood forest (C2)
  14. 14. Microsite NP addition in control plots did not cause increased local root production

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