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Harvard Forest Symposium Abstract 2016

  • Title: Progressive phosphorus limitation after prolonged soil warming at Barre Woods, Harvard Forest
  • Primary Author: Jerry Melillo (Marine Biological Laboratory)
  • Additional Authors: Michael Bernard (Marine Biological Laboratory); Frank Bowles (Research Designs); Alana Thurston (Haverford College); William Werner (Marine Biological Laboratory)
  • Abstract:

    Recent meta-analyses have reported simultaneous nitrogen (N) and phosphorus (P) limitation in terrestrial systems, including temperate forests. Perturbations to the N cycle (e.g. increased inputs or an enhanced rate of cycling) could induce periods of P limitation, which would run counter to predictions of productivity increasing with N availability. After 13 years of soil warming at the Barre Woods Soil Warming Experiment, we report that prolonged soil warming might lead to progressive phosphorus limitation and suggest that our findings fit a pattern observed in other experiments in which the N cycle is altered. Over the first 12 years of the study, we measured an annual increase in net N mineralization of approximately 72% (relative to a control plot), which was correlated with increased growth of woody tissue of approximately 53% until years 11 and 12, when no increase was detected. Over the entire study period, N:P ratios of litter inputs from canopy dominants have gradually increased on the heated plot, indicating that P has become a limiting resource. Observed reductions in fine root biomass and shifts in the ectomycorrhizae community within the heated plot suggest that these changes to the root/mycorrhizal network may limit the ability of trees to acquire P in proportion to the newly available N. Similar changes in litter chemistry and ectomycorrhizal communities in N amendment studies may indicate a shared pathway to progressive P limitation following exogenous inputs. A resumed increase in wood increment during year 13 may suggest that periods of P limitation may be temporary as uptake resources are redistributed; however, periods of co-limitation may be interrupted by periods of either P or N limitation as soil organic matter decay and N mineralization rates decelerate with shrinking labile carbon pools with prolonged soil warming.

  • Research Category: Large Experiments and Permanent Plot Studies
    Soil Carbon and Nitrogen Dynamics