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Harvard Forest Symposium Abstract 2016

• Title: Long Term Soil Warming Alters Carbon Allocation in Trees
• Primary Author: William Werner (Marine Biological Laboratory)
• Additional Authors: Michael Bernard (Marine Biological Laboratory); Jerry Melillo (Marine Biological Laboratory)
• Abstract:

  Over the first decade of soil warming at the Barre Woods Soil Warming experiment we consistently measured increases in aboveground woody increment and nitrogen mineralization. In a nitrogen-limited ecosystem, this may allow trees to meet their nitrogen requirements with a reduced belowground carbon investment, freeing carbon to be reallocated to aboveground growth. To investigate this hypothesis, we used a variant of Riach and Nadelhoffer’s root carbon allocation analysis, modified to account for increased heterotrophic soil respiration due to soil warming. We calculated a reduction in root carbon allocation in the heated plot roughly corresponding to our measured increases in aboveground woody increment. Our calculations also imply that reduced root respiration in the heated plot accounts for a much greater share of the reduction in root carbon allocation than reduced fine root production. Over the first 10 years of soil warming, we have measured a cumulative increase in aboveground woody increment of 9.74 Mg C ha-1, and calculated a cumulative reduction of root carbon allocation of 8.03 Mg C ha-1. We attribute about 89% of the reduced root carbon allocation to reduced root respiration. These results imply a small increase in net primary production that is consistent with our measurements of increased litterfall and increased green leaf nitrogen content for dominant canopy species in response to soil warming, but enough to account for the observed increases in aboveground woody increment. We conclude that most of the measured increase in aboveground woody increment reflects reallocation of carbon from belowground to aboveground, and especially from root respiration to aboveground woody increment.

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