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Harvard Forest Symposium Abstract 2009

  • Title: Root mass, carbon compounds and nitrogen content after six years of soil warming in a temperate forest
  • Primary Author: yumei zhou (Marine Biological Laboratory)
  • Additional Authors: Sarah Butler (Marine Biological Laboratory); Jerry Melillo (Marine Biological Laboratory); Jim Tang (Marine Biological Laboratory)
  • Abstract:

    The potential impacts of elevated soil temperature on soil respiration, root biomass, soil nitrogen availability, and root respiration has been studied with soil warming experiments. However, it is uncertain how tissue quality of roots responds to long-term soil warming. It is unclear how changes in chemical composition in live and dead roots respond to warming because of complicated nature and time consuming to study belowground roots.

    We assessed the effects of soil warming on root mass in organic and mineral soil layers, the chemical composition of tree fine roots (<1 mm) biomass and necromass, and coarse roots (>1 mm) biomass and necromass during the growing season from April to November, 2008 at Harvard Forest. Our results showed that total root mass from 10 cm depth soil (organic plus mineral layer) in warming plots was much less than in control plots, with an average of 378.35 gm-2 compared to 658.52 g m-2 in the control. On average, increased soil temperature decreased total root mass by 43% during the growing season. However, there was no significant difference in root mass in the organic layer between warming and control plots. The decrease in total mass due to soil warming was largely attributed to the decrease in mineral layer. In mineral layer, soil warming caused 70% (56.19 vs. 186.35 g m-2) and 64% decrease (43.80 vs. 121.32 g m-2) in fine roots biomass and coarse roots biomass, respectively. However, the necormass of fine and coarse roots in warming plots was only decreased by 28% (123.22 vs. 171.68 g m-2) and 32% (61.26 vs. 90.72 g m-2), respectively. Significant decline in the ratio of live fine biomass to dead fine necromass indicated soil warming increased mortality.

    Soil warming significantly increased total N concentration and decreased C/N ratio in live fine roots. The total carbon and carbon components (including soluble sugars, starch, hemicellulose, cellulose and lignin) in live fine, live coarse, dead fine and dead coarse roots were not significantly affected by soil warming. The total N concentration in live-fine roots from warming plot was 11% higher than that in control (1.37% vs. 1.24%). The total N concentration was not significantly affected by soil warming if live fine and live coarse roots were combined or live fine and dead fine roots were combined. Therefore, separating live versus dead roots, fine versus coarse roots is especially important in elucidating the responses of root systems to elevated soil temperature. The increase in fine root N content and C/N ratio is consistent with earlier studies that soil warming increased soil nitrogen availability.

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