Effects of elevated atmospheric CO2 on soil organic carbon dynamics in a mediterranean forest ecosystem

F.R. Gahrooee

Research output: Thesisinternal PhD, WU

Abstract

<p>Elevated atmospheric CO <sub>2</sub> has the potential to change the composition and dynamics of soil organic matter (SOM) and consequently C and N cycling in terrestrial ecosystems. Because of the long-lived nature of SOM, long-lasting experiments are required for studying the effect of elevated CO <sub>2</sub> on soil organic matter dynamics. Therefore, the study of ecosystems that have been exposed to long-term enhanced CO <sub>2</sub> concentrations is highly desirable for better understanding feedback mechanisms between litter production, litter quality, soil organic matter decomposability and the atmospheric CO <sub>2</sub> level.</p><p>This work deals with the effect of enhanced atmospheric CO <sub>2</sub> on chemical composition and C and N mineralization in a leaf litter-soil organic matter continuum around a mineral CO <sub>2</sub> spring in a Mediterranean woodland ecosystem. Leaf litter from <em>Quercus cerris</em> L., <em>Quercus pubescens</em> Willd. and <em>Smilax aspera</em> L., and soil samples from the forest floor (F and HA layers) and 0-10 cm mineral soil were taken at elevated and ambient CO <sub>2</sub> concentrations, and analyzed for chemical composition (C, N, lignin, cellulose, polyphenols). C and N mineralization in plant litter and soil samples were determined using litterbag and laboratory incubation methods.</p><p>Elevated CO <sub>2</sub> affected neither chemical composition nor elemental ratios of leaf litter. The C mineralization rate during litter decomposition was not affected by elevated CO <sub>2</sub> , <sub></sub> in accordance with the absence of a CO <sub>2</sub> effect on litter quality <sub>.</sub> Leaf litter produced at high CO <sub>2</sub> had a higher N mineralization during the initial stage of decomposition period. This difference, however, disappeared at the end of the incubation. <em>Q. pubescens</em> had a higher litter quality than <em>Q. cerris</em> , and subsequently <em>in vitro</em> faster C and N mineralization rates, but litter decomposition under field conditions did not differ significantly between the two species.</p><p>Total C contents in the forest floor were higher at elevated CO <sub>2</sub> , but not so in the 0-10 cm mineral soil. For the three layers, total N contents and C/N ratios were not affected by elevated CO <sub>2</sub> . Total C and N pool sizes in the forest floor were doubled by elevated CO <sub>2</sub> , but such effects were not seen in the 0-10 cm mineral soil. The C mineralization rates of the three soil layers of the areas exposed to elevated CO <sub>2</sub> did not differ from those of the areas under ambient conditions. Although N immobilization in the F and HA layers from the elevated CO <sub>2</sub> plots was lower, that of the 0-10 cm A horizon was not affected by high CO <sub>2</sub> .</p><p>The increase in the organic carbon pool of the forest floor in the absence of an effect of elevated CO <sub>2</sub> on litter quality and decomposability can be explained by increased biomass production under elevated CO <sub>2</sub> . Under elevated CO <sub>2</sub> soil N pools also increased, but the rate of N immobilization in forest floor was lower than that under ambient CO <sub>2</sub> . This study of long-term CO <sub>2</sub> effects casts some doubt on the common view that elevated CO <sub>2</sub> changes litter quality of plants, and thereby slows down decomposability of litter and N release. Because species composition has a strong influence on C and N cycles than elevated CO <sub>2</sub> , effects of increasing atmospheric CO <sub>2</sub> on species composition may be more important to feedbacks between CO <sub>2</sub> concentration and soil organic matter than the CO <sub>2</sub> effect on litter quality of a given species.</p>
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • van Breemen, N., Promotor
  • Buurman, P., Promotor, External person
Award date23 Jun 1998
Place of PublicationS.l.
Publisher
Print ISBNs9789054858799
Publication statusPublished - 1998

Keywords

  • carbon dioxide
  • carbon
  • forest soils
  • climatic change
  • atmosphere
  • forests
  • forest ecology
  • mediterranean region

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