Soil functioning in the ecotone between scots pine and pyrenean oak forests: effects of tree species on soil carbon and nitrogen cycling
- Autores: María José Fernández Alonso
- Directores de la Tesis: Agustín Rubio Sánchez (dir. tes.), Eugenio Díaz-Pinés López de los Mozos (codir. tes.)
- Lectura: En la Universidad Politécnica de Madrid ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Marta Benito Capa (presid.), Jesús Rodríguez Calcerrada (secret.), Jorge Curiel Yuste (voc.), Tommaso Chiti (voc.), Ana Rey Simó (voc.)
- Programa de doctorado: Programa de Doctorado en Investigación Forestal Avanzada por la Universidad Politécnica de Madrid
- Materias:
- Enlaces
- Tesis en acceso abierto en: Archivo Digital UPM
- Resumen
Background: Current composition and structure of the Scots pine-Pyrenean oak ecotone forest in the Guadarrama Range are the result of an intense and lasting human management. Although Scots pine forests have shown millennial stability in theseMountains, the global change may involve vegetation dynamics mainly fostering shifts of the dominant tree species in their lowest altitudinal range.
Aim: To assess future consequences driven by shifts in forest composition in the amount of carbon sequestered in the soil, we are interested in understanding the soil functioning in the ecotone to disclosure the effects of tree species, namely Scots pine or Pyrenean oak, and atmospheric nitrogen deposition that influence the belowground carbon and nitrogen cycling.
Methods: Three experimental plots were stablished in a pure Pyrenean oak forest, mixed oak-pine forest and pure Scots pine forest along a north-to-south transect at 1325 m a.s.l in the Valsaín Mountains (Guadarrama Range, Central Spain). Experiments at stand scale were combined with microcosm incubations and laboratory analysis to: (Chapter 4) disentangle tree species effects on the microclimate dependence of autotrophic and heterotrophic respiration components, (Chapter 5) identify how increases in atmospheric nitrogen decomposition may affect the causal relationships between edaphic properties and soil respiration, (Chapter 6) analyse how tree species influence litter decomposition, and (Chapter 7) understand how belowground carbon and nitrogen cycles could shift along the transitional stages of the forest vegetation succession from pine to oak.
Results: Our results revealed tree species-specific responses of soil respiration components to soil microclimate conditions being particularly Background: Current composition and structure of the Scots pine-Pyrenean oak ecotone forest in the Guadarrama Range are the result of an intense and lasting human management. Although Scots pine forests have shown millennial stability in these Mountains, the global change may involve vegetation dynamics mainly fostering shifts of the dominant tree species in their lowest altitudinal range.
Aim: To assess future consequences driven by shifts in forest composition in the amount of carbon sequestered in the soil, we are interested in understanding the soil functioning in the ecotone to disclosure the effects of tree species, namely Scots pine or Pyrenean oak, and atmospheric nitrogen deposition that influence the belowground carbon and nitrogen cycling.
Methods: Three experimental plots were stablished in a pure Pyrenean oak forest, mixed oak-pine forest and pure Scots pine forest along a north-to-south transect at 1325 m a.s.l in the Valsaín Mountains (Guadarrama Range, Central Spain). Experiments at stand scale were combined with microcosm incubations and laboratory analysis to: (Chapter 4) disentangle tree species effects on the microclimate dependence of autotrophic and heterotrophic respiration components, (Chapter 5) identify how increases in atmospheric nitrogen decomposition may affect the causal relationships between edaphic properties and soil respiration, (Chapter 6) analyse how tree species influence litter decomposition, and (Chapter 7) understand how belowground carbon and nitrogen cycles could shift along the transitional stages of the forest vegetation succession from pine to oak.
Results: Our results revealed tree species-specific responses of soil respiration components to soil microclimate conditions being particularly important the higher sensitivity of the pine autotrophic respiration to summer drought and the oak autotrophic respiration to low winter temperatures. Moreover, the strong and inverse water and thermal seasonality of the Mediterranean climate strongly constrained the heterotrophic microbial activity in the ecotone. Carbon turnover of soil and foliar litter from the pine forest were faster than values found from the oak forest, which may have contributed to the higher carbon stocks in both topsoil and forest floor beneath the Scots pine.
Overall, three-years of nitrogen additions simulating the increased in atmospheric deposition caused soil acidification, leaching of potassium base cation, changes in extractable organic carbon and substantial decrease in soil microbial biomass, although soil respiration was rather resilient. It seems that soil stoichiometry, seasonal climatic constraints for biological activity and doses of nitrogen fertilizer were factors that modulated the response of soil respiration to nitrogen additions and caused pine soil respiration to be more sensible to soil nitrogen enrichment.
Tree species directly affected the decomposition constants and N dynamics of decaying litter through the different litter chemistry between oak leaves and pine needles but also indirectly by affecting the colonization of microbial functional groups (K-strategists vs. r-strategists). Consequently, depending on whether the soil organic matter origin derives from pine or from oak the effects on the ecology and physiology of soil microbial communities will be different, causing the carbon and nitrogen cycling to decouple throughout the forest secondary succession from pine to oak. In the first stage of forest succession, an acceleration of the soil carbon cycling was found in the mixed forest with regard to pure pine forest together with a shift toward lower fungal to bacterial ratios. However, soil processes leading to an acceleration of the nitrogen cycling occurred later in the succession when there were only soil organic matter from oak. Hence, when secondary succession was completely accomplished, we found an alleviation of the nitrogen limitation for microbial growth, greater abundance of gram-negative bacteria, an accelerated carbon turnover and suppressed methane consumption.
Conclusions: In view of the different functionality of the plant-soil-microorganism system beneath pine and oak stands, the forest secondary succession from Scots pine to Pyrenean oak would have remarkable implications in the belowground carbon and nitrogen cycles that should be included as practical considerations in forest management.
