Almacenamiento de carbono y profundidad del suelo

secuestro-de-carbono-y-perfil-del-suelo

Almacenamiento de carbono a lo largo del perfil del suelo. Fuente: USGS

Como ya os mostramos en varios post relacionados con el tema que tratamos hoy, y que son almacenados en nuestra categoría: “Biomasa y Necromasa en los Suelos”, la ciencia del cambio climático (por llamarla de alguna manera) comete un gravísimo error al restringir la estimación del secuestro de carbono tan solo a los primeros centímetros del perfil edáfico. Se me antoja increíble que, saltándose todos los cánones científicos e ir acumulándose evidencias en contra, se persista en la idea de que basta muestrear cómodamente con una azada la parte superficial del suelo, cuando en realidad así alcanzamos conclusiones rotundamente erróneas, como mostramos por enésima vez en la nota y resumen de un nuevo artículo de investigación que avala las tesis que mantenemos en esta bitácora. Reiteremos que las conclusiones del artículo son claras en este sentido, tras once años de experimentación. Si se extraen a partir de los 30 cm superficiales nos llevamos una idea equívoca, al compararla con los muestreos hasta casi un metro de profundidad (y en muchas ocasiones deberíamos alcanzar tanta como para sondear todo el solum, ya hablemos de dos, tres o más metros). No entraremos aquí a discutir de nuevo el dudoso efecto a escala global en lo referente a que al aumentar el anhídrido carbónico en la atmósfera aumentará su concentración en el edafoclima y así se producirán cambios que (…). Del mismo modo soslayamos la coletilla repetida ad nauseam (“que falta de imaginación”: ¡siempre lo mismo!) de que estos resultados deben ser contemplados en las futuras predicciones que ofrezca los nuevos modelos de cambio climático, ya que si se hace caso a tanto cantamañanas, los modelizadores deberían modificar sus juguetes varias miles de veces al año. También resulta descorazonador que los autores defiendan que la fertilización de CO2  expandirá el ciclo biogeoquímico de los suelos en profundidad, ya que lo que pudiera ocurrir en un sitio sabemos que necesariamente no es extrapolable a otros. La Unión Europea en un alarde de generosidad considera que debe muestrearse tan solo hasta los 40 cm (antes bastaban 20). Por mucho que se empecinen políticos borricos y algunos colegas holgazanes si deseamos saber el carbono orgánico  (por no hablar del inorgánico) que almacenan los suelos, debe considerarse la totalidad del solum. Todo lo  demás es tirar el dinero y publicar conclusiones que ya solo cabe calificar de deliberadamente falsas: o somos analfabetos, o tenemos deficiencias de comprensión lectora, o no leemos, o hace falta que nos den mil y una bofetadas para que aceptemos las evidencias científicas. Como decimos en España, “hasta el rabo todo es toro” ¿Lo entendéis?.

Juan José Ibáñez    

Elevated Carbon Dioxide Concentrations Can Increase Carbon Storage in the Soil

ScienceDaily (Mar. 5, 2012) — Elevated carbon dioxide concentrations can increase carbon storage in the soil, according to results from a 12-year carbon dioxide-enrichment experiment at Oak Ridge National Laboratory.

The increased storage of carbon in soil could help to slow down rising atmospheric carbon dioxide concentrations.

 The Department of Energy-sponsored free-air carbon dioxide-enrichment, or FACE, experiment officially ended in 2009. The conclusion and final harvest of the ORNL FACE experiment provided researchers with the unique opportunity to cut down entire trees and to dig in the soil to quantify the effects of elevated carbon dioxide concentrations on plant and soil carbon.

 In a paper published in Global Change Biology, Colleen Iversen, ORNL ecosystem ecologist, and her colleagues quantified the effects of elevated carbon dioxide concentrations on soil carbon by excavating soil from large pits that were nearly three feet deep. Researchers saw an increase in soil carbon storage under elevated carbon dioxide concentrations, a finding that was different from the other FACE experiments in forests.

 Researchers found the increase in carbon storage even in deeper soil.  ”Under elevated carbon dioxide, the trees were making more, deeper roots, which contributed to the accumulation of soil carbon,” Iversen said.

 Iversen pointed out that processes such as microbial decomposition and root dynamics change with soil depth, and information on processes occurring in deeper soil will help to inform large-scale models that are projecting future climatic conditions.

 Co-authors on the paper, Soil carbon and nitrogen cycling and storage throughout the soil profile in a sweetgum plantation after 11 years of carbon dioxide-enrichment” are ORNL’s Charles Garten and Richard Norby, FACE project leader; and Chapman University’s Jason Keller.

 The research was sponsored by the DOE Office of Science. ORNL is managed by UT-Battelle for the Department of Energy’s Office of Science. DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.

Story Source: The above story is reprinted from materials provided by Oak Ridge National Laboratory, via Newswise.

Keywords: 13C; carbon mineralization; elevated [CO2]; fine roots; Liquidambar styraciflua; mineral-associated organic matter; net nitrogen mineralization; particulate organic matter; soil carbon; soil depth

Abstract

Increased partitioning of carbon (C) to fine roots under elevated [CO2], especially deep in the soil profile, could alter soil C and nitrogen (N) cycling in forests. After more than 11 years of free-air CO2 enrichment in a Liquidambar styraciflua L. (sweetgum) plantation in Oak Ridge, TN, USA, greater inputs of fine roots resulted in the incorporation of new C (i.e., C with a depleted δ13C) into root-derived particulate organic matter (POM) pools to 90-cm depth. Even though production in the sweetgum stand was limited by soil N availability, soil C and N contents were greater throughout the soil profile under elevated [CO2] at the conclusion of the experiment. Greater C inputs from fine-root detritus under elevated [CO2] did not result in increased net N immobilization or C mineralization rates in long-term laboratory incubations, possibly because microbial biomass was lower in the CO2-enriched plots. Furthermore, the δ13CO2 of the C mineralized from the incubated soil closely tracked the δ13C of the labile POM pool in the elevated [CO2] treatment, especially in shallower soil, and did not indicate significant priming of the decomposition of pre-experiment soil organic matter (SOM). Although potential C mineralization rates were positively and linearly related to total SOM C content in the top 30 cm of soil, this relationship did not hold in deeper soil. Taken together with an increased mean residence time of C in deeper soil pools, these findings indicate that C inputs from relatively deep roots under elevated [CO2] may increase the potential for long-term soil C storage. However, C in deeper soil is likely to take many years to accrue to a significant fraction of total soil C given relatively smaller root inputs at depth. Expanded representation of biogeochemical cycling throughout the soil profile may improve model projections of future forest responses to rising atmospheric [CO2].

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