Distribution of soil organic matter in forest soils developed on volcanic parent material in Campania (Italy)

Marta Álvarez Romero
E-mail: m.alvarez.romero@hotmail.com
Seconda Università di Napoli, Dipartimento di Scienze e Tecnologie Ambientali, Biologiche e Farmaceutiche, Via A. Vivaldi, 43 – 81100 Caserta, Italy

PhD Thesis cover.
PhD Thesis cover.

Soil is the largest carbon reservoir of terrestrial ecosystems, this reservoir is not inert, but it is constantly in a dynamic phase of accumulation an depletion.
After the addition, in the soil, of organic residues of different origin and nature, two processes can occur in charge of soil organic matter (SOM) during the pedogenesis: mineralization and humification. The accumulation of SOM in soil is controlled by the balance between carbon inputs and losses through mineralization and/or leaching.
In particular the humification process leads to the formation of organic compounds (in some cases even complex organo-mineral) chemically stable able to distribute itself in the soil second rules of site-specific pedogenesis. The transport process along the profile can take very different forms which may extend in the formation of Bh horizons of accumulation in depth also strongly cemented (so-called ortstein).
The transport process along the profile occurs for the occurrence of certain conditions:

  1. Deposition of high amounts of organic residues on the top of the profile;
  2. High porosity of the soil for the presence of coarse solid fractions (coarse sands or skeleton) that determinate a strong infiltrating capacity of the circulating waters;
  3. Extreme temperatures can slow or stop the process of mineralization and/or humification in one intermediate step of the degradation process releasing organic metabolites with high or medium solubility;
  4. High loads of percolating water related to intense rainfall.

The transport mechanism as described overlaps the input of organic matter in the profile by the biotic community resident in the soil (root exudates, bacterial enzymes, droppings, remains).
The nature of the forest cover influence the quantity and quality of the organic materials deposited with marked differences between coniferous and deciduous especially in relation to resistance to degradation and production of intermediate metabolites.
According to these premises during my Ph.D I studied the phenomenon of formation of depth horizons (Bh) of the accumulation of SOM in soils developed on volcanic parent material under different forest coverage and different degree of human interference (null, reforestation intervention, cultivation).
Have been researched soils in the environments of the Campania Region (Italy) that meets the requirements of the place and pedological formation suitable for the formation and accumulation of SOM in depth, having been identified, described and sampled four soil profiles in two different places, Bagnoli Irpino (Avellino, Italy) and Roccamonfina (Caserta, Italy). In particular:

  • Bagnoli Irpino (Avellino, Italy); Site: Lago Laceno; Pedogenic substrate: dissolved pyroclastic materials (deposited volcanic ash and pumice) coating surveys of carbonate nature; Forest cover: beech and pine;
  • Roccamonfina (Caserta, Italy); Site: Monte Santa Croce; Pedogenic substrate: dissolved pyroclastic materials (deposited volcanic ash and pumice) coating volcanic surveys; Forest cover: pine and chestnut.

The research methodology has been developed in several phases:

  1. Detection, description and sampling of soil profiles in the field, according to the main international taxonomic classification systems, Soil Taxonomy (1999, 2006) and the World Reference Base (2006);
  2. Analysis of the phenomenon of transport and accumulation of SOM in terms of quantity determining the Total Organic Carbon (TOC) with Springer Klee method, and chromatographic techniques for the SOM fractioning (proposed by Sequi and De Nobili, 2000). Were determined: Total Extractable Carbon (TEC); Humic Acid (HA); Fulvic Acid (FA); Not Humic Carbon (NHC).
  3. Also were calculated parameters of humification, provided that the use of these parameters of humification represents a peculiar line of research proposal by Italians soil researchers:
    • Humification Degree: DH = [(HA+FA)/TEC] x 100;
    • Humification Rate: HR = [(HA+FA)/TOC] x 100;
    • Total Level of Humification: HU= {100 x [(HA+HF)+(TOC-TEC)]/TOC};
    • Humification Index: HI = NHC/(HA+FA).
  4. It was also of interest in this thesis perform procedures to extract the lipid fractions of the soil (Soil Lipidic Matter) soluble in organic solvents and determinate the amount of organic carbon that they represent.

With this work it was intended to achieve three goals:

  1. Description of the distribution of the SOM fractions in soil profiles developed in volcanic rocks in different forest areas of the Campania Region (Italy) in relation to their possible pedogenic meaning.
  2. Use of the technique of the SOM fractioning as an new indicator for characterization of horizons of accumulation of SOM of surface (Ah) and of depth (Bh).
  3. Application of the parameters of humification proposed by the MIPAAF to the detection of a unique key for the characterization of the pedogenetic process of transport and accumulation of SOM in depth.

The findings of this work were:

  1. The pedological research carried out have led to the conclusion that the soils of the Campania Region developed on volcanic deposits in site of medium-high allowances (800-1000 m above sea level) in the absence or with low human disturbance, can accumulate in depth important shares of SOM with high stability through mechanisms of accumulation and transport entirely similar to those observed commonly in Italy in the alpine environment and in the european continental environments.
  2. Against a very similar pedogenetic context (parent material, topography, climate) with the parameters of humification proposed, is possible to assess the difference due to the accumulation in depth of SOM in the individual profiles.
  3. Considering the high variability of the humification parameters values of Bh horizons between the different profiles, it is not considered possible to identify a trait that unites them.
  4. It is necessary to extend the observations for groups of vegetation (e.g. deciduous and/or coniferous) or for human impact, on a greater number of soil profiles well characterized from the pedogenetic point of view for the phenomenon of the transport and accumulation of the SOM.
  5. In relation to the major difference observed between horizons of surface and depth, of new and specific interest is the study of lipid fractions, mostly investigated in the surface part of the soil, and generally considered in the qualitative appearance rather than quantitative.



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