Almendros Martín Gonzalo

Investigación

Laboratory of Humus Chemistry

The so-called humic substances are widely distributed in soil, water and fossil organic resources and represent the greatest reservoir of organic carbon on the surface of the Earth. They include complex mixtures of altered biosynthetic materials in addition to newly-formed macromolecules. Consequently, the research on humic substances can be carried out using perspectives typical of Pedology, Ecology and Soil Microbiology, Organic Geochemistry or Macromolecular Chemistry. Apart from ecologically assessing the spatial variability of the humus composition, the aim of such a research is to provide a comprehensive model determining their functional relationship in the environment and their bearing on the carbon balance and physico-chemical processes in the soil.

Current objectives

I.   BASIC RESEARCH INTO THE ORIGIN, STRUCTURE AND FUNCTION OF HUMIC SUBSTANCES

In spite of the considerable progress made in Humus Chemistry in the last twenty years, the molecular structure of the soil organic matter is not yet understood very well. While the early concepts depicted humic substances as consisting mainly of modified plant macromolecules, further research has shown their distinctive chemical features, their simultaneous origin by alteration and neoformation processes and their active role in regulating physical and chemical processes in the soil. While about 20 or 30 additional years will probably be required to reach a comprehensive model of humic colloidal systems, we are facing increasing research developments severely limited by the generalised application of classical conceptions inherited from the chemistry of lignin or coal. Apart from the basic interest representing the possibility of gaining a clear insight into the fundamental features of the synthesis, composition and reactions of chaotic humic macromolecular structures, such knowledge is also necessary to explain the soil mechanisms which are reflected in the conservation and productivity of terrestrial ecosystems.

II.   ECOLOGICAL ASSESSMENT OF THE HUMIFICATION PROCESS

The ecological factors with a bearing on the biodegradation of soil litter and the accumulation of humic substances (both from microbial reworking of biomacromolecules and abiotic or microbial synthesis) are still partially quite known. The chemical structure of humic substances is different and more complex than that of biomacromolecules and depends on the differential impact of biotic and environmental factors, hence reflecting the structure and activity of the trophic system. Apart from the physico-chemical activity characteristic of the soil organic matter, in this line of research soil humus is regarded as a compartment integrator of variable ecological processes and as a source of information for the early diagnosis of soil degradation mechanisms.

III.   SOIL ORGANIC MATTER AND ITS ROLE IN THE AGROSYSTEMS. MICROBIAL TRANSFORMATION OF PLANT BIOMASS AND ORGANIC WASTES. ORGANIC GEOCHEMISTRY OF FOSSIL RESOURCES

Soil humus is traditionally considered a continuous source of slow-release nutrients and a reservoir of organic colloids with a chief role in the regulating processes of plant nutrition, toxic ion mobility and the aggregation, structure and water holding capacity of the soil. As a consequence of the progressive decrease in soil organic matter concentrations in industrialized Mediterranean countries, most efforts are currently directed to the production or upgrading of organic amendments and/or the sustainable management of the humus levels through a rational disposal of agroindustrial wastes and sedimentary humic resources (peat, lignites and their transformation products). As an alternative to these classical applications of residual organic matter, recent research has gone into non-traditional recycling technologies of waste biomass generated by agricultural or forestry activities, including microbial transformation focusing on cellulose industries and enzymatic fermentation.

Research lines  

Basic research

• Molecular characterization of humus fractions (humic acids, fulvic acids and humins). Wet chemical methods, analytical degradation, pyrolysis, thermochemolysis... followed by GC/MS, ATD, MALDI...) and non-destructive, spectroscopic methods (IR, NMR...). Organization and reactivity of humic surfaces and soil physico-chemical processes.

• Synthesis and evolution of humic substances. Laboratory-prepared homologues (abiotic or microbially-reworked macromolecules). Microbial synthesis of humic precursors and melanins. Microbial alteration patterns of lignin and resistant aliphatic biomacromolecules in soil. Origin of humic structural variation.

•  Assessment of biomarker compounds and signature molecules in soils and sediments. Their relationships with the biotic and environmental factors (diterpenes, steroids, index phenols, perylenequinonic pigments...).

• Organic geochemistry of humic substances. Molecular palaeontology; palaeoenvironmental reconstruction based on plant microfossils and kerogen degradations. Chemotaxonomic appraisal of organic remains in ancient sediments.

Applied  research

• Spatial variability in the composition of soil organic matter in undisturbed soils under different phytosociological formations or in situations representative of environmental disturbance (the impact of climate, vegetation, soil management, etc., as reflected by the composition of organic matter).

• The role of organic matter in sustainable soil fertility. Composting organic wastes. Assessment of compost maturity. Optimization models of compost substrates and kinetic studies. Plant response in field and greenhouse experiments. Cultural parameters and physical properties of dryland soils under different organic amendments and tillage practices.

• Research on waste biomass and fossil resources applied on degraded soils after its transformation into e.g., pollutant scavengers, biofumigants, soil microbial amendments, soluble humates and biochar.

• Interactions between humic substances and compounds of low molecular weight in soil. Sorption of pesticides and pollutants on the soil organic matrix. Solubilization of hydrophobic compounds. Specific reactions of organo-mineral adducts; interactions of plant nutrients and heavy metals with soil organic matter. Physical and physico-chemical speciation of mineral ions.