Humus Carbon Sequestration. How humus forms contribute in carbon sequestration in the Mediterranean forest ecosystem at Castel Porziano Reserve (CPR), central Italy
ABSTRACT
Objective: This work reports the results of an investigation on humus forms in a Mediterranean area. The study allows to test the effectiveness of the recent European humus forms classification (Zanella et al. 2011a), based on morpho-genetic characters of diagnostic organic and organo-mineral horizons. Furthemore it reveals how the humus forms data, at the level of diagnostic horizons, are related to vegetation/soil types and Carbon storage capacity of the soil.
Methods: The humus forms were investigated in different substrate, soil types, and vegetation units of a Mediterranean forest ecosystem in Central Italy (Castelporziano Reserve). Classical parameters were measured and statistically analysed: thickness, Organic Carbon (OC) and total Nitrogen (Ntot) contents in organic and organo-mineral horizons, whilst pH and texture in the organo-mineral horizon.
Results: The three main humus forms (Mull, Moder and Amphi) covering the soil of the Reserve appeared well separated on the PCA diagram. Thickness, OC and Ntot showed a high correlation with the axes of the PCA. Kruskall-Wallis results disclosed differences among Mull, Moder and Amphi: 1) the thickness of A horizon was larger in Amphi; 2) OC in A horizon was lesser in Moder form; 3) Mull had less OC in organic horizons than Moder and Amphi; 4) Mull and Amphi raised twice the OC of Moder in organic and organo-mineral summed horizons.
Two main ecological gradients, from neutral/aerated Mull to acid/asphyxiated-water saturated Moder on one side and from fresh Mull to dry Amphi on the other, explain the distribution of humus forms in the Reserve. The first gradient concerns circular belts around periodically filled small basins and is peculiar to the more or less impermeable plain of Castelporziano; on the contrary, the second progressive transition is very common in Mediterranean forests.
Conclusion: A clear trend in Carbon storage capacity is visible in humus forms of Mediterranean forest where Mull and Amphi, with a good mixing of organics and minerals particles in the A horizon, show at least twice more OC than Moder.
Practice: The European humus forms classification is a very practical tool and allows to survey the humus forms and better understand the functioning of forest ecosystems even in Mediterranean area. The carbon cycle of Mediterranean forests seems to gravitate around a still scarcely investigated and very rich in OC Amphi humus form.
Implications: The European humus forms classification seems to be appropriate to a large scale survey of humus forms in forest ecosystems. It allows to better understand the organic matter cycle at the level of soil bio-structures. The crucial role played by the here investigated Amphi forms could increase with the prospect of climate change