Decomposizione della lignina in lettiere di aghifoglie e latifoglie incubate in una foresta temperata e in una foresta boreale

In questa ricerca è stata seguita la dinamica della lignina durante la decomposizione delle lettiere di Populus tremula L. (foglie verdi e brune), Betula pubescens Ehrh., Pinus contorta L., Pinus pinea L., e Pinus sylvestris L. (foglie verdi e brune) incubate in due differenti condizioni climatiche, in una abetina sul Monte Taburno (Italia) e in una foresta boreale a Jädraås (Svezia). I risultati mostrano che le sette lettiere presentano modelli diversi di degradazione della lignina e che le condizioni dei due siti ne regolano la velocità di decomposizione e la concentrazione nel peso residuo. In P. tremula L., foglie verdi, la degradazione della lignina a Jädraås inizia fin dalle prime fasi di decomposizione della lettiera. Nelle altre lettiere si osserva una fase di accumulo prima della fase di decomposizione; quest’ultima è sempre più veloce a Jädraås. La concentrazione di lignina nella lettiera residua negli stadi avanzati di decomposizione è sempre più elevata nelle lettiere incubate al Monte Taburno. I risultati della ricerca indicano che le condizioni ambientali influenzano la degradazione della lignina e esercitano un importante controllo sull’accumulo di carbonio nel suolo

Elements dynamics, from leaf to stable leaf litter residue and soil, for two functional types of tree planted on volcanic deposits

Purposes: The aim of this paper was to characterize elements dynamics, including resorption before leaf shedding and accumulation/release during decompo sition, of two functionally diferent tree species, the N-fxing, broadleaf, deciduous black locust (Robinia pseudoacacia L.), and the Mediterranean black pine (Pinus nigra Arn.), planted on recent unconsolidated volcanic deposits. Methods: In two paired, 40 years old stands, we investigated the stoichiometry of thirteen elements in green leaves, newly shed leaf litter, stable litter resi due and soil. Results: Black locust leaves were richer in N, P, K, Mg and Mn; black pine needles were richer in Na, Fe, Zn, Cr, and Pb. Resorption efciency was Pb>Zn>Fe~N~Mn~Mg>Cd~K>P in black locust, and Pb~Cu>Zn~Na>Mn>K~Cr in black pine. Com pared to black pine, black locust newly shed litter was richer in K, Na, Mn, Cu, and Ni. During decomposi tion, black locust leaf litter released N, K, Mg, Na, Mn, Zn, Cu and Cd, and accumulated Fe, Ni, Cr and Pb, whilst black pine needles released N, Zn and Cd, and accumulated all the other elements. Compared to black locust black pine had a stable needle litter resi due richer in all elements but N, whilst the mineral soil was poorer in all elements but Pb. Conclusions: The two functionally diferent tree species have distinct element dynamics from leaf to far decomposed litter. Element sequestration in the stable residue of black pine litter, likely prevents their release in the mineral soil that is thus poorer in nutrients and minor elements compared to the soil of black locust

In vitro effects of polyhalogenated hydrocarbons on liver mitochondria respiration and microsomal cytochrome P-450

The present study evidenced the critical levels of six major polyhalogenated hydrocarbons (PHH's), namely chloroform, carbon tetrachloride, 1,1,1-trichloroethane, 1,2-dibromoethane,perchloroethylene, hexachlorobutadiene, over which significant inhibitory effects of the mitochondrial respiratory chain take place in vitro. At these critical levels, even in PB-induced animals only a very little fraction of cytochrome P-450 is saturated by the compounds and therefore the microsomal metabolism plays no effective role either in decreasing the levels of the test chemicals under the threshold of clear direct adverse effects in mitochondria, nor to the formation of toxic metabolites. Our data show also that phenobarbital not only enhances both the direct and metabolism-mediated interaction of most tested PHH with microsomal cytochrome P-450, but also increases the affinity of hexachlorobutadiene, chloroform and carbon tetrachloride for the mitochondrial sites resulting in respiration inhibition