Chemical and spectroscopic properties of leaf litter and decomposed organic matter in the Carmel Range, Israel

The characteristics of litter and soil organic matter (SOM) from the Carmel Range woodland, Israel, were investigated. Pinus Halepensis ('pine') is the dominant tree species with Quercus calliprinos ('oak') as the dominant understory species. In situ leachates were collected and aqueous extracts and humic acids (HA) were obtained from litter and sub-surface horizons under both tree species. Salts of atmospheric origin, mainly CaSO₄, accumulate on pine needles, facilitating enhanced breakdown of the needles as compared to oak leaves, apparently causing less litter to accumulate under pine trees compared to oaks. Pine litter exhibited a greater degree of oxidation. ¹³C-nuclear magnetic resonance (NMR) results, supported by Fourier-transform infrared spectroscopy (FTIR) and chemical analyses, indicated that pine litter HA has more aliphatic-C (60.5% of total C) and less aromatic-C (28.1%) compared to oak HA (52.3 and 31.1%, respectively). FTIR also suggested that under both species polysaccharides decreased and oxidation increased with increasing soil depth. Concentrations of N and organic C were higher under oak. C:N ratios were higher for pine litter compared to oak litter (51.3 and 44.0, respectively), although ratios for A₁ horizons were equal (20.6). Concentrations of S, Na, Mg, K and Ca in the leachates were significantly higher under pine. The pH values (7.1-7.9) were buffered by high CaCO₃ content in the soil with the exception of the thick litter layer under oak (pH 5.8). Evidence of metal transport as a result of OM leaching was not detected. Correlations between Na, Mg, Ca concentrations and S concentration in leachates (r²=0.88; 0.89; and 0.84, respectively) suggest these elements originate from salt deposited on the litter. The high content of pine needles (51%) in the oak litter of the mixed woodland mitigates the extent of the differences below the two species.