Decomposition of litterfall from four forest species in Northern Portugal: Decomposition rate, and structural components and nutrient dynamics

Abstract

Decomposition of senescent leaves of Castanea sativa (CS), and needles of Pinus pinaster (PP), Pinus nigra (PN) and Pseudotsuga menziesii (PM) was studied during 3.1 to 3.5 years through weight loss and nutrient concentration evolution, using the litter bag technique, whereas the variation of chemical structural compounds was followed during 391 to 518 days. The highest contents of N were measured in PM and CS (respectively 14.5 and 12.1 g kg^-1), which showed lower C/N ratio (39.0, 46.8) than PN and PP (122.2 and 147.7, respectively). Highest contents of Ca (9.1 g kg^-1) and of alcohol and water soluble compounds (384 against 95 to 160 g kg^-1 to other species) were measured in PM needles, which also showed the lowest contents of holocelulose (253 g kg^-1against about 500 g kg^-1 in the other species). The lignin Klason/N ratio decreased according to PP>PN>PM>CS, (71.2, 58.3, 20.5 and 20.3 respectively), and the holocelulose/lignin ratio ranged from 0.9 (PM) to 1.9-2.1 in the other species. Annual decay rates, according to the negative exponential model, were ordered according to CS>PN>PM>PP (respectively -0.35, -0.27, -0.19 and -0.16), but with higher values during the first year for CS (-0.60) and PM (0.31). Soluble compounds and hemicelulose strongly decreased during the decomposition period, while lignin and cellulose amounts showed a low variability, mainly in PP and PM needles. Nutrient amounts decreased during the decomposition process, but remaining quantities for N (41 to 121 %) and P (33 to 104 %) were higher than those estimated for K, Ca and Mg (respectively 17 to 65%, 30 to 60 % and 18 to 59%). A strong decreasing of C/N ratio was observed especially for PP and PN, where reached 53.2 and 47.1.