Carbon isotope behaviour in wood and cellulose during artificial aging

Modern wood was subjected to an artificial decay process to investigate its behaviour with respect to the stable carbon isotope composition of wood and the corresponding cellulose. Four different woods were used, namely: oak (Quercus robur), beech (Fagus sylvatica), pine (Pinus sylvestris), sequoia (Sequoiadendron giganteum) and pure spruce cellulose. The process of decay was simulated by heating samples in water at 180°C from minutes to months. During the decay period, the carbon content of wood increased to almost 70% while the cellulose content decreased gradually to zero. The degradation proceeds according to a two stage process: an initial very fast break down is followed by a rather slow degradation. After a strong discrimination against 13C during the initial phase, the 13C/12C ratio increases again, mostly up to its initial value. The carbon isotope trend for cellulose shows a similar pattern though it is less pronounced. Maximum discrimination was 1‰ relative to the untreated wood. δ13C values of cellulose decreased by up to 0.3‰. The 13C depletion is presumably a consequence of the preferential decomposition of cellulose as compared to lignin. Data on fossil trees are compared with the results obtained from this treatment of aging. The 13C decrease is in line with observations from these fossil woods, but the ensuing 13C enrichment is at most weakly to be seen.