During microbial breakdown of leaf litter a

fraction of the C lost by the litter is not released to the

atmosphere as CO2 but remains in the soil as microbial

byproducts. The amount of this fraction and the factors

influencing its size are not yet clearly known. We performed

a laboratory experiment to quantify the flow of C

from decaying litter into the soil, by means of stable C

isotopes, and tested its dependence on litter chemical

properties. Three sets of 13C-depleted leaf litter (Liquidambar

styraciflua L., Cercis canadensis L. and Pinus taeda

L.) were incubated in the laboratory in jars containing 13Cenriched

soil (i.e. formed C4 vegetation). Four jars containing

soil only were used as a control. Litter chemical

properties were measured using thermogravimetry (Tg) and

pyrolysis-gas chromatography/mass spectrometry-combustion

interface-isotope ratio mass spectrometry (Py-GC/

MS-C-IRMS). The respiration rates and the d13C of the

respired CO2 were measured at regular intervals. After

8 months of incubation, soils incubated with both L. styraciflua

and C. canadensis showed a significant change in

d13C (d13Cfinal = 20.2 ± 0.4% and 19.5 ± 0.5%,

respectively) with respect to the initial value (d13Cinitial =

17.7 ± 0.3%); the same did not hold for soil incubated

with P. taeda (d13Cfinal:18.1 ± 0.5%). The percentages

of litter-derived C in soil over the total C loss were not

statistically different from one litter species to another.

This suggests that there is no dependence of the percentage

of C input into the soil (over the total C loss) on litter

quality and that the fractional loss of leaf litter C is

dependent only on the microbial assimilation efficiency.

The percentage of litter-derived C in soil was estimated

to be 13 ± 3% of total C loss