Abstract
There have been increasing efforts to understand
the dynamics of organic carbon (OC) associated with measurable
fractions of bulk soil.We compared the decomposition of
native OC (native C) with that of an added substrate (glucose)
on physically separated fractions of a diverse suite of soils.
Five soil orders were selected from four contrasting climate
zones (Mollisol from temperate, Ultisol and Oxisol from
tropics, Andisol from sub-arctic, and Gelisol from arctic region).
Soils from the A horizon were fractionated into particulate
OC (POC) and mineral-associated OC (MOC) by a sizebased
method. Fractions were incubated at 20 °C and 50 %
water-holding capacity in the dark after the addition of unlabeled
D-glucose (0.4 mg C g−1 fraction) and U–14C glucose
(296 Bq g−1 fraction). Respiration of glucose 14C indicated 64
to 84 % of added glucose 14C which was respired from POC
and 62 to 70 % from MOC within 150 days of incubation,
with more than half of the cumulative respiration occurring
within 4 days. Native C respiration varied widely across
fractions: 12 to 46 % of native C was respired from POC
and 3 to 10 % was respired from MOC fractions. This suggested
that native C was more stabilized on the MOC than on
the POC, but respiration from the added glucose was generally
similar for MOC and POC fractions. Our study suggests a
fundamental difference between the behavior of freshly added
C and native C from MOC and POC fractions of soils.
