Carbon rhizodeposition and root respiration during eight development stages
of Lolium perenne were studied on a loamy Gleyic Cambisol by (CO2)-C-14 pu
lse labelling of shoots in a two compartment chamber under controlled labor
atory conditions. Total (CO2)-C-14 efflux from the soil (root respiration,
microbial respiration of exudates and dead roots) in the first 8 days after
C-14 pulse labelling decreased during plant development from 14 to 6.5% of
the total C-14 input. Root respiration accounted for was between 1.5 and 6
.5% while microbial respiration of easily available rhizodeposits and dead
root remains were between 2 and 8% of the C-14 input. Both respiration proc
esses were found to decline during plant development, but only the decrease
in root respiration was significant. The average contribution of root resp
iration to total (CO2)-C-14 efflux from the soil was approximately 41%. Clo
se correlation was found between cumulative (CO2)-C-14 efflux from the soil
and the time when maximum (CO2)-C-14 efflux occurred (r=0.97). The average
total of CO2 efflux from the soil with Lolium perenne was approximately 21
mu g C-CO2 d(-1) g(-1). It increased slightly during plant development. Th
e contribution of plant roots to total CO2 efflux from the soil, calculated
as the remainder from respiration of bare soil, was about 51%. The total C
-14 content after 8 days in the soil with roots ranged from 8.2 to 27.7% of
assimilated carbon. This corresponds to an underground carbon transfer by
Lolium perenne of 6-10 g C m(-2) at the beginning of the growth period and
50-65 g C m(-2) towards the end of the growth period. The conventional root
washing procedure was found to be inadequate for the determination of tota
l carbon input in the soil because 90% of the young fine roots can be lost.