C - Lublin

CARBON CYCLING IN RHIZOSPHERE AND BULK SOIL AFTER
13 C PULSE-CHASE LABELING
OBJECTIVES
Yevdokimov I., Ruser R., Buegger F., Marx M., Goerke K.,
Schneider D., Munch J.C.
Complex interactions in plant roots – microorganisms – soil system depend on
partitioning of assimilated C between plant roots, microbes, and CO 2 respired by
microorganisms and roots. Besides, they are strongly determined by the turnover
rates of C in roots and different soil carbon pools, especially of the most labile
pools of microbial biomass and dissolved organic carbon (DOC). In this connection
the objectives of our investigation were to determine:
i)
13 C partitioning between roots, soil carbon pools and CO 2 emission after
pulse chase labeling;
ii) Kinetic characteristics of microbial populations in rhizosphere and bulk
soil during all the period of plant growth.
EXPERIMENTAL DESIGN AND METHODOLOGICAL APPROACHES
Dynamics of total and labeled carbon in roots and the main C pools of soil and
rhizosphere were studied periodically during the first 80 – 90 h after the 13 C pulsechase
labeling (duration 5 h) in greenhouse experiment with oats (Avena sativa L.,
day 47after emergence, shooting growth stage). Soil (Cambisol, 1.4±0.2% C,
0.14±0.01% N, pH KCl 5.9±0.2, with sand, silt and clay fractions of 42%, 30% and
28% respectively) was sampled near Munich, Germany. Before starting the
greenhouse experiment, soil was sieved (5 mm) and air-dried. To isolate
rhizosphere from bulk soil, plants seedlings were put into special nylon bags filled
with soil and placed in the center of pots.
Kinetic characteristics of microbial populations in bulk soil and rhizosphere
were determined by kinetic method (Panikov and Sizova, 1996). The method
involves simulation of both lag and exponential phases of microbial growth after
addition of the excess quantities of readily decomposable C substrate using the
following equations (Blagodatsky et al., 2000):
v(t) = v u + v c × exp(µ max × t)
x 0 = (v C × 0.9 × Y x/p )/ (r 0 × µ max )
r 0 = (v C × 0.1)/(v U + v C × 0.1)
x’ = x 0 × r 0 ,
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