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