C - Lublin

The dynamics of 13 C in rhizosphere microbial C and DOC were opposite to
that for CO 2 – 13 C fluxes from soil with plants immediately after the pulse- labeling
(Fig.1): minimums in microbial C and DOC coincided with the maximums in CO 2
emissions, and vice versa. 13 C values in the carbon pools oscillated periodically
depending on day – night changes (i.e. on activity of the processes of photoassimilation
and translocation of photo-assimilates to roots and rhizosphere):
maximums in 13 C in DOC and microbial biomass in rhizosphere were revealed
after nighttime. After 66 h this tendency was smoothed over because of decrease in
total 13 C content in soil (Fig.1, 2).
100
80
60
%
40
20
0
2 17 26 40 47 66 90
hours after labeling
1 2 3
Fig .2. Partitioning of 13 C in rhizosphere between DOC (1), microbial biomass (2),
roots (3) and CO 2 respired (4)
Considerable part of 13 C translocated (about ¼ of total 13 C below-ground
translocation) was found in biomass of rhizosphere microorganisms as soon as by
2h after pulse labeling (Fig. 2). Sum of 13 C in microbial biomass and DOC was
approximately equal to the total 13 C pool in rhizosphere soil till the sampling at 90
h when sufficient incorporation of 13 C to soil organic matter was revealed. It might
be explained in two ways: i) only low-molecular substances readily decomposable
by rhizosphere microorganisms were exuded in first 3 – 4 days after pulse labeling;
ii) no sufficient microbial synthesis of high-molecular substances on the base of
freshly exuded components took place on this period. Thus, close inter-relations
between 13 C dynamics in C pools in rhizosphere and plant activity were revealed in
a short-term (hrs or few days) scale for rhizosphere of oats. Freshly – exuded
165
4