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