drivers of soil respiration of root and microbial ... - Unitus DSpace

3.4.2. Allocation patterns
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Kuzyakov and Domanski (2000) reviewed grassland C budgets based on pulse labeling
studies and found that typically for cereals about 30% of total assimilates is transferred into the soil.
Of this quantity about half is found in root biomass, the rest of the belowground allocation being
respired through root respiration, excreted by root exudation or found in the soil microorganisms or
soil organic matter. The relative C translocation of pasture plants into soil was 1.5-2 times higher
than that of cereals. Leake at al. (2006) for sub mountain grasslands with lower productivity and
soil temperatures and slower turnover rates reported a lower proportion of C allocation to root
biomass (12-22% of the shoot pulse 13 C). Two distinct pools of C could be recognized from our
data: a fast-turning over pool that becomes enriched in a pulse following labeling and a slower
turning over pool that remains enriched, but at much lower levels for long after the pulse labeling
have been performed. An equal quantity of recently fixed C was allocated to below and above
ground respiration during the first day, which represent a pool with a high turnover rates. However,
the origin of this C is uncertain with a great probability that it is coming just from the aboveground
plant parts (see above).The C with a lower turnover rates on the contrary was allocated preferably to
root respiration. Consequently, the aboveground growth and maintenance respiration is fuelled
mainly by the assimilates of the current day, while in root respiration the C with higher MRTs
values is involved.
The root/shoot ratio reported by Gadghiev et al. (2002) for various grassland ecosystems of
Central Asia varies from 7 to 17, stating that grasslands invest heavily in the production of
belowground biomass. The root/shoot ration of Amplero (data not shown), estimated in 2007 varied
in the course of the year from 10 to 18, confirming that the most part of the net primary production
is concentrated belowground. Consequently, the majority of the new coming C is expected to be
allocated to belowground also, and would be used then to support the growth of the new roots and
the maintenance of existing one. The beginning of June in Amplero, when the pulse labeling was
performed is characterized by an intensive accumulation of root biomass (data of 2007, are shown
in chapter 2 and 6). Nevertheless, Carbone and Trumbore (2007) showed that the allocation patterns
vary slightly during the growing season, with an increased proportion of recently assimilated C
allocated to aboveground during the late growing season, which is associated with flowering period,
when aboveground biomass reaches its peak. Further experiments with a pulse labeling isotope
technique application are needed for the detailed study of the changes in seasonal C allocation
patterns.