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

an annual mowing the measurement was taken only once, so we are not able to account for a short
term effect of defoliation.
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Summarizing, our result show that factors affecting canopy C status and carbohydrate
supply to roots influence both root and microbial soil respiration components being microbial
respiration affected both in short and long term and root-derived respiration affected clearly on the
long-term bases. The effects were however buffered by increased soil temperature and soil water
content under defoliation.
4.4.2. Microbial activity and defoliation
Our results prove a significant effect of grazing and mowing on microbial biomass
community and its metabolic activity. The ratio of biomass C to soil organic C (qmic) reflects the
contribution of microbial biomass to soil organic carbon (Anderson & Domsch, 1989). It also
indicates the substrate availability to the soil microflora or, in reverse, the fraction of recalcitrant
organic matter into the soil (Brookes, 1995). After a change, the soil microbial biomass responds
more quickly to the change than does the amount of organic matter in the soil, which is relatively
slower. Thus, qmic ratio will increase for a certain time if the input of organic matter to a soil is
increased, and decreases if the input is decreased (Anderson and Domsch, 1989). The elevated
value of qmic observed in this study in MG soils, indicates a major availability of C substrates as
confirmed also by the increase of easily available C source (Cext) which is considered an active
organic fraction playing an important role in the substrate availability for microbes (Dumonent et
al., 2001). Similar results were found by Uhlirova et al. (2005) reporting a significantly higher
amount of potassium sulphate-extractable C in mowed grassland soils. In fact the positive effect of
defoliation on microbial biomass is often explained as due to an increase of root exudation,
resulting in a larger supply of easily available C and energy sources to microbial communities,
enhancing their biomass and nutrient cycling (Bardgett and Leemans, 1995; Bardgett et al. 1998;
Guitian and Bardgett 2000; Kuzyakov et al., 2002; Kuzyakov and Domanski 2000; Rice et al.,
1996; Zhou et al., 2006; Hamilton III et . al., 2008). Compounds that are exuded by roots of
defoliated grasses are comprised of organic acids, sugars and amino acids (Bokhari, 1977; Whipps,
1990; Marschner, 1995) which stimulate rhizospheric processes and also the availability of
nutrients to the defoliated plants. Moreover microbial population in grazed grasslands is sustained
by inputs of labile C from dung deposition and increased root turnover/rhizodeposition beneath
grazed plants (Tracy and Frank, 1998).
Significant differences were observed in the metabolic activity of microorganisms between
MG and UM plots: the respiration rates were significantly decreased by mowing and grazing either
in the short term (MR24h) or in the long term (Cm). Also the initial potential mineralization rate