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

(C0k) was negatively affected by the treatment indicating a different quality or different sources of
decomposing substrates with respect to UM soils (Riffaldi et al., 1996).
All these evidences support the hypothesis that microorganisms decreased their
mineralization activity in MG soils as other easily available energy sources were present.
It is widely documented that the soil metabolic quotient (qCO2) is elevated when the soil
microbial biomass is operating inefficiently and is diverting a high proportion of C to maintenance
requirements than biosynthesis (Anderson and Domsch, 1985).
In our results qCO2 and soil enzymatic activity were significantly lower in MG plots and
suggested that the increase of easily available C in the rhizosphere of defoliated plants, resulting
from a short-term flux of photoassimilate C below-ground, decreased the maintenance energy
requirements and shifted the energy from maintenance to biosynthesis processes as the increase of
qmic also demonstrated (Bardgett et al., 1998; Holland et al., 1996; Dilly, 2005). According to
Schjonning et al. (2002) the decrease in qCO2 and specific enzyme activity indicates: a) a more
efficient microbial community and b) a better use of the available organic substrates. Higher C use
efficiency under defoliation was also reported by Guitian and Bardgett (2000) and Uhlirova et al.
(2005).
In our study almost all enzymes, involved in the cycling of S, P and C have demonstrated to
be valid indicators of changes under management practices and have diminished its activity in
managed soil. Only ß-cellobiohydrolase and arylsulphatase didn’ t show a significant decrease in
MG plots, even so the negative trend for these enzymes was also observed. More likely that
enhanced root exudation, leading to a larger supply of easily available C and energy sources to
microbial communities resulted in general suppression of decomposition activities just after the
mowing procedure. A significant relationship between SEI and qCO2 (Fig.14b) could be used as an
extra prove of the bacterial community “ relax” in terms of C gaining in that period. N-acetyl-ß-
glucosaminidase and arylsulphatase are also considered as indirect indicators of the presence of the
fungal biomass because sulphate esters (substrates of arylsulphatase) and chitin are major
components in fungal cells (Bandick and Dick, 1999). These could suggest a presence of a more
efficient microbial community in the managed plots.
The enhanced N mineralization activity just after the mowing and increase in the activity of
leucine amino-peptidase (involved in the N cycling) suggest that in grassland community the
defoliation practise stimulated the flow of C to roots and into the soil, increased the size of
microbial community, which in turn stimulated potential net N mineralization rates. Herbivores for
example often enhance soil N cycling (McNaughton et al., 1997) which can result in the improved
N availability to plants. In particular key microbially mediated processes involved in soil N cycling
(nitrification, denitrification and N2-fixation) that largely control the balance the forms of soil
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