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

length could determine the range in which varies the delay between the photosynthetic C uptake and
its following respiration. Inside this limits the speed and the quantity of the translocated C to
belowground is more likely determined by plant growing stage (Kuzyakov et al., 1999; Kuzyakov
and Domanski, 2000; Gavrichkova and Kuzyakov, 2008; Carbone and Trumbore, 2007). The spped
and quantity of C flow to roots will be regulated depending on the current size of rooting system, its
growth rate, metabolic activity and relative contribution of fine and coarse roots to total
belowground biomass (Dickson, 1991; Desrochers et al., 2002; Larionova et al., 2006; Carbone and
Trumbore, 2007) as well as by level of nutrients supply (Veen, 1981; Lambers et al., 1981; Kuiper
1983; Gavrichkova and Kuzyakov, 2008).
The effect of photosynthetic C supply on root respiration is often masked by temperature
because root biomass typically peaks in summer (Lyr and Hoffmann, 1967), however roots can
only respire a proportion of what they are allocated, so the effect of temperature on root respiration
is likely to be constrained by GPP (Janssens et al. 2001). In fact, at Amplero, subjected to
management based on the defoliation practices, the decrease in C supply from defoliated plants
resulted in further decrease in correlation strength between temperature and root-derived
respiration.
The effect was less pronounced for total soil respiration as the root component account for a
minor part of soil CO2 efflux at Amplero (av.30%, Fig. 3). Microbial respiration is more sensitive to
changes in soil temperature and soil water content and more likely is independent of GPP, as in the
soil there are large amounts of substrates waiting to be decomposed. Microbes however prefer the
easily available C substrates, the quantity of which is determined by the litter input and root
rhizodeposition processes (Parton et al., 1987; Trumbore et al., 1990; Schimel et al., 1994; Schulze
et al., 2000; Bahn et al., 2006), and thus indirectly or with a considerably higher time lags could
be dependant on the site productivity.
Temperature sensitivity of microbial respiration decreased from winter to summer (Table 2),
which could be explained by physiological acclimation of soil microorganisms to high temperatures
as well as by the increase in the microbial population in autumn period (Fig. 9). Similar seasonal
changes were observed also by Luo et al (2001), Janssens and Pilegaard (2003) and Moyano et al.
(2007). Increasing temperature in winter time could also activate dormant microbes and thus
augment its C mineralization activity (Andrews et al., 2000), resulting in a sudden increase of
respiration rates. Andrews et al. (2000) reported a stronger temperature effect on microbial
population at lower temperatures. Low value of Q10 during the summer drought indicates as well a
reduction in the diffusion rates of organic molecules and thus in microbes nutrient availability.
Q10 of microbial derived respiration in the end of the growing season, was however un
proportionally high than the overall one and the Q10 reported in literature (Schleser , 1982; Raich
59