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

2.1. Introduction
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Soil respiration (Rs) is an important component of the ecosystem C budgets. It is a major
source of CO2 released by terrestrial ecosystems and after the photosynthesis, CO2 efflux from soil
remains the second largest C flux accounting for 60-90% of total ecosystem respiration (Goulden et
al., 1996; Longdoz et al., 2000; Raich and Schlesinger, 1992). Rs is known to experience high
spatial and temporal variation with different controlling factors involved on different time-scales.
However, up to now not so many studies have deal with the interannual variability of soil
respiration and only few of them were performed in grassland ecosystems (Craine et al., 1999;
Mielnick and Dugas 2000; Raich et al., 2002; Zhou et al., 2007; Bahn et al., 2008) despite the fact
that it is one of the world’ s most widespread vegetation types which comprises 32% of the earth’ s
area of natural vegetation (Adams et al., 1990).
Rs integrate the CO2 produced by soil microorganisms in the root-free and root-affected soil
and actual root respiration. Microbial respiration in the root-affected soil, so called rhizomicrobial
respiration, is closely coupled to roots distribution and activity and could be hardly separated from
the last one (Kuzyakov, 2006). We will call this type of respiration as ‘root-derived’ (Ra), and the
CO2 originated from the root-free soil as ‘microbial-derived’ respiration (Rh). According to recent
reviews the relative contribution of Ra and Rh generally accounts for approximately one half of the
total CO2 efflux (Hanson et al., 2000, Subke et al., 2006), but varies significantly among studies
(10-90%) Quantifying the contribution of these two major respiratory sources to the total CO2
efflux and understanding the seasonal and interannual variability and their response to climate
change is very important for succeed modelling and prediction of the ecosystem C cycling. The
potential change in soil CO2 efflux will largely depend on the relative contribution of Ra and Rh to
the total CO2 efflux.
The dynamic of the two components of soil respiration may be controlled by different
abiotic and biotic factors, such as temperature, water availability, nutrient supply, plant
phenological development. In addition, the response of Ra and Rh to the temperature changes is
different, exhibiting various Q10 value (Boone et al., 1998; Rey et al., 2002). Recent studies have
shown that apart of well studied effect of soil temperature and soil water content, the supply of
assimilates from photosynthetically active plant organs have a significant effect on the root-derived
respiration (Moyano et al, 2008; Carbone and Trumbore, 2007). Due to the fact that in many
ecosystems the contribution of root respiration is quite high and could arrive up 90 % of total soil
respiration (Hanson et al., 2000), the last could be also affected at a high level by the canopy
photosynthetic activity. In fact, Bahn et al. (2008), Janssens et al. (2001), Reichstein et al. (2003),
Bremer and Ham (2002) have shown that within and across various grassland and forest