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2.1. Introduction 36 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
ecosystems soil respiration on annual scale is closely related to gross primary production (GPP) and its surrogate leaf area index (LAI). Isotope studies, applying the isotope pulse labeling techniques have demonstrated that the processes of photosynthetic C uptake and its following evolution through the rooting systems are coupled with a time lag in the range of minutes to days (Gavrichkova & Kuzyakov, 2008; Carbone and Trumbore 2007; Staddon et al., 2003; Ostle et al., 2003), suggesting the diurnal variation in soil respiration is also affected photosynthetic C supply. Summarizing the above findings and uncertainties the aims of this study were: 1) to partition the soil respiration into root and microbial derived CO2 efflux in a Mediterranean grassland 2) to characterize what factors are responsible for the variation of respiration of different origin on various time scales: from daily to interannual. We hypothesize that root-derived and total soil respiration would be positively correlated to changes in GPP. 2.2. Materials and Methods 2.2.1. Study site The study was carried out at the Amplero grassland site. Amplero was established as a main CarboEurope site in central Italy near the city Collelongo (AQ) in the year 2002. A Mediterranean grassland site, located at 900 m a.s.l. Amplero is a nearly flat to gently south sloping (2-3%) doline bottom with an average annual temperature of 10°C and average annual precipitation of 1365 mm. The site is subjected to a long-term management since 1950, which consists in a once-a-year mowing during the peak of the growing season and the rest of the growing season the site is used as a pasture for cattle grazing. The soil is classified as Haplic Phaeozem (FAO classification) and contains 13% of sand, 33% of silt and 56% of clay, pHH2O of 6.6, total carbon (C) 3.48 % and total nitrogen (N) 0.28%. The plant cover is mainly represented by the following families: Caryophyllaceae (19%), Faseolaceae (30%) and Poaceae (34%). 2.2.2. Partitioning technique Soil respiration was measured every two weeks in the course of three years: 2006, 2007, and 2008. Measurements were made manually with an infrared gas analyzers (IRGA) operated in the closed path mode. Two closed dynamic systems were involved in the measurements: LI-COR 6400, connected to soil chamber LI-6400 09 (LI-COR Inc., Lincoln, NE, USA), which was used in 2006 and EGM-4, connected to soil chamber SRC-1 (PP systems, UK), which was used in 2007 and 2008. A confront between the systems was performed, to ensure the comparability of the data. 37
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Page 4 and 5: explain diurnal and seasonal change
Page 6 and 7: sull’intensità del flusso respir
Page 8 and 9: 8 3.2.4. Data analyses and definiti
Page 11 and 12: 1. INTRODUCTION AND OVERVIEW 11
Page 13 and 14: times as much carbon as the terrest
Page 15 and 16: Fig. 3 Different soil C pools with
Page 17 and 18: 1.3. Soil respiration sources Soil
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Page 21 and 22: For grasslands, the nature, frequen
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Page 25 and 26: magnitude of root respiration and o
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Page 31 and 32: Houghton R.A., 2003. Revised estima
Page 33: Vleeshouwers L.M., Verhagen A. 2002
Page 38 and 39: 38 In the year 2005 ten PVC collars
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Page 44 and 45: CO 2 efflux (mmol m -2 s -1 ) 44 CO
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Page 48 and 49: 48 Q10 R 2 p Rs 2.51 0.77 0.000 Ra
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Page 54 and 55: 54 RS RHET 8 6 6 4 25 4 2 2 25 20 T
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Page 58 and 59: measurements, the possibility to fi
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Page 62 and 63: Janssens I.A., Pilegaard K., 2003.
Page 64: Xu X., Kuzyakov Y., Wanek W., Richt
Page 67 and 68: 3.1. Introduction Soil respiration
Page 69 and 70: Our experiment was conducted in a m
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Page 79 and 80: Total Label Recovered (TLR, %) Ra R
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Gavrichkova O., Kuzyakov Y., 2008.
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Chapter source: 90 4. THE EFFCT OF
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Bardgett et al. (1997) showed that
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94 Partitioning plots were installe
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Microbial C was calculated as a dif
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taken from 1 µg N-NO2 ml -1 soluti
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ates between clipped and unclipped
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Fig. 7 Total (Rs), root (Ra)- and m
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104 Rh, (CO 2 , mmolm -2 s -1 ) 7 6
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Fig. 11 Cumulative microbial respir
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108 After the calculation of synthe
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Fig. 16: a) Relationship between sy
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an annual mowing the measurement wa
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mineral N available to plants and N
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Cambardella C.A., Elliott E.T., (19
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Rice C.W., Moorman T.B., Beare M, 1
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120
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5.1. Introduction 122 Nitrogen (N)
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specie, c) an additional aim was to
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5.2.4. Sampling and analyses 126 Na
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the differences between N and contr
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130 specific root respiration (max
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Fig. 4 a) Intensity of 14 CO2 efflu
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Fig. 6 a) values above zero: root-d
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136 Zea mays: A clear diurnal dynam
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plants. The growth stage could cont
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nitrates. At temperatures of 15 - 2
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experiment could be responsible for
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Horwath W.R., Pretziger K.S., Paul,
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146
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148 6.1 . Introduction In studies o
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Regression analyses technique, whic
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152 The respiratory response with g
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154 100% 80% 60% 40% 20% 0% 85% 13%
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6.3.2. 2008: Mesh- exclusion vs. re
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6.4. Discussion 6.4.1. Mesh-exclusi
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introduction in a small soil sample
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component, expressing a total soil
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Kucera C.L., Kirkham D.R., 1971. So
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Acknowledgements This work was poss
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