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change and soil processes and to predict ecosystem responses to climate change (Melillo et al., 2002; Ryan and Law, 2005). Fig. 4 Five main sources of soil CO2 efflux from soil, ordered according the turnover rates and residence time in soil. Modified after Kuzyakov (2006). 18 In regard to the CO2-driven green house effect, the last three sources of CO2, because of their fast turn over rates, do not have a significant effect on the C sequestration in the long and short term. The long MRT of SOM and low turn over rates means that it is the only C pool that can be a real long term sink for C in soil. Being a very large reservoir of C, it makes it also a huge potential source of CO2 if decomposition exceeds humification. Plant-derived respiration in this context masks the contribution of microbial-derived respiration to the total CO2 efflux, making the total CO2 efflux unsuitable for direct estimation of the contribution of the soil the changes in atmospheric CO2. Root-derived respiration Root respiration Turnover rate Plant-derived respiration Microbial-derived respiration Rhizo-microbial respiration Total CO 2 efflux from soil (Rs) Microbial respiration of plant residues Priming effect respiration Basal respiration Residence time in soil The fact that total soil respiration is not all SOM-derived and do not provide a sufficient information on whether the soil is a net source or sink of CO2 have led to an augment of the number of both laboratory and field studies and methods which allow to separate different sources of soil CO2 and to calculate their contribution to total soil respiration. Partitioning of soil respiration allows researchers to measure the contribution of each respiration source to total fluxes and to account for the individual response of each source to environmental factors. However, the basis assumptions and results obtained by these methods vary significantly among the studies. It remains unclear if the observed variation in results is method-dependant due to the fact that each partitioning approach integrates the biases associated with the proper limitations and shortcomings, or reflects varying experimental
conditions, like soil type, plants cover, equipment, environmental conditions etc. Comprehensive reviews of these methods are given by Hanson (2000), Kuzyakov and Larionova (2005), Kuzyakov (2006), and Subke (2006). Most methods involve a certain degree of disturbance of the soil system that changes natural fluxes to an uncertain degree. Increasing number of studies have explored soil respiration in relation to environmental factors and across bioclimatic area, pointing out a different role of various ecosystems in the terrestrial C cycle and its feedbacks to climate change. Whilst soil respiration has been well characterized for range of forest ecosystems (recent synthesis by Janssens and al., 2001 Kane and al., 2003; Hibbard et al., 2005; Rodeghiero and Cescatti, 2005) comparatively little is known about grasslands. 1.4. Importance of Grassland ecosystems in global C balance. Grasslands are one of the world’ s most widespread vegetation types and comprise 32% of the earth’ s area of natural vegetation (Adams et al., 1990). Grasslands play a significant role in carbon storage and is an important component of the global carbon cycle. Even so, there have been relatively few long-term studies of grassland at the ecosystem level. At least in part, this is caused by the focus of many scientists on forests (e.g., Dolman et al., 2002; Valentini, 2003). Some researchers have tried to assess the carbon budget in grassland (Kim et al . 1992; Dugas et al . 1999; Frank & Dugas 2001; Sims & Bradford 2001; Suyker & Verma 2001; Flanagan et al. 2002; Sousanna, 2004, Belelli et al. 2007). These studies suggest that grassland ecosystems can be a sink of CO2 during their growing periods. However the grassland estimate, which is derived from a simple model CESAR (Vleeshouwers and Verhagen, 2002), is the most uncertain (coefficient of variation of 130%) among all land-use types (Janssens et al., 2003). And the contribution of this sink to the global carbon budget has not been adequately clarified. Grassland ecosystems are particularly complex and difficult to investigate because of the wide range of management and environmental conditions to which that they are exposed. Currently, the net global warming potential (in terms of CO2 equivalent) from the greenhouse gas exchanges with grasslands is not known. It is clear that an integrated approach, that would allow quantifying the fluxes from all three radiatively active trace gases (CO2, CH4, N2O), would be desirable. Besides their natural aspect, grasslands have a pure agricultural destination as a primary food source for wild herbivores and domesticated ruminants. Actually, grasslands being a mixture of different grass species, legumes and herbs may act as carbon sinks, erosion preventives, bird directive areas, habitat for small animals, nitrogen fixation (Carlier et al. 2004). The grassland’ s carbon cycle integrates exchanges of carbon in the form of organic matter among three compartments (soil, vegetation, herbivores) and under inorganic form as CO2 between 19
Page 1: !!"% ( !"+ "!$ (!'! ,' - !"+ "!$ ##
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: 1.3. Soil respiration sources Soil
Page 21 and 22: For grasslands, the nature, frequen
Page 23 and 24: (a) (b) (c) Fig.7 Amplero (AQ, Ital
Page 25 and 26: magnitude of root respiration and o
Page 27 and 28: efficiency, indicating future posit
Page 29 and 30: approaches for studying of the cont
Page 31 and 32: Houghton R.A., 2003. Revised estima
Page 33: Vleeshouwers L.M., Verhagen A. 2002
Page 36 and 37: 2.1. Introduction 36 Soil respirati
Page 38 and 39: 38 In the year 2005 ten PVC collars
Page 40 and 41: 2.2.4. Biochemical analyses Microbi
Page 42 and 43: 42 Variation of soil respiration fr
Page 44 and 45: CO 2 efflux (mmol m -2 s -1 ) 44 CO
Page 46 and 47: 46 All diurnal measurements of root
Page 48 and 49: 48 Q10 R 2 p Rs 2.51 0.77 0.000 Ra
Page 50 and 51: the photosynthesis and its followin
Page 52 and 53: 2.3.3. Inter-annual variation of so
Page 54 and 55: 54 RS RHET 8 6 6 4 25 4 2 2 25 20 T
Page 56 and 57: 2.4. Discussion 2.4.1. Partitioning
Page 58 and 59: measurements, the possibility to fi
Page 60 and 61: and Schlesinger, 1992; Moyano et al
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
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Our experiment was conducted in a m
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Lactic acid 13 C 13 CO2 Root-derive
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At the end of the process, the subl
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where, MAs - the mean age of the co
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13C of respiration ( o / oo ) 155 1
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Total Label Recovered (TLR, %) Ra R
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GPP (mmol m -2 s -1 ) 25 20 15 10 5
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frequent and possibly they missed t
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3.4.3. Destructive vs. Non-destruct
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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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