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3.2.4. Data analyses and definition of terms 74 The 13 C signature of belowground respiration and total respiration were combined with the measurement of CO2 concentration in the respective flask. These allowed estimating the fractional contribution of the belowground respiration to the total one, and then applying a two-source mixing model, to estimate the 13 C signature of the aboveground respiration: 13 Ctot =((f* 13 Cb)+((1-f)* 13 Ca))/1 (eqn. 1) where, 13 Ctot, 13 Cb and 13 Ca is the 13 C signature of total, below and aboveground respiration respectively, and f is a fractional contribution of each of the component to the total respiration. As the continuous measurement of the soil and total CO2 efflux were not available, we assumed that the respiration rates and 13 C contributions from all the sources varied linearly between the measurement events. These allowed estimating the total amount of 13 C respired during the period from 1 hours to 10 days following the application of the label (Carbone et al., 2007). The total label recovered (TLR) was defined as the calculated sum of the label ( 13 C, g) from below- and aboveground components between 1h and 240h after pulse labeling. This quantity was defined as a 100% for each labeling. The below and aboveground components were then partitioned into percentage of TLR. The fraction of respiration from label (FRL) for below and aboveground components was defined using the same equations as described by Carbone et al. (2007) and Carbone and Trumbore (2007). The isotope mass balance approach was used to partition the fraction of respiration coming from the label: FRL = ( 13 Cs - 13 CB)/( 13 CL - 13 CB) (eqn. 2) where 13 Cs is the measured sample respiration; 13 CB - is the background respiration signature, 13 CL is the label signature. 13 CL was estimated as the measured mean 13 C of CO2 during the 1h labeling period. The mean residence time (MRT) of the label in the below and above ground components was calculated fitting an exponential decay function to the FRL. All the data were separated in two periods for the better fit of the exponential curve. MRT represent the time which is required for the amount of label to be reduced to 1/e times of its initial value. Using the data of TLR and MRT was calculated the mean age (MA) of respired C (Carbone and Trumbore, 2007): MAs = (TLRs(0-24h)*MRTs(0-24h) + TLRs(24-240h)*MRTs(24-240h))/TLRs(0-240h) (eqn.3)
where, MAs – the mean age of the component; TLRs(0-24h), TLRs(24-240h), TLRs(0-240h) is the percentage of total label recovered from the component for the first 0-24 hours, for 24-240 hours and total (0-240h) respectively. MRTs(0-24h) and MRTs(24-240h) is a corresponding mean residence time. 3.2.5. Time lag by mesh bag technique Partitioning experiment aiming to separate the contribution of root-derived and microbial- derived respiration from the total CO2 efflux was established in Amplero in 2006. New partitioning plots were added in 2007. Biweekly measurements were performed during the growing seasons 2006-2008. Soil respiration was partitioned by excluding roots from soil cores using nylon mesh bags of 1µm pore size (Leake et al., 2004; Moyano et al., 2007; Moyano et al., 2008). An advantage of the micro pore nylon bag is that it permits to maintain an exchange of water and other substances between the enclosed plot and exterior soil, keeping the conditions inside the mesh equal to the surrounding one. Briefly, the procedure was the following: soil cores, 20 cm in diameter and 30 cm deep (the depth of the soil core depends on the rooting depth in the study site) were sampled from the study site. Half of the sampled soil was placed to the nylon meshes with 1µm pore size and was returned to the site. The CO2 measured from these meshes was considered as microbial respiration (Rh). Another half of the sampled and sieved soil was placed back without any barriers for the roots growing (bags with 1.0 cm pore size). The CO2 efflux, coming from these bags is a sum of microbial and root-derived respiration (Rh+Ra). Root-derived respiration was calculated as a difference between the above treatments: ((Rh+Ra)-Rh). Additionally, total soil respiration (Rs) was also measured from the undisturbed soil and was used as a control and to determine the true value of microbial respiration by subtracting from the value of Ra from Rs. Ecosystem net carbon and water vapour fluxes have been measured at Amplero continuously since 2002. The eddy covariance system integrates a sonic anemometer (Solent R3, Gill Instruments, Lymington, UK) and a LI 7500 open path infrared gas analyzer (LiCor, Lincoln, NE, USA). The flux data were calculated for 30 min intervals by means of the post-processing program Eddyflux. GPP was calculated from the difference between NEE and TER (Reichstein et al., 2005), where functional dependencies of total ecosystem respiration (TER) with temperatures were determined with CO2 fluxes measured at night (fluxes measured during low mixed periods were discarded, Aubinet et al., 2000). These functions were then applied to daytime data to derive GPP. To calculate the time lag between the photosynthetic CO2 uptake and its following respiration, the data from the partitioning experiment were plotted vs. GPP from the eddy 75
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explain diurnal and seasonal change
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sull’intensità del flusso respir
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8 3.2.4. Data analyses and definiti
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1. INTRODUCTION AND OVERVIEW 11
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times as much carbon as the terrest
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Fig. 3 Different soil C pools with
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1.3. Soil respiration sources Soil
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conditions, like soil type, plants
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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
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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
Page 69 and 70: Our experiment was conducted in a m
Page 71 and 72: Lactic acid 13 C 13 CO2 Root-derive
Page 73: At the end of the process, the subl
Page 77 and 78: 13C of respiration ( o / oo ) 155 1
Page 79 and 80: Total Label Recovered (TLR, %) Ra R
Page 81 and 82: GPP (mmol m -2 s -1 ) 25 20 15 10 5
Page 83 and 84: frequent and possibly they missed t
Page 85 and 86: 3.4.3. Destructive vs. Non-destruct
Page 87 and 88: Gavrichkova O., Kuzyakov Y., 2008.
Page 90 and 91: Chapter source: 90 4. THE EFFCT OF
Page 92 and 93: Bardgett et al. (1997) showed that
Page 94 and 95: 94 Partitioning plots were installe
Page 96 and 97: Microbial C was calculated as a dif
Page 98 and 99: taken from 1 µg N-NO2 ml -1 soluti
Page 100 and 101: ates between clipped and unclipped
Page 102 and 103: Fig. 7 Total (Rs), root (Ra)- and m
Page 104 and 105: 104 Rh, (CO 2 , mmolm -2 s -1 ) 7 6
Page 106 and 107: Fig. 11 Cumulative microbial respir
Page 108 and 109: 108 After the calculation of synthe
Page 110 and 111: Fig. 16: a) Relationship between sy
Page 112 and 113: an annual mowing the measurement wa
Page 114 and 115: mineral N available to plants and N
Page 116 and 117: Cambardella C.A., Elliott E.T., (19
Page 118 and 119: Rice C.W., Moorman T.B., Beare M, 1
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Page 122 and 123: 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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