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24 The experiment on partitioning of soil respiration was started in the beginning of the growing season of 2006 and terminated in September 2008. In particular, the following results can be highlighted: Average contribution of root-derived respiration to total CO2 efflux from soil in three years of measurements amounted to 30% with a great variation during the growing seasons (2- 70%). An increase in root contribution, observed mainly during the drought periods in summer, was associated with higher sensibility of microbial respiration to changes in the soil water content. Daily variation of soil respiration of various origin couldn’ t be explained only by changes in soil temperature and soil moisture. Other factors are involved in controlling of diurnal variation of soil respiration. Seasonal variation of respiration of different origin was controlled by various factors: GPP resulted as a best predictor of changes in root-derived respiration. The correlation between photosynthesis and the effect on respiration was strongest after a lag of 20 hours. Soil temperature which often masks the GPP dependence, failed to explain changes in root respiration at Amplero. In fact, the biomass increment which is usually observed under favourable temperatures and soil humidity was restricted by mowing and grazing. However, changes in soil temperature and soil water content explained well seasonal variation of microbial component of soil respiration. Being a larger part of total CO2 efflux from soil at Amplero (≈ 70%), these factors exert a significant influence also on total soil respiration dynamic. Interannual variability of total soil respiration is controlled by the number of days with SWC
magnitude of root respiration and on the speed of translocation and respiration of recently assimilated C through roots (on a single species in laboratory, chapter 5). Speed of C cycling In situ pulse labeling in 13 CO2 atmosphere was performed in Amplero. Raw isotopic values of respired 13 CO2, mean residence time and mean age of this C in aboveground and belowground compartments were estimated. Results of two methods for assessment of the time lag between photosynthetic C uptake and its following respiration through the rooting system ((1) in situ pulse labeling and (2) root-derived respiration by mesh exclusion vs. GPP from eddy covariance) were compared. The main results are the following: Two distinct pools of C could be recognized: a fast turning over pool, which integrates the assimilates of a current day, and slower turning over pool, which integrates the assimilations during the growing season; Aboveground growth and maintenance respiration is fuelled mainly by the assimilates of the current day, while in root respiration the C with higher mean residence time values is involved; The peak in root-derived respiration by isotope pulse labeling technique was registrated between 16-24h after the label introduction, indicating a general strong and fast link between C assimilation and root activity; The time lag obtained by destructive mesh-exclusion technique was confirmed by the non destructive pulse labeling method. The fact that such type of partitioning techniques are widely used in environmental studies and often are coupled with eddy covariance measurements, makes it promising for the estimation of the speed of the C cycling within and between various ecosystems. Effect of different plant species, growing stage and nutrient supply Pulse labeling of different plant species in 14 CO2 atmosphere under laboratory conditions, varying their growing stage and type of N supply have demonstrated that root respiration is a complex process: the limits of its variation are more likely determined by the photosynthetic C supply from shoots, inside these limits the magnitude of root respiration depends on ion uptake expenses and costs associated with nitrate reduction. 25
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 and 18: 1.3. Soil respiration sources Soil
Page 19 and 20: conditions, like soil type, plants
Page 21 and 22: For grasslands, the nature, frequen
Page 23: (a) (b) (c) Fig.7 Amplero (AQ, Ital
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
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 and 74: 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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