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each of these and the atmosphere (Fig. 5 and 6). The vegetation exchanges actively CO2 with the atmosphere through the biological processes of photosynthesis and respiration and contributes to inputs of organic matter into the soil by the decomposition of the dead tissues. The herbivores consume grass matter, return part of the ingested carbon through excrements, which naturally serve as fertilizing substrate for grasses, and emit CO2 to the atmosphere as a result of respiration. In managed grasslands the excreted carbon may be incorporated directly into soil as manure by farming practices. For natural steppe ecosystems, in absence of livestock, the fraction of primary productivity consumed by herbivores, typically rodents, is very small and generally does not exceed 1-2% of NPP. Up to 98% of the total carbon store in temperate grassland ecosystems can be found sequestered in the below ground pool (Hungate et al., 1997) which generally has much slower turnover rates than aboveground C (Schlesinger, 1977). Carbon dioxide is lost from grassland soils by root respiration and microbial respiration from decomposition of soil organic matter. Changes in organic carbon content is a function of the balance between inputs to soil of carbon fixed by photosynthesis and losses of soil carbon via decomposition. Soil erosion can also result in the loss (or gain) of carbon locally, but the net effect of erosion on carbon losses as CO2 for large areas on a national scale is unclear. 20 Manure/Slurry Fig. 5 Schematic diagram of the greenhouse gas fluxes and main organic matter (OM) fluxes in a grazed grassland (modified after Sousanna, 2004). Moreover, grasslands contribute to the biosphere – atmosphere exchange of non CO2 greenhouse gases, with fluxes intimately linked to management practices. Of the three greenhouse gases that are exchanged by grasslands, CO2 is exchanged with the soil and vegetation, N2O is emitted by soils and CH4 is emitted by livestock at grazing and can be exchanged with the soil (Fig. 5 and 6). Herbivore Vegetation Soil Dissoved Organic C CH 4 CO 2 CO 2 CH 4 CO 2 N 2 O atmosphere
For grasslands, the nature, frequency and intensity of disturbance plays a key role in the C balance. In agricultural systems, land use and management act to modify both the input of organic matter via residue production, organic fertiliser application, grazing management and the rate of decomposition (by modifying microclimate and soil conditions through crop selection, soil tillage, mulching, fertiliser application, irrigation and liming) (IPCC, 1997). Management practices that increase soil and root respiration cause short-term effluxes of CO2 to the atmosphere, whilst practices that increase the rate of decomposition of organic matter lead to longer-term losses of soil organic carbon in the form of carbon dioxide. Herbage harvesting by cutting also results in carbon exports from grassland plots. Most of the carbon harvested and stored in hay or silage will be released as CO2 to the atmosphere shortly after harvest. In a cutting regime, a large part of the primary production is exported from the plot as hay or silage, but part of these C exports is compensated for by farm manure and slurry application. Under intensive grazing, up to 60 % of the above ground dry matter production is ingested by domestic herbivores (Lemaire and Chapman, 1996). However, this percentage can be much lower during extensive grazing. The largest part of the ingested carbon is digestible (up to 75% for highly digestible forages) and, hence, is respired shortly after intake. Only a small fraction of the ingested carbon is accumulated in the body of domestic herbivores or is exported as milk. Large herbivores, such as cows, respire approximately one ton C per year (Vermorel, 1995). Additional carbon losses occur through methane emissions from the enteric fermentation. However, grazing practices which increase grassland productivity have the potential to increase SOC and C sequestration (Conant et al. 2001). Fig. 6 Carbon cycle in grazed grassland. The main carbon fluxes (t C ha -1 yr -1 ) are illustrated for grassland grazed continuously by cattle at an annual stocking rate of two livestock units per ha (Soussana et al., 2004) 21
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: conditions, like soil type, plants
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
Page 69 and 70: 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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