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28 Three partitioning methods showed comparable results in seasonal variation patterns of root- derived respiration The magnitude of root-derived respiration however differed between methods due to particulate shortcomings of each one: Mesh exclusion: the presence of lateral flow of CO2 in the soil respiration measured from the nylon mesh bags was confirmed by pulse labeling of the surrounding soil in 13 CO2 atmosphere overestimation of microbial component of soil respiration; Combined SIR: a possible boosting of root respiration after the addition of glucose solution, which could be especially true under insufficient soil moisture conditions. This could result in the subsequent overestimation of microbial component of soil respiration. The coefficient of respiration increase after the glucose addition (k) differs, depending on the source of microbial respiration: microbial decomposition of dead roots, falloff, detritus or soil organic matter. It was not possible to account for the k associated with the decomposition of fine roots. This implies a certain underestimation of the coefficient and again further overestimation of microbial respiration. Regression technique: Regression technique, given the most uncertain results with low R2 and non significant regression coefficients, during the whole period of measurements was overestimating the root-derived respiration in confront with mesh exclusion method, sometimes calculating the root contribution as a 100% to total CO2 efflux from soil. To overcome all the uncertainties, which were mainly associated with the particularities of the grassland ecosystems, the method requires further development and standardization. 1.7. Conclusions Estimating the contribution of individual sources of CO2 to the total CO2 efflux from soil and response of each component to different controlling factors is important for dipper understanding of the terrestrial carbon cycle and its feedbacks to climate change as well as for developing models that can effectively predict the future changes. Whilst measurements of soil respiration and partitioning experiments have been widely diffused for a range of forest ecosystems, comparatively little is known about grasslands. In this study we have investigated the response of soil CO2 efflux and its components: root- and microbial-derived respiration to different biotic and abiotic factors as well as to widely diffused management activities over a period of three years in a mediterranean grassland site. A particular attention was dedicated to studying of the aboveground-belowground interactions in terms of C gaining and its translocation velocity within a plant community. Different methodological
approaches for studying of the contribution of various respiration sources to total CO2 efflux from soil and the speed of C cycling within the plant community were tested. The use of micro pore mesh bags, utilized previously in forest ecosystems and agricultural crops, resulted as a promising tool for partitioning of soil respiration fluxes in grassland ecosystems, however some specific modifications are necessary. Its combination with the eddy covariance measurements, which is widely used for the monitoring of the CO2 exchange between vegetation and atmosphere, gives the possibility to study the speed of C cycling within and between various ecosystems. The reliability of time lag between the photosynthetic C uptake and its following evolution through the rooting systems obtained by mesh exclusion technique was confirmed by the results of the pulse labeling of plants in 13 CO2 atmosphere. Another promising advantage of the method is an option of variation of the mesh pore size: depending on the scope of the research and changing the aperture diameter it is possible not only to separate root-derived from microbial-derived respiration, but also allowing the in-growth of only mycorrhizal hyphae in the inclosed soil to separate actual root from mycorrhizal respiration sources. The obtained results showed an importance of C assimilate supply in the determination of the variability of root component of soil respiration. It was closely related to gross primary production with a time lag of circa 20h for time scales from daily to annual. Soil temperature which often masks the direct relationship between root respiration and photosynthetic C supply failed to explain diurnal and seasonal changes in root-derived respiration. Confront between defoliated and non defoliated soils revealed a tight coupling of root respiration with photosynthetic C supply from aboveground. Laboratory experiments with a single plant species have shown however that the observed time lag is not stable during the plant ontogenesis, and varies depending on the plant growing stage. The same photosynthetic activity could also result in different magnitude of root respiration, depending on the type of nutrient supply (ex: N in form of NH + 4 or NO - 3). All these finings suggest that root respiration is a complex process, tightly coupled to plant canopy activity and could not be explained simply by changes in soil temperature and moisture. Further studies are needed to verify the bonds between aboveground and belowground processes for different species and vegetation types, as well as for various plant growing stages. Soil temperature and soil water content exerted a significant effect on microbial component of soil respiration. Being a larger part of total CO2 efflux from soil at Amplero (≈ 70%), these factors influenced also total soil respiration dynamic on different time scales. Introduction of a management regime have modified however the activity of microbial community by an increase of the quantity of easily available C substrates from the rhizodeposition process, resulting in a general suppression of microbial enzymatic activity and further decrease in C mineralization rates. Combination of laboratory studies and in situ measurements is necessary for understanding of the 29
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 and 24: (a) (b) (c) Fig.7 Amplero (AQ, Ital
Page 25 and 26: magnitude of root respiration and o
Page 27: efficiency, indicating future posit
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
Page 75 and 76: where, MAs - the mean age of the co
Page 77 and 78: 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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