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experiment could be responsible for the observed difference in the quantity of nitrates reduced in roots. 142 Its worth to note that some studies (Ashley et al., 1975; Breteler et al., 1980; Talouizte, et al., 1984; Gojon et al., 1986) have found that root contribution to the whole plant nitrate reduction may be important in the early phase of nitrate utilization, during so called induction process which appears just after the fertilizer addition and could last up to a couple of days. In our experiment the maximum difference in 14 CO2 respiration between two types of N fell exactly on this phase - the first hours after 15 N addition and uptake. Generally, after the termination of the induction period, the contribution of roots to the nitrate reduction process decreases due to several possible reasons: 1) the nitrate reductase level in roots could be depressed by the supply of amino acids from the shoots; 2) decrease in the nitrate uptake after induction phase could be responsible for a limitation of the nitrate supply to root nitrate reductase, particularly because translocation, which could compete with reduction in roots (Rufty et al., 1981) 3) Both nitrate and ammonium assimilation during the first period could depress the carbohydrate content of the roots and curtailed further nitrate uptake and reduction which appear to depend on it (Fiedler et al., 1975; Jackson et al., 1976). The above findings indicate that the observed difference in the quantity of respired CO2 between two types of N could change after concluding of the initial phase of N uptake. Such possibility could be verified in the future experiments applying 14 CO2 pulse labeling technique. 5.4.6. Conclusions Various factors could influence the contribution of vegetation to soil CO2 efflux from soil. Difference in plant species composition, growth stage, and environmental factors such as intensity of photosynthetically active radiation and temperature are well known one. This study brings out another factor, which could influence radically the contribution of autotrophic component of soil respiration to the total CO2 efflux. Pulse labeling of plants in 14 CO2 atmosphere allowed evaluating the effect of N form (nitrate or ammonia) on recently assimilated CO2 efflux from rhizosphere. Nitrate affected negatively the carbohydrate metabolism and energy economy of corn and lupine: in respect to ammonium, nitrate nutrition increased root-derived CO2 efflux up to 47%. However, comparison of 14 CO2 efflux from soil at two plant development stages showed that root contribution to the whole plant nitrate reduction process is not stable during a plant ontogenesis. Contribution of roots could be more important during the early phases of plant growth, following by a decrease in nitrate reduction in roots with time. These, consequently reduces C costs associated with nitrate reduction for more mature plants. All these should be taken into account while modelling and interpreting the data of CO2 efflux from soil, particularly separating estimation of individual CO2 sources which contribute to the total soil CO2 efflux.
References Agrell D., Larsson C.M., Larsson M., Mackown C.T., Rufty T.W. Jr., 1997. Initial kinetics of 15N-nitrate labelling of root and shoot N fractions of barley cultured at different relative addition rates of nitrate-N. Plant Physiol Biochem 35, 923-931. Ashley D.A., Jackson W.A., Volk R.J., 1975. Nitrate uptake and assimilation by wheat seedlings during initial exposure to nitrate. Plant Physiol 55, 1102- 1106. Aslam M., Huffacker R.C., 1982. In vivo nitrate reduction in roots and shoots of barley (Hordeum vulgare L.) seedlings in light and darkness. Plant Physiol 70, 1009–1013. Atkins CA, Pate JS, Layzell DB (1979) Assimilation and transport of nitrogen in nonnodulated (NO_3 grown) Lupinus albus L. Plant Physiol 64: 1078–1082 Atkins C.A., Pate J.S., Griffiths G.J., White S.T., 1980. Economy of carbon and nitrogen in nodulated and nonnodulated (NO_3 grown) cowpea [Vigna unguiculata (L.) Walp.]. Plant Physiol 66, 978–983. Beevers H., Hageman R.H., 1980. Nitrate and nitrite reduction. In: Stumpf P.K., Conn E.E. (Eds.) Biochem Plants, Vol 5 Academic Press, New York, pp115-168. Blacquiere T., 1987. Ammonium and nitrate nutrition in Plantago lanceolata and P. major ssp. major. II: Efficiency of root respiration and growth. Comparison of measured and theoretical values of growth respiration. Plant Physiol Biochem 25, 775-785. Breteler H., Hanisch Ten Cate C.H., 1980. Fate of nitrate during initial nitrate utilization by nitrogen-depleted dwarf bean. Physiol Plant 48, 292-296. Carbone M.S., Trumbore S.E., 2007. Contribution of new photosynthetic assimilates to respiration by perennial grasses and shrubs: residence times and allocation patterns. New Phytol 126, 124-135. Cruz C., Lips S.H., Martins-Loucao M.A., 1995. Uptake regions of inorganic nitrogen in roots of carob seedlings. Physiol Plant 95, 167–175. Dickson R.E., 1991. Assimilate distribution and storage. In: Raghavendra A.S. (Ed.) Physiol Trees. New York, USA: Wiley J and Sons, Inc., pp 51-85. Di Laurenzio L.,Wysocka-Diller J., Malamy J., et al., 1996. The scarecrow gene regulates an asymmetric cell division that is generating the organization of the Arabidopsis root. Cell 86, 423–433. Dobrowolski J.P., Caldwell M.M., Richards J.H., 1990. Basin hydrology and plant root systems. In: Osmond C.B., Pitelka L.F., Hidy G.M., (Eds.) Plant biology of the basin and range. Berlin, Germany: Springer-Verlag, pp 243–292. Ekblad A., Nordgren A., 2002. Is growth of soil microorganisms in boreal forests limited by carbon or nitrogen availability? Plant Soil 242, 115-122. Farrar J.F., Jones D.L., 2000. The control of carbon acquisition by roots. New Phytol 147, 43-53. Fiedler R., Proksch G., 1975. The determination of nitrogen- 15 by emission and mass spectrometry in biochemical analysis: a review. Anal Chim Acta 78, 1-62. Fitter A.H., Self G.K., Brown T.K., et al., 1999. Root production and turnover in an upland grassland subjected to artificial soil warming respond to radiation flux and nutrients, not temperature. Oecologia 120, 575–581. Friedlingstein P., Joel G., Field C.B., Fung I.Y., 1999. Toward an allocation scheme for global terrestrial carbon models. Glob Change Biol 5, 755–770. Gojon A., Soussana J.F., Passama L., Robin P., 1986. Nitrate reduction in roots and shoots of barley (Hordeum vulgare L.) and corn (Zea mays L.) seedlings. Plant Physiol 82, 254-260. 143
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1. INTRODUCTION AND OVERVIEW 11
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times as much carbon as the terrest
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1.3. Soil respiration sources Soil
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conditions, like soil type, plants
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efficiency, indicating future posit
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approaches for studying of the cont
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2.1. Introduction 36 Soil respirati
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38 In the year 2005 ten PVC collars
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2.2.4. Biochemical analyses Microbi
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42 Variation of soil respiration fr
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CO 2 efflux (mmol m -2 s -1 ) 44 CO
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46 All diurnal measurements of root
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48 Q10 R 2 p Rs 2.51 0.77 0.000 Ra
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the photosynthesis and its followin
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54 RS RHET 8 6 6 4 25 4 2 2 25 20 T
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2.4. Discussion 2.4.1. Partitioning
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measurements, the possibility to fi
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Janssens I.A., Pilegaard K., 2003.
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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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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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