Priming Effects of Dissolved Organic Substrates on the Mineralisation of Lignin, Peat, Soil Organic Matter and Black Carbon Dete

Priming effects of dissolved organic substrates on the mineralisation of lignin, peat, soil organic matter and black carbon determined with 14C and 13C isotope techniques Dissertation zur Erlangung des Grades Doktor der Naturwissenschaften (Dr. rer. nat.) an der Fakultät für Geowissenschaften der Ruhr-Universität Bochum vorgelegt von Dipl.-Geographin Ute Hamer geboren 01.05.76 in Wickede (Ruhr) 2004 Contents 2 Contents Abbreviations ............................................................................................................. 3 Chapter 1 .................................................................................................................... 5 Introduction Chapter 2 .................................................................................................................. 29 Priming effects of sugars, amino acids, organic acids and catechol on the miner- alization of lignin and peat Journal of Plant Nutrition and Soil Science (2002), 165: 261-268 Chapter 3 .................................................................................................................. 53 Priming effects in different soil types induced by fructose, alanine, oxalic acid and catechol additions Soil Biology & Biochemistry (2004), in press Chapter 4 .................................................................................................................. 78 Priming effects in soils after combined and repeated substrate additions Geoderma (2004), in press Chapter 5 ................................................................................................................ 110 Interactive priming of black carbon and glucose mineralisation Organic Geochemistry (2004), 35: 823-830 Chapter 6 ................................................................................................................ 129 Isotopic 13C fractionation during the mineralisation of organic substrates Rapid Communications in Mass Spectrometry (2004), in review Chapter 7 ................................................................................................................ 151 Epilogue Summary................................................................................................................. 167 Zusammenfassung.................................................................................................. 170 Acknowledgements................................................................................................. 174 Curriculum vitae .................................................................................................... 175 Abbreviations 3 Abbreviations BC black carbon Bq bequerel C carbon C3 plant plant with the C3 pathway of photosynthesis C4 plant plant with the C4 pathway of photosynthesis CaCl2 calcium chloride CFE chloroform fumigation extraction CHCl3 chloroform Cmic microbial biomass C CO2 carbon dioxide Corg organic carbon /13C 13C/12C ratio expressed relative to the PDB standard DGGE denaturing gradient gel electrophoresis DOC dissolved organic carbon DOM dissolved organic matter dw dry weight KOH potassium hydroxide N nitrogen n number of replicates ND not determined NMR nuclear magnetic resonance spectroscopy NPK fertilisation with nitrogen, phosphorus and potassium n. s. not significant at p < 0.05 Abbreviations 4 PDB PeeDeeBelemnite, standard for 13C-analysis PE priming effect Py-GC/MS-IRMS pyrolysis - gas chromatography/mass spectrometry - isotope ratio mass spectrometry r correlation coefficient SD standard deviation SOC soil organic carbon SOM soil organic matter TOC total organic carbon WHC water holding capacity Chapter 1 Introduction Chapter 1 Introduction 6 Global carbon cycle On a global basis, terrestrial soil carbon exceeds that within aboveground biomass by far. It is estimated that about 1580 Gt carbon have been accumulated over centuries and millennia in our soils while the global pools of living biomass and atmospheric carbon amount to 620 and 720 Gt C, respectively (Gleixner et al., 2001). About two- thirds of soil carbon worldwide is stored in forest soils (Sedjo, 1993; Solomon et al., 1993). On the background of increasing atmospheric CO2 levels there is much inter- est whether soils act as net carbon sink or source in the global carbon cycle (Kätterer and Andrén, 1999; Ehleringer et al., 2000; Gleixner et al., 2001; IPCC, 2001; Krull et al., 2003). Therefore, it is important to know the processes resulting in a sequestra- tion of CO2 into soil organic carbon (SOC) and those leading to the mineralisation of SOC resulting in a release of CO2 to the atmosphere. Atmospheric CO2 is trans- formed into plant organic matter via photosynthesis. The amount and the composi- tion of plant litter inputs into soils are essential controlling factors for the formation of SOC (Kögel-Knabner, 2002). In addition to the above-ground input of litter, a considerable proportion of organic material is incorporated into soils below-ground. Cereals, for example, translocate between 20 and 30 % of assimilated CO2-C into the below-ground. However, only a portion of this carbon is incorporated in soil microorganisms and in SOC (Kuzyakov and Domanski, 2000). The stability of SOC is influenced by many different factors. In addition to the physical and chemical envi- ronment (e.g. moisture, temperature, pH, mineralogy), the chemical structure of organic matter as well as the location of organic matter within the soil matrix deter- mine their susceptibility to degradation by microorganisms and enzymes (Sollins et al., 1996; Baldock and Skjemstad, 2000). Although conceptual models about stabili- sation mechanisms of SOC exist, quantitative knowledge about the processes is scarce. There is considerable disagreement over carbon pool sizes and fluxes for various ecosystems. It is estimated that on a global scale between 68 and 100 Gt carbon are released to the atmosphere per year due to soil respiration (Rustad et al., 2000). Although soils contain considerable amounts of SOC, most of it is not available for microorganisms. However, substrates may be available locally, e.g. in decaying ma- Chapter 1 Introduction 7 terial of plant and animal origin. Due to this inhomogenity there are “hot spots” of microbial activity and growth in soils (van Elsas and van Overbeek, 1993). Priming effect As early as 1926 Löhnis observed an increase in SOC mineralisation after the addition of fresh organic residues to soil. This phenomenon was termed “priming effect” by Bingemann et al. (1953). The term priming effect is used until today although this sometimes causes confusion, since it was observed that the addition of organic substrates to soil may also retard the mineralisation of SOC. Therefore, the term “positive priming effect” is used when the mineralisation of SOC is accelerated by the substrate addition compared to the control (Figure 1). The term “negative priming effect” is used when the mineralisation of SOC is retarded (Kuzyakov et al., 2000). Within this thesis, the amount of SOC which is mineralised more than in the control is designated as additional SOC mineralised (Figure 1). Positive priming effect Substrate SOC additional SOC Negative n o priming effect i t a s li a r e n i M Soil without Soil with Soil with substrate substrate substrate Figure 1: Schematic diagram of the influence of organic substrate additions on the mineralisation of soil organic carbon (SOC). The acceleration of SOC mineralisation is termed as positive priming effect and the retardation as negative priming effect (changed after Kuzyakov et al., 2000). The research on priming effects between 1950 and 1970 mainly focused on arable soils. In agriculture, the main goal was the maintenance of the soil organic matter content. Therefore, the carbon balance of the soils after incorporation of plant resi- Chapter 1 Introduction 8 dues was investigated experimentally. As reviewed by Sauerbeck (1966), most studies of this period showed that more carbon of the plant residues remained in soil than additional SOC was lost by priming. Sauerbeck (1966) concluded that priming effects in arable soils are not important for their carbon stocks. Recent research on priming effects has shown that especially in experiments with planted and unplanted soils a stimulation of SOC mineralisation in the planted soils of up to 300 % occurred (Cheng et al., 2003). These so-called rhizosphere priming effects are discussed in detail by Kuzyakov (2002). Such high positive priming effects have also been reported after the incorporation of fresh plant shoot residues into the soil (Kuzyakov et al., 1997). It has been shown that not only plant residues in- duce positive priming effects (Liang et al., 1999; Stemmer et al., 1999; Bell et al., 2003; Malosso et al., 2004), but also simple easily available substrates such as glucose or different amino acids (Dalenberg and Jager, 1989; Vasconcellos, 1994; De- gens and Sparling, 1996; Shen and Bartha, 1997; Aoyama et al., 2000; De Nobili et al., 2001; Falchini et al., 2003). In some cases, positive priming effects due to sew- age sludge or compost addition were reported (Luna-Guido et al., 2001; Leifeld et al., 2002). The addition of model root exudates, root mucilage or roots to soil can also enhance SOC mineralisation (Mary et al., 1993; Traoré et al., 2000; De Nobili et al., 2001). However, most of the above mentioned substrates have also induced negative priming effects in several studies. For example, Szolnoki et al. (1963) and De- gens and Sparling (1996) observed negative priming

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