Showing papers by "Karsten Kalbitz published in 2011"

A new conceptual model for the fate of lignin in decomposing plant litter

Abstract: Lignin is a main component of plant litter. Its degradation is thought to be critical for litter decomposition rates and the build-up of soil organic matter. We studied the relationships between lignin degradation and the production of dissolved organic carbon (DOC) and of CO2 during litter decomposition. Needle or leaf litter of five species (Norway spruce, Scots pine, mountain ash, European beech, sycamore maple) and of different decomposition stage (freshly fallen and up to 27 months of field exposure) was incubated in the laboratory for two years. Lignin degradation was followed with the CuO method. Strong lignin degradation occurred during the first 200 incubation days, as revealed by decreasing yields of lignin-derived phenols. Thereafter lignin degradation leveled off. This pattern was similar for fresh and decomposed litter, and it stands in contrast to the common view of limited lignin degradation in fresh litter. Dissolved organic carbon and CO2 also peaked in the first period of the incubation but were not interrelated. In the later phase of incubation, CO2 production was positively correlated with DOC amounts, suggesting that bioavailable, soluble compounds became a limiting factor for CO2 production. Lignin degradation occurred only when CO2 production was high, and not limited by bioavailable carbon. Thus carbon availability was the most important control on lignin degradation. In turn, lignin degradation could not explain differences in DOC and CO2 production over the study period. Our results challenge the traditional view regarding the fate and role of lignin during litter decomposition. Lignin degradation is controlled by the availability of easily decomposable carbon sources. Consequently, it occurs particularly in the initial phase of litter decomposition and is hampered at later stages if easily decomposable resources decline.

Heavy metal concentrations in particle size fractions from street dust of Murcia (Spain) as the basis for risk assessment

Abstract: Street dust has been sampled from six different types of land use of the city of Murcia (Spain). The samples were fractionated into eleven particle size fractions (<2, 2–10, 10–20, 20–50, 50–75, 75–106, 106–150, 150–180, 180–425, 425–850 μm and 850–2000 μm) and analyzed for Pb, Cu, Zn and Cd. The concentrations of these four potentially toxic metals were assessed, as well as the effect of particle size on their distribution. A severe enrichment of all metals was observed for all land-uses (industrial, suburban, urban and highways), with the concentration of all metals affected by the type of land-use. Coarse and fine particles in all cases showed concentrations of metals higher than those found in undisturbed areas. However, the results indicated a preferential partitioning of metals in fine particle size fractions in all cases, following a logarithmic distribution. The accumulation in the fine fractions was higher when the metals had an anthropogenic origin. The strong overrepresentation of metals in particles <10 μm indicates that if the finest fractions are removed by a vacuum-assisted dry sweeper or a regenerative-air sweeper the risk of metal dispersion and its consequent risk for humans will be highly reduced. Therefore, we recommend that risk assessment programs include monitoring of metal concentrations in dust where each land-use is separately evaluated. The finest particle fractions should be examined explicitly in order to apply the most efficient measures for reducing the risk of inhalation and ingestion of dust for humans and risk for the environment.

Microbial immobilization and mineralization of dissolved organic nitrogen from forest floors

Abstract: Dissolved organic nitrogen (DON) plays a key role in the N cycle of many ecosystems, as DON availability and biodegradation are important for plant growth, microbial metabolism and N transport in soils. However, biodegradation of DON (defined as the sum of mineralization and microbial immobilization) is only poorly understood. In laboratory incubations, biodegradation of DON and dissolved organic carbon (DOC) from Oi and Oa horizons of spruce, beech and cypress forests ranged from 6 to 72%. Biodegradation of DON and DOC was similar in most samples, and mineralization of DON was more important than microbial immobilization. Nitrate additions (0–10 mg N L−1) never influenced either DON immobilization by microorganisms or mineralization. We conclude that soil microorganisms do not necessarily prefer mineral N over DON for meeting their N demand, and that biodegradation of DON seems to be driven by the microbial demand for C rather than N. Quantifying the dynamics of DON in soils should include consideration of both C and N demands by microbes.

Stability of organic matter in soils of the Belgium Loess Belt upon erosion and deposition

Abstract: Stability of organic matter in soils of the Belgium Loess Belt upon erosion and deposition X. Wang, L.H. Cammeraat, Z. Wang, G. Govers, K. Kalbitz. Abstract: Soil erosion has significant impacts on terrestrial C dynamics, which removes C from topsoil and continually exposes subsoil that has lower C content. However limited studies have paid attention to the mechanisms of stabilization of the eroded and deposited carbon against microbial decay. We analyzed factors governing organic C mineralization in topsoil (from depths of 5-10 cm) and subsoil (from depths of 75-100 cm and 160-200 cm) from depositional and eroding sites of Belgian Loess Belt. In 28-days incubations we studied the effects of oxygen concentrations (0%, 5%, and 20%), soil microbial biomass, substrate (glucose) availability and the amount and chemical features of soil organic carbon (SOC) on C mineralization. Soil erosion and deposition significantly affected SOC concentrations in 0~200 cm profiles and microbial biomass C, N in the topsoil. Carbon enrichment at the depositional site could be related to smaller mineralization. Concentrations of water-extractable C were larger in the soils of the eroding sites. Glucose addition stimulated microbial growth, enhanced soil respiration in all soils, particularly in the topsoil.. Carbon mineralization per unit organic carbon was larger in topsoils than in subsoils at both depositional and eroding sites. Oxygen availability showed the expected positive relationship to C mineralization in topsoils. However, small O2 concentrations did not result in decreased C mineralization in subsoils indicating that the controls on C dynamics might be different in different soil layers. The experimental results suggest that the observed C accumulation at depositional sites are also the result of smaller C mineralization. However, we are just at the beginning of understanding the reasons of this decreased mineralization. Keywords: Soil erosion and deposition; organic carbon and nitrogen; oxygen availability; mineralization; methane; microbial biomass C