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Publication Pathways of C and N turnover in soil under elevated atmospheric CO2(2008) Dorodnikov, Maxim; Fangmeier, AndreasIn the present thesis the C and N transformations in soil as influenced by indirect effect of elevated atmospheric CO2, soil physical structure and land use change were studied in four laboratory experiments using stable-C and N isotopes, as well as soil microbiological techniques. To test the interrelations between chemical and biological characteristics of soil organic matter (SOM) as affected by land use change and elevated atmospheric CO2 an approach for SOM partitioning based on its thermal stability was chosen. In the first experiment C isotopic composition of soils subjected to C3-C4 vegetation change (grassland to Miscanthus x gigantheus, respectively) was used for the estimation of C turnover in SOM pools. In the 2nd (Free Air CO2 Enrichment ? FACE ? Hohenheim) and 3rd (FACE Braunschweig) experiments CO2 applied for FACE was strongly depleted in 13C and thus provided an opportunity to study C turnover in SOM based on its δ13C value. Simultaneous use of 15N labeled fertilizers allowed N turnover to be studied (in the 2nd experiment). We hypothesized that the biological availability of SOM pools expressed as the mean residence time (MRT) of C or N is inversely proportional to their thermal stability. Soil samples were analysed by thermogravimetry coupled with differential scanning calorimetry (TG-DSC). According to differential weight losses between 20 and 1000 °C (dTG) and energy release or consumption (DSC), SOM pools (4 to 5 depending on experiment) with increasing thermal stability were distinguished. Soil samples were heated up to the respective temperature and the remaining soil was analyzed for δ13C and δ15N by IRMS. For all three experiments the separation of SOM based on its thermal stability was not sufficient to reveal pools with contrasting turnover rates of C and N. A possible explanation for the inability of thermal oxidation for isolating SOM pools of contrasting turnover times is that the fractionation of SOM pools according to their thermal stability is close to chemical separation. In turn, it was found that chemical separations of SOM failed to isolate the SOM pools of different turnover time because different biochemical plant components (cellulose, lignin) are decomposed in a wide temperature range. Individual components of plant residues may be directly incorporated into, or even mixed with the thermal stable SOM pools and will so mask low turnover rates of these pools. To evaluate the interactions between availability of SOM for decomposition by soil microbial biomass (biological characteristic) under elevated atmospheric CO2 and protection of SOM due to the occlusion within aggregates of different sizes (physical property, responsible for SOM sequestration) we measured the activity of microbial biomass (indicated by enzyme activities) and growth strategies of soil microorganisms (fast- vs. slow growing organisms) in isolated macro- and microaggregates. The contribution of fast (r-strategists) and slowly growing microorganisms (K-strategists) in microbial communities was estimated by the kinetics of the CO2 emission from bulk soil and aggregates amended with glucose and nutrients (Substrate Induced Growth Respiration method). Although Corg and total Cmic were unaffected by elevated CO2, maximal specific growth rates were significantly higher under elevated than ambient CO2 for bulk soil, small macroaggregates, and microaggregates. Thus, we conclude that elevated atmospheric CO2 stimulated the r-selected microorganisms. Such an increase in r-selected microorganisms could increase C turnover in terrestrial ecosystems in a future elevated atmospheric CO2 environment. The activities of β-glucosidase, phosphatase and sulphatase were unaffected in bulk soil and in aggregate-size classes by elevated CO2, however, significant changes were observed in potential enzyme production after substrate amendment. After adding glucose, enzyme activities under elevated CO2 were 1.2-1.9-fold higher than under ambient CO2. This indicates an increased activity of microorganisms, which leads to accelerated C turnover in soil under elevated CO2. Significantly higher chitinase activity in bulk soil and in large macroaggregates under elevated CO2 revealed an increased contribution of fungi to turnover processes. At the same time, less chitinase activity in microaggregates underlined microaggregate stability and the difficulties for fungi hyphae penetrating them. We conclude that quantitative and qualitative changes of C input by plants into the soil at elevated CO2 affect microbial community functioning, but not its total content. Future studies should therefore focus more on the changes of functions and activities, but less on the pools. In conclusion, elevated CO2 concentrations in the atmosphere along with soil physical structure have a pronounced effect on qualitative but not quantitative changes in C and N transformations in soil under agricultural ecosystem. The physical parameters of soil such as aggregation correlate more with biological availability of SOM than the chemical properties of soil organic materials. The increase of soil microbial activity under elevated CO2 detected especially in soil microaggregates, which are supposed to be responsible for SOM preservation, prejudice sequestration of C in agroecosystems affected by elevated atmospheric CO2.Publication Variability of the protein and energy values of European dried distillers´ grains with solubles for ruminants(2013) Westreicher Kristen, Edwin; Rodehutscord, MarkusThe increasing demand of energy together with the implementation of the European Program for the use of energy from renewable sources are favourable scenarios to increment the ethanol production in the coming years in the EU. Ethanol production yields dried distillers´ grains with soluble (DDGS) as the main by-product, a valuable feedstuff for ruminants. A great number of publications mainly form USA and Canada has demonstrated the great variability of the feed value of corn-DDGS, the main by-product from ethanol production in these countries. In the EU, different and diverse technological conditions predominate and little was investigated to evaluate the feed value of DDGS. The variability of feeding value in conjunction with expected increase of DDGS production demands for further and more specific characterization of this by-product in the EU. Therefore, a project was conceived to characterize the chemical composition and evaluate the protein and energy value for ruminants of DDGS from different European countries. Thirteen samples of DDGS originating from wheat, corn, barley, and blends of different substrates were used. In the first study, the objective was to characterize variations in the composition and nutritive value of DDGS, and to estimate the undegradable crude protein (UDP) in DDGS. The rumen degradation of crude protein (CP) was determined using the nylon bag technique. Samples were incubated for 0, 1, 2, 4, 8, 16, 32, and 72 h, and in situ degradation kinetics were determined. UDP was estimated using a passage rate of 8 %/h. In vitro gas production was measured to estimate the metabolizable energy (ME), net energy for lactation (NEL) and in vitro digestibility of organic matter (IVDOM). Chemical profiles varied among samples (in g/kg dry matter (DM) ± standard deviation, the values were 310 ± 33 CP, 86 ± 37 ether extract, 89 ± 18 crude fibre, 408 ± 39 neutral detergent fibre, 151 ± 39 acid detergent fibre, and 62 ± 31 acid detergent lignin), as well as in protein fractions according to the Cornell Net Carbohydrate and Protein System (in g/kg CP, the values were 161 ± 82 for fraction A, 24 ± 11 for fraction B1, 404 ± 105 for fraction B2, 242 ± 61 for fraction B3, and 170 ± 87 for fraction C). ME, NEL (MJ/kg DM) and IVDOM (%), also varied among samples: 12.1 ± 0.59, 7.3 ± 0.39, and 72.5 ± 4.30, respectively. The in situ rapidly degradable CP fraction (a) varied from 10.2 to 30.6%, and the potentially degradable fraction (b) averaged to 66.8%. UDP varied from 8.6 to 62.6% of CP. This first study suggests significant variations in composition and nutritive value among different sources of DDGS. UDP could be predicted on the basis of analysed CP fractions, but the accuracy of UDP prediction improved upon the inclusion of neutral-detergent insoluble nitrogen, explaining 94% of the variation in the UDP values. To conclude, chemical protein fractions may be used to predict the UDP values of DDGS and the variability in the protein fractions of DDGS should be considered when formulating diets for dairy cows. To provide additional information on the nutritional value of DDGS, a second study was carried out to determine and compare the in situ ruminal degradation of CP and amino acids (AAs) of DDGS and to characterize the in vitro pepsin-pancreatin solubility of CP (PPS) from dietary DDGS (d-DDGS) and DDGS residue (DDGS-r) obtained after 16-h ruminal incubation. The rumen degradation of AAs and CP was determined using nylon bag incubations in the rumen of cows. Lysine and methionine content of d-DDGS varied from 1.36 to 4.00 and 1.34 to 1.99 g/16 g N, respectively. The milk protein score (MPS) of d-DDGS was low and ranged from 0.36 to 0.51, and lysine and isoleucine were estimated to be the most limiting AAs in d-DDGS and DDGS-r. DDGS-r contained slightly more essential AAs than did the d-DDGS. Rumen degradation of CP after 16 h varied from 44% to 94% between DDGS samples. Rumen degradation of lysine and methionine ranged from 39% to 90% and from 35% to 92%, respectively. Linear regressions showed that ruminal degradation of individual AAs can be predicted from CP degradation. The PPS of d-DDGS was higher than that of DDGS-r and it varied from 70% to 89% and from 47% to 81%, respectively. There was no significant correlation between the PPS of d-DDGS and PPS of DDGS-r (R2 = 0.31). The estimated intestinally absorbable dietary protein (IADP) averaged 21%. Moderate correlation was found between the crude fibre content and PPS of DDGS-r (R2 = 0.43). This study suggests an overestimation of the contribution of UDP of DDGS to digestible protein supply in the duodenum in currently used protein evaluation systems. More research is required and recommended to assess the intestinal digestibility of AAs from DDGS. Finally, in a third study, three sources of DDGS were evaluated in diets of mid-lactating dairy cows on milk production and milk composition and on digestibility in sheep. DDGS from wheat, corn and barley (DDGS1), wheat and corn (DDGS2) and wheat (DDGS3) were studied and compared with a rapeseed meal (RSM). RSM and DDGS were characterized through in situ CP degradability. Nutrient digestibility was determined in sheep. Twenty-four multiparous cows were used in a 4 × 4 Latin square design with 28-day periods. Treatments included total mixed rations containing as primary protein sources RSM (control), DDGS1 (D1), DDGS2 (D2) or DDGS3 (D3). RSM contained less rapidly degradable CP (fraction a), more potentially degradable CP (fraction b) and more UDP than the three DDGS. In vivo organic matter digestibility of RSM was similar to DDGS. Calculated NEL was lower for RSM (7.4 MJ/kg DM) than for DDGS, which averaged 7.7 MJ/kg DM. Cows? dry matter intake did not differ between diets (21.7 kg/d). Cows fed D1 yielded more milk than those fed D3 (31.7 vs. 30.4 kg/d); no differences were found between control and DDGS diets (31.3 vs. 31.1 kg/d). Energy-corrected milk was similar among diets (31.2 kg/d). Diets affected neither milk fat concentration (4.0%) nor milk fat yield (1.24 kg/d). Milk protein yield of control cows (1.12 kg/d) was significantly higher than D3 (1.06 kg/d) but not different from D1 and D2 (1.08 kg/d each). Feeding DDGS significantly increased milk lactose concentration (4.91%) compared to control (4.81%). DDGS can be a suitable feed compared to RSM and can be fed up to 4 kg dry matter per day in rations of dairy cows in mid-lactation. To conclude, DDGS is a suitable feedstuff for ruminants in terms of chemical composition, energy and protein value. However, the variability should be considered when included in diets of ruminants, especially in animals with high performance. For this purpose, prediction approaches initated in this study should be further developed into tools for routine application for rapid DDGS evaluation and estimation of feed values. These approaches might also be usefull for the evaluation of other feed protein sources and taked into consideration for practical feeding and diets formulation.