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Soil Incubations (soil + incubation)
Selected AbstractsPhosphate buffer,extractable organic nitrogen as an index of soil-N availability for sorghum and pearl milletJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2010Asako Mori Abstract The availability of soil nitrogen (N) is usually quantified by the amount of mineralized N as determined after several weeks of soil incubation. Various alternative methods using chemical solvents have been developed to extract the available organic N, which is easily mineralized. We compared one such solution, neutral phosphate buffer (NPB), with conventional incubation and 0.01 M,CaCl2 extraction, as measures of soil N available to two major cereal crops of the semiarid tropics, based on the total N uptake by plants in a pot experiment. Mineralized N had the highest correlation with N uptake by pearl millet (Pennisetum glaucum L., r = 0.979***) and sorghum (Sorghum bicolor [L.] Moench, r = 0.978***). NPB-extractable N was also highly correlated with N uptake (pearl millet, r = 0.876***; sorghum, r = 0.872***). Only one major peak was detected when NPB extracts were analyzed using size-exclusion high-performance liquid chromatography, regardless of soil properties. In addition, the organic N extracted with NPB was characterized by determining the content of peptidoglycan, the main component of bacterial cell walls. Although the characteristics of NPB-extractable organic N are still unclear, it offers a promising quick assay of available N. [source] Localization of processes involved in methanogenic degradation of rice straw in anoxic paddy soilENVIRONMENTAL MICROBIOLOGY, Issue 8 2001Kristin Glissmann In anoxic paddy soil, rice straw is decomposed to CH4 and CO2 by a complex microbial community consisting of hydrolytic, fermenting, syntrophic and methanogenic microorganisms. Here, we investigated which of these microbial groups colonized the rice straw and which were localized in the soil. After incubation of rice straw in anoxic soil slurries for different periods, the straw pieces were removed from the soil, and both slurry and straw were studied separately. Although the potential activities of polysaccharolytic enzymes were higher in the soil slurry than in the straw incubations, the actual release of reducing sugars was higher in the straw incubations. The concentrations of fermentation products, mainly acetate and propionate, increased steadily in the straw incubations, whereas only a little CH4 was formed. In the soil slurries, on the other hand, fermentation products were low, whereas CH4 production was more pronounced. The production of CH4 or of fermentation products in the separated straw and soil incubations accounted in sum for 54,82% of the CH4 formed when straw was not removed from the soil. Syntrophic propionate degradation to acetate, CO2 and H2 was thermodynamically more favourable in the soil than in the straw fraction. These results show that hydrolysis and primary fermentation reactions were mainly localized on the straw pieces, whereas the syntrophic and methanogenic reactions were mainly localized in the soil. The percentage of bacterial relative to total microbial 16S rRNA content was higher on the straw than in the soil, whereas it was the opposite for the archaeal 16S rRNA content. It appears that rice straw is mainly colonized by hydrolytic and fermenting bacteria that release their fermentation products into the soil pore water where they are further degraded to CH4. Hence, complete methanogenic degradation of straw in rice soil seems to involve compartmentalization. [source] Sensitivity of organic matter decomposition to warming varies with its qualityGLOBAL CHANGE BIOLOGY, Issue 4 2008RICHARD T. CONANT Abstract The relationship between organic matter (OM) lability and temperature sensitivity is disputed, with recent observations suggesting that responses of relatively more resistant OM to increased temperature could be greater than, equivalent to, or less than responses of relatively more labile OM. This lack of clear understanding limits the ability to forecast carbon (C) cycle responses to temperature changes. Here, we derive a novel approach (denoted Q10,q) that accounts for changes in OM quality during decomposition and use it to analyze data from three independent sources. Results from new laboratory soil incubations (labile Q10,q=2.1 ± 0.2; more resistant Q10,q=3.8 ± 0.3) and reanalysis of data from other soil incubations reported in the literature (labile Q10,q=2.3; more resistant Q10,q=3.3) demonstrate that temperature sensitivity of soil OM decomposition increases with decreasing soil OM lability. Analysis of data from a cross-site, field litter bag decomposition study (labile Q10,q=3.3 ± 0.2; resistant Q10,q=4.9 ± 0.2) shows that litter OM follows the same pattern, with greater temperature sensitivity for more resistant litter OM. Furthermore, the initial response of cultivated soils, presumably containing less labile soil OM (Q10,q=2.4 ± 0.3) was greater than that for undisturbed grassland soils (Q10,q=1.7 ± 0.1). Soil C losses estimated using this approach will differ from previous estimates as a function of the magnitude of the temperature increase and the proportion of whole soil OM comprised of compounds sensitive to temperature over that temperature range. It is likely that increased temperature has already prompted release of significant amounts of C to the atmosphere as CO2. Our results indicate that future losses of litter and soil C may be even greater than previously supposed. [source] Stable isotope natural abundance of nitrous oxide emitted from Antarctic tundra soils: effects of sea animal excrement depositionsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2008Renbin Zhu Nitrous oxide (N2O), a greenhouse gas, is mainly emitted from soils during the nitrification and denitrification processes. N2O stable isotope investigations can help to characterize the N2O sources and N2O production mechanisms. N2O isotope measurements have been conducted for different types of global terrestrial ecosystems. However, no isotopic data of N2O emitted from Antarctic tundra ecosystems have been reported although the coastal ice-free tundra around Antarctic continent is the largest sea animal colony on the global scale. Here, we report for the first time stable isotope composition of N2O emitted from Antarctic sea animal colonies (including penguin, seal and skua colonies) and normal tundra soils using insitu field observations and laboratory incubations, and we have analyzed the effects of sea animal excrement depositions on stable isotope natural abundance of N2O. For all the field sites, the soil-emitted N2O was 15N- and 18O-depleted compared with N2O in local ambient air. The mean , values of the soil-emitted N2O were ,15N,=,,13.5,±,3.2, and ,18O,=,26.2,±,1.4, for the penguin colony, ,15N,=,,11.5,±,5.1, and ,18O,=,26.4,±,3.5, for the skua colony and ,15N,=,,18.9,±,0.7, and ,18O,=,28.8,±,1.3, for the seal colony. In the soil incubations, the isotopic composition of N2O was measured under N2 and under ambient air conditions. The soils incubated under the ambient air emitted very little N2O (2.93,µg,N2ON,kg,1). Under N2 conditions, much more N2O was formed (9.74,µg,N2ON,kg,1), and the mean ,15N and ,18O values of N2O were ,19.1,±,8.0, and 21.3,±,4.3,, respectively, from penguin colony soils, and ,17.0,±,4.2, and 20.6,±,3.5,, respectively, from seal colony soils. The data from in situ field observations and laboratory experiments point to denitrification as the predominant N2O source from Antarctic sea animal colonies. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||