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Microbial Biomass C (microbial + biomass_c)
Selected AbstractsNitrifier denitrification can be a source of N2O from soil: a revised approach to the dual-isotope labelling methodEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2010D. M. Kool Nitrifier denitrification (i.e. nitrite reduction by ammonia oxidizers) is one of the biochemical pathways of nitrous oxide (N2O) production. It is increasingly suggested that this pathway may contribute substantially to N2O production in soil, the major source of this greenhouse gas. However, although monoculture studies recognize its potential, methodological drawbacks prohibit conclusive proof that nitrifier denitrification occurs in actual soils. Here we suggest and apply a new isotopic approach to identify its presence in soil. In incubation experiments with 12 soils, N2O production was studied using oxygen (O) and nitrogen (N) isotope tracing, accounting for O exchange. Microbial biomass C and N and phospholipid fatty acid (PLFA) patterns were analysed to explain potential differences in N2O production pathways. We found that in at least five of the soils nitrifier denitrification must have contributed to N2O production. Moreover, it may even have been responsible for all NH4+ -derived N2O in most soils. In contrast, N2O as a by-product of ammonia oxidation contributed very little to total production. Microbial biomass C and N and PLFA-distinguished microbial community composition were not indicative of differences in N2O production pathways. Overall, we show that combined O and N isotope tracing may still provide a powerful tool to understand N2O production pathways, provided that O exchange is accounted for. We conclude that nitrifier denitrification can indeed occur in soils, and may in fact be responsible for the greater proportion of total nitrifier-induced N2O production. [source] Microbial biomass and activity in composts of different composition and ageJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2004Andreas Gattinger Abstract The aim of this study was to perform a comparison of microbial activity and biomass in biowaste (BWC), yard waste (YWC), and cattle-manure composts (CMC) of different age. Two different methods for either biomass (microbial C following fumigation-extraction and microbial lipid phosphate) or activity measurements (CO2 -production rate and fluorescein diacetate hydrolysis) provided comparable information, as judged from their strong correlation. Microbial biomass and activity declined with time in all composts. Microbial biomass C was strongly correlated with microbial activity but was even stronger correlated with pH. CMC proved to be very distinct from the two other compost types by having the highest biomass and the lowest specific activity (i.e., activity per unit biomass). The microbiological properties analyzed allow us to discriminate among different compost types, helping to assign their potential applications. Mikrobielle Biomasse und Aktivität in Komposten unterschiedlicher Zusammensetzung und unterschiedlichen Alters Ziel dieser Studie war es, Bioabfall-, Grünabfall- und Rindermistkomposte unterschiedlicher Altersgruppen hinsichtlich ihrer mikrobiellen Aktivität und Biomasse zu vergleichen. Die zwei unterschiedlichen Methoden für die Bestimmung der mikrobiellen Biomasse (Cmik mittels Fumigation-Extraktion und Lipidphosphat) und Aktivität (CO2 -Produktion und Hydrolyse von Fluoresceindiacetat) lieferten jeweils vergleichbare Aussagen, die Parameter waren eng miteinander korreliert. Mikrobielle Biomasse und Aktivität nahmen mit zunehmendem Alter in den einzelnen Komposten ab. Mikrobieller C war eng mit der mikrobiellen Aktivität korreliert, jedoch war die Korrelation zwischen dem pH-Wert und Cmik stärker ausgeprägt. Die größte mikrobielle Biomasse und die niedrigste spezifische Aktivität (Aktivität pro Biomasseeinheit) wurden im CMC festgestellt, wodurch sich dieser Kompost deutlich von den beiden anderen Komposten unterschied. Die in dieser Untersuchung beschriebenen mikrobiellen Eigenschaften ermöglichen es, zwischen Komposten unterschiedlicher Zusammensetzung zu unterscheiden und daraus mögliche Anwendungsbereiche für Komposte abzuleiten. [source] Flux and turnover of fixed carbon in soil microbial biomass of limed and unlimed plots of an upland grassland ecosystemENVIRONMENTAL MICROBIOLOGY, Issue 4 2005J. Ignacio Rangel-Castro Summary The influence of liming on rhizosphere microbial biomass C and incorporation of root exudates was studied in the field by in situ pulse labelling of temperate grassland vegetation with 13CO2 for a 3-day period. In plots that had been limed (CaCO3 amended) annually for 3 years, incorporation into shoots and roots was, respectively, greater and lower than in unlimed plots. Analysis of chloroform-labile C demonstrated lower levels of 13C incorporation into microbial biomass in limed soils compared to unlimed soils. The turnover of the recently assimilated 13C compounds was faster in microbial biomass from limed than that from unlimed soils, suggesting that liming increases incorporation by microbial communities of root exudates. An exponential decay model of 13C in total microbial biomass in limed soils indicated that the half-life of the tracer within this carbon pool was 4.7 days. Results are presented and discussed in relation to the absolute values of 13C fixed and allocated within the plant,soil system. [source] Distribution of microbial biomass and phospholipid fatty acids in Podzol profiles under coniferous forestEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2000H. Fritze Summary Microbial-derived phospholipid fatty acids (PLFAs) can be used to characterize the microbial communities in soil without the need to isolate individual fungi and bacteria. They have been used to assess microbial communities of humus layers under coniferous forest, but nothing is known of their distribution in the deeper soil. To investigate the vertical distribution we sampled nine Podzol profiles on a 100-m-long transect in a coniferous forest and analysed for their microbial biomass and PLFA pattern to a depth of 0.4 m. The transect covered a fertility gradient from Vaccinium vitis-idaea forest site type to Vaccinium myrtillus forest site type. The cores were divided into humus (O) and eluvial (E) layers and below that into 10-cm sections and designated as either illuvial (B) or parent material (C), or as a combination (BC). Two measures of microbial biomass analyses were applied: substrate-induced respiration (SIR) to determine microbial biomass C (Cmic), and the sum of the extracted microbial-derived phospholipid fatty acids (totPLFA). The soil fertility had no effect on the results. The Cmic correlated well with totPLFA (r=,0.86). The microbial biomass decreased with increasing depth. In addition the PLFA pattern changed with increased depth as assessed with principal component analysis, indicating a change in the microbial community structure. The composition of the PLFAs in the O layer differed from that in the E layer and both differed from the upper part of the B layer and from the rest of the BC layers. The deeper parts of the B layer (BC1, BC2 and BC3) were similar to one other. The O layer had more 18:2,6, a PLFA indicator of fungi, whereas the E layer contained relatively more of the PLFAs 16:1,9, 18:1,7 and cy19:0 common in gram-negative bacteria. With increased depth the relative amount of 10Me18:0, the PLFA indicator for actinomycetes, increased. We conclude that the PLFA method is a promising discriminator between the microbial community structures of the horizons in Podzols. [source] Several components of global change alter nitrifying and denitrifying activities in an annual grasslandFUNCTIONAL ECOLOGY, Issue 4 2006R. BARNARD Summary 1The effects of global change on below-ground processes of the nitrogen (N) cycle have repercussions for plant communities, productivity and trace gas effluxes. However, the interacting effects of different components of global change on nitrification or denitrification have rarely been studied in situ. 2We measured responses of nitrifying enzyme activity (NEA) and denitrifying enzyme activity (DEA) to over 4 years of exposure to several components of global change and their interaction (increased atmospheric CO2 concentration, temperature, precipitation and N addition) at peak biomass period in an annual grassland ecosystem. In order to provide insight into the mechanisms controlling the response of NEA and DEA to global change, we examined the relationships between these activities and soil moisture, microbial biomass C and N, and soil extractable N. 3Across all treatment combinations, NEA was decreased by elevated CO2 and increased by N addition. While elevated CO2 had no effect on NEA when not combined with other treatments, it suppressed the positive effect of N addition on NEA in all the treatments that included N addition. We found a significant CO2,N interaction for DEA, with a positive effect of elevated CO2 on DEA only in the treatments that included N addition, suggesting that N limitation of denitrifiers may have occurred in our system. Soil water content, extractable N concentrations and their interaction explained 74% of the variation in DEA. 4Our results show that the potentially large and interacting effects of different components of global change should be considered in predicting below-ground N responses of Mediterranean grasslands to future climate changes. [source] Fifteen years of climate change manipulations alter soil microbial communities in a subarctic heath ecosystemGLOBAL CHANGE BIOLOGY, Issue 1 2007RIIKKA RINNAN Abstract Soil microbial biomass in arctic heaths has been shown to be largely unaffected by treatments simulating climate change with temperature, nutrient and light manipulations. Here, we demonstrate that more than 10 years is needed for development of significant responses, and that changes in microbial biomass are accompanied with strong alterations in microbial community composition. In contrast to slight or nonsignificant responses after 5, 6 and 10 treatment years, 15 years of inorganic NPK fertilizer addition to a subarctic heath had strong effects on the microbial community and, as observed for the first time, warming and shading also led to significant responses, often in opposite direction to the fertilization responses. The effects were clearer in the top 5 cm soil than at the 5,10 cm depth. Fertilization increased microbial biomass C and more than doubled microbial biomass P compared to the non-fertilized plots. However, it only increased microbial biomass N at the 5,10 cm depth. Fertilization increased fungal biomass and the relative abundance of phospholipid fatty acid (PLFA) markers of gram-positive bacteria. Warming and shading decreased the relative abundance of fungal PLFAs, and shading also altered the composition of the bacterial community. The long time lag in responses may be associated with indirect effects of the gradual changes in the plant biomass and community composition. The contrasting responses to warming and fertilization treatments show that results from fertilizer addition may not be similar to the effects of increased nutrient mineralization and availability following climatic warming. [source] Plant and microbial N acquisition under elevated atmospheric CO2 in two mesocosm experiments with annual grassesGLOBAL CHANGE BIOLOGY, Issue 2 2005Shuijin Hu Abstract The impact of elevated CO2 on terrestrial ecosystem C balance, both in sign or magnitude, is not clear because the resulting alterations in C input, plant nutrient demand and water use efficiency often have contrasting impacts on microbial decomposition processes. One major source of uncertainty stems from the impact of elevated CO2 on N availability to plants and microbes. We examined the effects of atmospheric CO2 enrichment (ambient+370 ,mol mol,1) on plant and microbial N acquisition in two different mesocosm experiments, using model plant species of annual grasses of Avena barbata and A. fatua, respectively. The A. barbata experiment was conducted in a N-poor sandy loam and the A. fatua experiment was on a N-rich clayey loam. Plant,microbial N partitioning was examined through determining the distribution of a 15N tracer. In the A. barbata experiment, 15N tracer was introduced to a field labeling experiment in the previous year so that 15N predominantly existed in nonextractable soil pools. In the A. fatua experiment, 15N was introduced in a mineral solution [(15NH4)2SO4 solution] during the growing season of A. fatua. Results of both N budget and 15N tracer analyses indicated that elevated CO2 increased plant N acquisition from the soil. In the A. barbata experiment, elevated CO2 increased plant biomass N by ca. 10% but there was no corresponding decrease in soil extractable N, suggesting that plants might have obtained N from the nonextractable organic N pool because of enhanced microbial activity. In the A. fatua experiment, however, the CO2 -led increase in plant biomass N was statistically equal to the reduction in soil extractable N. Although atmospheric CO2 enrichment enhanced microbial biomass C under A. barbata or microbial activity (respiration) under A. fatua, it had no significant effect on microbial biomass N in either experiment. Elevated CO2 increased the colonization of A. fatua roots by arbuscular mycorrhizal fungi, which coincided with the enhancement of plant competitiveness for soluble soil N. Together, these results suggest that elevated CO2 may tighten N cycling through facilitating plant N acquisition. However, it is unknown to what degree results from these short-term microcosm experiments can be extrapolated to field conditions. Long-term studies in less-disturbed soils are needed to determine whether CO2 -enhancement of plant N acquisition can significantly relieve N limitation over plant growth in an elevated CO2 environment. [source] Microbial biomass in arable soils of Germany during the growth period of annual cropsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 6 2008Rolf Nieder Abstract Results from several field studies involving numerous measurements were used to describe the change of soil microbial biomass C (Cmic) and N (Nmic) during the growth period of annual crops (years 1988,1992, 1994, 1995) under the temperate climatic conditions of central Europe. The data were taken from our own investigations as well as from the literature. Only studies with at least eight measurements on one plot during the growth period were used. The total number of farms (cash crop,production farms) was 7, that of experimental plots was 15. The evaluation of these results through regression analysis demonstrated that Cmic and Nmic from the beginning of a year increased only slightly until summer and subsequently decreased until autumn to their initial levels. This increase on an average corresponded to a C assimilation of approx. 100,kg ha,1 and an N immobilization of approx. 20,kg ha,1 (30,cm),1. The increase in Nmic alone could not explain N immobilization rates frequently observed in different studies using 15N-labeled fertilizers. Most of the labeled N that was immobilized (>50,kg N ha,1) might have accumulated in the matrix of soil organic matter (SOM). Therefore, the changes in microbial biomass may be of less importance for changes in soil N storage as frequently assumed. [source] Responses of phosphatases and arylsulfatase in soils to liming and tillage systemsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2003Mine Ekenler Abstract This study was carried out to investigate the long-term influence of lime application and tillage systems (no-till, ridge-till, and chisel plow) on the activities of phosphatases and arylsulfatase in soils at four research sites in Iowa, USA. The activities of the following enzymes were studied: acid and alkaline phosphatases, phosphodiesterase, and arylsulfatase at their optimal pH values. With the exception of acid phosphatase, which was significantly (P < 0.001) but negatively correlated with soil pH (r ranged from ,0.65** to ,0.98***), the activities of other enzymes were significantly (P < 0.001) and positively correlated with soil pH, with r values ranging from 0.65** to 0.99*** for alkaline phosphatase, from 0.79*** to 0.97*** for phosphodiesterase, and from 0.66*** to 0.97*** for arylsulfatase. The , activity/, pH values were calculated to determine the sensitivity of each enzyme to changes in soil pH. Acid phosphatase was the most sensitive and arylsulfatase the least sensitive to changes in soil pH. Activities of the enzymes were greater in the 0 , 5,cm depth samples than those in 0 , 15,cm samples under no-till treatment. With the exception of acid phosphatase, enzyme activities were mostly significantly (P < 0.001) and positively correlated with microbial biomass C (Cmic), with r values ranging from 0.28 (not significant) to 0.83*** and with microbial biomass N (Nmic), with r values ranging from 0.31 (not significant) to 0.94***. Liming and tillage systems significantly affected the activities of some enzymes but not others, as was evident from the specific activity values (g of p -nitrophenol released kg,1 Corg h,1). Reaktionen von Phosphatasen und Arylsulfatasen in Böden auf Kalkung und differenzierte Bodenbearbeitung In vier langjährigen Feldversuchen in Iowa, USA, wurde der Einfluss von Kalkung und differenzierter Bodenbearbeitung (Direktsaatverfahren, reduzierte Bearbeitung und Grubberverfahren) auf die Aktivitäten von Phosphatasen und Arylsulfatase in Böden untersucht. Die Aktivitäten von saurer und alkalischer Phosphatase, Phosphodiesterase und Arylsulfatase wurden unter dem optimalen pH-Wert für das jeweilige Enzym bestimmt. Mit Ausnahme der sauren Phosphataseaktivität, welche signifikant negativ (P < 0.001) mit dem pH-Wert des Bodens korreliert war (r = ,0.65** bis ,0.98***), waren die Aktivitäten der anderen Enzyme signifikant (P < 0.001) positiv mit dem Boden-pH korreliert. Dabei variierten die Korrelationskoeffizienten zwischen r = 0.65** und 0.99*** für die alkalische Phosphatase, zwischen r = 0.79*** und 0.97*** für die Phosphodiesterase und zwischen r = 0.66*** und 0.97*** für die Arylsulfatase. Die Verhältnisse von , Aktivität / , pH-Wert wurden berechnet, um die Empfindlichkeit der untersuchten Enzyme gegenüber pH-Wertveränderungen im Boden festzustellen. Dabei erwies sich die saure Phosphatase als das emfindlichste und die Arylsulfatase als das am wenigsten emfindlichste Enzym. In der Direktsaatvariante waren die Enzymaktivitäten in 0 , 5,cm Bodentiefe höher als in 0 , 15,cm Tiefe. Mit Ausnahme der sauren Phosphatase waren die Enzymaktivitäten signifikant positiv mit dem mikrobiell gebundenen C (Cmik) und N (Nmik) korreliert. Die Korrelationskoeffizienten variierten dabei zwischen r = 0.28 (nicht signifikant) und 0.83*** für Cmik und zwischen r = 0.31 (nicht signifikant) und 0.94*** für Nmik. Die spezifischen Enzymaktivitäten (g p -Nitrophenol kg,1 Corg h,1) zeigten, dass die Aktivitäten von einigen Enzymen signifikant von Kalkung und Bodenbearbeitungssystem abhängig waren. [source] Effect of cropping systems on phosphatases in soilsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2003Daniel E. Dodor Abstract Phosphatases are widely distributed in nature and play a major role in phosphorus nutrition of plants. The effects of crop rotations and nitrogen fertilization on the activities of phosphatases (acid phosphatase, alkaline phosphatase, and phosphodiesterase) were studied in soils from two long-term cropping systems at the Northeast Research Center (NERC) in Nashua and the Clarion Webster Research Center (CWRC) in Kanawha, Iowa, USA. Surface soils (0,15 cm) were taken in 1996 and 1997 from replicated field plots in corn, soybeans, oats, or meadow (alfalfa) that received 0 or 180 kg N ha,1 before corn. Because of differences in organic C contents among soils of the two sites, the soils from the CWRC sites contained greater enzyme activity values than those from the NERC site. Plots under oats or meadow showed the greatest activity values, whereas those under continuous corn at the CWRC site and soybean at the NERC site showed the least activities. Analysis of variance indicated that the activities of the phosphatases were significantly affected by crop rotation (P < 0.001) in both years at the NERC site but not at the CWRC site. Nitrogen fertilization affected the activity of acid phosphatase in soils from the CWRC site in both years and alkaline phosphatase only in 1997; but it did not affect the activities of the phosphatases in the soils from the NERC site. With the exception of alkaline phosphatase (CWRC) and phosphodiesterase (NERC) in soils sampled in 1997, activities of alkaline phosphatase and phosphodiesterase were significantly correlated with microbial biomass C (C mic) in soils from both sites and years, with r values ranging from 0.366* to 0.599***. Cropping systems and N fertilization affected the specific activities of phosphomonoesterases, especially acid phosphatase, but not of phosphodiesterase. Regression analysis showed that activities of phosphatases were significantly correlated with organic C contents of soils from the NERC site but not from the CWRC site. Einfluss von Managementsystemen auf Phosphatasen in Böden Phosphatasen sind weit verbreitet in der Natur und spielen eine entscheidende Rolle in der Phosphorversorgung von Pflanzen. Die Auswirkungen von Managementsystemen und Stickstoffdüngung auf Phosphataseaktivitäten in Böden (saure und alkalische Phosphatase, Phosphodiesterase) wurden in zwei langjährigen Feldversuchen am Northeast-Research Center (NERC) in Nashua und am Clarion-Webster Research Center (CWRC) in Kanawha, Iowa, USA untersucht. In den Jahren 1996 und 1997 wurden Oberbodenproben (0,15cm) von Parzellen unter Mais, Sojabohne, Hafer und Luzerne entnommen, welche in jeweils drei Wiederholungen angelegt waren. Die Parzellen erhielten zusätzlich Düngergaben von 0 bzw. 180 kg N ha,1 , die vor Mais appliziert wurden. Infolge der unterschiedlichen Gehalte der Böden an organischem Kohlenstoff waren die Enzymaktivitäten auf den CWRC-Flächen höher als auf den NERC-Flächen. Die Parzellen unter Hafer und Luzerne wiesen die höchsten, Parzellen unter Monokulturen von Mais (CWRC) bzw. Soja (NERC) die geringsten Aktivitäten auf. Die Ergebnisse der Varianzanalyse zeigten, dass die Phosphataseaktivitäten auf den NERC-Flächen in beiden Jahren signifikant durch das Managementsystem beeinflusst wurden (P < 0, 001). Die Stickstoffdüngung hatte auf den CWRC-Flächen in beiden Jahren einen signifikanten Einfluss auf die saure Phosphataseaktivität und auf die alkalische Phosphataseaktivität im Jahr 1997. Auf den NERC-Flächen war hingegen kein Düngungseinfluss nachzuweisen. Die alkalische Phosphatase und Phosphodiesterase waren, mit Ausnahme der alkalischen Phosphatase auf den CWRC-Flächen und der Phosphodiesterase auf den NERC-Flächen, signifikant mit dem Gehalt der Böden an mikrobieller Biomasse (C mic) korreliert (r = 0, 366* bis 0, 599***). Die Management- und N-Düngungssysteme beeinflussten die spezifischen Aktivitäten von Phosphomonoesterasen, v.a. von saurer Phosphatase, jedoch nicht die spezifischen Phosphodiesteraseaktivitäten. Regressionsanalysen ergaben einen signifikanten Zusammenhang zwischen den Phosphataseaktivitäten und dem Gehalt der Böden an organischem C für die NERC-Flächen, jedoch nicht für die CWRC-Flächen. [source] | |||||||||||||