Effect of Replacement of Headspace Gas on N_2O and CO_2Emissions in Anaerobic Incubation of Soil

To study effect of C2H2 and change of headspace gas on N2O emission, denitrification, as well as CO2emission, slumes of an agricultural soil were anaerobically incubated for 7 da3’s at 25 ℃. Both N2O reduction and CO2 emissions were inhibited by the addition of 100 mL L-1 of C2H2. However, the inhibition to CO2 emission was alleviated by the replacement of headspace gas, and the N2O emission was enhanced by the replacement. Acetylene disappeared evidently from the soil slumes during the incubation. Consequently results obtained from the traditional C2H2 blocking technique for determination of denitrification rate, especially in a long-time incubation, should be explained with care because of its side effect existing in the incubation environments without change of headspace gas. To reduce the possible side effect on the processes other than denitrification, it is suggested that headspace gas should be replaced several times during a long-time incubation.

Dissimilatory Fe(Ⅲ) reduction characteristics of paddy soil extract cultures treated with glucose or fatty acids

Dissimilatory Fe(Ⅲ) reduction is a universal process with irreplaceable biological and environmental importance in anoxic environments. Our knowledge about Fe(Ⅲ) reduction predominantly comes from pure cultures of dissimilatory Fe(Ⅲ) reducing bacteria (DFRB). The objective of this study was to compare the effects of glucose and a selection of short organic acids (citrate, succinate, pyruvate, propionate, acetate, and formate) on Fe(Ⅲ) reduction via the anaerobic culture of three paddy soil solutions with Fe...

N Mineralization as Affected by Long-Term N Fertilization and Its Relationship with Crop N Uptake

A field experiment established in 1997 was conducted to study the effect of long-term N fertilizer application on N mineralization in a paddy soil determined using a laboratory anaerobic incubation followed with a field incubation and to measure the relationship between in situ N mineralization and crop N uptake. To estimate N mineralization in the laboratory, soil samples were collected from plots with N application at different rates for six years and were incubated. Soils treated with fertilizer N mineralized more N than unfertilized soils and mineralization increased with N application rates. Also, the fraction of total N mineralized increased with increasing N fertilizer application. These findings meant that a substantial portion of previously applied N could be recovered slowly over time in subsequent crops. The field incubation of the plot receiving no fertilizer N showed that the NH4^＋-N concentration varied greatly during the rice-growing season and seasonal changes of N mineralization were due more to accumulation of NH4^＋-N than NO3^-N. Hice N uptake increased up to a maximum of 82 kg N ha^-1 during the season. The close agreement found between in situ N mineralization and rice N uptake suggested that the measurement of in situ N mineralization could provide useful recommendations for adequate fertilizer N application.

Modeling Nitrogen Mineralization in Paddy Soils of Shanghai Region

Six paddy soils of Shanghai, China, were studied after 120 days of anaerobicincubation at 25 deg C and 35 deg C. Four models, the effective accumulated temperature model, theone-component first-order exponential model (the one-pool model), the two-component first-orderexponential model (the two-pool model), and the two-component first-order plus zero-orderexponential model including a constant term (the special model), were fitted to the data of observedmineral-N during incubation using non-linear regression procedures. The two-pool model and thespecial model gave the best fits amongst the four models, and parameters in the special model weremore reasonable than those in the other three. Results showed that the special model gave a betterprediction of nitrogen mineralization under flooded conditions than the other three models.

Degradation of black tea theaflavin through C-ring cleavage by gut microbiota

Increasing evidence has shown that gut microbiota plays important roles in metabolizing large molecular polyphenols to bioavailable and bioactive microbial metabolites.Theaflavin(TF)is one of the major color compounds in black tea and has demonstrated anti-inflammation,antioxidant,and anticancer effects properties.However,little is known about the metabolism of TF by gut microbiota in vivo.In this study,following the administration of TF to mice,the C-ring cleavage metabolites,dihydro-and tetrahydro-theaflavin(DH-TF and TH-TF)were detected in mouse feces by LC-MS and validated by authentic standards from in situ chemical reaction.The observation of the C-ring cleavage metabolites in TF-treated conventionalized mice but not in germ-free(GF)mice confirmed the role of gut microbiota in cleaving the C-rings of TF.The detection of DH-TF from the anaerobic incubation of TF with catechin-converting gut bacteria,Eggerthella lenta(Eggerth),suggested that the microbes with the capacity to cleave the C-ring of catechins were able to metabolize TF following the same mechanism.Additionally,three small phenolic metabolites were detected in mouse feces,and one of them was primarily detected in SPF mice not GF mice,which revealed that TF,subsequent to the cleaved C-ring,can be further metabolized into smaller phenolic metabolites by gut microbiota.Dose-dependent production of these metabolites were observed from the administration of 100 mg/kg to 400 mg/kg body weight of TF.In conclusion,gut microbiota can metabolize TF to the open-ring metabolites and the phenolic metabolites through the C-ring cleavage in mice.

Role of Amorphous Manganese Oxide in Nitrogen Loss

Studies have been made, by 15N-tracer technique on nitrogen loss resulting from adding amorphous manganese oxide to NH4+-N medium under anaerobic conditions. The fact that the total nitrogen recovery was decreased and that 15NO2, 15N2O, 15N14NO, 15NO, 15N2and 15N14N were emitted has proved that, like amorphous iron oxide, amorphous manganese oxide can also act as an electron acceptor in the oxidation of NH4+-N under anaerobic conditions and give rise to nitrogen loss. This once again illustrates another mechanism by which the loss of ammonium nitrogen in paddy soils is brought about by amorphous iron and manganese oxides. The quantity of nitrogen loss by amorphous manganese oxide increased with an increase in the amount of amorphous manganese oxide added and lessened with time of its aging. The nitrogen loss resulting from amorphous manganese oxide was less than that from amorphous iron oxide. And the nitrogen loss by cooperation of amorphous manganese oxide and microorganisms (soil suspension ) was larger than that by amorphous manganese oxide alone. In the system, nitrogen loss was associated with the specific surface area and oxidation-reduction of amorphous manganese oxide. However, their quantitative relationship and the exact reaction processes of nitrogen loss induced by amorphous manganese oxide remain to be further studied.