Denitrification process of Casuarina root nodule endophyte Frankia.

To examine the characteristic of denitrification in Frankia, a symbiotic nitrogen-fixing microbe associated with non-leguminous plants, and its role as a N2O source or sink, Casuarina root nodule endophyte Frankia was isolated using sectioning method, which was then purely cultured to investigate the denitrification process under NO3- addition. The results showed that after addition of NO3- to the medium under anaerobic condition, the concentration of NO3- decreased with time, while the concentrations of NO2- and N2O initially increased and then decreased over time. Key denitrification genes and nitrogenase gene were detected at 26 h, 54 h and 98 h during incubation. Abundances of these genes significantly differed among each other, and their dynamics were asynchronous. Redundancy analysis of the effect of NO3-, NO2-, N2O concentrations on abundances of denitrification genes and nitrogenase gene indicated that 81.9% of the total variation in gene abundances could be explained by the first two axes. Frankia had a denitrifying activity under anaerobic condition, with denitrification genes, including nitrous oxide reductase gene (nosZ), being identified. Our results suggested that Frankia possessed a complete denitrification pathway and the ability of N2O reduction under anaerobic condition.

[Analysis of the Traits of Nitrogen Metabolism Pathways for Several Forest Soils in Eastern China].

Nitrogen metabolism pathways mediated by microorganisms play an important role in maintaining the structure and functional stability of soil ecosystems. Clarifying the relationships between microbial communities and nitrogen metabolism pathways can expand our understanding of nitrogen metabolism pathways at a microscopic level. However, the horizontal gene transfer of microorganisms means that taxonomy-based methods cannot be easily applied. A growing number of studies have shown that functional traits affect community construction and ecosystem functions. Using methods based on functional traits to study soil microbial communities can, therefore, better characterize nitrogen metabolism pathways. Here, five typical forest soils in China, namely black soil(Harbin, Heilongjiang), dark-brown earth(Changbaishan, Jilin), yellow-brown earth(Wuhan, Hubei), red earth(Fuzhou, Fujian), and humid-thermo ferralitic soil(Ledong, Hainan), were selected to study the traits of nitrogen metabolism pathways using metagenomic technology combined with the trait-based methods. The studied nitrogen metabolism pathways were ammonia assimilation, nitrate dissimilatory reduction, nitrate assimilatory reduction, denitrification, nitrification, nitrogen fixation, and anaerobic ammonia oxidation. The results showed that bacteria dominated the metagenomic library, accounting for 98.02% of all the sequences. Across all domains, the most common pathway was ammonia assimilation. For example, an average of 2830 ammonia assimilation pathway genes were detected for every million annotated bacterial sequences. In comparison, nitrogen fixation and anaerobic ammonia oxidation were the least detected pathways, accounting for 28.3 and 10.7 per million sequences, respectively. Different microorganisms can participate in a same nitrogen metabolism pathway, and the community structure of different soils was variable. The five typical forest soils in China show the same microbial nitrogen metabolism pathway traits; however, the community structure of the microorganisms mediating these processes was found to vary.

[Effects of Feedstock Material and Pyrolysis Temperature on Dissolved Organic Matter in Biochars].

The aim of this study was to investigate the effects of feedstock material and pyrolysis temperature on the content and spectral properties of dissolved organic matter(DOM) in biochars. Biochars were produced from the pyrolysis of rice straw and Cunninghamia lanceolata litter at three temperatures(350, 500, and 650℃). The results showed that the pH values of the two biochars with pyrolysis temperature increases were improved from 8.10 and 6.56 to 10.53 and 8.23, respectively. The pyrolysis temperature had no significant effect on the total C content of biochar, but the feedstock material and their interaction had significant effects on the total C content of the biochar(P<0.05). The dissolved organic carbon(DOC) content of the two types of biochar first decreased and then increased with increasing pyrolysis temperature, and the content of DOC of the biochar derived from rice straw was significantly higher than that from Cunninghamia lanceolata litter under the same temperature(P<0.05). The feedstock material had no significant effect on the SUVA254 value of DOM, but temperature and its interactive effect with the feedstock material had a significant effect on the SUVA254 values(P<0.05). Maximum DOC SUVA254 values occurred at 500℃ in the two types of biochar, indicating the highest degree of aromatization. Three-dimensional fluorescence spectra showed that the DOM components of the two types of biochar were dominated by fulvic acid-like and humic acid-like material, which had different responses to pyrolysis temperature. FTIR spectra suggested that the DOM of the biochars had absorption peaks at similar positions, in five regions, and the stretching vibration of aliphatic C-H gradually weakened with an increase in pyrolysis temperature. Therefore, the biochars produced at higher pyrolysis temperatures(500℃ and 650℃) had lower DOC contents but a higher aromatization degree and humification degree, and were more stable, compared to the biochars produced at a lower pyrolysis temperature(350℃).

[Effects of litter removal and nitrogen addition on carbon and nitrogen in different soil fractions in a subtropical broad-leaved forest.] / å‡‹è½ç‰©åŽ»é™¤å’Œæ°®æ·»åŠ å¯¹äºšçƒ­å¸¦é˜”å¶æž—åœŸå£¤ä¸åŒç»„åˆ†ç¢³ã€æ°®çš„å½±å“.

The increasing nitrogen deposition due to human activities has impacted forest ecosystems to a large extent. The organic carbon and nitrogen released from decomposing litters play an important role in the formation, stability and transformation of soil organic carbon and nitrogen. We collected soil samples from a subtropical evergreen broadleaved forest experiment with nitrogen deposition [control (0), LN (75 kg·hm-2·a-1), HN (150 kg·hm-2·a-1)] and litter control (litter retained and litter removal) for eight years. After extracted by solution of K2SO4, Na2B4O7, Na4P2O7, NaOH, H2SO4, Na2S2O4 and HF step by step, carbon and nitrogen in each extraction was analyzed. The results showed that overall most of soil carbon and nitrogen existed in the Humin fraction, accounting for 33.5% of the total carbon and 33.3% of the total nitrogen. The soluble total carbon and nitrogen extracted by Na2B4O7 solution was the highest, followed by NaOH and Na4P2O7 solution. The soluble total carbon, soluble total nitrogen and soluble organic nitrogen of soil extracted by three reagents accounted for 46.2%, 47.9%, and 76.5% of the total extractions, respectively. In addition, nitrogen addition significantly increased carbon and nitrogen content in Na2S2O4 and Humin fractions. Litter removal reduced carbon content in Na2B4O7, H2SO4, Na2S2O4 and Humin fractions, and nitrogen content in NaOH, HF and Humin fractions. The nitrogen content in the K2SO4 extraction was significantly increased by both litter remained and nitrogen addition. Our results demonstrated that litter and nitrogen added could mutually affect carbon and nitrogen concentration of soil fractions with different chemical stability, with consequences on the process of soil carbon and nitrogen.

[Effects of biochar addition on the mineralization of native soil organic carbon in Cunninghamia lanceolata plantation.] / ç”Ÿç‰©è´¨ç‚­æ·»åŠ å¯¹æ‰æœ¨äººå·¥æž—åœŸå£¤åŽŸæœ‰æœ‰æœºç¢³çŸ¿åŒ–çš„å½±å“.

Effects of addition of different biochars on soil organic carbon (SOC) mineralization were studied by the 13C-labelling technique for a better understanding of biomass resource utilization and carbon sequestration in subtropical Chinese fir (Cunninghamia lanceolata) plantation. An incubation experiment under 25 ℃ was performed over a period of 112 days to address how different biochar addition would affect the mineralization of native SOC. Biochars were produced from Schimasuperba or C. lanceolata litter at 350, 550 and 750 ℃, respectively. Results showed that the mineralization of native SOC was significantly accelerated during the first three days and subsequently suppressed from 7 to 112 days of incubation after C. lanceolata biochar addition compared to the control. In the S. superba biochar addition treatment, there was a significant increase in mineralization of native SOC within the first 14 days of incubation and then a rapid decrease from days 28 to 112. After 112 days incubation, all the three C. lanceolata biochar (350, 550 and 750 ℃) additions significantly inhibited the mineralization of native SOC. A similar trend was observed for the two S. superba biochar (350 and 550 ℃) additions but not for the S. superba biochar (750 ℃) addition. The decomposition rates of S. superba biochar and C. lanceolata biochar were 0.8%-2.8% after 112 days incubation and decreased with the increases of pyrolysis temperature. Under the same pyrolysis temperature, the decomposition rate of the S. superba biochar was significantly higher than that of the C. lanceolata biochar. In conclusion, both the raw material and pyrolysis temperature of biochars would be important factors driving the mineralization of native SOC and biochar degradation.

[Effects of water-soluble organic matter and residue of litter on nitrogen transformation in subtropical forest soil.] / å‡‹è½ç‰©ä¸­æ°´æº¶æ€§æœ‰æœºç‰©å’Œæ®‹æ¸£å¯¹äºšçƒ­å¸¦æ£®æž—åœŸå£¤æ°®ç´ è½¬åŒ–çš„å½±å“.

An incubation experiment was carried out with the addition of litter filtrate, litter residue and alanine at 25 ℃ for 36 days under 60% and 90%WHC (water holding capacity) conditions. The results showed that alanine was rapidly mineralized in soil, and soil NH4+-N content significantly increased by 5.4%-44.7% and 16.1%-41.3%, respectively under 60% and 90%WHC conditions compared with the control. The soil net nitrogen mineralization and ammonification rates in the two treatments were also higher than those in the control at the early stage of incubation. However, the soil NH4+-N content was reduced by the addition of filtrate and residue, and the reduction degree of residue was greater. During the incubation, soil NO3--N content showed a linear increasing trend with the incubation time, and it was significantly higher under the 60%WHC condition than that under 90%WHC condition at the end of incubation. The mineralization of soil organic matter was limited by higher soil moisture. Therefore, the soil soluble organic carbon (SOC) content under 90%WHC condition was obviously lower than that under 60%WHC, but nitrous oxide (N2O) emission was 1.5-63.0 times higher than that under 60%WHC. Furthermore, N2O emission was induced significantly by the addition of litter residue under 60%WHC condition. These results indicated that there were different effects of soluble matter and litter residue on soil nitrogen transformation, and these differences would change dynamically in the decomposition process.

[Soil microbial community structure of two types of forests in the mid-subtropics of China].

Soil microbial community structures were analyzed by biomarker method of phospholipid fatty acid (PLFA) for a natural forest dominated by Castanopsis fabri (CF) and an adjacent plantation of Cunninghamia lanceolata (CL) in the mid-subtropics of China. The results showed that the amounts of total PLFAs, bacterial PLFAs, fungal PLFAs, gram-positive bacterial PLFAs and gramnegative bacterial PLFAs in the 0-10 cm soil layer were higher than in the 10-20 cm soil layer, and each type of PLFAs in CF were higher than in CL. In either soil layer of the two forest types, the contents of bacterial PLFAs were significantly higher than those of fungal PLFAs. In the two forests, the contents of bacterial PLFAs accounted for 44%-52% of total PLFAs, while the contents of fungal PLFAs just accounted for 6%-8%, indicating the bacteria were dominant in the soils of the two vegetation types. Principal component analysis showed that the influence of vegetation types was greater than soil depth on the microbial community structures. Correlation analysis showed that gram-negative bacterial PLFAs, gram-positive bacterial PLFAs and bacterial PLFAs were significantly negatively correlated with pH, positively with water content, and the PLFAs of main soil microorganism groups were significantly positively correlated with soil total nitrogen, organic carbon, C/N and ammonium.

[Effects of L-methionine on nitrification and N2O emission in subtropical forest soil].

The objective of this study was to investigate the influence of L-methionine on nitrification and nitrous oxide emission in a red soil under laboratory incubation experiments. A subtropical broad-leaved forest soil sample was collected from Wanmulin natural reserve in Fujian Province, Southeast China. Five treatments were carried out with three replications, i. e., control (CK), L- methionine addition (M), L-methionine and NH(4+)-N addition (MA), L-methionine and NO(2-)-N addition (MN), L-methionine and glucose addition (MC). The soil moisture was maintained at 60% WHC or 90% WHC. The results indicated that the soil NH(4+)-N content in the M treatment significantly increased by 0.8%-61.3%, while the soil NO(3-)-N content reduced by 13.2%-40.7% compared with CK. Under 60% WHC condition, soil NO(2-)-N content in the MC treatment was higher than in the M treatment, soil NO(3-)-N content in the MA and MN treatments were greater than that in the M treatment, and greater in the MN treatment than in the MA treatment. The soil NO(3-)-N content was lowest in the M treatment after incubation. These results suggested that L-methionine could inhibit nitrosation process of autotrophic nitrification. To some extent, carbon addition as glucose with L-methionine decreased the NH(4+)-N content, inhibited the autotrophic nitrification and their effects were dependent on water level. Under 90% WHC condition, carbon addition improved denitrification more obviously, but the decrease of NO(3-)-N content was not sufficient to prove the inhibition of hetero-nitrification due to carbon addition in the presence of L-methionine. The nitrous oxide emission from soil was increased by L-methionine addition. Compared with 60% WHC condition, the nitrous oxide emission was higher under 90% WHC condition, and the promotion of L-methionine addition on N2O was greater when glucose added.

[Organic carbon decomposition rate in different soil types].

With incubation experiment, this paper studied the decomposition rate of organic carbon in black soil, fluvo-aquic soil, and red soil. It was shown that these three soil types had significantly different decomposition rate constant of organic carbon (P < 0.05 ), with the corresponding value being 2.2 x 10(-4) x d(-1), 6.0 x 10(-4) x d(-1), and 3.4 x 10(-4) x d(-1), respectively. The decomposition rate constant had a significant correlation with soil pH, which was increased greatly when the soil pH was < 5.5 or > 8.0, and a significant negative correlation with the contents of soil clay and silt, indicating that soil clay and silt content was one of the dominant factors affecting the decomposition rate of organic carbon in these soil types.

Relationship between light and heavy fractions of organic matter for several agricultural soils in China.

Although numerous studies about the nature and turnover of soil organic matter(SOM) in light and heavy fractions(LFOM and HFOM, respectively) have been made, little information is available in relation to the relationship between LFOM and HFOM, and no attempts have been made to quantify a general relationship between LFOM and HFOM for agricultural soils under field condition. Our hypothesis is there may be an inherent relationship between LFOM and HFOM for agricultural soils under certain unaltered management practices for a long period, to this end, we therefore studied typically soils taken from different parts in China by using a simple density fractionation procedure. The results indicated that LFOM was positively correlated with LFOM/HFOM ratio for three typical soils. This information will be of particular use not only in deepening our understanding of the dynamics of SOM fractions but also in evaluating the potential of agricultural soils to sequestrate C under different management practices in a long term.