[Effects of different long-term fertilization on the activities of enzymes related to carbon, nitrogen, and phosphorus cycles in a red soil].

Using a microplate fluorimetric assay method, five fertilization treatments, i.e. no-fertilizer control (CK) , sole application of nitrogen (N), balanced application of nitrogen, phosphorus, and potassium fertilizer (NPK), application of pig manure (M), and combination of pig manure with balanced chemical fertilizer (MNPK) were selected to investigate the effects of different long-term fertilization regimes on the activity of five enzymes (ß-1, 4-glucosidase, ßG; cellobiohydrolase, CBH; ß-1, 4-xylosidase, ßX; ß-1, 4-N-acetylglucosaminidase, NAG; acid phosphatase, AP) in a red soil sampled from Qiyang, Hunnan Province. The results showed that compared with CK treatment, N treatment had no impact on ßG, ßX, CBH, and NAG activities but reduced AP activity, while NPK, M and MNPK treatments increased the activities of all the five enzymes. Correlation analysis indicated that all the five enzyme activities were positively correlated with the content of nitrate (r=0.465-0.733) , the content of available phosphorus (r=0.612-0.947) , soil respiration (r=0.781-0.949) and crop yield (r=0.735-0.960), while ßG, CBH and AP were positively correlated with pH (r= 0.707-0.809), only AP was significantly correlated with dissolvable organic carbon (r = -0.480). These results suggested that the activities of the measured enzymes could be used as indicators of red soil fertility under different fertilization regimes, but the five enzymes tested provided limited information on the degree of acidification induced by application of mineral nitrogen.

[Altered microbial communities change soil respiration rates and their temperature sensitivity].

Inoculating common sterilized soil with different non-sterilized soils was used to investigate the potentials of altered microbial communities to change rate and temperature sensitivity of soil microbial respiration. Results showed that accumulative CO2 emission of sterilized Hailun black soils inoculated with non-sterilized Harbin black soil, Fengqiu fluvo-aquic soil and Qiyang red soil were 684.25, 753.97 and 644.91 microg, respectively, at 15 degrees C; were 963.06, 1 015.44 and 852.31 microg, respectively, at 25 degrees C; and were 1 252.55, 380.36 and 1 177.88 microg, respectively, at 35 degrees C. The soil accumulative CO2 emissions increased with pH of inoculant soils, but did not relate to organic content of and geographical distance from inoculant soils. Difference of microbial respiration rates among the three inoculant soils kept for 104, 277 and 1 177 h at 15 degrees C, 25 degrees C and 35 degrees C, respectively. Temperature sensitivity quotients (Q10) of microbial respiration of sterilized Hailun black soils inoculated with non-sterilized Harbin black soil, Fengqiu fluvo-aquic soil and Qiyang red soil were 1.63, 1.49 and 1.80, respectively, during 0-104 h; were 1.43, 1.39 and 1.46, respectively, during 0-277 h and were 1.35, 1.35 and 1.35, respectively, during 0-1 609 h. The Q10 decreased with pH of inoculant soils and incubation time. The results suggest that altered microbial community would change rate and temperature sensitivity of soil microbial respiration.

[Influences of long-term application of organic and inorganic fertilizers on the composition and abundance of nirS-type denitrifiers in black soil].

The objectives of this study were to explore the effects of long-term organic and inorganic fertilizations on the composition and abundance of nirS-type denitrifiers in black soil. Soil samples were collected from 4 treatments (i. e. no fertilizer treatment, CK; organic manure treatment, OM; chemical fertilizer treatment (NPK) and combination of organic and chemical fertilizers treatment (MNPK)) in Gongzhuling Long-term Fertilization Experiment Station. Composition and abundance of nirS-type denitrifiers were analyzed with terminal restriction fragment length polymorphism (T-RFLP) and real-time quantitative PCR (Q-PCR), respectively. Denitrification enzyme activity (DEA) and soil properties were also measured. Application of organic fertilizers (OM and MNPK) significantly increased the DEAs of black soil, with the DEAs in OM and MNPK being 5.92 and 6.03 times higher than that in CK treatment, respectively, whereas there was no significant difference between NPK and CK. OM and MNPK treatments increased the abundances of nirS-type denitrifiers by 2.73 and 3.83 times relative to that of CK treatment, respectively. The abundance of nirS-type denitrifiers in NPK treatment was not significantly different from that of CK. The T-RFLP analysis of nirS genes showed significant differences in community composition between organic and inorganic treatments, with the emergence of a 79 bp T-RF, a significant decrease in relative abundance of the 84 bp T-RF and a loss of the 99 bp T-RF in all organic treatments. Phylogenetic analysis indicated that the airS-type denitrifiers in the black soil were mainly composed of alpha, beta and gamma-Proteobacteria. The 79 bp-type denitrifiers inhabiting exclusively in organic treatments (OM and MNPK) were affiliated to Pseudomonadaceae in gamma-Proteobacteria and Burkholderiales in beta-Proteobacteria. The 84 bp-types were related to Burkholderiales and Rhodocyclales. Correlation analysis indicated that pH, concentrations of total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), nitrate (NO3(-) -N) and ammonia (NH4(+) -N) were significantly related to abundances of nirS-denitrifers (r = 0.724-0.922, P < 0.05) and the DEA (r = 0.453-0.938, P < 0.01). In addition, the DEAs were linearly and positively correlated with the abundances of nirS-type denitrifers (r = 0.85, P < 0.01). Redundancy analysis showed that except moisture, pH and concentrations of TP, TP, TOC, NH4(+) -N and NO3(-) -N were significantly correlated with the community structure of nirS-type denirifiers (r = 0.440-0.862, P < 0.01). Furthermore, the DEAs were significantly correlated with the compositions of nirS-denirifiers (r = 0.863, P < 0.01). In conclusion, the airS-type denitrifiers in the black soil are more responsive to the organic treatments than to the inorganic treatments in terms of community composition and abundance, both of which are correlated with the changes of DEAs.

[Effects of different long-term fertilizations on community properties and functions of methanotrophs in dark brown soil].

The microbial mechanisms of how different long-term fertilizations change methane oxidation of Chinese upland arable soil is unclear so far. In the present study, we attempted to investigate the "soil properties-community properties of methanotrophs-methane oxidation" relation of dark brown soil in Northeastern China under different long-term fertilization regimes. Community structure and abundance were monitored with PCR-DGGE and real time PCR, respectively. Methane oxidizing rate and soil properties were measured as well. The results show that combined use of mineral fertilizer and compost (MNP) reduce soil methane oxidation by 61.2%, whereas either mineral fertilizer (NP) or compost (M) shows no effect. Comparing with no fertilizer (CK), M and MNP increase the Shannon index of methanotrophs by 91.9% and 102.5%, respectively, whereas NP has no effect. Similarly, M ( M or MNP) significantly increases pmoA gene abundance by up to 12.7 folds compared with no M addition (CK or NP). Methane oxidizing rates are significantly correlated with community structure and specific activity of methanotrophs, with correlation coefficients of 0.363 and 0.684, respectively. However, methane oxidizing rates do not correlate with abundance and diversity of methanotrophs. In addition, community structures and specific activity of methanotrophs are significantly correlated with soil pH and content of total nitrogen and organic matter. Our results suggest that long-term different fertilizations may change soil properties (such as pH and content of total nitrogen and organic matter) and thereafter the community structure and specific activity of soil methanotrophs, by which long-term different fertilizations influence soil methane oxidizing rate. The opposite change of methane oxidation to methanotrophs diversity and abundance in MNP suggests that only parts of the methanotrophs are active, which needs further research.