| There are large amounts of waste such as straw and straw-lignin resulting from industrial and agricultural production in China. Although part of them has been used as feed, fuels, straw returning or graft modifying, there is still good deal of them has been discarded or burned in field. Thus, the development use of straw and lignin is getting an increasing attention nowadays. In this study, a soil incubation, a pot experiment and a mesh bag method were carried out in calcareous fluro-aquic soil and acid red soil to determine the effects of straw, lignin and biochars obtained from the pyrolysis straw and lignin on content of organic carbon, nitrogen, mineralization of soil organic carbon and response of microbial community structure. The study was aimed to assess the effects of straw, lignin and its biochar on soil organic carbon, nitrogen and microbial diversity. The results were showed as following:1. As pyrolysis temperature increased, p H, ash content, carbon stability, and total content of carbon increased while biochar yield, volatile matter, total content of hydrogen, oxygen, nitrogen and sulfur decreased. The ratios of hydrogen/carbon, oxygen/carbon and(oxygen+ nitrogen)/carbon tended to decrease with temperature. The data of scanning electron microscope image and nuclear magnetic resonance spectra indicated an increase in aromaticity and porosity of biochar produced at a high temperature. The results showed that feedstock types could also influence characteristics of the biochars but heating time did not have a significant effect on properties of biochar.2. The decomposition rate and carbon release rate of straw increased with increasing incubation time, while the C/N rate generally showed the opposite trend. In the present study, the decomposition rate of straw in fluvo-aquic soil and red soil reached 81% and 68% respectively. In addition, the decomposition curve conformed to logarithmic equation. The equation were y=14.85ln(t)-8.238(R2=0.989,P﹤0.01)(fluvo-aquic soil) and y=13.19ln(t)-18.60(R2=0.882,P﹤0.01)(red soil). There was no markedly change in the carbon release rate and the C/N rate of biochars with increasing incubation time. Compared with the initial composition of straw, the percentage of aromatic carbon increased and the ratio of O-alkyl C/alkyl C decreased after 360 days, indicating decomposition of straw. Analysis of 13 C data showed that biochars did not decomposed at less than one year. This could be explained by the fact that the recalcitrant carbons were accumulated in biochars. The decomposition rate of straw in fluvo-aquic soil was higher than that in red soil, resulting from its higher percentage of aromatic carbon and lower ratio of O-alkyl C/alkyl C when compared to that of red soil. The environmental factors could affect the process of decomposition, while the characteristic of material can be the key factor.3. There were significant differences on the CO2 emission of soil after straw, lignin and biochars added(the same amount of C). Compared with control, the emission rate and accumulative emission of CO2, mineralization intensity, metabolic quotient and microbial quotient of soil were markedly improved by application of straw or straw-lignin, while mineralized indicator was no significant difference in biochar treatments. The organic carbon mineralization intensity, metabolic quotient and microbial quotient of soil after straw added were 11 times, 5 times and 3 times as many as them of control in fluvo-aquic soil.In the first cultivation stage(30 d), all kinds of materials significantly increased the soil organic carbon. But after one year time, the organic carbon in soil with biochars applied was higher than other treatments. The dissolved organic carbon, readily oxidized organic carbon and microbial biomass carbon were significantly improved by application of straw or lignin, while there was no significant difference in biochars treatments and control. Compared with straw and lignin, biochars could enhance soil organic carbon without increasing CO2 emission of soil. Agricultural application of biochars has positive significance on fixing carbon and reducing emission of CO2.4. The accumulative emission of N2 O with straw-lignin applied were 2998 μg·kg-1 and 592 μg·kg-1 respectively, which were significant higher than other treatments. At the same treatment under the conditions of two soils, the N2 O accumulative emission of fluvo-aquic soil was higher than that in red soil. Compared with control, the nitrogen of soil was markedly improved by application of lignin, while lignin biochar only increased total nitrogen of soil. In the first cultivation stage(30 d), straw decreased NO3--N of soil, but significantly increased MBN of soil. Every kind of nitrogen of soil straw applied increased after 360 days. Straw biochr did not have a significant effect on content of soil nitrogen.5. With the increasing time, the AWCD(average well color development) tested by Biolog-Eco plate increased in every treatment. But soil and organic material had significant effects on the carbon metabolism of microorganism. The depression of AWCD could exist up to 48 h, while the increase and difference of treatments appeared at 48 h-168 h.The straw treatment showed the highest AWCD, while the lowest value was found for lignin in the whole test process. AWCD data is used to calculate microbial diversity index Shannon, Mclntosh and Simpson. Lignin could decrease the functional diversity of soil microbial community, which confirmed the decline of soil biological properties and biochemical function, despite of the high emission rate of CO2 and mineralization intensity of soil organic carbon.6. Compared with control, the total content of PLFAs(phospholipid fatty acid) in fluvo-aquic soil with straw and lignin increased by 110%( P﹤0.05) and 32%( P﹤0.05) respectively. The maximum kinds of PLFAs(58) were detected in the soil applied with straw, but the lignin had no effect on the species of PLFAs. Straw could benefit the multiplication of bacteria and fungi, while only the content of bacteria was significantly improved by lignin applied. The species and quantity of the PLFAs were no significant difference in biochars treatments. The active organic carbon(dissolved organic carbon, readily oxidized organic carbon and microbial biomass carbon) had significant effects on differentiation of soil microbial community as indicated by redundancy analysis. Effects of dissolved organic carbon, readily oxidized organic carbon and microbial biomass carbon on soil microbial community were superior to soil organic carbon. In addition, the changes of soil microbial diversity in red soil related to p H.Conclusion, the material easy to decompose contained in straw, such as soluble carbon, protein, sugar and cellulose, can be used as carbon source, nitrogen source for microbial metabolism. So straw could significantly increase soil microbial quantity and diversity, which enhance soil CO2 and N2 O release rate and accumulative emission. Lignin could increase soil CO2 and N2 O release because its solubleness in water and high content of C, N. The straw could increase the content and species of soil microorganism. Lignin promoted the part of the microbial breeding, but inhibited some microbial flora. Biochar was stronger ability against thermal degradation, chemical degradation and biodegradation than raw material, therefore biochar does not significantly affect soil microbial community structure. |
PDF Full Text Request