Effect Of Fertilization Practice On The Constitution And Bioavailability Of Dissolved Organic Carbon In Red Paddy Soil

Dissolved organic carbon is considered to be an important chemical component of terrestrial ecosystem, which not only affects the structure and function of soil organism community but also plays a key role in the global carbon cycling. This thesis focused on investigating the effects of different fertilization practices on soil dissolved organic carbon (DOC) by collecting soil from different long-term fertilization practices including four organic fertilization treatments:the single application of green manure with annual application rate of 22500 kg·hm-2 (G), application of pig manure compost at rate of 22500 kg·hm-2 on the basis of G(GC), application of winter cover straw at 4500 kg·hm-2 on the basis of GC (GCS), on the basis of G with additional winter cover straw at 4500 kg·hm-2 (GS), and including chemical fertilizer (IF), taking no fertilizer as control(CK). Through comprehensively characterizing DOC in soil collected from the above six treatments, we tried to explore:(1) effects of fertilization practice on DOC derivate from different aggregate structure; (2) effects of fertilization practice and soil aggregate structure on biological stability of DOC in paddy soil; (3) carbon sources utilization capability of soil microbial communities under different fertilization practice; (4) the mechanism of microorganisms selective utilization for substrates contributing to soil organic carbon stability. The thesis will be helpful for understanding the effects of different fertilization practice on constitution and bioavailability of DOC in paddy soil and have important implications for understanding the mechanisms of soil organic carbon sequestration. The main results were as follows:(1) Different fertilization treatments significantly affected DOC concentration in soil of different aggregate structure. Compared to chemical fertilizer (IF) treatment, the organic fertilizer treatments greatly increased the DOC concentration in soil and showed significant interactions with soil aggregation structure. Concentration of soil dissolved organic carbon was much higher in soil of inter-microaggregate within large macroaggregate than in soil of other aggregates. The organic fertilization also exerted significant effects on DOC components in soil and concentrations of all components showed similar responses with total DOC concentration except HON. Although the composition of DOC depended on organic fertilization and soil aggregation structure, HOA and HIA were the main components of DOC in all treatments.(2) The effect of fertilization on biodegradable DOC was significantly, biodegradable of DOC in chemical fertilizer treatment was more effectively, biodegradable of DOC under control treatment and winter cover rice straw were less effectively. DOC of different organic fertilization biodegradable had different effects.DOC of winter cover straw treatment reduces biodegradability of DOC, pig manure treatment enhanced the biodegradability of DOC. Different aggregate structure position effected biodegradability of DOC, biodegradable of DOC was less effectively in microaggregates than inter-microaggregate within macroaggregate, suggesting that the biological stability of microaggregate protection DOC had stronger. Microaggregate biodegradability and carboxylic acids compounds DOC aggregates were similar, large aggregates of DOC biodegradability of carbohydrates compounds were similar. The results showed that, under long-term different fertilization measures, properties of soil organic carbon was changed, and in a different position on the physical structure were also different, reflecting the differences of soil organic carbon biological stability.(3) Research utilization ability of soil microbial communities could reflect stability of organic carbon. Three different methods were used to study effects of fertilization practice on utilization ability of soil microbial communities, especially bacterial and fungal communities, for carbon source. The results showed that soil microbial communities under different fertilization treatments differed in their ability for utilizing carbon source. The treatment of green manure+pig manure+straw processing (GCS) showed the most beneficial effects on utilization ability of soil microbial community for carbon source. Besides, soil microbial community showed better ability to utilize soil carbon source in winter cover straw treatment than in pig manure treatment, while lowest utilization was observed in control treatment (CK). The results of principal component analysis also indicated the differences in ability of microbial community for utilizing soil carbon source in different organic fertilization treatments. Carbohydrate was the main substrate which was utilized by microorganisms and the organic fertilizers improved the utilization of microbial community for amino acids. Fungal community showed better utilization for carbon sources than bacterial community, and the effects of organic fertilizer practice on utilization ability were more significant for fungal community than bacterial community. The utilization capacity of fungal community for soil carbon sources was higher in organic fertilizer treatments than in chemical fertilizer and control treatments.(4) Application of organic fertilizers promoted ability of soil microbial community for utilizing glucose, cellulose and lignin, and different organic fertilizers varied in their effects. Winter cover straw treatment significantly increased the ability of fungal communities to utilize glucose-cellulose, while pig manure increased utilization of glucose-lignin with bacterial commnunities. Different with the bacterial community, fungal community showed the best utilization of glucose-lignin in green manure treatment and control treatment. Our results indicated that microorganisms tended to show prefered utilization for the labile carbon sources. The addition of glucose had no effect on cellulose but showed stress effects on lignin.To conclude, fertilization practice significantly affected concentrations of DOC in red paddy soil. Organic fertilizers increased the concentration of DOC, depending on soil aggregate structure. The application of organic fertilizers increased the concentration of DOC in soil of large aggregates, while reduced the DOC concentration in soil of micro aggregates.Fertilization practice and soil aggregate structure also greatly affect composition of DOC. Biological stability and chemical properties of DOC were associated with each other. Carbohydrates are the main group of substrates utilized by microorganisms. The application of organic fertilizer increased the utilization of microbial community for amino acids. Bacterial and fungal microbial communities differed in their utilization ability for substrates.