Effect Of Nitrogen Deposition On Soil Carbon Fractions Of Several Forest Stands In Muchuan County

The forest soil carbon reserves accounted for 45% of the terrestrial soil carbon pool, the small changes can cause significant changes in atmospheric CO2 concentration. Due to the terrestrial ecosystem carbon and nitrogen cycling processes tightly coupled, excess atmospheric nitrogen settlement will significantly influence forest ecosystem structure and function, also may change the carbon cycle process, thereby causing changes in forest soil carbon storage. Therefore, the state-owned forest farm of Muchuan County, Leshan City, Sichuan Province in the southwest of natural evergreen broadleaved forest and its artificial regeneration after formation of Sassafras tzumu, Metasequoia glyptostroboides and Cryptomeria fortunei forest, bamboo forest as the object of study of nitrogen deposition on four kinds of forest soil carbon fractions content changes. The nitrogen additions are Blank (0 kg N·hm-2·a-1), Low Nitrogen (50 kg N·hm-2·a-1), Medium Nitrogen (100 kg N·hm-2·a-1), and High Nitrogen (150 kg N·hm-2·a-1). The results as follows:(1) Within one year of the research, nitrogen deposition increased the content of soil organic carbon in natural evergreen broadleaved forest, Sassafras tzumu, Metasequoia glyptostroboides and Cryptomeria fortunei forest, but the difference was not significant (P >0.05). The effect of MN treatment on the content of SOC in natural forest soil was the strongest,1.20?2.14%. HN treatment makes Sassafras tzumu, Metasequoia glyptostroboides and Cryptomeria fortunei forests' SOC content increased the most,0.68? 1.20%,1.04?1.81% and 0.72?1.21%.(2) Within one year of the research, nitrogen deposition increased the content of soil POC in natural evergreen broadleaved forest, Sassafras tzumu, Metasequoia glyptostroboides and Cryptomeria fortunei forest,but the difference was not significant (P >0.05). The effect of HN treatment on the content of soil POC in four style of stands were the strongest,2.53?2.62%,2.40?2.53%,1.86?2.06% and 2.10?2.36%.(3) Within one year of the research,nitrogen deposition increased the content of soil LC in natural evergreen broadleaved forest, Sassafras tzumu, Metasequoia glyptostroboides and Cryptomeria fortunei forest.The active carbon content of 0?10 cm and 10?20 cm soil layer was significantly affected by nitrogen deposition (P<0.05), and the order of LC contents in all treatments was MN>HN>LN. MN treatment increased the soil LC of each stand by 2.62?2.40%,2.53?2.53%,1.86?2.06%,2.10? 2.06%.(4) Within one year of the research,nitrogen deposition increased the content of soil humus carbon, CHA and CFA in natural evergreen broadleaved forest, Sassafras tzumu, Metasequoia glyptostroboides and Cryptomeria fortunei forest, but the difference was not significant (P>0.05). The order of soil humus carbon, CHA and CFA in all treatments was HN>MN>LN. The effect of HN treatment on the content of soil humus carbon in four style of stands were the strongest,1.54%,1.65%,1.67%,2.01%; on the content of CHA in four style of stands were 1.58%,1.69%,1.72% and 2.1%; on the content of CFA in four style of stands were 1.54%,1.65%,1.67% and 2.01%. Each treatment did not significantly alter the quality of soil humus.(5) Within one year of the research, the same nitrogen deposition levels in different soil layers of the various indicators had obvious changes in the profile,0?10 cm> 10? 20 cm> 20?30 cm> 30?40 cm. Due to the addition of nitrogen, soil organic carbon content of different components had changed. MN treatment increased the total organic carbon content of natural evergreen broadleaved forest. Under the effect of HN treatment, the content of SOC in Sassafras tzumu, Metasequoia glyptostroboides and Cryptomeria fortunei forest was the highest. HN treatment had significant effects on the content of soil organic carbon, humus carbon, humic acid carbon and fulvic acid carbon. While, MN treatment on the growth of forest soil carbon is the most obvious. The content of each index in natural evergreen broadleaved forest was the highest on the same soli layer under the same nitrogen deposition treatment, then Cryptomeria fortune was the lowest. It showed that the content of the soil total organic carbon, particulate organic carbon, activated carbon, humus carbon, humic acid carbon and fulvic acid carbon in natural evergreen broadleaved forest which was be updated had declined.