Effect Of Nitrogen Fertilization Of Soil Respiration In Cinnamomum Camphora Plantation

Since the industrial revolution, a large number of emissions of active nitrogen during nitrogen fertilization, fuel consumption and biomass burning cause the increase of active nitrogen in the air through atmospheric dry and wet deposition. Human activity had caused the global terrestrial ecosystem nitrogen input increased3to5times since last century, which had significantly increased soil nitrogen input in the terrestrial ecosystem, with the serious influence of the global nitrogen cycle. And the more serious reality is that reactive nitrogen emissions caused by human activity will continue to increase in the future, and lead to higher terrestrial input of nitrogen, and this process has an important impact on the global carbon cycle. Atmospheric nitrogen input on terrestrial ecosystem in subtropical area, south China is at high levels, so the study on the influence of high nitrogen input to subtropical forest soil respiration and other carbon cycles are very urgent. Cinnamomum camphora is the typical subtropical evergreen broad-leaved forest in Subtropical area, south China and distributes widely in south China. We studied the soil respiration in subtropical Cinnamomum camphora plantation under experiment of fixed position N application with the treatments of Control (CK, no nitrogen fertilization), low nitrogen (LN,50kg N·hm-2·yr-1), medium nitrogen (MN,150kg N·hm-2·yr-1) and high nitrogen(HN,300kg N·hm-2·yr-1). The main conclusions are as follow:(1) There were obvious seasonal patterns of total litter amount and monthly litter amount, and the seasonal dynamic was not changed with nitrogen fertilization, but can significantly change the monthly litter amount. The annual litter amount in Cinnamomum camphora forest with the treatment of nitrogen fertilization less than in control, and there was significant inhibition effect on litter amount with LN and MN nitrogen addition treatments of litter decomposition residual rate is lower than the contrast, differences were not significant, showed that nitrogen treatment for decomposition of forest litter branch there is a certain degree of inhibition. Litter decomposition of branches with the treatment of nitrogen fertilization less than control, but there was no significant difference. This could indicate that there was inbibitional effect of nitrogen fertilization on Litter decomposition of branches in Cinnamomum camphora forest. The residual rate of litter decomposition of leaf decreased with the increase of nitrogen application, but there was no significant difference of litter decomposition of leaf at all levels of nitrogen, which showed that nitrogen fertilization had inhibition effect on litter decomposition of leaf in Cinnamomum camphora forest. The nitrogen content of litter obviously stimulated with the treatment of nitrogen fertilization but little impact on the carbon content. There was significant improvement of nitrogen content of litter with the treatment of LN and MN, but there was slight inhibition with HN. It showed similar effect on carbon content with nitrogen content with the treatment of nitrogen fertilization, but there was no significant difference in all the treatments. Nitrogen fertilization could significantly inhibit the C/N in litter of branch, but little effect on litter of leaf. The treatment of nitrogen fertilization changed litter productivity and elements content of litter and then changed the amount of elements returned. Nitrogen fertilization reduced the amount of carbon returned and added the amount of nitrogen returned.(2)At the beginning of nitrogen fertilization, the inhibitory effect on soil microbial biomass was observed; the inhibition effect was only embodied in LN, and minor inhibition with the treatment of MN. There was significantly inhibitory effect on the amount of carbon in Cinnamomum camphora forest with nitrogen fertilization. The amount of nitrogen had significantly increased than control, but there was a significant reduction in in the second year than in the first year with the treatment of nitrogen fertilization. Nitrogen fertilization could significantly inhibit the C/N of soil microbial biomass, and there was a significant linear correlation between soil respiration rate and soil respiration. The treatment of LN and MN could increase diversity of soil microorganism. Fine root biomass in sample plot with nitrogen fertilization lower than control, but with no obvious difference between them.(3)The ammonium nitrogen content in Cinnamomum camphora forest soil significantly reduced with the treatment of nitrogen fertilization, but the ammonium nitrogen content with the treatment of HN higher than the treatment of LN and MN, the ammonium nitrogen content increased with the amount of nitrogen fertilization. The nitric nitrogen content could increase with the treatment of nitrogen fertilization, and the relation between them showed positive correlation. The available nitrogen content in forest soil could decrease with the treatment of nitrogen fertilization. At annual level soil nitrification rate and ammonification rate would increase with nitrogen fertilization, and increasing extent increased with nitrogen fertilization. At all levels of nitrogen fertilization, there were promoting effects on the ammonium nitrogen content in soil with the treatment of litter addition and litter removal, and the promoting effects increased with the level of Nitrogen fertilization. The ammonium nitrogen content in soil was higher with the treatment of litter addition than litter removal at all levels of Nitrogen fertilization. The nitrate nitrogen content in soil with the treatment of litter addition and litter removal were higher than control at all levels of nitrogen fertilization(except the treatment of HN), and there was no obvious difference among controls. The effective nitrogen content in Cinnamomum camphora forest soil could increase with the promotion of the treatment of litter addition and litter removal, and the promoting effects increased with the treatment of nitrogen fertilization.(4)Soil respiration in Cinnamomum camphora forest showed obvious seasonal variation with higher value in summer and lower value in winter, and the soil respiration of sample plot with nitrogen fertilization was similar to the control. The treatments of nitrogen fertilization could suppress the soil respiration of the forest, and the annual CO2release amount in Cinnamomum camphora forest is4.09×104kg·hm-2. The annual cumulant of soil respiration with the treatment of LN、MN、HN were2.55×104kg·hm-2、2.84×104kg·hm-2and2.50×104kg·hm-2, relatively, and a lower compared with control were37.66%、30.62%and38.95%relatively. The annual cumulant of soil respiration had no significant differences with different treatment. The comparison of the two growing seasons shows a weaken inhibition effects of nitrogen fertilization on soil respiration. The change of soil moisture is mainly dominated by rainfall, mainly caused by rainfall. The relationship between soil respiration rate and soil temperature at5cm with different litter treatment was significant. Soil temperature at5cm explained the49.39%-51.98%of soil respiration rate. There was no significant impact between soilmoisture and soil respiration, but there is significant correlation between soil respiration and soil moisture with the treatment of LN, and the correlation coefficient is very low. Low nitrogen and high nitrogen has little effect on soil Q10values, but the treatment of medium nitrogen had significantly inhibited effect on soil respiration Q10values.(5) There was significant seasonal dynamic of soil respiration with litter treatment. There was inbibitional effect on soil respiration at different nitrogen application level with the treatment of litter, and the effect decreased with the increase of nitrogen application. The treatment of litter removal can significantly decrease the soil respiration rate at natural condition, but nitrogen fertilization can promote soil respiration with the increase of nitrogen gradient. The difference of soil respiration caused by the treatment of litter addition and litter removal mainly reflected in apparent of plants (April to October).There was significant difference in soil respiration with different treatment of litter at that time. There was significant seasonal variation of soil temperature with the treatment of litter removal and addition. But the treatment of litter had no significant effect on soil temperature. Litter addition increased soil moisture and litter removal decreased soil moisture, and with the increase of nitrogen, soil moisture showed a trend of increase. The relationship between soil respiration rate and soil temperature at5cm with different litter treatment was significant with the treatment of litter removal and litter doubled. Soil temperature can explain the47.76%-72.61%of soil respiration rate.(6)Litter addition increased the contribution rate of litter on soil respiration. With the increase of nitrogen, the treatment of litter addition on soil respiration contribution rate also increased. Soil respiration Q10with litter addition were higher than with litter removal and controls at different nitrogen levels. Naturally, the treatment of litter removal could reduce the soil respiration, but the treatment of litter removal instead promoted litter respiration with nitrogen treatment. There was a clear seasonal variation on soil respiration with the treatment of root removing. There was still inbibitional effect of nitrogen fertilization on soil respiration with root removing, but the effect deceased with the increase of nitrogen. There was little effect on soil temperature in Cinnamomum camphora forest with root removing, but there was significantly reduction on soil moisture at5cm with root removing. There was a significant exponential correlation between soil respiration rate and soil temperature at5cm with root removing. Soil temperature can explain the47.76%-58.54%of soil respiration rate. There was no coherency between soil moisture and soil respiration with root removing at different level of nitrogen.