Soil Respiration, Soil Carbon And Its Response To Simulated Nitrogen Deposition In After Clear-cutting Cryptomeria Fortunei Forest

The whole world changes warm (especially CO₂ density's ascension) and the nitrogen deposition's increasing induces a series significant environment problems, which includes threat the human survival and development directly, so it has become to the global significant ecology and environment problems which arouse the many countries' government and scientists to pay attention. China has become to the second greenhouse gas emissions country in the world, if cannot solve "the Kyoto Protocol" (Kyoto Protocol)'s pivotal points, which about the carbon's reducing and increasing collection. It will possibly fall into the future global environment negotiations. China is the largest area of the plantation in the world, not only to improve our country's ecological environment condition to play the vital role, moreover has also displayed the positive role to in fixing atmospheric CO₂. The plantation's carbon collect function is considered the one kind of possibility mechanism and the most hopeful choice to solve the global climate change, so it becomes the global change slow-down's core content. Therefore, this paper choose the West China's artificial cryptomeria forest, which was cut down, investigate the soil respiration and the soil organic carbon's change after simulated nitrogen deposition, and collect the function of artificial forest carbon to provide the foundation data, for raising the theory basis in artificial forest management. The results shows that:(1)After the artificial cryptomeria forest was cut down for one year, the difference of the four seasons' soil organic carbon stocks is not remarkable, and they respectively is 187.2±6.8 tC/hm², 193.3±7.4 tC/hm², 177.4±8.6 tC/hm² and 183.6±5.8 tC/hm², with the comparison (spring, summer, fall, winter) compares the difference is not remarkable too. But After the artificial cryptomeria forest was cut down for one year the, total soil organic carbon stocks is 185.4±6.6 tC/hm², compared to CK1 is reduced 20.97 tC/hm² by obviously(p<0.05). The efforts of cutting to the artificial cryptomeria forest is mainly displays in the 0-20cm soil layer, compare with the comparison, the two in this soil difference is remarkable (p<0.05), but influence of the soil layer organic carbon stocks is not obvious to 20cm below. Overall, clearing-cut can cause the artificial cryptomeria forest to reduce soil organic carbon stocks in the management initial period by obviously.(2)After the artificial cryptomeria forest was cut down for one year, the soil respiration's diurnal variation presents single apex curve in each season, the maximum appears in the high noon's 12:00-14:00, and the minimum value appears in the early morning's 8:00 or the evening's 18:00, also the soil respiration's diurnal variation is higher than CK1 in four seasons. The single factor mode) to carry on the fitting demonstration for the CK2 and CK1's soil respiration, it shows that the 5cm soil temperature could explain 72%⁸6.6% in cut forest (CK2) and comparison (CK1). But the soil water content has not remarkable relevance for cut forest (CK2) and comparison (CK1). Obviously, cutting could promote the artificial cryptomeria forest's soil respiration, also the 5cm soil temperature becomes main factor in the artificial cryptomeria forest's soil respiration, which was cut down.(3)After the artificial cryptomeria forest was cut down for one year, under the different level nitrogen deposition the soil total average organic carbon stocks is difference obviously(P<0.05), the change tendency is reducing gradually along with the nitrogen deposition level's ascension. Respectively they are LN:147.0±9.46 tC/hm², MN:135.9±4.16 tC/hm², HN: 121.6±8.69 tC/hm². Comparing with the none nitrogen deposition's cut forest (CK2), they have been reduced 38.4 tC/hm², 49.5 tC/hm² and 63.8 tC/hm². Furthermore the LN, MN, HN and CK2's soil total average organic carbon stocks has remarkable difference(P<0.05). After cutting the artificial cryptomeria forest's soil organic carbon stocks to response the three kind level of nitrogen deposition is: the LN gradually be low from the spring to summer, rises to the highest in the autumn and enter the winter once more to approach in execute nitrogen initial period like the spring's level. The MN and HN's processing on the clearing-cut forest, the condition is that soil organic carbon stocks in spring is low, with the passage of time, increase in the summer, and from autumn into winter's change is the spring to summer's repetition. Overall, the nitrogen deposition could lead the artificial cryptomeria forest, which has been cut down by one year, the soil carbon stocks "losing". Furthermore, after the artificial cryptomeria forest was cut down for one year, when the soil receives the moderate and higher nitrogen input, the resoult is release to enrichment's cycle in all responsing.(4)After the artificial cryptomeria forest was cut down for one year, under the different level nitrogen deposition the soil respiration's diurnal variation presents single apex curve in each season, the maximum appears in the high noon's 12:00-14:00, and the minimum value appears in the early morning's 8:00 or the evening's 18:00. The single factor model to carry on the fitting demonstration for the different nitrogen depositon(LN, MN, HN) clearing-cut forest, it shows that the 5cm soil temperature could explain 66%～90.4%. But the soil water content has not remarkable relevance for LN, MN and HN. Cryptomeria plantation forest after clear-cutting on three levels of soil respiration in response to nitrogen deposition respectively expressed as: nitrogen deposition to deal with 3-5 months (spring), only inorganic nitrogen concentrations≥100 Kg N/hm²Â·a nitrogen inputing can gradual promotion of soil respiration, and low nitrogen(50 Kg N/hm²Â·a) in the input stage has no significant effect on soil respiration. Nitrogen deposition to deal with 6-8 months (summer) to 9 months (autumn), the concentration of inorganic nitrogen>50 Kg N/hm2·a nitrogen, which enter the soil, began to curb the trend of CO₂ emissions, and emissions of CO₂ from the soil is close to the CK2 level. To deal with nitrogen deposition by 11 months after (winter), the soil respiration rate range to meet the minimum, and were lower than CK2, three levels of nitrogen input have shown to reduce the response of soil CO₂ emissions. Overall, forest clear-cutting on soil respiration in response of nitrogen deposition shows that in the early time the nitrogen deposition can promote soil CO₂ emissions, at later it has a gradual inhibition of soil respiration rate, and ultimately to reduce CO₂ emissions from soil.