Effects Of Temperature And Soil Water Content Changes To Seed Germination And Soil Organic Matter Decomposition In Northern Slope Of Qilian Mountains

Global climate change and its impacts on earth condition are one of the greatest human environmental problems. The rapidly elevation of the temperature and precipitation is the critical issue. To find out the effects of varying soil temperature and changing water content on the germination of alpine plants and decomposition of soil organic carbon (SOC), a simulated germination test experiment and an aerobic incubation experiment with orthogonal design in an artificial climatic chamber was conducted to dispose seeds and soil. The analysis of variance, the test of significance of difference, range analysis, the first order dynamic model and so on were used to investigate how germination of alpine plants and mineralization of SOC in the northern slope of Qilian Mountains was affected by the temperature, soil water content, soil depth and altitudes. We hoped to provide more information to the further study about configuration and function of typical alpine ecosystem in the northern slope of the Tibetan Plateau. The main results are as follows:1,The soil water content was the most important factor affecting germination of Picea carassifolia and Potentilla fruticosa, a higher soil water content improved their germination capacity and index remarkably. While the response of germination of Caragana jubata to soil water content isn't significant. An acceptable elevation of temperature would benefit for germination of Picea carassifolia and Potentilla fruticosa, while lower temperature was good to improve the germination capacity and index of Caragana jubata. None of three alpine plants could germinate at 35℃. There was a sharp positive interaction between soil temperature and soil water content to the germination of Picea carassifolia and Potentilla fruticosa. A higher temperature and few soil water content restrained germination of three species.2, Soil temperature and soil water content are important factors affecting mineralization of SOC. The results showed that the effects of varying soil temperature on the cumulative SOC mineralization, mineralization rate and their ratios were the highest; next were the effects of changing the soil water content. At 1% critical level, the cumulative SOC mineralization, mineralization rate and their ratios were the highest at 35℃. At 5% critical level, the cumulative SOC mineralization, mineralization rate and their ratios in soil water content of 10% were the lowest; there was no significant difference among the different altitudes. At 10% critical level, the SOC mineralization was higher in 0～15cm soil depth than in 15～35cm soil depth, and the difference between the mineralization ratio was not significant different among different soil depths. SOC mineralization potential increased with the rising soil temperature and declined to the lowest when the soil water content fell to 10%. The rate constant of SOC mineralization was the highest in 35℃(P<0.05). Based on the rate of SOC mineralization or its ratio, Q₁₀ was 1.5～7.5 from 5℃ to 15℃, 1～2 from 15℃ to 25℃, and 1～3 from 25℃ to 35℃. The study indicated that the mineralization rate of SOC under mountain forest and alpine meadows in the Qilian Mountains would increase by 3～10 times if soil water content reached 20%～40% following the changing of temperature from 5℃to 35℃.3, Soil temperature and soil water content are the same important factors affecting soil nitrogen mineralization. In the aerobic condition, the results showed that based on the range of soil nitrogen mineralization and its ratio, the effects of interaction of soil temperature and soil water content on soil nitrogen mineralization was the highest among the effects of different factors. And the effects of soil temperature, soil water content, altitudes and soil depths on soil nitrogen mineralization was lower. At 10% critical level, the soil nitrogen mineralization was the highest at 35℃, while the soil nitrogen mineralization in soil water content of 20% was the lowest. The soil nitrogen mineralization was higher significantly in altitude of 3500m than in other altitudes; and which in 0～15cm soil depth was higher than in 15～35cm soil depth. Additionally, the effects of different factors on the ratio of soil nitrogen mineralization were all not significant at 10% critical level. Based on the rate of soil nitrogen mineralization or its ratio, Q₁₀ ranged from 0.7～2, and it was lower from 5℃ to 15℃ than which from 15℃ to 25℃ or from 25℃ to 35℃, and which was almost same from 15℃ to 25℃ and from 25℃ to 35℃.The relationship between soil nitrogen mineralization and soil temperature was analysed by leaching at intervals. The results showed that the soil nitrogen mineralization and its rate increased with soil temperature increasing. And the soil nitrogen mineralization in 0～15cm soil depth was higher than which in 15～35cm soil depth; the degressive trend of soil nitrogen mineralization rate with incubation days decreased slower significantly in low temperature than which in higher temperature. It showed that mountain forest and alpine meadows soil nitrogen mineralization in the Qilian Mountains would be affected greatly by the changing of soil temperature.4, Contrasted the results by aerobic incubation experiment with orthogonal design with which by leaching at intervals, we found they had a good coherence at the varying trend of the soil nitrogen mineralization and its rate with soil temperature. It showed that the orthogonal experimental design preferably indicated the variability collectively while limitedly about the interaction of factors.