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The Effects of Global Climate Change on the Changes of Alpine Grassland Ecosystem and Its Carbon Emission in Head-water Region of the Yangtze River

Author: BaiZuo
Tutor: WangGenXu
School: Lanzhou University
Course: Environmental Science
Keywords: Global climate change Warming Nitrogen fertilizer Alpine meadow Swamp meadow Hydrothermal process Biomass Carbon flux Ecosystem respiration Qinghai-Tibet Plateau
CLC: S812.1
Type: PhD thesis
Year: 2011
Downloads: 231
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Abstract

The two most prominent environmental issues as global change, global warming and atmospheric nitrogen deposition has become the focus of attention in recent years. According to the IPCC predicts, the 21st century global temperature will rise by 1.5 ℃ .4.5 ℃. The same time, in the past few decades, human activities of fossil combustion, fertilizer use, and industrial emissions to the atmosphere emissions lot of nitrides, they accumulated in the atmosphere and to keep the settlement of land and water ecosystems, it is estimated that the settlement in The activity of nitrogen in terrestrial ecosystems to 43.47 Tg / a, and a sustained increase in the trend. With the intensification of global change, climate warming and increased nitrogen deposition inevitable ecosystem plant growth, physiology, population structure, function, and the carbon cycle process have a profound impact. In the high latitudes of the Northern Hemisphere, the high-altitude region, ecosystem response to global change may be more sensitive and rapid. As Eurasia highest geomorphic units, the Qinghai-Tibet Plateau because of its unique geographical location and special features of the climate system, is considered a sensitive area of ??climate change. And widely distributed in the region of alpine grassland ecosystem, the ecological environment in the plateau and alpine environment is extremely fragile and sensitive to human disturbance and global change, the response to these disturbances and changes in advance. In this study, two kinds of typical alpine grassland ecosystem in alpine meadow and swamp meadow as an object of study, the use of open-top warming chamber and artificially applied nitrogen fertilizer simulated global warming and nitrogen deposition test temperatures rise, nitrogen deposition increase their interaction on alpine grassland ecosystem biomass production, the underlying surface hydrothermal process and ecosystem respiration rate, the results are as follows: (a) different magnitude of warming on alpine grassland ecosystem change and its carbon the impact of emissions, the study found: (1) temperature rise makes alpine meadow ground, below-ground biomass increased significantly, and at the same time in the plant growing season and plant growth stage on the OTC-Mainland the underground biomass compared to the control point growth were less than the magnitude of OTC-1; the swamp meadow different ranges warming processing, above and below ground biomass compared to the control points were significantly increased, and in different seasons, and biomass with warming margin increase gradually increases. (2) As temperatures rise, both meadow activities layer shallow freeze starting time delayed melting starting ahead of time, that higher temperatures makes freeze shortened; the freeze period negative isotherms largest invasion depth and duration invasion depth and duration of that rising temperatures gradually increase as temperatures rise, making the active layer thickness increases; temperatures rise as temperatures rise and reduce the freeze period is isotherm on the freezing process and thawing process have a significant impact, the greater the variation of temperature, the slower the freezing process, and more rapid melting process. (3) the magnitude of warming conditions, alpine meadow and swamp meadow ecosystem respiration. Showed obvious single peak daily variation in different phenological phases at the same time, two meadow CO2 emission flux showed obvious seasonal variation of CO2 emission rate in each treatment in the peak of the growing season. (4) The temperature rise very significantly affect the alpine meadow ecosystem CO2 emissions, CO2 emission flux in different phenological phases, OTC-1 compared to the control point 1.4% to 22.5%, while the OTC-2 compared to the OTC- 1 29.1% to 171.7%; CO2 emission flux swamp meadow with the variation of temperature increases gradually increased, and the larger the temperature rises, the ecosystem respiration rate accelerated trend more obvious . (5) under different warming treatment conditions, between the two types of the meadow ecosystem CO2 emissions flux and environmental factors showed a good correlation. Meet the exponential relationship between CO2 emission flux and temperature, as well as 5cm ground temperature, and with between 5cm moisture is more in line with the quadratic polynomial relationships; same time, with the variation of temperature increase, both relational schema intends the aggregate goodness and significant showed a decreasing trend. But between the the swamp meadow CO2 emission flux and temperature did not exhibit such a law. (B) to simulate the impact of nitrogen deposition on alpine grassland ecosystem carbon emissions, the study found: (1) under two levels of nitrogen input processing conditions, the two types of typical alpine grassland ecosystem respiration showed a significant seasonal variation . CO2 emission fluxes from vegetation growth early May began to rise, vegetation exuberant on August peak, a gradual decline in September until the end of vegetation growth process. (2) continuous nitrogen input conditions, at various periods during the growing, the alpine meadow N5 processing within the CO2 emission fluxes greater than the control, indicating that the simulated nitrogen deposition on the role of the CO2 emission flux, but this promoting effect is more obvious early in Nitrogen, at a later stage is not obvious; swamp meadow, to simulate the impact of nitrogen deposition on ecosystem respiration very significant CO2 emission flux is always significantly greater than in the entire growing season, N5 processing control treatment, and in various periods from May to September, the CO2 emission flux differences among the treatments are very significant, did not show a trend gradually decreases as the nitrogen application time. (3) different nitrogen treatments between two typical alpine grassland ecosystem CO2 emission flux and environmental factors have shown a good correlation. Which meet the different treatment of alpine meadow CO2 emission flux and temperature as well as between 5cm ground temperature exponential model is more consistent with the quadratic polynomial relationship between 5cm water; the different handling the swamp meadow CO2 emissions flux 5cm ground temperature are in line with the exponential relationship between quadratic polynomial relations with between 5cm moisture conform, is more consistent with a linear relationship with the temperature between; nitrogen input makes the goodness of fit of the three kinds of relational schema and significant showed decreased gradually. (4) by a stepwise multiple regression analysis found that the ecosystem respiration rate changes from alpine meadow and control treatment, soil temperature and air temperature together after nitrogen, soil temperature and soil moisture flux of CO2 emissions main control factor; swamp meadow, control processing ecosystem respiration flux change comes mainly from the combined effect of soil temperature and soil moisture, temperature and soil moisture as the main controlling factor of CO2 emission flux after nitrogen. (C) With regard to the combined effects of simulated global warming and nitrogen deposition on ecosystem carbon emissions, the study found: (1) 4 different treatment (CK, N, T and NT) alpine meadow ecosystem respiration showed significant season changes characteristic peak at the same time, and the exuberant vegetation growth period (August); NT processing within the CO2 emission flux throughout the growing season is always higher than other treatments, and the control treatment (CK) within the CO2 emission flux in different seasons in other treatments, N treatment (N) and warming treatment (T) did not show obvious rule; analysis showed main effects on ecosystem respiration, temperature rise or nitrogen deposition on CO2 emissions through there is a significant amount, and the existence of a significant interaction between the two factors. Swamp meadow, four different treatments ecosystem respiration showed significant seasonal variation, and CK, N, T such changes are consistent and that the vegetation growing period gt; the regreening period of gt; brown period, its peak appeared in August, but in the NT treatment, CO2 emission flux peak in August, but the minimum was in June; the different seasons swamp meadow CO2 emission flux response to different treatment is basically the same, that the NT gt; N gt; T gt; CK; analysis showed that the main effect, rising temperatures or CO2 emission flux significant increase in nitrogen deposition and relatively significant interaction between the two factors role. (2) the combined treatment of warming and nitrogen fertilization, between the two types of typical alpine grassland ecosystem CO2 emission flux and environmental factors showed a good correlation, but compared to the other three treatments, this correlation are weaker. Where, NT treatment between CO2 emission flux and temperature as well as 5cm ground temperature are in line with the exponential model, more in line with the quadratic polynomial relationship between 5cm water, compared to the goodness of fit of the two models and significant The lower other three treatments, especially between the the swamp meadow CO2 flux and soil moisture, the goodness of fit of the regression equation is very low (R2 = 0.289), seen in the combined effects of rising temperatures and increased nitrogen deposition makes alpine grassland ecosystem CO2 emissions is more complex relationship between the flux and environmental factors. (3) Multiple stepwise regression analysis found that warming and nitrogen fertilizer joint processing conditions, changes in the alpine meadow ecosystem respiration. Mainly affected by soil temperature and moisture regulation; swamp meadow ecosystem respiration The changes are mainly derived from the combined effect of soil temperature and air temperature.

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