【摘要】：工業(yè)革命以來,人類活動(dòng)已經(jīng)改變了全球氣候變化。在干旱、半干旱草地系統(tǒng)中,生產(chǎn)力隨降雨和氮沉降的增加而增加。同時(shí),預(yù)期的CO2增加和全球變暖也會(huì)導(dǎo)致半干旱草地生態(tài)系統(tǒng)生產(chǎn)力提高,因此將會(huì)有更多的凋落物進(jìn)入土壤。凋落物的增加可通過直接影響土壤微環(huán)境和有機(jī)物的輸入,或間接影響微生物活動(dòng),進(jìn)而影響生物化學(xué)循環(huán)過程。草地占全球陸地面積的25%,是全球重要的生態(tài)系統(tǒng)之一。同時(shí),草地生態(tài)系統(tǒng)極易受全球氣候變化的影響。然而,凋落物的積累如何影響草地生態(tài)系統(tǒng)對增雨和氮沉降的響應(yīng)尚不清楚。2013-2015年,在內(nèi)蒙羊草草地上進(jìn)行3年的水、氮和凋落物添加實(shí)驗(yàn),通過對羊草草地群落生產(chǎn)力和資源利用效率、群落結(jié)構(gòu)和土壤碳氮固持,及優(yōu)勢種羊草的養(yǎng)分利用策略進(jìn)行探討,目的闡明水和氮添加對羊草草地的影響機(jī)制,及水限制解除條件下,氮和凋落物對羊草草地植被變化的影響。主要結(jié)果如下：(1)水、氮和凋落物添加顯著增加了地上地下初級(jí)生產(chǎn)力。水、氮和凋落物添加主要通過影響了土壤水分、溫度、土壤無機(jī)氮含量和容重,影響了植物的水分利用效率和氮吸收,最終增加了羊草草地生產(chǎn)力。此外,水促進(jìn)了地下初級(jí)生產(chǎn)力對凋落物的響應(yīng)。水分添加促進(jìn)了優(yōu)勢種羊草的莖葉比,氮和凋落物添加降低了其比葉面積,影響了植物對光的捕獲能力和光合作用。(2)水、氮和凋落物添加增加了禾草高度,減少了到達(dá)地面的光合有效輻射,降低了群落底層闊葉草的多度,降低了物種多樣性。此外,少量凋落物添加不影響群落多樣性,而凋落物累積到一定量會(huì)在土壤表面形成物理阻隔,降低種子的萌發(fā)和種苗的建植。(3)水分添加促進(jìn)了土壤有機(jī)碳含量,對土壤全氮無顯著影響,進(jìn)而提高了土壤的碳氮比。氮添加對土壤有機(jī)碳和全氮無顯著影響。水促進(jìn)了凋落物對土壤有機(jī)碳的固持作用。水、氮和凋落物添加不同程度的影響了微生物量和微生物群落結(jié)構(gòu)。(4)水分添加引起的“稀釋效應(yīng)”,降低了羊草成熟莖和葉中的氮磷含量,進(jìn)而提高了莖的磷重吸收能力。而氮和凋落物添加都促進(jìn)了植物對氮磷的吸收,進(jìn)而降低了羊草莖葉的氮磷吸收能力,但僅氮添加降低了莖和葉的重吸收效率,凋落物對氮磷重吸收效率無影響。綜上所述,本研究工作表明,在中國北方溫帶典型草原,水、氮和凋落物影響了羊草草地生產(chǎn)力、多樣性、土壤碳氮固持,及優(yōu)勢種的養(yǎng)分利用策略。水是影響植被變化的主要因素,氮是影響群落植被變化的第二重要因素,凋落物對植被的影響隨水、氮的變化而變化。在全球氣候變化下,要充分考慮生態(tài)系統(tǒng)的復(fù)雜性,水、氮和凋落物是影響生態(tài)系統(tǒng)的重要因子。
[Abstract]:Since the Industrial Revolution, human activity has changed global climate change. In arid and semi-arid grassland systems, productivity increases with the increase of rainfall and nitrogen deposition. At the same time, the expected increase in CO2 and global warming will also lead to higher productivity of semi-arid grassland ecosystems, so more litter will enter the soil. The increase of litter can directly affect soil microenvironment and organic matter input, or indirectly affect microbial activities, and then affect the biochemical cycle process. Grassland accounts for 25% of the world's land area, and is one of the most important ecosystems in the world. At the same time, grassland ecosystems are vulnerable to global climate change. However, it is not clear how the accumulation of litter affects the response of grassland ecosystem to precipitation and nitrogen deposition. From 2013 to 2015, three years of water, nitrogen and litter supplementation experiments were conducted on Leymus chinensis grassland in Inner Mongolia. In order to elucidate the influence mechanism of water and nitrogen supplementation, the productivity and resource utilization efficiency, community structure, soil carbon and nitrogen sequestration, and nutrient utilization strategies of dominant herbage were discussed in this paper. And the effects of nitrogen and litter on the vegetation change of Aegilops chinensis under the condition of water restriction release. The main results were as follows: (1) addition of water, nitrogen and litter significantly increased primary productivity. Water, nitrogen and litter addition affected the soil moisture, temperature, soil inorganic nitrogen content and bulk density, water use efficiency and nitrogen absorption of plants, and finally increased the productivity of grassland. In addition, water promotes the response of underground primary productivity to litter. Water supplementation promoted the ratio of stem to leaf, nitrogen and litter decreased the specific leaf area, and affected the light capture ability and photosynthesis of plants. (2) Water, nitrogen and litter increased the height of grasses. The photosynthetic effective radiation to the ground was reduced, the abundance of broadleaved grass in the bottom layer of the community was reduced, and the species diversity was reduced. In addition, a small amount of litter addition did not affect community diversity, but the accumulation of litter in a certain amount would form physical barriers on the soil surface, reducing seed germination and seedling establishment. (3) soil organic carbon content was promoted by water addition. There was no significant effect on soil total nitrogen, and then the ratio of carbon to nitrogen was increased. Nitrogen addition had no significant effect on soil organic carbon and total nitrogen. Water promotes the retention of soil organic carbon by litter. The addition of water, nitrogen and litter affected microbial biomass and microbial community structure to varying degrees. (4) the "dilution effect" caused by water addition decreased the nitrogen and phosphorus contents in mature stems and leaves of Leymus chinensis. Thus, the phosphorus reabsorption capacity of stems was improved. The addition of nitrogen and litter promoted the absorption of nitrogen and phosphorus, and then decreased the absorption of nitrogen and phosphorus in the stems and leaves of Leymus chinensis, but only the addition of nitrogen decreased the reabsorption efficiency of stems and leaves, and the litter had no effect on the efficiency of nitrogen and phosphorus reabsorption. To sum up, this study shows that water, nitrogen and litter affect the productivity, diversity, soil carbon and nitrogen sequestration, and nutrient utilization strategies of dominant species in typical temperate steppe of northern China. Water is the main factor affecting vegetation change, nitrogen is the second important factor affecting vegetation change, and the influence of litter on vegetation changes with the change of water and nitrogen. In the context of global climate change, the complexity of ecosystems should be fully considered. Water, nitrogen and litter are important factors affecting ecosystems.
【學(xué)位授予單位】：中國農(nóng)業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：S812

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