水和氮及凋落物添加对羊草草地的影响机制

发布时间：2018-12-28 08:16

【摘要】：工业革命以来,人类活动已经改变了全球气候变化。在干旱、半干旱草地系统中,生产力随降雨和氮沉降的增加而增加。同时,预期的CO2增加和全球变暖也会导致半干旱草地生态系统生产力提高,因此将会有更多的凋落物进入土壤。凋落物的增加可通过直接影响土壤微环境和有机物的输入,或间接影响微生物活动,进而影响生物化学循环过程。草地占全球陆地面积的25%,是全球重要的生态系统之一。同时,草地生态系统极易受全球气候变化的影响。然而,凋落物的积累如何影响草地生态系统对增雨和氮沉降的响应尚不清楚。2013-2015年,在内蒙羊草草地上进行3年的水、氮和凋落物添加实验,通过对羊草草地群落生产力和资源利用效率、群落结构和土壤碳氮固持,及优势种羊草的养分利用策略进行探讨,目的阐明水和氮添加对羊草草地的影响机制,及水限制解除条件下,氮和凋落物对羊草草地植被变化的影响。主要结果如下：(1)水、氮和凋落物添加显著增加了地上地下初级生产力。水、氮和凋落物添加主要通过影响了土壤水分、温度、土壤无机氮含量和容重,影响了植物的水分利用效率和氮吸收,最终增加了羊草草地生产力。此外,水促进了地下初级生产力对凋落物的响应。水分添加促进了优势种羊草的茎叶比,氮和凋落物添加降低了其比叶面积,影响了植物对光的捕获能力和光合作用。(2)水、氮和凋落物添加增加了禾草高度,减少了到达地面的光合有效辐射,降低了群落底层阔叶草的多度,降低了物种多样性。此外,少量凋落物添加不影响群落多样性,而凋落物累积到一定量会在土壤表面形成物理阻隔,降低种子的萌发和种苗的建植。(3)水分添加促进了土壤有机碳含量,对土壤全氮无显著影响,进而提高了土壤的碳氮比。氮添加对土壤有机碳和全氮无显著影响。水促进了凋落物对土壤有机碳的固持作用。水、氮和凋落物添加不同程度的影响了微生物量和微生物群落结构。(4)水分添加引起的“稀释效应”,降低了羊草成熟茎和叶中的氮磷含量,进而提高了茎的磷重吸收能力。而氮和凋落物添加都促进了植物对氮磷的吸收,进而降低了羊草茎叶的氮磷吸收能力,但仅氮添加降低了茎和叶的重吸收效率,凋落物对氮磷重吸收效率无影响。综上所述,本研究工作表明,在中国北方温带典型草原,水、氮和凋落物影响了羊草草地生产力、多样性、土壤碳氮固持,及优势种的养分利用策略。水是影响植被变化的主要因素,氮是影响群落植被变化的第二重要因素,凋落物对植被的影响随水、氮的变化而变化。在全球气候变化下,要充分考虑生态系统的复杂性,水、氮和凋落物是影响生态系统的重要因子。
[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.
【学位授予单位】：中国农业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：S812

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