Knowledge Resource Center for Ecological Environment in Arid Area
| 高寒草地土壤氮的可利用性及其放牧对主要植物有效氮吸收的影响 | |
| 其他题名 | The availability of nitrogen in alpine grassland and the effects of grazing on plants available nitrogen |
| 庞哲 | |
| 出版年 | 2015 |
| 学位类型 | 硕士 |
| 导师 | 王艳芬 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 作为地球上最高和最大的高原，青藏高原拥有广阔的高寒草地（高寒荒漠、草原、草甸、灌丛、沼泽化草甸）生态系统，占据着青藏高原总面积的60%，且拥有多种土壤类型。大量研究认为无机氮是植物生长的限制性元素，近10年，越来越多的研究认为难降解的有机物分解为可溶性有机氮（DON）过程是植物氮供应的主要限速步骤。但我们对植物有效性N库及植物对不同N形式的吸收了解的还很少，特别是在青藏高原地区。 因此,我们在青藏高原高寒草地生态系统不同植被类型采样，并在高寒草甸生长季不同时期围封放牧样地设置三种N形式的15N标记实验【(15NH4)2SO4 (99.2%), Na15NO3 (99.2%) or glycine-15N (98.7%)】，探讨高寒草地土壤氮的可利用性及其放牧对主要植物有效氮吸收的影响。以期通过此研究，了解青藏高原不同植被类型植物有效性N的含量变化和影响因子并深入探讨青藏高原植物对有效性N的吸收能力。这些问题的研究对于理解全球气候变化和高寒草甸利用情形下植物群落的生态学过程和稳定性机制具有重要的理论意义。本研究的主要结果如下： （1）在所有的植被类型中，土壤可溶性有机N (DON)占土壤可溶性全N (TDN)的比例为60%,高寒荒漠植物生产力最低,但DON所占的比例最大(占TDN 77.22±2.32%)，而在高生产力的高寒草甸，DON所占的比例最低（52.03±2.00%）。 （2）该研究中DON（沼泽化高寒草甸：37 mg N l-1，高寒灌丛9.6 mg N l-1，高寒草甸27 mg N l-1，高寒草原18 mg N l-1，高寒荒漠6 mg N l-1）的平均浓度比之前报道的温带森林（0.2-3 mg N l-1）和温带草原（2.5-12.1 mg N l-1）0-10cm的土壤DON的浓度高很多，这些值的大小顺序为沼泽化高寒草甸=高寒草甸>高寒草原>高寒灌丛=高寒荒漠。逐步回归分析表明，在区域范围内，植物地下生物量、土壤水分、总磷、和MBC解释土壤DON变化的84%以上。 （3）高山嵩草草甸的植物主要利用无机N，但也能吸收有机N。 （4）N吸收速率具有强烈的种特异性。高山嵩草的氮吸收速率最低，这与其相对缓慢的生长速度相符合。生长快的物种二裂委陵菜和多裂委陵菜有更高的氮吸收速率。 （5）放牧对植物氮吸收的影响随植物种类和季节变化而不同。在放牧和围封小区，二裂委陵菜和多裂委陵菜总生物量相近，6月份放牧导致两个物种由偏好NH4-N/glycine-N的吸收转向偏好NO3-N的吸收，7月份在放牧小区增加了对NH4-N的利用。相比之下，高山嵩草在放牧和围封的小区总生物量是显著不同的，但其N吸收模式基本不受放牧影响。 （6）高的N吸收速率出现在生长季的中期(7月),而不是在生长季初期(6月)。 综上所述：在高寒草地所有植被类型中，土壤DON含量都高于DIN。DON应该作为常规监测指标，在高寒生态系统陆地N模型中加以考虑。高山嵩草草甸的植物能吸收有机N，但无机N 仍是植物主要的N利用形式。我们的研究中三种植物，在整个生长季吸收的无机和有机N形式显示出生态位分离。此外,放牧改变了植物吸收无机和有机N的季节性分离, 植物吸收N形式的分离受植物种类、季节、放牧共同作用影响。这些发现表明, 我们通过考虑植株N吸收模式可以更好地理解植物多样性和共存的机制。 |
| 英文摘要 | The Tibetan Plateau, as the highest and largest plateau on the Earth, has a wide range of alpine grasslands ecosystems (i.e. alpine desert, steppe, meadow, shrub, swamp meadow ) that cover more than 60% of the total area of the Tibetan Plateau and span a wide range of soil types. In recent 10 years, numerous studies have been carried out to find that the degradation of refractory organics to low molecular weight DON is a limiting step on plant absorbing nitrogen. However, plants available N pool and absorption from different forms N remain poorly understood, especially in the Tibetan Plateau. Therefore，field work was conducted on the Tibet plateau to investigate the amount of plants available N in grassland soil under different vegetable types. Moreover , we performed a 15N tracer experiment of three N forms【(15NH4)2SO4 (99.2%), Na15NO3 (99.2%) or glycine-15N (98.7%)】in enclosure and grazing plots under field conditions across one full growing season and investigate the effects of grazing on plants available nitrogen. We want to have a clear understanding of the plant available N content changes and impact factor under different vegetation types in Tibetan Plateau and deeply explore the ability of available N absorption about Tibetan Plateau plants. The research of these problems has important theoretical significance to understand plant community ecology process and stability of the mechanism with the global climate change and land use case in alpine meadow. The results are listed as follows: (1) DON accounted for more than 60% of the TDN pool across all vegetation types, with the maximum contribution as observed in alpine desert (77.22±2.32% of TDN) with the lowest plant productivity, while being least in alpine meadow (52.03±2.00% of TDN) with higher plant productivity. (2)The average concentrations of DON (37 mg N l-1 in swamp meadow , 9.6 mg N l-1 in alpine shrub, 27 mg N l-1 in alpine meadow, 18 mg N l-1 in alpine steppe; and 6 mg N l-1 in alpine desert) were much higher than those reported previously in temperate forests (0.2-3 mg N l-1) and temperate grasslands (2.5-12.1 mg N l-1) at 0-10cm soil depth, and those values decreased in the order of swamp meadow = alpine meadow > alpine steppe > alpine shrub = alpine desert. Stepwise regression analysis showed that at the regional scale, plant belowground biomass, soil moisture, total P, and microbial biomass C (MBC) accounted for more than 84% variation of soil DON. (3) Plants in Kobresia pygmaea meadow can take up substantial amounts organic N, although inorganic N is the main N form utilized. (4) N uptake rates were strongly species-specific. The most dominant of the three plant species, K. pygmaea, showed the lowest plant N uptake rate, which is consistent with its relatively slow growth rate. The faster growing species P. bifurca and P. multifida showed higher plant N uptake rates. （5）The effect of grazing on plant N uptake varied with plant species and season. P. bifurca and P. multifida demonstrated similar total biomass at grazed and ungrazed plots, and showed a similar pattern switching from NH4-N/glycine-N uptake in ungrazed plots to NO3-N uptake in grazed plot in June and increased NH4-N utility in grazed plots in July. In contrast, total biomass of K. pygmaea differed significantly between ungrazed and grazed plots, but its N uptake pattern was largely unaffected by grazing. （6）Higher N uptake was observed in the middle of the growing season (July) rather than early in the growing season (June). In conclusion，soil DON contents represent significant N pools across all the vegetable types in alpine grasslands and DON should be considered as a key component of terrestrial N models in alpine ecosystems and be monitored as regular indicators. Plants in Kobresia pygmaea meadow can take up substantial amounts organic N, although inorganic N is the main N form utilized. The three plant species in our study showed partial niche partitioning for uptake of |
| 中文关键词 | 高寒草地 ; 高寒草甸 ; 植被类型 ; 放牧 ; 有效氮 |
| 英文关键词 | alpine grassland alpine meadow vegetation type grazing available nitrogen |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 生物工程 |
| 来源机构 | 中国科学院大学 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287479 |
| 推荐引用方式 GB/T 7714 | 庞哲. 高寒草地土壤氮的可利用性及其放牧对主要植物有效氮吸收的影响[D]. 中国科学院大学,2015. |
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