放牧对高寒草甸群落结构和生产力的影响

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	放牧对高寒草甸群落结构和生产力的影响
其他题名	EFFECT OF GRAZING ON THE PLANT COMMUNITY STRUCTURE AND PRODUCTIVITY IN APLINE MEADOW
	晁增国
学位类型	硕士
导师	汪诗平
	2009-06-03
学位授予单位	中国科学院西北高原生物研究所
学位授予地点	西北高原生物研究所
关键词	冬春季放牧和夏秋季放牧高寒草甸高寒灌丛草甸群落组成和生产力种群空间分布格局粪便分解温度敏感性
摘要	由于人口的增加和对草地的不合理利用，高寒草地的退化日趋严重。许多学者对不同退化程度的高寒草甸的恢复模式进行了跟踪研究。然而，这些研究大多是对恢复状态和结果的描述，很少从植物个体或种群的空间分布格局探讨退化草甸的恢复过程和机理。另外，不同海拔高度的群落对放牧的响应可能不完全相同，这些不同除了与家畜的选择性采食和植物的适应性不同有关外，还可能与不同海拔高度粪便归还（即分解）特性不同有关，因为，不同的植物对养分的需求量是不同的。为了回答以上问题和假设，我们选取了青藏高原两类放牧草场（冬春草场和夏秋草场）为研究对象，在冬春草场上选择了两个主要植被类型高寒草甸和高寒灌丛草甸，在夏秋草场选择了两个海拔（3600 m和3800 m）的高寒草甸群落，应用样线法调查了放牧和围封条件下各群落的结构特征、主要种群空间分布格局（50 cm×50 cm）、多样性和生产力的变化；同时，开展了不同放牧季节（冬春放牧和夏秋放牧）对高寒草甸群落结构和生产力影响的控制放牧试验，以及牛粪分解的温度敏感性试验。 1. 放牧对夏秋草场的影响与围封1年的草场相比，在两个海拔（3600 m和3800 m）高度上放牧显著降低了大多数植物的高度和群落的地上生物量，对群落多样性的影响不显著。在3600 m海拔上，放牧显著降低了群落的地上地下总生物量，但显著增加了矮嵩草(Kobresia humilis)、高山唐松草(Thalictrum alpinum)和雪白委陵菜(Potentilla nivea)的重要值，而降低了线叶龙胆(Gentiana farreri)的重要值；在3800 m海拔上，放牧显著降低了冷地早熟禾（Poa crymophila）的重要值，而增加了小大黄的重要值。就主要种群空间分布特征而言，放牧显著降低了3600 m海拔上矮嵩草、高山唐松草、珠芽蓼(Polygonum viviparum)、线叶嵩草(Kobresia capillifolia)和金露梅(Potentilla fruticosa)等种群的聚集强度，但增加了黑褐苔草(Carex atrofusca)的聚集强度；而在3800 m海拔上，放牧增加了矮嵩草和矮火绒草（Leontopodium nanum）的聚集强度，同时降低了冷地早熟禾和祁连山黄芪（Astragalus chilienshanensi）的聚集强度。 2．放牧对冬春草场的影响与围封5-6年的草场相比，放牧显著降低了高寒草甸群落中大多数植物的高度，对高寒灌丛草甸大多数植物高度却没有显著影响；在高寒草甸，显著增加了一叶米口袋（Gueldenstaedtia monophylla）和垂穗披碱草（Elymus nutans）的盖度，显著降低了麻花艽（Gentiana straminea）的盖度和地上生物量。在金露梅灌丛草甸，除显著增加了金露梅（Potentilla fruticosa）的高度外，放牧显著降低了金露梅的盖度、生物量、重要值和个体生物量；显著降低了珠芽蓼（Polygonum viviparum）的高度、重要值和个体生物量及垂穗披碱草的高度，而显著增加了肉果草（Lancea tibetica）的个体生物量。放牧显著增加了两个群落的多样性和均匀度、以及高寒草甸的地上生物量。放牧使退化高寒草甸主要种群矮嵩草的聚集强度增加，但降低了高寒草甸异针茅（Stipa aliena）的聚集强度；放牧降低了高寒灌丛草甸矮嵩草、金露梅、刺芒龙胆（Gentiana arstata）和甘青老鹳草（Geranium pylzowianum）的聚集强度，而增加了高山唐松草、蕨麻（Potentilla anserina）、矮火绒草（Astragalus chilienshanensis）、垂穗披碱草和疏齿银莲花（Anemone obtusiloba）的聚集强度。 3．不同放牧季节对高寒草甸群落的影响经过两年的放牧试验发现，冬春季放牧所有小区、夏秋季放牧所有小区和不放牧所有小区出现的物种总数分别为38个、37个和35个。地上最大现存生物量处理间存在显著差异，处理和年际间交互效应对地下生物量（0-40 cm）产生显著影响，不同层次的地下生物量对放牧季节的响应有所不同。处理间的地上地下总生物量在处理和年际间存在交互效应。夏秋季放牧处理地下生物量与地上现存量的比明显高于冬春季放牧和不放牧处理，各处理的地上净初级生产力差异不显著。 4．牛粪分解的温度敏感性在3200-4200 m的海拔高度梯度上，海拔高度每增加100 m，粪便化学组分的分解量降低2.3-2.9%,粪便的化学组分（有机碳、纤维素、半纤维素、木质素、氮、磷、钾、钙和镁）分解速率每天降低了3-96 μg，不同组分的变化差异较大。化学组分损失速率的温度敏感性随时间而降低。例如，对有机碳、纤维素、半纤维素、木质素、氮、磷、钾、钙和镁来讲，在前273天的分解时间内，温度每升高1 ℃，平均的温度敏感性大概分别为37、75、168、41、29、37、29、34和31%，而到705天时，温度每升高1 ℃，它们的温度敏感性则仅为8、9、63、19、21、14、12、10和13%。有机碳的损失速率的温度敏感性与牛粪中的碳氮比成正相关。与氮相比，在前273天的分解中,磷的损失速率更高，之后这种情况却相反。因此，通过该项研究，得出如下初步结论： 1.对于轻-中度退化的高寒草甸夏秋草场来说，围封初期（1年）可以显著提高群落地上生物量，但对群落物种组成和植物多样性影响不大。 2．对于轻-中度退化的高寒草甸冬季草场而言，长时间的围封（5-6年）由于改变了主要种群的空间分布格局及其对资源的竞争策略，同时增加了立枯量，因而降低了群落的植物多样性和均匀度，并使群落活体生物量有下降趋势。因此，对于此类草场，建议适度的利用是有益的，以避免过多立枯的积累所带来的不利。 3.粪便的分解在高寒草甸存在较强的温度敏感性，随着海拔高度的升高，粪便的化学组分的分解量和分解速率都在降低，不同组分的变化差异较大。因此，粪便的分解在不同海拔上的差异会影响不同海拔上植物对养分的利用，进一步会影响植物的生长。
其他摘要	Degradation of alpine grasslands on the Tibetan Plateau was increasingly strengthened because of increasing population and the unreasonable use of grasslands. The modes to restore the degraded grasslands have been extensively studied, which mainly focused on the description of the states and outcomes, however, little research was done to discuss the processes and mechanisms of the restoration through spatial heterogeneity of population. The response of the plant communities to grazing may vary with different elevations of above the sea. Besides the selective defoliation and adaptabilities of species, the effect of dung decomposition along the elevation gradient should also be considered，for nutrient requirement varied with different species. The objectives of this study were to determine the effects of freely grazing on plant community composition, spatial distribution patterns of the main populations on the small scale (50 cm×50 cm), plant diversity and productivity on the alpine meadows at 3600 and 3800 m during summer grazing, an alpine meadow (3200 m) and a shrub meadow during winter grazing (3400 m) along a elevation gradient. At the same time, the effect of different grazing seasons (winter grazing and summer grazing) on alpine meadow at 3200 m was measured under the controlled grazing experiment in 2007 and 2008. We also measured the temperature sensitivity of nutrient release rate from dung decomposition along an elevation gradient from 3200 to 4200 m. 1. Effect of grazing on alpine meadows during summer grazing Grazing decreased the height of most plant species and the aboveground biomass of the communities at the 3600 and 3800 elevations. The total biomass (aboveground biomass + belowground biomass) at the 3600 m elevation was decreased by grazing, however, the plant diversity on the two elevations was not changed significantly. The important values of Kobresia humilis, Thalictrum alpinum and Potentilla nivea increased significantly under grazing and the important value of Gentiana farreri was decreased significantly by grazing on the 3600 m elevation. Grazing decreased the important value of Poa crymophila and increased the important value of Rheum pumilum on the 3800 m elevation. Grazing made Kobresia humilis, Thalictrum alpinum, Polygonum viviparum and, Kobresia capillifolia and Potentilla fruticosa to be little aggregated, however, Carex atrofusca was aggregated on the 3600 m elevation. Grazing made Kobresia humilis and Leontopodium nanum to be aggregated, and made Poa crymophila and Astragalus chilienshanensis to be little aggregated on the 3800 m elevation 2. Effect of grazing on alpine meadow and shrub meadow during winter grazing The height of most plants in alpine meadow was decreased significantly compared to enclosure, however, the height of most plants in alpine shrub meadow was not changed. Grazing increased significantly the cover of Gueldenstaedtia monophylla and Elymus nutans, and decreased significantly the cover and biomass of Gentiana straminea in alpine meadow; except the height of Potentilla fruticosa, grazing significantly decreased its cover, biomass, important value and individual biomass, decreased significantly the height, important value and individual biomass of Polygonum viviparum, and increased the individual biomass of Lancea tibetica in alpine shrub meadow. Grazing significantly increased the plant diversity and evenness of the two communities, and aboveground biomass of alpine meadow. Grazing made Kobresia humilis to be aggregated and made Stipa aliena to be little aggregated in the alpine meadow at 3200 m. However, grazing made Kobresia humilis to be little aggregated in alpine shrub meadow at 3400 m, and made Gentiana aristata and Geranium pylzowianum be little aggregated and Thalictrum alpinum, Potentilla anserine, Leontopodium nanum, Elymus nutans and Anemone obtusiloba to be aggregated. 3. Effect of different grazing seasons on alpine meadow After grazing in alpine meadow for two years, 38, 37, 35 species richness were found in all winter-grazing plots, summer-grazing plots and no-grazing plots, respectively. Aboveground biomass of the three different treatments was different significantly. There was an interactive effect between treatment and grazing time on under-ground biomass (0-40 cm), the belowground biomass from different depths responded differently to different grazing seasons. Similar results were found for total biomass (aboveground biomass + belowground biomass) in the three different treatments. The average ratio of belowgroung and aboveground biomass in summer grazing plots was higher than that in winter grazing plots and that in control plots. The net above-ground productivity (aboveground present biomass + intake by sheep for summer grazing treatment) in three treatments was not changed significantly. 4. Temperature sensitivity of nutrient release rate from dung decomposition With each 100-m increase in elevation, mass losses of dung decreased by 2.3-2.9%, and mass loss rates of chemical components of dung [organic carbon (C), cellulose, hemicellulose, lignin, N, P, potassium (K), calcium (Ca) and magnesium (Mg)] decreased by 3-96 μg d-1. The temperature sensitivity of mass loss rates of chemical components in dung decreased with decomposition time. For example, the average temperature sensitivities were approximately 37, 75, 168, 41, 29, 37, 29, 34, and 31% per 1℃ warming within a 273-day decomposition period; but only 8, 9, 63, 19, 21, 14, 12, 10 and 13% per 1℃ warming after 705 days for organic C, cellulose, hemicellulose, lignin, N, P, K, Ca, and Mg, respectively. The temperature sensitivity of organic C mass loss rate was positively related to the C: N ratio in dung. In particular, higher temperature sensitivity of mass loss rate of P compared with N was observed within the first 273 days of decomposition, and thereafter this situation was reversed. We drawed the following conclusions based on this study: 1) To the moderately-degraded summer grasslands in alpine meadow, at the early stage of restoration, fencing increased the belowground biomass, however, the effect of fencing on the community composition and the plant diversity was not significant. 2) To the moderately -degraded winter grasslands in alpine meadow,long-time fencing changed spatial heterogeneity of main populations and the abilities of different species to compete recourses, and increased litter,accordly, decreased the plant diversity and the live biomass.So it is beneficial to utilize these grasslands properly to avoid the disadvantage of the much litter. 3) The temperature sensitivity of dung decomposition was large in alpine meadow .The amount and the mass loss rate of different chemical components in dunge decreased with increasing elevations, and the decomposition of different chemical components in dunge varied.Therefore, the decomposition of different chemical components in dung had a large impact on the nutrition of different species on different elevations and further affected the growth of these species.
页数	70
语种	中文
文献类型	学位论文
条目标识符	http://210.75.249.4/handle/363003/3268
专题	中国科学院西北高原生物研究所
推荐引用方式 GB/T 7714	晁增国. 放牧对高寒草甸群落结构和生产力的影响[D]. 西北高原生物研究所. 中国科学院西北高原生物研究所,2009.

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