IMHE OpenIR  > 山地表生过程与生态调控重点实验室
高寒紫花针茅群落对不同形态氮素的利用策略与生态适应机制
Alternative TitleUtilization strategy and ecological adaptation mechanisms of the Stipa purpurea community response to different nitrogen forms on the Tibetan alpine steppe
Language中文
洪江涛
Thesis Advisor王小丹
2017
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Name博士
Degree Discipline自然地理学
Keyword生态位 功能型 竞争 高寒草原 氮素 生态化学计量学特征
Other Abstract

基于竞争排斥法则的生态位理论通常认为处于同一生态位上的物种很难共存,并且物种共生的数量不能超过群落限制性资源的限制范围。在全球尺度来看,超过三十万个陆地植物物种仅仅受20余种资源的限制,包括:光、水、二氧化碳以及矿质营养等,但是野外试验发现对植物群落稳定性的维持影响最大的限制性因素一般不超过三四种。氮素通常是这仅有的三四种共性的限制性因素的主角之一,特别是在一些氮矿化度较低的生态系统中(例如极地和高山地区),其限制作用更为强烈。藏北地区位于青藏高原腹地,其高海拔、低气温和大风日数多的极端环境可能导致植物生长和繁殖受氮素限制作用较为明显。为了避免对稀缺资源(氮素)的激烈竞争,物种之间可能具备多元化的氮素吸收策略,即会产生对不同形态氮素(铵态氮、硝态氮和氨基酸等)吸收的生态位分化。并且植物的资源利用策略究竟会不会因临近物种的存在而发生改变,尚不清楚。除此之外,基于短期的同位素试验,仅仅探讨某几个物种对不同形态氮素的吸收特征,其结论还难以推演到更高的生态学尺度上(群落或功能群),因此还需要将短期和长期的定位数据相结合去阐明植物在个体 - 种间关系 - 群落(功能群)尺度上对不同形态氮素的吸收策略和适应机制。本文立足于申扎高寒草原与湿地生态系统观测试验站,在紫花针茅实验样地内开展短期的15N同位素(硝酸钠Sodium nitrate (15N,98%),硝酸铵Ammonium sulfate (15N,98%),甘氨酸Glycine (13C, 99%; 15N,98%))标记实验和物种剔除实验,测定植物冠层和根系的同位素15N含量,揭示高寒草原物种多元化的氮素吸收策略,阐明种间关系对高寒草原植物氮素利用策略的影响。同时,在实验样地内开展长期的不同形态氮素的添加实验,测定高寒紫花针茅群落物种多样性、生产力和C:N:P生态化学计量学特征的变化,探究植物对不同氮素形态吸收策略与群落稳定性之间的关系,揭示添加不同的外源性氮素对高寒草原生态和生产协调的影响,为西藏高寒草地生态系统的可持续发展与科学管理以及适应未来气候变化提供理论基础。从个体 - 种间关系 - 群落(功能群)尺度上分别主要取得以下研究成果:1. 高寒草原由于低温、干旱和大风日数多等极端的环境,限制了土壤的氮矿化,物种具备多元化的氮素吸收策略。同位素15N标记结果研究显示物种之间对氮素类型的偏好均存在一定的差异。紫花针茅、矮火绒草、早熟禾和昆仑蒿对15N-NO3-的吸收量显著高于15N-NH4+ 和15N-Gly,但是苔状蚤缀对15N-NH4+的吸收量显著高于15N-NO3-和15N-Gly,而青藏苔草、藏菠萝花、丛生黄耆、冰川棘豆和小叶棘豆对三种氮素的吸收量之间没有显著性差异,但是对群落生产力贡献较大的物种其吸收15N-NO3-的比例较高。非豆科植物对氮素的吸收量高于豆科植物。轴根型植物对氮素的吸收量显著低于非轴根型植物。2. 短期同位素标记实验表明临近物种的存在会改变群落中主要物种对氮素的吸收策略,这种改变不仅表现在氮素类型偏好的变化,还表现在吸收量上的变化。种间关系对氮素吸收量的影响表现为抑制作用(紫花针茅和青藏苔草对矮火绒草的抑制作用)和促进作用(紫花针茅和青藏苔草相互促进作用)并存,种间这一灵活资源利用策略是建立在物种相互竞争/互利基础之上的。植物对资源的灵活资源利用策略(弹性资源利用策略)可能是高寒草原植物群落中重要的生态位互补机制,也是植物应对极端环境而表现出的适应策略之一。3.长期定位实验结果显示,与对照区相比,随着氮素添加量的增加群落盖度呈显著增加趋势。群落冠层高度也随氮梯度的增加而逐渐增高,但是不同氮素类型的影响则比较微弱。施肥第一年物种丰富度变化不明显,但是第二年施肥样地物种出现大量的消失。并且物种的丧失绝大部分都发生在杂类草和豆科功能群内部,特别是杂草类中垫状植物和一年生植物迅速减少(例如:藏菠萝花、蒲公英和苔状蚤缀),豆科植物中伏地植物(例如:丛生黄耆和小叶棘豆等)也逐渐减少,可能与杂草和豆科植物的在群落中处于冠层中的位置(冠层下层,光竞争能力偏弱)和根型(轴根,吸收营养能力偏弱)有关。然而,禾草和莎草多样性则维持相对稳定。4.长期定位实验显示,禾草偏好硝态氮,莎草可以偏好铵态氮和硝态氮,杂草则偏好硝态氮、豆科植物对不同形态氮素吸收则没有表现出偏好性。在营养比较贫瘠地区,物种对氮素形态偏好具有一定程度的分化,但是对群落生产力贡献较大的功能群(禾草、莎草和杂草)均变现出对15N-NO3-的偏好。虽然研究发现各功能群植物冠层和根系生物量均与氮梯度和氮类型有一定的关联,但是冠层生物量与氮梯度关系更紧密,而根系生物量与氮梯度的关系则不紧密(与氮类型关系紧密)。可见植物冠层和根系生产力对氮素的响应出现不一致性,原因可能是他们器官功能的差异导致的。随着氮素梯度的增加,植物对土壤营养元素的竞争减弱,所以对根系生物量的促进作用微弱,植物优先将更多的物质用于冠层部分的生长(光合作用需求),导致氮梯度对冠层生物量的影响要高于对根系生物量的影响。另一方面,植物根系作为重要的吸收营养的器官,则表现出对氮素类型更强的偏好性(挑食性)。5. 随着N素梯度的增高,禾草、莎草和杂草的冠层和根系的N浓度逐渐提高,而高N处理下禾草和莎草冠层的P浓度也有升高趋势,可能与N素的添加会提高植物根系的磷酸酶活性从而促进植物对磷素的吸收有关。本研究发现不同类型氮素的施入,禾草和莎草的冠层N的浓度差异不显著,而根系N浓度有不同程度的差异性。与之相反,不同氮素类型对杂草植物冠层N浓度有显著影响,而对其根系N浓度无显著的影响。这说明不同功能型植物光合器官(冠层)和吸收储存物质器官(根系)在应对外界环境变化时存在差异性响应。禾草和莎草作为优势功能群,冠层氮含量在应对不同形态氮素施入时,维持相对的稳定的状态,有利于其进行光合物质的合成。虽然我们之前已经证实不同功能型植物对不同氮素形态有偏好,但是它们可能会改变其生长速率以维持其N元素的相对稳定。而杂草作为非优势功能群,在应对不同氮素形态施入时,其维持冠层氮素稳定能力的相对较差。

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The theory of niche based on the competitive exclusion principle considered that species with the same niche can not coexist in one plant communities and the number of species can not exceed the number of limiting resources. More than 300,000 plant species may have 20 different limiting resources (light, water, CO2 and the soil nutrients) across the terrestrial ecosystems, and field experiments found that only three or four resources are the most limited factors in a given plant community. Nitrogen is the common factor for the most limited three or four resources, especially in some ecosystems with low rate of nitrogen mineralization (e.g. arctic and alpine regions). Northern Tibet was located in the hinterland of Qinghai-Tibet plateau with high altitude, low temperature and many gale days, which would lead to the strongly nitrogen limited for plant growth and reproduction in alpine regions. In order to reduce the fierce competition for the nitrogen, the alpine plant may have the uptake diversity of soil nitrogen or niche differentiation of uptake for different nitrogen form (NO3- /NH4+/ amino acid). In addition, whether the neighboring species existed would change plant resource utilization strategy is not clear still now. Furthermore, the short-time isotopes tests only investigated nitrogen absorption characteristics for a few species and the result can not deduce to larger ecological scales (e.g. community or functional groups). We should combine the short and long term experimental data to explore the utilization strategy and ecological adaptation mechanisms of the alpine plant response to different nitrogen forms at individual- interspecies relation-community or functional groups levels.The study site was conducted on the Xainza Alpine Steppe and Wetland Ecosystem Observation Station. We used removed species experiment and short-term 15N isotope labeling experiment (Sodium nitrate (15N, 98%), Ammonium sulfate (15N, 98%), Glycine (13C, 99%; 15N, 98%)), and determined the shoot and root 15N contents to explore the nitrogen absorption preference and flexible nitrogen utilization strategy for different nitrogen froms for alpine plant. Meanwhile, we also investigated thechanges of species diversity, productivity and C: N: P ecological stoichiometry characteristic from long-term monitoring experiment to explore the relationship between nitrogen absorption preference and the community stability and the effects on different exogenous nitrogen on ecology and production for alpine grassland. The experiment would offer a new insight to understanding the ecosystem sustainable development and scientific management and provides the theoretical foundation of adaption response to future climate change for alpine ecosystem. Main results of this dissertation are as follows:1.Mineralization is generally extremely slow in alpine steppe due to the low temperature, limited precipitation and many gale days, and the species may have different strategies for N uptake. Short-term 15N isotope labeling experiment data showed that plant had different preferences of different nitrogen forms. Stipa purpurea, Leontopodium nanum, Poa litwinowiana and Artemisia nanschanica prefer 15N-NO3- to15N-NH4+ and 15N-Gly, while Arenaria musciformis prefer15N-NH4+ to 15N-NO3- and 15N-Gly. Carex moorcroftii, Lncarvillea compacta, Astragalus confertus, Oxytropis glacialis and Oxytropis microphylla had no obvious preferences of the three nitrogen forms. Different plant functional groups showed different absorbing capacity for nitrogen. Non-legumes had lower absorbing capacity for nitrogen than legumes. Axial root species had lower absorbing capacity for nitrogen than non-axial root species.2.Short-term 15N isotope labeling experiment data showed that the neighbor species could change plant preferences of different nitrogen forms and absorbing capacity. Interspecific relationship could play an inhibiting effect (Stipa purpurea / Carex moorcroftii suppress Leontopodium nanum) or an auxo-action (Stipa purpurea with Carex moorcroftii) for nutrient uptake. Flexible resource utilization strategy was established on the theory of competition/mutually beneficial among species. This resource utilization pattern may be an important complementary mechanism of niche in alpine grassland community and was an adaptive strategy of plants respond to extreme environment.3.Compared to control plots, nitrogen addition significantly increased the cover and the height of the community, while nitrogen forms had little effects on that of them. The species changed a liitle in the first year, while the species dispersed significantly in the second year. Most dispersed species were from the forbs and legumes, especially for the cushion plant and annual herbs (e.g. Incarvillea compacta, Taraxacum maurocarpum, Arenr muscorms), and legume species (Astragalus confertus Benth. ex Bunge, Oxytropis microphylla). Those dispersed species were located under the canopy (weaker competition for light) and belonged to axial root plant (weaker ability to absorb nutrients). However, the richness of grasses and sedges exhibited more stable in alpine ecosystem.4.Long-term experiments data showed that grasses preferred nitrate nitrogen, sedges could absorb ammonium nitrogen and nitrate nitrogen and forbs preferred nitrate nitrogen. Niche differentiation of nitrogen uptake for different nitrogen forms (NO3- /NH4+/ amino acid) in poor soil regions may be an important mechanisms for maintain ecosystem biodiversity and stability in alpine area. There is a certain correlation between nitrogen rates/forms and shoot/root biomass. However, the shoot biomass was related closely with nitrogen rates, while the root biomass was related closely with nitrogen forms. This may be caused by variations in organ function. With the nitrogen addition rate increasing, the plant would allocate more biomass to the shoot to enhance the ability to capture light. As the most important organ for uptake nutrition, root showed more sensitively responses to the nitrogen forms.5.With the increases of nitrogen addition, the nitrogen concentrations of grasses, sedges and forbs increased significantly, and the phosphorus concentrations of grasses and sedges also could be improved. This may arise from the higher root phosphomonoesterase activity (improving absorptive capacity for P) of the grasses and sedges. Different nitrogen forms had no effects on shoot nitrogen concentrations for grasses and sedges, while had significantly influence on root nitrogen concentrations. On the contrary, different nitrogen forms had significantly influence on shoot nitrogen concentrations of forbs, while had no effects on root nitrogen concentrations. This indicated that organs (root and shoot) showed different responses to changing environmental conditions. The shoot is the most important organ for photosynthesis, but the root is the most important organ for storage nutrition substance. Grasses and sedges as the dominant functional groups, could kept their shoot nutrient relatively stable response to different form of nitrogen addition, which is conducive to plant photosynthesis. Although previous experiment has proved that species have preferences for different nitrogen forms, plant had the ability to maintain the shoot nutrient stable by changes their growth rate. The forbs were the non-dominant functional groups and had the relatively poor ability for maintain the shoot nutrient stable. 

Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/18972
Collection山地表生过程与生态调控重点实验室
Affiliation中国科学院成都山地灾害与环境研究所
Recommended Citation
GB/T 7714
洪江涛. 高寒紫花针茅群落对不同形态氮素的利用策略与生态适应机制[D]. 北京. 中国科学院大学,2017.
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