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施氮对川滇柳(Salix rehderiana)和冬瓜杨(Populus purdomii)幼苗竞争关系的影响
Alternative TitleEffects of nitrogen addition on intra- and interspecific competition between Populus purdomii and Salix rehderiana seedlings
宋蒙亚
Subtype博士
Thesis Advisor李春阳
2017
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline生态学
Keyword土壤龄级 原生演替 植物竞争 土壤微生物 化学计量关系
Abstract由于全球气候变化,致使贡嘎山冰川退缩加剧,而在冰川退缩区发生了植被原生演替现象。贡嘎山海螺沟冰川经过120 a的退缩演化,形成了长约2000 m、宽50-200 m、海拔在2850-3000 m并且可以定龄的土壤序列,该区域为研究土壤发育过程、植物-植物相互关系、植物-土壤互作反馈以及原生演替过程提供了一个理想的研究平台。海螺沟冰川退缩区域,随着退缩迹地时间的延长,土壤氮(N)含量逐渐积累,而N又是植物生长所必要的营养元素,因此N元素可能是调控植物相互关系和群落演替的重要环境因子。该试验从以下两个科学问题切入:(1)群落演替过程中随着土壤养分的积累植物之间相互关系如何转变;(2)土壤养分增加以及植物相互关系转变与地下微生物群落组成的关系如何?本试验选择了冰川退缩迹地20年龄级和40年龄级的土壤基质,同时进行施加N肥处理,来研究演替早期物种川滇柳(Salix rehderiana Schneider)与冬瓜杨(Populus purdomii Rehder)在原生演替过程中相互关系转化的机理。主要研究结果如下:(1) 不同土壤龄级(20年龄级和40年龄级)与种植模式(种内种植和种间种植)处理下川滇柳与冬瓜杨相互关系发生明显转化。环境压力梯度假说模型(The Stress Gradient Hypothesis)预测植物之间相互关系会随着外界环境压力梯度的变化而在互助合作与种间竞争之间转化,这一现象在亚高山植物群落中表现更为明显。本研究表明川滇柳与冬瓜杨之间的相互关系伴随着土壤龄级的增加(20年龄级到40年龄级)出现由积极影响(Positive effect)到消极影响(Negative effect)的转变,同时发现土壤微生物与养分是群落中邻近植物之间竞争与合作相互关系转化重要的环境因子。在不同土壤龄级上,川滇柳与冬瓜杨种内种间种植在生物量积累与分配、养分吸收与利用、非结构性碳水化合物、叶片超微结构、土壤微生物群落结构、土壤酶活性、土壤有机碳(SOC)、土壤全氮(TN)、铵态氮(NH4+-N)和硝态氮(NO3–-N)参数上具有明显差异。研究发现在20年土壤龄级处理下川滇柳与冬瓜杨种间种植与种内种植相比,具有更高的地上部、地下部和总的生物量积累。此外,土壤微生物磷脂脂肪酸(PLFA)分析显示40年土壤龄级处理下川滇柳与冬瓜杨种间种植与种内种植相比呈现出更低的革兰氏阳性细菌(G+)、真菌(18:1 ω9c)、放线菌和总的PLFA含量。冗余分析(redundancy analysis, RDA)显示土壤N是影响微生物群落组成特征最重要的参数指标。此外。15N稳定性同位素标记技术用于辨明川滇柳与冬瓜杨种内种间种植下不同的N吸收形态(δ15N-NO3–和δ15N-NH4+),结果显示40年土壤龄级处理下种间种植(PS)与种内种植(PP和SS)相比具有更高的δ15N-NO3–水平。结果表明在养分贫瘠的土壤(20年土壤龄级)条件下,川滇柳与冬瓜杨之间相互关系表现为种间互利合作(Facilitative interaction),而当土壤养分达到适中条件后(40年土壤龄级),川滇柳与冬瓜杨之间相互关系转变为种间竞争关系(Competitive interaction)。由上可知,在贡嘎山冰川退缩迹地原生演替过程中,土壤微生物与养分是驱动植物之间相互关系转化的关键因素。(2) 40年土壤龄级处理下,川滇柳与冬瓜杨之间相互关系转变为种间竞争关系。需要进一步明确川滇柳与冬瓜杨竞争能力随土壤N含量的变化特征。本研究发现土壤养分(N元素)能够调控川滇柳与冬瓜杨种间竞争优势关系。在对照处理(未施N)下,川滇柳与冬瓜杨种间竞争过程中,川滇柳占据竞争优势地位,而冬瓜杨生长受到竞争胁迫的影响,生长特征表现为川滇柳比冬瓜杨具有更高的生物量积累、光合能力、N吸收能力、氨基酸含量以及光合N利用效率(PNUE)。然而,在施N处理后,情况发生了明显转变,川滇柳与冬瓜杨种间竞争过程中,冬瓜杨占据了竞争优势地位,具体表现为冬瓜杨比川滇柳具有更高的生长率、更高的碳获取能力、高的氨基酸含量以及水分利用效率,而川滇柳的生长显著减少。由此可知,海螺沟冰川退缩迹地原生演替过程中,土壤N在调控演替早期杨柳科植物相互关系方面扮演了一个重要的角色。植物-植物相互关系与N有效性是驱动贡嘎山冰川退缩迹地原生演替过程的关键机理。总的来讲,贡嘎山冰川退缩迹地植物群落原生演替过程中川滇柳与冬瓜杨的相互关系明显受到土壤N有效性的调控。冰川退缩迹地随着N含量的逐渐积累(20年龄级到40年龄级),川滇柳与冬瓜杨之间相互关系发生由互助合作到种间竞争的转化。当土壤N缺乏时(不施N)川滇柳在种间竞争中占据优势,竞争能力更强,而当土壤N丰富时(施N),冬瓜杨在竞争中占据优势,结果同时发现土壤微生物是驱动原生演替过程的关键生物学因素。
Other AbstractThe Hailuogou Glacier has decreased in size due to climate change. Its glacier retreat area covers a chronosequence, with a length of around 2,000 m, width of about 50-200 m, and elevation between 2,850-3,000 m during the past 120 years. This area has been utilized when studying soil formation processes, plant primary succession, plant-soil feedbacks and plant-plant interactions. Soil nutrients are inadequate during the early primary succession, particularly N, which plays a key role in plant growth. Litter decomposition by N-fixing species contributes to the accumulation of soil nutrients during succession, the top soil having the highest amounts of nutrients. Early-successional species could improve the microclimate as well as the physical and chemical properties of soil, and late-successional species would benefit from that. We hypothesized the following: 1) plant-plant interactions predominate via facilitation in severe environments during the early stages of primary succession, whereas under relatively benign nutrient conditions, the interactions between neighboring plants change into competition; 2) soil microorganisms and nutrient abundance are the main driving forces for the shift in Populus-Salix interactions from positive to negative with an increasing soil age. 3) P. purdomii and S. rehderiana utilize different competitive strategies under interspecific competition and N fertilization; and 4) environmental N conditions determine asymmetric competition patterns, and N is likely to play a pivotal role and serve as a major driving factor in transforming the dominant species from S. rehderiana to P. purdomii in glacier retreat areas. The main results and conclutions are follows:(1) The stress gradient hypothesis predicts that plant-plant interactions shift between facilitation and competition along stress environment gradients, particularly those involving subalpine plant communities. Our aim was to confirm whether the interactions between Populus purdomii Rehder and Salix rehderiana Schneider had switched from positive to negative effects with increasing soil aging during the early stages of primary succession at the Gongga Mountain glacier forefields. We also investigated whether soil microbes and nutrients are major driving factors for the transformation from positive to negative interactions between neighboring plants. We analyzed differences in Populus and Salix intra- and interspecific interactions under various soil age-specific conditions such as biomass accumulation and allocation, nutrient absorption and utilization, non-structural carbohydrates, leaf ultrastructure, soil microbial biomass and composition, soil enzyme activities, soil total carbon (C), soil total nitrogen (N), soil ammonium (NH4+-N) and soil nitrate (NO3--N). We found that P. purdomii and S. rehderiana interspecific treatments had greater aboveground dry matter, belowground dry matter, and total dry matter than that of intraspecific treatments in 20-year-soil age condition, respectively. Furthermore, phospholipid fatty acid (PLFA) analysis showed that Populus-Salix interspecific interactions exhibited lower soil gram-positive bacteria, fungi (18:1 ω9c), actinomycetes, and total PLFA levels than those of intraspecific treatments under 40-year-soil age conditions. Redundancy analysis (RDA) demonstrated that soil N was the most important parameter contributing to the composition of microbial communities. In addition, the 15N stable isotope labeling method was used to distinguish differential absorption of N forms (15NH4+-N or 15NO3--N) by P. purdomii and S. rehderiana, and the results showed that Populus-Salix interspecific interactions had higher foliage δ15N derived from NO3– (δ15N-NO3–) than those under intraspecific treatments with 20-year-soil age. Populus-Salix interactions exhibited facilitative effects in harsh environments (e.g., 20-year-soil age) for survival. Conversely, under moderate environmental conditions (e.g., 40-year-soil age), Populus-Salix interactions presented competitive effects for occupying more nutrients and avoiding being eliminated by neighboring plants in the subalpine glacier retreat areas. Moreover, our study demonstrated that soil microbes and nutrients (particularly N) are major drivers for plant-plant interactions that shift from facilitation to competition in the Gongga Mountain glacier retreat areas.(2) Intra- and interspecific competition were investigated in early-successional Salix rehderiana and later appearing Populus purdomii under non-fertilized (control) and nitrogen (N)-fertilized conditions in the Hailuogou glacier retreat area. Our aim was to discover, whether N is a key factor in plant-plant competition and whether N drives the primary succession process in a glacier retreat area. We analyzed differences in responses to intra- and interspecific competition and N fertilization between P. purdomii and S. rehderiana, including parameters, such as biomass accumulation, nutrient absorption, non-structural carbohydrates, photosynthetic capacity, hydrolysable amino acids and leaf ultrastructure. In the control treatments, S. rehderiana individuals subjected to interspecific competition benefited from the presence of P. purdomii plants, as indicated by higher levels of biomass accumulation, photosynthetic capacity, N absorption, amino acid contents, and photosynthetic N-use efficiency. However, in the N-fertilized treatments, P. purdomii individuals exposed to interspecific competition benefited from the presence of S. rehderiana plants, as shown by a higher growth rate, enhanced carbon gain capacity, greater amino acid contents, and elevatedwater use efficiency, whereas the growth of S. rehderianawas significantly reduced. Our results demonstrate that N plays a pivotal role in determining the asymmetric competition pattern among Salicaceae species during primary succession. We argue that the interactive effects of plant-plant competition and N availability are key mechanisms that drive primary succession in the Gongga Mountain glacier retreat area.In conclutions, the present study shows that there are soil microbes- and nutrient-driven changes in Populus-Salix interactions from facilitation to competition during the early stages of primary succession in the Gongga Mountain glacier retreat area. Our study revealed that Populus-Salix interactions exhibit interspecific facilitation for survival under poor conditions (i.e., 20-year-old soil), whereas under moderate soil (i.e., 40-year-old soil), Populus-Salix interactions involve interspecific competition to avoid elimination. On the other hand, N fertilization can alter competitive relationships between P. purdomii and S. rehderiana. Under low N conditions (control), S. rehderiana displayed a competitive advantage over P. purdomii, whereas under N fertilization, P. purdomii showed a competitive advantage over S. rehderiana. Moreover, soil microbes and nutrients (particularly N) drive the transformation process from plant-plant facilitation to competition. These findings will improve understanding of plant-plant interactions and plant-soil feedbacks in plant communities in subalpine ecosystems. We argue that this evidence provides important insights into plant-plant competition in glacier retreat areas and contributes to the knowledge of nutrient limitation during soil development in successional ecosystems. Further research is still needed on energy flow and nutrient cycles in plant-soil-microbe systems, on neighboring plants’ effects and microbial feedbacks, on the balance between facilitation and competition, and on the dynamic models of primary succession in a glacier retreat area.
Pages90
Language中文
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/24564
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
First Author Affilication中国科学院水利部成都山地灾害与环境研究所
Recommended Citation
GB/T 7714
宋蒙亚. 施氮对川滇柳(Salix rehderiana)和冬瓜杨(Populus purdomii)幼苗竞争关系的影响[D]. 北京. 中国科学院大学,2017.
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