兰州大学机构库 >草地农业科技学院
氮沉降对黄土高原典型草原植物群落稳定性及土壤微生物养分利用过程的影响
Alternative TitleEffects of N deposition on plant community stability and soil microbial nutrient utilization processes in typical grassland on Loess Plateau
袁晓波
Subtype博士
Thesis Advisor傅华 ; 牛得草
2020-07-28
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name农学博士
Degree Discipline草学
Keyword植物群落生产力 植物群落稳定性 植物-微生物交互作用 土壤微生物呼吸 化学计量不平衡 微生物养分限制性 土壤碳氮矿化率
Abstract草地是陆地生态系统中对全球气候变化响应最为敏感的类型之一,长期大气氮沉降对草地生态系统结构与功能影响的环境效应研究备受关注。目前,关于大气氮沉降对植物群落结构及生产力的研究较多,而对土壤微生物养分利用过程及其与植物群落互馈关系的影响研究较少,且众多氮沉降试验研究中氮素添加量较当前或者预测的未来大气氮沉降量普遍偏高,致使上述成果可能难以科学评估和预测大气氮沉降对生态系统结构和功能的影响。另外,干旱半干旱区草地植物生长受氮素限制更为强烈,且水资源短缺和土壤偏碱性导致植物和土壤微生物活力较弱,特殊的地域环境是否会缓解大气氮沉降的环境效应,还有待于研究。因此,本研究在黄土高原典型草原设置了6个氮素添加量梯度(0,1.15,2.3,4.6,9.2和13.8 g N m-2 yr-1),基于为期8年的试验监测,研究了氮沉降对植物群落物种多样性、生产力和稳定性的影响及引起群落稳定性改变的机制分析了氮沉降对土壤理化和微生物性质的影响及其与植物群落的互馈过程明晰了氮沉降对土壤微生物养分利用策略的影响及其对土壤碳氮矿化的调控过程,旨在深入理解氮沉降对草地生态系统结构与功能的影响过程,为黄土高原草地养分管理及科学评估与预测未来大气氮沉降在本区域的生态环境效应提供科学依据。主要结论如下: 1. 氮素添加降低了植物群落物种多样性,且随氮素添加量增加,植物群落地上生物量先增加后降低,而植物群落稳定性先降低后增加,二者整体表现为非线性响应。群落稳定性对氮素添加的非线性响应与物种异步性、物种丰富度、物种多样性、优势物种稳定性以及禾草功能群稳定性呈正相关关系。当前大气氮沉降水平对群落稳定性无显著影响。 2. 氮素添加改变了土壤理化性质和微生物养分利用特征。随氮素添加量的增加,土壤pH略有降低、土壤有机碳(SOC)含量后期增加,而土壤全氮(TN)变化较小土壤溶解性有机养分含量及其计量比变化规律不一致,土壤溶解性有机碳(DOC)和土壤溶解性有机氮(DON)的比值呈先增加后降低的趋势,DOC和土壤溶解性有机磷(DOP)的比值除2014年均显著降低,而DON:DOP各年份变化规律不一致。土壤资源计量比变化,导致土壤微生物C限制增强,并由此减弱了土壤微生物呼吸。氮素添对真菌群落组成变化的影响高于细菌,显著增加土壤真菌丰富度,改变了其群落组成但对土壤细菌多样性和其群落组成均无显著影响。 3. 氮素添加通过改变土壤理化性质间接影响了植物物种丰富度和土壤微生物呼吸以及两者间的互馈关系。植物物种丰富度和土壤微生物呼吸的降低与土壤溶解性无机养分(NO3--N、NH4+-N和速效磷)、全量养分、DOC及土壤含水量(SWC)有关,而与DOP和pH无关。植物地上生物量和植物丰富度表现出显著的负相关关系,而这种负相关关系通过微生物呼吸路径转变成正相关关系。上述结果表明,当生态系统处于低的大气氮沉降量水平下,植物和微生物的改变并非pH的变化引起,而主要由土壤资源的变化所致,且这种改变增强了植物-微生物互馈关系,并由此影响植物群落组成。 4. 氮素添加改变了资源的化学计量比,但土壤微生物具有较强的化学计量内稳态,致使土壤微生物与其资源间化学计量不平衡发生改变,且随氮素添加量的增加,C:N、C:P和N:P不平衡均表现为先增加后降低的趋势,致使土壤微生物生长受C限制性增强该情况下,土壤微生物通过调控胞外酶的生产和养分代谢阈值比(TER)维持自身化学计量内稳。氮素添加引致的土壤微生物呼吸的降低与TER的增加直接相关,而与胞外酶化学计量比和微生物生物量化学计量比间接相关,表明微生物生物量化学计量比和胞外酶化学计量比的协同调节导致土壤微生物具有高的碳利用效率和低的氮磷利用效率,进而降低土壤微生物呼吸。 5. 氮素添加、季节及两者交互作用均对土壤碳矿化(Cmin)率产生显著影响,而土壤矿化(Nmin)率仅季节对其产生显著影响。土壤Cmin率主要受DOC、SWC、过氧化氢酶、脲酶、蔗糖酶、微生物生物量碳(MBC)、SOC:TN和TN的影响,而土壤Nmin率主要受过氧化氢酶、DOC、NO3--N、脲酶、TN、NH4+-N、SWC和MBC与微生物生物量氮(MBN)比值的影响。氮素添加下上述驱动土壤Cmin率和Nmin率变化的因素会随季节的变化而发生改变,且土壤Cmin率和Nmin率间基本无显著相关关系。
Other AbstractGrassland is one of the most sensitive terrestrial ecosystem types in terms of response to global climate change. The environmental effects of long-term atmospheric nitrogen (N) deposition on the structure and functioning of grassland ecosystems have attracted much attention. Effects of simulated N deposition on the structure and productivity of plant communities have been explored in many studieshowever, its effects on soil microbial nutrient utilization processes and plant-microbe interactions have remained underexplored. Meanwhile, previous studies often experimented N addition with levels higher than current and future projected N deposition rates, producing highly uncertain predictions of ecosystem structure and functioning. In particular, it remains unclear whether the environmental effects of atmospheric N deposition can be alleviated in the special regional environment of arid and semi-arid grassland ecosystems ‒ where the growth of plants is more strongly limited by N and the shortage of water resources and alkaline soil suppresses plant and soil microbial activities. In this study, we manipulated a long-term experiment, consisting of six N addition levels (0, 1.15, 2.30, 4.60, 9.20, and 13.80 g N m-2yr-1), in a semiarid grassland on the Loess Plateau of China. Based on eight years of experimental monitoring, we evaluated the effects of N deposition on species diversity, productivity and stability of plant communities, and the mechanisms underlying the changes in plant community stability. Additionally, we investigated the effects of N deposition on soil physicochemical and microbial properties and plant-microbe interactions. We also studied the effects of N deposition on soil microbial nutrient utilization strategy and its regulation on soil carbon and nitrogen mineralization processes. The results of this dissertation study have important theoretical and practical significance for understanding the influence of atmospheric N deposition on the structure and functioning of grassland ecosystem and the scientific management and sustainable utilization of grassland nutrients. The main results are as follows: 1. N addition altered community diversity, reduced species richness, evenness, diversity, and dominance. With the increase of N addition, the aboveground biomass of plant communities increased first and then decreased, while the stability of plant communities first decreased and then increased. Both the aboveground biomass and stability of plant communities showed non-linear responses to N addition. The nonlinear change in community stability was positively correlated with species asynchrony, species richness, and species diversity, as well as the stability of dominant species and the stability of the grass functional group. The current level of atmospheric N deposition had no significant influence on the stability of plant communities. 2. N addition changed soil physiochemical properties and microbial nutrient utilization characteristics. With increasing N addition, soil pH slightly decreased and soil organic carbon (SOC) increased at the later stagein contrast, soil total nitrogen (TN) barely changed. The ratios of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in soils first increased and then decreased. The ratios of DOC and dissolved organic phosphorus (DOP) in soils decreased significantly in 2014, but DON:DOP varied among years. The change of soil resource stoichiometry resulted in the enhancement of soil microbial C limitation, and thus weakened soil microbial respiration. The effects of N addition were much larger on fungal community compositions than on bacteria compositions, which significantly increased soil fungal richness and changed community composition. However, it had no significant effect on the diversity of soil bacteria and its community compositions. 3. N addition indirectly affected plant species richness, soil microbial respiration, and their interactions by changing soil physiochemical properties. Reduced plant richness and soil microbial respiration were associated with the changes in soil dissolved inorganic nutrients (NO3--N、NH4+-N and available phosphorous), soil total nutrients, DOC, and soil water content (SWC), rather than DOP and pH. In addition, aboveground biomass had a significantly negative effect on plant richness, whereas this effect became somewhat positive via the pathway of soil microbial respiration path. These results indicate that changes in plants and microbes are mainly due to changes in soil resources rather than pH when ecosystems are exposed to low levels of atmospheric N deposition and further enhanced plant-microbe interactions and consequently, impacted plant community composition. 4. N addition altered resource stoichiometry while soil microbes still maintained stronger stoichiometric homeostasis, which resulted in changes in the stoichiometric imbalances between soil microbial communities and their resources. All stoichiometric imbalances, including C:N, C:P, and N:P imbalances, increased up to intermediate doses and then decreased. These nonlinear responses implied that increasing N addition enhanced microbial C limitation rather than P limitation. Data on microbial adaptive responses to resource stoichiometric imbalances revealed that, under C limitation, soil microbial communities regulated their ecoenzyme production and threshold element ratios (TER) to maintain stoichiometric homeostasis. Additionally, we found that the N-induced reduction of soil microbial respiration was directly linked to increasing TER but indirectly linked to soil ecoenzyme stoichiometry and microbial biomass stoichiometry. These results suggest that coordinated regulation of microbial biomass stoichiometry and soil enzyme stoichiometry can lead to higher C use efficiency (CUE) and lower nutrient use efficiency, further lowering soil microbial respiration. 5. N addition, season, and their interactions had significant effects on soil carbon mineralization (Cmin) rates. In contrast, we observed a significant seasonal effect on the soil nitrogen mineralization (Nmin) rate only. Across all seasons, DOC, SWC, catalase, urease, sucrase, MBC, SOC:TN, and TN were the most pivotal predictors of the soil Cmin rate. Comparatively, catalase, MBC, DOC, NO3--N, urease, TN, NH4+-N, SWC, and MBC:MBN ratio were the dominant drivers of soil Nmin rate. The identified potential drivers that regulated the soil Cmin and Nmin rates in responses to N addition varied seasonally. With elevated N addition, the soil Cmin and Nmin rates became decoupled, which was a consistent relationship among most seasons.
Pages130
URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/467293
Collection草地农业科技学院
Affiliation
草地农业科技学院
First Author AffilicationCollege of Pastoral Agriculture Science and Technology
Recommended Citation
GB/T 7714
袁晓波. 氮沉降对黄土高原典型草原植物群落稳定性及土壤微生物养分利用过程的影响[D]. 兰州. 兰州大学,2020.
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