Knowledge Resource Center for Ecological Environment in Arid Area
| 荒漠生物土壤结皮的固氮作用及其影响因素研究 | |
| 其他题名 | Studies on the nitrogen fixation of desert biological soil crusts and its influencing factors |
| 郑娇莉 | |
| 出版年 | 2018 |
| 学位类型 | 博士 |
| 导师 | 邱东 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 荒漠化是我国目前面临的重要环境问题，生物土壤结皮（BSCs）作为荒漠生态系统重要的地表覆盖类型，和荒漠化土地恢复过程中最初的拓殖生物，其发育演替对于荒漠化土地的生态恢复与重建具有重要意义。氮素是干旱半干旱地区仅次于水分的限制因子，BSCs的发育能够促进荒漠生态系统的氮素积累，但是目前国内外关于BSCs的氮素输入过程以及氮素输入对BSCs发育的影响的研究较少。本研究以人工生物土壤结皮演替系列为研究对象，首先研究了不同演替阶段BSCs在不同降雨模式（降雨间隔、降雨时刻）和降水形式下的生长和生物固氮过程；其次研究了苔藓拓殖和发育对BSCs固氮生物的分布以及固氮作用的影响；最后研究了外源性氮输入（氮添加，即模拟氮沉降）对BSCs生长发育和氮素循环过程的影响。希望通过以上研究揭示BSCs在荒漠生态系统氮素输入过程中的作用及外源性氮输入对BSCs演替的影响，从而理解BSCs的生态功能，为荒漠化土地防治及生态修复提供理论支持。论文的主要研究内容和结果如下：(1) 通过室内模拟实验研究了不同降雨模式下BSCs叶绿素荧光参数（Fv/Fm）和固氮酶活性（NA）的恢复过程。结果发现，早期演替阶段BSCs的Fv/Fm恢复速率几乎不受干燥时长的影响（蓝藻结皮：r = 0.127，p = 0.073；藻-藓结皮：r = -0.046，p = 0.522），而晚期演替阶段的苔藓结皮Fv/Fm的恢复速率与干燥时长呈负相关（r = -0.514，p < 0.001）。BSCs的NA在0-7.7 nmol C2H4·cm-2·h-1。早期演替阶段的BSCs显示出相同的NA恢复模式和不同的NA速率，而苔藓结皮显示不同的NA恢复模式：NA恢复过程有24 h的延迟。干燥时长不超过8天时，则干燥时间越长，早期演替阶段BSCs的NA越低，但在此较短的干燥时长范围内，苔藓结皮的NA恢复并不受干燥时长的影响。相反，较长时间的干燥后（4-6个月），所有演替阶段的BSCs均恢复了较高的NA。不同演替阶段BSCs对降雨格局的响应存在差异，频繁降雨能够增加早期演替阶段BSCs的固氮，而长时间的湿润时间（较大的降雨或者长时间降雨）将有利于晚期演替阶段的苔藓结皮的固氮。(2) 原位研究了不同降水形式下（非降雨水分和降雨）BSCs生理活性的恢复过程。结果发现非降雨水分能够诱导BSCs生理活性（包括Fv/Fm、碳交换以及固氮酶活性）的恢复，然而，非降雨水分带来负的碳平衡以及较低的固氮酶活性。模拟降雨条件下，复水后3小时内BSCs能够恢复各项生理活性并开始固碳，而非降雨水分条件下BSCs的生理活性较低且恢复较慢。所有演替阶段BSCs的非降雨水分捕获量和Fv/Fm最大恢复值之间呈显著正相关（蓝藻结皮：r2 = 0.681， p < 0.001; 藻-藓结皮：r2 = 0.495， p < 0.001; 苔藓结皮：r2 = 0.480，p < 0.001）。随着BSCs演替，年有效的非降雨水分事件随着结皮演替而增加，蓝藻结皮、藻-藓、苔藓结皮时间分别为29.8、89.2、110.7天。苔藓结皮和藻-藓结皮能更有效地利用非降雨水分，因此非降雨水分可能是苔藓适应荒漠干旱环境的重要水分来源。但是，荒漠生物主要利用非降雨水分维持存活，其生物量的积累仍然需要大的降雨。（3）苔藓拓殖和发育对固氮生物和固氮作用的影响。通过研究苔藓结皮中固氮微生物群落结构、分布和固氮酶活性，以及苔藓对BSCs固氮作用的影响，发现苔藓结皮的固氮生物群落中，具异形胞的丝状蓝藻丰度高达98.6%，同时苔藓结皮的固氮酶活性需要光照，表明具异形胞丝状蓝藻发挥主要的固氮作用。大量的丝状固氮蓝藻附生于苔藓假根，分布于数毫米深的土层中，苔藓附生蓝藻固氮能力与完整结皮相当。添加葡萄糖溶液48 h以后，苔藓结皮的固氮酶活性和固氮基因的表达量在分别升高约16倍和5倍。苔藓叶片部分固氮酶活性很低，但是去掉叶片后假根部分固氮酶活性显著降低（p < 0.01），添加葡萄糖能够显著提高假根部分的固氮酶活性（p < 0.01），推测苔藓可能通过为附生蓝藻提供光合产物来促进其固氮活性。苔藓取代表层自由生长的蓝藻后，附生蓝藻成为主要的固氮生物，固氮过程受到复杂的调控及苔藓光合作用的影响，可能解释为何苔藓结皮固氮活性恢复更为缓慢。（4）BSCs生长过程对氮沉降的响应。在人工诱导形成的BSCs区域，选择蓝藻结皮、藻-藓结皮、藓-藻结皮和苔藓结皮4个演替阶段的BSCs建立原位样方，分3次添加0、3、9、18 kg N ha-1yr-1 4个水平的NH4NO3以模拟氮沉降，分析不同季节BSCs的生理活性、速效养分、生物量和碳氮比（C:N）等指标。结果发现：各演替阶段BSCs的生理活性、速效养分和生物量等指标均表现出明显的季节动态；各演替阶段BSCs的光合作用（Fv/Fm和净光合作用）和呼吸作用的变化类似；早期演替阶段BSCs的固氮酶活性在7月份和11月份较高，而苔藓结皮则是7月份和9月份较高。早期演替阶段BSCs的速效养分均在生长季降低，在非生长季升高，而苔藓结皮只有无机氮有类似趋势。苔藓结皮的有机碳和叶绿素a（Chl a）的动态变化不同于早期结皮。氮添加对不同演替阶段BSCs无机氮含量没有促进作用，对各阶段BSCs微生物群落结构没有影响。但是氮添加促进了各阶段BSCs尤其是苔藓结皮的净光合作用以及Chl a、有机质和总氮的积累。C:N和固氮酶速率等指标反映BSCs中仍然存在氮素限制。BSCs的氮限制程度具有结皮类型和生长季节差异性。在未来氮沉降增加时，氮沉降可能部分缓解氮限制，但生物固氮仍然是不可替代的重要氮源。（5）BSCs氮素循环过程对氮沉降的响应。对各演替阶BSCs建立原位样方，分3次添加0，3，9，18 kg N ha-1yr-14个水平的NH4NO3，分析不同季节BSCs的氮素形态、氮素转化过程和氮循环功能基因丰度。结果表明：氮添加对BSCs中不同氮形态含量的影响比较小，但是对结皮的氮循环产生重要影响，导致氮素的雨季淋溶损失增加，以NO3--N形式淋溶损失的氮素占氮素添加量约有6-56%；外源性氮输入对BSCs的固氮活性有抑制作用，但并不能完全抑制；氮添加促进氨氧化速率和反硝化速率，从而促进保留在土壤的无机氮持续损失。BSCs能够快速地响应氮沉降，通过减少固氮，增加淋溶、硝化和反硝化过程调节土壤氮库，从而对氮沉降有一定的缓冲作用。综上所述，水分是荒漠生态系统首要的限制因子。单次降水以及季节或年际降水格局决定了BSCs的生长动态。BSCs演替过程中，苔藓逐渐占据土壤表层，取代藻类成为主要的光合生物；附生固氮蓝藻也取代自由生固氮蓝藻成为主要的固氮生物，其固氮过程受到复杂的调控和苔藓的影响，导致苔藓结皮光合固碳和固氮作用对降水的响应发生显著变化，从而表现出与早期结皮不同的生长动态。BSCs的氮限制程度具有结皮类型和生长季节差异性。氮沉降可能部分缓解氮限制，这是由于BSCs对氮素的保留能力很低，使得氮添加后土壤无机氮库很快恢复至正常水平。生物固氮仍然是不可替代的重要氮源。BSCs氮循环过程能够快速地响应氮沉降，通过减少输入、增加输出调节土壤氮库，从而对氮沉降有一定的缓冲作用。关键词：生物土壤结皮，演替，生物固氮，降水，生理活性，氮循环 |
| 英文摘要 | AbstractDesertification is one of the most important environmental problems in China. Biological soil crusts (BSCs) are important surface cover type in desert ecosystem and are also the initial colonizer in the restoration of desert, thus the BSCs succession is of vital significance for the ecological restoration and reconstruction of desertification land. Nitrogen is the second limiting factor after water in arid and semi-arid region, and the BSCs succession can promote nitrogen accumulation in desert ecosystem. However, the study of nitrogen input process of BSCs and influence of nitrogen input on BSCs development are rarely either in domestic or in foreign. In this study, taking the successional series of artificial BSCs as research objects, we firstly studied the growth and nitrogen fixation of BSCs at different successional stages under different rainfall patterns (include rainfall time and rainfall interval) and precipitation types. Then the effects of moss colonization and development on the distribution as well as the nitrogen fixation of nitrogen-fixing microorganisms were studied. Thirdly, we studied the effects of exogenous nitrogen (nitrogen addition, namely simulated nitrogen deposition) on the growth and nitrogen cycling processes of BSCs at different successional stages. Based on the above researches, we aimed to understand the role of BSCs on nitrogen input in desert ecosystems and the effects of exogenous nitrogen input on BSCs succession and to recognize the ecological functions of BSCs, thus providing theoretical support for control and ecological restoration of desertification. The main results were summarized as follows:(1) We conducted an indoor simulation experiment to test the recovery processes of chlorophyll fluorescence (Fv/Fm) and nitrogenase activity (NA) in BSCs followed different rainfall pattern. Prior desiccation durations had no effect on the recovery of Fv/Fm in early successional stages (Cyanobacterial Crust, r = 0.127, p = 0.073；Cyanobacteria-moss Crust, r = -0.046, p = 0.522), but were negatively correlated with the recovery rates of Fv/Fm in the Moss Crust (r = -0.514, p < 0.00001). The NA of BSCs was in the range of 0-7.7 nmol C2H4·cm-2·h-1. The early successional stages showed the same recovery pattern of NA with different values, while the moss dominant crust showed different recovery pattern that the recovery process has a delay of 24 hours than early stages. Within 8 days, longer desiccation decreased the NA in the early three stages of crusts, but had no impact on NA in the moss dominant crust. In the dark, two days desiccation resulted in nearly no NA in any of the crusts. Four to six months of desiccation resulted in high NA in both the light and dark in all crusts. Different successional stages of BSCs respond differently to precipitation pattern, frequent precipitation can increase nitrogen fixation of early stages of BSCs, and long hydration duration (heavy precipitation or a long period of precipitation) would promote nitrogen fixation of later stage of BSCs (Moss Crust).(2) In-situ experiments were conducted to test the recovery process of physiological activities in BSCs followed different precipitation types (including non-rainfall water and rainfall). Results showed that non-rainfall water (NRW) inputs hydrated and activated the physiological activities (Fv/Fm, carbon exchange, and nitrogen fixation) in BSCs but led to a negative carbon balance and low rates of nitrogen fixation in BSCs. Following simulated rainfall, the physiological activities recovered within 3 h, and net carbon gain occurred until 3 h after hydration, whereas NRW-induced physiological recovery processes were slower and exhibited lower activities. There were significant positive correlations between NRW amounts and the recovered values of Fv/Fm in all the three BSC stages (Cyanobacterial Crust, r2 = 0.681; p < 0.001; Cyanobacteria-moss Crust, r2 = 0.495, p < 0.001; Moss Crust：r2 = 0.480，p < 0.001). The thresholds for Fv/Fm activation decreased with the succession of BSCs, and the annual effective NRW events increased with the succession of BSCs, with values of 29.8, 89.2, and 110.7 in cyanobacteria crust, cyanobacteria-moss crust and moss crust, respectively. The results suggest that moss crust and moss-cyanobacteria crust use NRW to prolong metabolic activity and reduce drought stress more efficiently than cyanobacteria crust. However, BSCs utilize NRW to sustain life while growth and biomass accumulation require precipitation (rainfall) events over a certain threshold.(3) The effect of moss colonization and develop on diazotroph and nitrogen fixation.The composition, distribution and NA of nitrogen-fixing organisms in moss crust and the effect of moss on nitrogen fixation were studied. In moss crust, heterocyst forming filamentous cyanobacteria had absolute predominance in the community of nitrogen-fixing microorganisms with anoundance of 98.6%. And the NA of moss crust requires illumination, indicating that the filamentous cyanobacteria played a major role in nitrogen fixation. A number of filamentous nitrogen-fixing cyanobacteria were epiphyte on the moss rhizoid and distributed in soil layers of several millimeters deep. The moss-epiphytic cyanobacteria showed high rates of NA that comparable to intact crusts. In compare to distilled water, Moss Crust with glucose solution rewetted showed increasing of nitrogen fixation to about 16 times and increasing of nifH expression to about 5 times after 48 hours of rewetting. Moss leaves showed very low rates of NA, but removing the leaves significantly reduced NA in remain crust parts (p < 0.01), while remain crust parts can be stimulated to fix nitrogen after glucose added (p < 0.01). Thus we speculated that moss could promote nitrogen fixation by providing photosynthetic products to epiphytic cyanobacteria. After moss taking place of surface free-living cyanobacteria, epiphytic cyanobacteria become main nitrogen fixer and their nitrogen fixation was controlled by complex regulation and affected by photosynthesis of moss. This may explain the slower recovery of NA in moss crust in compare to early stages of BSCs.(4) The growth of BSCs in response to nitrogen deposition. In induced BSCs area, we established in situ quadrats for each BSC stage and added four levels of NH4NO3: 0, 3, 9 and 18 kg N ha-1yr-1 in three times. We analyze the physiological activities, available nutrients, biomass, and C/N ratio of BSCs in different seasons. All BSCs stages showed distinct seasonal dynamics in physiological activities, available nutrients and biomass. The dynamics of photosynthesis (Fv/Fm and net photosynthesis) and respiration were similar in different succession stages. In early successional stages, the rates of NA were high in July and November, while in moss crust, NA was high in July and September. In early successional stages, available nutrients increased during non-growth season while decreased in growth season, while in moss crust only inorganic nitrogen had similar dynamics. The dynamics of Chlorophyll a (Chl a) and organic carbon were also different between early successional stages and moss crust. Nitrogen addition had little effect on the inorganic nitrogen content and microbial community in all BSCs, while it promoted the net photosynthesis and facilitated the accumulation of Chl a, organic matters, and total nitrogen in BSCs, especially in moss crust. However, C:N ratios and nitrogen fixation rates suggested that nitrogen limitation still existed. Nitrogen limitation degree in BSCs varied among crust types and seasons. In the future, increasing of nitrogen deposition may only partly alleviate nitrogen limitation, and biological nitrogen fixation wil be still irreplaceable nitrogen resource.(5) The effect of nitrogen deposition on nitrogen cycle of biological soil crusts. We established in situ quadrats for each BSC stage and added four levels of NH4NO3: 0, 3, 9 and 18 kg N ha-1yr-1 in three times. We analyze the nitrogen forms, nitrogen transformation rates, and abundances of nitrogen cycle related genes of BSCs in different seasons. Nitrogen addition had little effect on the content of nitrogen forms, while it had significant effect on nitrogen transformation. Nitrogen addition increased leaching loss of added nitrogen during rainy season, and about 20-32 % of added nitrogen was lost in form of nitrite via leaching. The nitrogen addition suppressed nitrogen fixation to some extent. Nitrogen addition increased ammonia oxidation rate and denitrification rate, thus promoted continuous loss of inorganic nitrogen that remains in the soil. Nitrogen addition decreased nifH, nirS, nirK abudance while seems had no effect on AOA amoA and AOB amoA. In this study we observed fast response of nitrogen transformation in BSCs to nitrogen addition, and BSCs modulated nitrogen pool balance by decreasing input and increasing output. The nitrogen cycling of BSCs respond rapidly to nitrogen deposition. BSCs regulated soil nitrogen pool via decreasing input and increasing output, and thus to some extent BSCs have buffer capacity to nitrogen deposition.In summary, water is the first limitation factor in desert ecosystems. Single precipitation event，seasonal precipitation pattern and annual precipitation pattern determined the dynamic growth of BSCs. During the process of BSCs succession, moss gradually occupied the soil surface and became main photosynthetic organism in place of cyanobacteria crust; meanwhile, epiphytic cyanobacteria replaced surface free-living cyanobacteria and become main nitrogen fixer, and their nitrogen fixation was controlled by complex regulation and affected by photosynthesis of moss. The succession of photosynthetic organisms and diazotization led to different response to precipitation, and at last lead to different growth dynamics in compare with early stages. Nitrogen limitation degree in BSCs varied among crust types and seasons. Increasing of nitrogen deposition may partly alleviate nitrogen limitation, because BSCs have low ability to retain inorganic nitrogen and increased inorganic nitrogen returned to normal level rapidly after nitrogen addition. Therefore, biological nitrogen fixation is a still irreplaceable nitrogen resource in the presence of nitrogen deposition. The nitrogen cycling of BSCs respond rapidly to nitrogen deposition. BSCs regulated soil nitrogen pool via decreasing input and increasing output, and thus to some extent BSCs have buffer capacity to nitrogen deposition.Key words：Biological nitrogen fixation; Biological soil crust; Nitrogen cycling; Physiological activation; Precipitation; Succession |
| 中文关键词 | 生物土壤结皮 ; 演替 ; 生物固氮 ; 降水 ; 生理活性 |
| 英文关键词 | Biological nitrogen fixation Physiological activation Precipitation Succession |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 水生生物学 |
| 来源机构 | 中国科学院水生生物研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/288118 |
| 推荐引用方式 GB/T 7714 | 郑娇莉. 荒漠生物土壤结皮的固氮作用及其影响因素研究[D]. 中国科学院大学,2018. |
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