|Alternative Title||Influences of soil microorganisms on phosphorus bioavailability in Hailuogou glacier retreat area|
|Place of Conferral||北京|
|Keyword||海螺沟土壤年代序列 生态系统发育早期 磷的生物有效性 微生物量磷 有机磷矿化|
因山地冰川退缩加剧、地质灾害和人类工程活动等，山区存在大量“新鲜”地质体和发育初期的生态系统。磷（P）的有效供给是这些“年轻”生态系统土壤发育和植被演替的必要条件。微生物参与P循环的各个阶段，而生态系统发育早期土壤微生物对P的生物有效性的影响程度和控制机理尚不明确。发育在冰川退缩迹地上的土壤年代序列一方面提供了用空间代替时间，研究成土早期微生物和P循环在世纪尺度上演化规律的条件；另一方面有助于利用环境因素、微生物特征和P的生物有效性的明显变异，探讨成土早期微生物对P的生物有效性的影响程度和控制机理。本研究选区海螺沟冰川退缩区为研究对象，设置了冰川退缩年龄约为2年（样点1）、35年（样点2）、45年（样点3）、85年（样点4）和125年（样点5）的5个采样点和一个年龄约为1400年（样点6）参考点。在调查生态系统基本性质和养分状况的基础上，分析了土壤微生物群落和P循环的演化特征，并探讨了微生物量P和微生物参与的有机P矿化过程对P的生物有效性的影响。主要研究结果和结论如下：（1）冰川退缩区发生快速的土壤有机C、N积累，N的养分状况在不同演替阶段差异明显。在发育125年后，土壤有机C和N的积累速率分别为55.6和3.4 g m-2 yr-1，其中有机层对有机C、N的积累的贡献明显超过矿质土壤表层。冰川退缩后125年内，固氮灌丛阶段（35 yr）的N养分状况最高；退缩~1400年后，N养分状况明显高于之前演替阶段。（2）PLFA分析和氯仿熏蒸提取结果显示海螺沟冰川退缩区微生物的群落组成和微生物量随演替阶段而异。微生物真菌细菌比和有机层微生物量（浓度）普遍在固氮灌丛阶段达到最高，体现了植被类型对微生物群落结构的影响。土壤C含量与微生物量的关系、微生物C:N:P计量比和土壤酶活性计量比的分析结果显示，C可能是海螺沟冰川退缩区土壤微生物的主要限制因子。（3）退缩区土壤P的生物有效性随演替阶段发生明显变异。土壤P的生物有效性的分布与N类似，冰川退缩后125年内，在固氮灌丛阶段最高，退缩~1400年后，明显高于之前阶段。植物针叶N:P和土壤C:Po计量比数据显示退缩区植被可能存在P限制，但这一推断需要直接证据的支持。在退缩区的各演替阶段，土壤微生物P储量与植物P储量比较接近（微生物P储量与植物P储量比例为0.3-2.7），是生物P库的主要组成部分，体现了微生物量P周转在生物有效态P更新中的作用。土壤有机P储量随土壤发育快速增加（发育125年后积累速率为0.08 g m-2 yr-1），说明有机P矿化过程对生物有效态P供给的贡献逐渐增加。（4）微生物量P一方面是生物有效态P的潜在来源，另一方面对溶解和弱吸附态无机P起固持作用。在野外条件下，微生物量P与生物有效态P（Hedley方法）呈显著正相关（R2 = 0.40, p < 0.0001），说明微生物量P是生物有效态P的潜在来源；微生物量P与resin-Pi和P的释放速率没有线性关系，说明微生物对无机P固定与土壤中无机P的释放处于动态平衡，使溶解和弱吸附态P处于较低水平。极端条件下（如干湿、冻融交替），微生物量P释放导致生物有效态P增加，这体现在微生物量P与风干处理后resin-Pi的增加显著正相关（R2 = 0.65, p < 0.0001）。另外，在风干处理过程中微生物量P释放是导致基于Hedley方法计算的生物有效态P储量与植物P养分状况不一致的重要原因。（5）土壤发育早期，微生物对C的需求可能是驱动土壤有机P矿化的主要机制。退缩区土壤中有机P的矿化速率主要受C的矿化速率影响（R2 = 0.41-0.69, p < 0.0001），而与P的生物有效性相关性较差（R2 = 0.05-0.09, p ≤ 0.05）；在C矿化速率较高时，磷酸根在微生物细胞内发生积累（微生物量C:P计量比低至8:1），表明磷酸根可能作为C矿化的副产物释放出来；发育早期（2-125年），土壤有机P和C按计量比同步积累（R2 = 0.85, p < 0.0001）。这些证据表明成土早期土壤有机P的矿化受微生物C矿化过程的驱动。因为发育早期植物可能受P限制，C驱动的有机P矿化对演替早期植物的P养分获取意义重大。本研究有助于理解生态系统发育早期P的生物地球化学循环和植被的演替规律，也可以为恢复和管理由冰川退缩、地质灾害和工程活动导致的“新鲜”地质体提供理论支持。;
Large amount of recently exposed bare lands and young ecosystems exist in the mountain area, due to accelerated retreat of mountain glacier, mountain hazards, and engineering activities. The adequate supply of phosphorus (P) is prerequisite for soil development and plant succession in these young ecosystems. Microorganisms are involved in each phase of P cycling, whereas the extents and mechanisms of the microbial influences on P bioavailability in the early stage of soil development remain unclear. Chronosequences developed on the glacier retreat area provide an ideal tool to investigate the biogeochemical cycling of P during the early stage of soil development. By substituting space for time, the succession of soil microorganisms and the changes in P cycling may be surveyed on a century scale. Moreover, the environmental factors, structure and function of microbial community, and P bioavailability vary markedly among soil horizons and along succession stages, which provides the opportunity to decipher the mechanisms underlying the microbial influences on P bioavailability in the early stage of soil development. In this study, 5 sites with ages of 2 (Site 1), 35 (Site 2), 45 (Site 3), 85 (Site 4) and 125 (Site 5) yr in the Hailuogou glacier retreat area and 1 reference site of 1400 yr (Site 6) were selected. The general properties, especially the nutrient statuses, of the young ecosystem in the retreat area were studied. The succession of soil microorganisms and the changes in P cycling were surveyed. Based on these results, the influences of microbial biomass P (MBP) and the microbial mineralization of soil organic P (Po) on P availability were analyzed. The main results and conclusions are as follows: (1) Fast accumulation of soil organic carbon (C) and nitrogen (N) occurred in the retreat area. After 125 yr of glacier retreat, the accumulation rates of soil C and N were 55.6 and 3.4 g m-2 yr-1, respectively, with the organic horizons contributing the majority of C and N stocks. The N status was highest in the stage of N-fixing shrubs during the 125 yr after glacier retreat, and further increased after 1400 yr. (2) FLFA and chloroform fumigation-extraction analysis indicated that composition and biomass of the microbial community varied among succession stages. The fungi:bacteria ratio, and microbial biomass (concentration) in the organic horizon were generally highest in the stage of N-fixing shrubs, indicating the influences of vegetation type on the structure of microbial community. The relationships between soil C concentration and microbial biomass, as well as the stoichiometry of microbial biomass and soil enzymes suggested that soil microorganisms in the retreat area may be mainly limited by C. (3) The soil P availability varied significantly among succession stages. The distribution of P status was similar to that of N. During the 125 yr of glacier retreat, soil P availability was highest in the stage of N-fixing shrubs, whereas after 1400 yr, the soil P availability was significantly higher than the earlier stages. Needle N:P of saplings and C:Po (organic P) of soils indicated possible P limitation for the vegetation, but direct evidence was needed to confirm this speculation. In the retreat area, the microbial biomass P stocks were of similar magnitude with the plant P stocks with the ratios between microbial biomass P stocks and plant P stocks being 0.3-2.7. This indicated that microbial biomass P was a major biological P pool and the turnover of microbial biomass P can be crucial for the replenishment of bioavailable P during the early stage of ecosystem development. Fast accumulation of Po occurred with soil development with a rate of 0.08 g m-2 yr-1 after 125 year of glacier retreat. This suggested that the mineralization of Po may gradually become a vital source of bioavailable P. (4) MBP was a potential source of bioavailable P, and meanwhile immobilized the dissolved and weakly adsorbed inorganic P. Under field conditions, MBP was positively correlated with bioavailable P (determined using Hedley fractionation method; R2 = 0.40, p < 0.0001), indicating the potential role of MBP as a source of bioavailable P; no linear relationship was observed between MBP and resin-Pi or net P release rate, which suggested that the dynamic balance between microbial immobilization and gross inorganic P release led to low concentrations of labile P in the soil. Under extrame conditions (dry-rewetting or freeze-thaw cycles), the release of MBP may lead to increases in bioavailable P, as indicated by the positive relationship between MBP and increases in resin-Pi after air-drying (R2 = 0.65, p < 0.0001). In addition, the release of MBP during air-drying may partly explain the discrepancy between bioavailable P stocks (based on Hedley fractionation) and plant P status. (5) At the early stage of soil development, microbial demand for C may be the driving factor of Po mineralization. The main evidence for the "C-driven" mineralization of Po included: the mineralization rate of soil Po in the retreat area was more associated with the rate of C mineralization (R2 = 0.41-0.69, p < 0.0001) than with the P availability (R2 = 0.05-0.09, p ≤ 0.05); at high C mineralization intensity, P was accumulated in the microbial biomass (microbial biomass C:P ratio as low as 8:1), suggesting phosphate in excess of microbial demand was released as the byproduct of C mineralization; at the young sites (2-125 yr), the significant correlation between Po and C concentrations in the surface mineral horizon (R2 = 0.85, p < 0.0001) indicated the accumulation of Po and C at the same pace according to the stoichiometry ratios. Considering the fact that vegetation may be P limited in the retreat area, the C-driven mineralization of Po can be significant for the P acquisition of plants in the young ecosystems. The results obtained in this study can be helpful to understand the biogeochemical cycling of P and the succession of vegetation. Meanwhile, they provide theoretical supports for the restoration and management of the recently exposed bare lands.
|王吉鹏. 海螺沟冰川退缩区土壤微生物对磷的生物有效性的影响[D]. 北京. 中国科学院大学,2016.|
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