A New Method to Investigate InGaAsP Single-Photon Avalanche Diodes Using a Digital Sampling Oscilloscope

A near-infrared single-photon detection system is established by using pigtailed InGaAs/InP avalanche photodiodes. With a 50GHz digital sampling oscilloscope, the function and process of gated-mode (Geiger-mode) single-photon detection are intuitionally demonstrated for the first time. The performance of the detector as a gated-mode single-photon counter at wavelengths of 1310 and 1550nm is investigated. At the operation temperature of 203K,a quantum efficiency of 52% with a dark count probability per gate of 2. 4 * 10~(-3), and a gate pulse repetition rate of 50kHz are obtained at 1550nm. The corresponding parameters are 43% , 8. 5 * 10~(-3), and 200kHz at 238K.

岷江上游人工针叶、阔叶林土壤可溶性有机物质特征及其对凋落物分解的响应

土壤可溶性有机物质（Dissolved organic matter，DOM）作为土壤有机质的活性组分，在陆地生态系统物质循环中扮演非常重要的角色。土壤DOM的主要成分可溶性有机碳（Dissolved organic carbon，DOC）和氮（Dissolved organic nitrogen，DON）参与C、N循环过程。为深入揭示全球C、N循环过程机制，在未开展DOC和DON的地区进行相关研究是有必要的。森林土壤（包括枯枝落叶层）DOC、DON动态及调控机理的研究是目前国际上森林生态系统C、N循环研究热点之一。本研究立足于暖温带岷江上游茂县地区人工林植被，对土壤DOC和DON的库容量，季节动态及其与其它养分之间的关系进行了系统研究，旨在了解DOC和DON在该区生态系统中的重要作用，并探讨作为DOM主要来源的叶凋落物对DOC和DON的动态影响，研究有助于更加详细地了解该区生态系统C和N循环过程。本论文主要研究结论如下： 1研究了岷江上游地区两大主要土壤类型（棕壤和褐土）不同植物群落下土壤的DOC和DON含量及特征，结果表明：DOC和DON在两种土壤类型中均有库容量存在，DOC在0-10cm和10-20cm土层的含量幅度分别111.96~159.95 mg kg-1和69.02~100.84 mg kg-1。DON在0-10cm和10-20cm土层的含量幅度分别11.88~23.08 mg kg-1和4.70~10.77 mg kg-1。游离氨基酸在0-10cm和10-20cm土层的含量幅度分别0.84~1.66 mg kg-1和0.39~0.73 mg kg-1。DOC、DON与土壤中的一些养分因子表现出了显著的相关关系，共同反映了土壤的状况和质量，在该区开展DOC和DON的系统研究是有必要的。 2 对油松与连香树林地土壤DOC、DON以及其它化学指标的季节动态进行了研究，结果表明：油松与连香树林地土壤DOC和DON的季节动态变化表现了类似的规律，DOC和DON的含量均以秋季最高。DOC和DON的季节动态变化主要受凋落物生物因素的影响，但其微生物活力的生物因素以及降雨、温度等非生物因素也是控制土壤DOC和DON含量的重要因素。土壤DON在土壤中的行为不同于矿质氮，其季节动态不同于NO3--N和NH4+-N的季节动态，在研究N循环过程中，应考虑DON的变化情况。 3 对油松与连香树林地分解层和表层土壤（0-10cm）氨基酸周转动态进行了研究，结果表明：油松林地和连香树林地均以分解层的氨基酸含量高于矿质表层土壤的含量。每个取样时期，油松林地内各层次的氨基酸含量高于连香树林地内相应层次的含量。两林地各层次无机氮含量均超过了氨基酸的含量，并且室内培养30天后无机N的含量仍然高于氨基酸的含量，所以可以认为该区立地条件下无论是在有机分解层还是矿质土层植物吸收利用的氮素仍是以无机N为主。 4 松林下松针凋落物易于累积，这与松针凋落物分解缓慢有关，从而导致松林内养分周转缓慢。通过用不同性质凋落物和灌丛地土壤构建微生态系统，比较油松、辐射松、连香树、灌丛虎榛子凋落物分解对C、N循环过程的影响，结果显示油松和辐射松针叶凋落物比连香树、虎榛子凋落物分解更慢，减缓了养分循环过程。然而将针叶凋落物与阔叶凋落物混合后，油松和辐射松针叶凋落物的分解加快，C、N元素的循环过程也加速。此结果表明在松林内维持具有高质量凋落物的灌丛植被或在松林内栽植一些阔叶树种如连香树对维持和增进松树人工林的土壤肥力有重大的作用。室内培养的结果还显示添加凋落物后土壤DOC和DON的含量显著增加，表明凋落物是土壤DOM的直接来源。然而不同物种凋落物处理下土壤DOC和DON的含量有所不同，并随时间发生改变。混合凋落物处理下土壤DOC和DON的含量均高于松针凋落物单独处理下土壤DOC和DON的含量。DON是一个主要的水溶性N库，随时间的变化趋势与无机N的变化趋势不同，在土壤N循环过程中起到了中间N库的作用。 As a labile fraction of soil organic matter, dissolved organic matter (DOM) plays a very important role in material cycling of terrestrial ecosystem. The turnover of DOM is now being considered as main components in nutrient cycling. DOM mainly includes dissolved organic carbon (DOC), -nitrogen (DON), -phosphorous (DOP) and –sulfur (DOS). Among these constituents, DOC and DON directly participate in C and N cycling. It is essential to study DOC and DON dynamics and their controlling factors in the areas where no related study has ever been carried out. Study about them can provide data supports on understanding the mechanism of the global C and N cycling. DOC and DON dynamics and their controlling factors have been focused on in the research of C and N cycling of forest ecosystems. Based on forest plantations of Maoxian, Minjiang River in warm temperate zone, soil DOC and DON pool size, their seasonal dynamics, and the correlation between DOC, DON and other nutrients were studied in order to understand the importance of DOC and DON in the study area. Soil DOC and DON dynamics induced by leaf litter decomposition were also studied. The study contributed to comprehensively understanding C and N cycling processes and providing baseline data for including DOC and DON into the indices system of evaluating nutrient conditions. The results were as follows: 1 Several different plant communities under brown soil and Cinnamon soil were chosen as sampling plots. The contents and features of soil DOC and DON were evaluated. The results showed that DOC and DON were present under the two soil types. DOC contents in the top soil (0-10 cm) and the subsoil (10-20 cm) respectively varied from 111.96 mg kg-1to 159.95 mg kg-1, and 69.02 mg kg-1 to 100.84 mg kg-1. DON contents in the top soil (0-10 cm) and the subsoil (10-20 cm) respectively varied from 11.88 mg kg-1to 23.08 mg kg-1, and 4.70 mg kg-1 to 10.77 mg kg-1. Free amino acid contents in the top soil (0-10 cm) and the subsoil (10-20 cm) respectively varied from 0.84 mg kg-1to 1.66 mg kg-1, and 0.39 mg kg-1 to 0.73 mg kg-1. Significant correlations were found between DOC, DON and some nutrient indices, which together reflected soil condition and quality. It was hence essential to study DOC and DON in the study area. 2 Seasonal dynamics of DOC, DON, inorganic N, microbial biomass C and N were studied under Pinus tabulaeformis and Cercidiphyllum japonicum plantation. The results indicated that seasonal dynamics of soil DOC and DON under the two plantations performed similar change pattern, with the highest values in autumn. The seasonal dynamics of soil DOC and DON were mainly influenced by the litterfall. However, biotic factors such as soil microbial activities and abiotic factors such as precipitation and temperature also controlled the dynamics of soil DOC and DON. The seasonal dynamic of DON was different from that of NO3--N and NH4+-N, which showed that the behavioral differences between DON and inorganic nitrogen. And hence, it was proposed to include DON into soil N cycling in the study area. 3 Amino acid dynamics in Oa and topsoil (0-10 cm) under P. tabulaeformis and C. japonicum plantation were studied. The results showed that amino acid content in Oa was significantly higher than that in mineral soil. At each sampling time, significantly higher amino acid contents were found in P. tabulaeformis plantation than in C. japonicum plantation. The content of inorganic nitrogen was much higher than the content of amino acid in each sampling layer at each sampling time. After a 30-days laboratory incubation the content of amino acid was still lower than the content of inorganic nitrogen. The results implicated that the form of N absorbed by plants in these study sites were mainly inorganic nitrogen. 4 Usually needle litter is more resistant to decomposition, which leads to needle litter accumulation in pure coniferous stands and slows down the rate of nutrient circulation. By constructing microcosms with local shrubland soil and containing the four single-species (P. tabulaeformis, P. radiata, C. japonicum, Ostryopsis davidiana) litters, the decomposition rates and related C and N dynamics of needle litters and broadleaved litters during the early stage were compared. The results showed that the decomposition rates of pine needles were lower than those of broadleaved litters, which descended C and N cycling processes. However, the presence of C. japonicum or O. davidiana litter into pine needles increased the decomposition rates of pine needles and also dramatically promoted C and N cycling processes. It should be appropriate for plantation managers to consider C. japonicum as an ameliorative species or remain O. davidiana in pine plantations to improve soil conditions and help maintain soil fertility. The laboratory incubation still showed that DOC and DON contents in all litter-amended treatments were significantly higher than no litter-amended treatment, which proved that litter could be a direct source of DOM in soils. Different species litters induced different soil DOC and DON contents, which correspondingly changed over time. DOC and DON contents in mixed litter treatments were higher than those in pine needle litter treatments. As a major soluble N pool, DON developed a different changing pattern over time compared with inorganic N and played a role of interim N pool in soil N cycling.

Assessing soil erosion rates on manually-tilled hillslopes in the Sichuan Hilly Basin using Cs-137 and Pb-210(ex) measurements

IEECAS SKLLQG

Late Pliocene-Pleistocene changes in mass accumulation rates of eolian deposits on the central Chinese Loess Plateau

IEECAS SKLLQG