Contribution of zooplankton to the fishery of Dharamtar Creek, adjoining Bombay Harbour

The rich zooplankton standing stock of Dharamtar Creek showed a variation of 8 to 5261 (av. 1032) mg C/100 m super(3)/d which led to a turnover of 29 tonnes C/km super(2)/y. The estimated fishery potential from zooplankton production was 0.079 tonnes C/km super(2) or 29.00 tonnes/km/y. The worked out yield in terms of wet weight of fish was 0.059 tonnes/km2u2/d. Experimental trawling within the creek showed a potential of 0.19 tonnes/km super(2)/d suggesting a transfer coefficient of only 31.4% form secondary to tertiary level. Fish eggs and larvae were very common in the area but contributed collectively only 1% to the total zooplankton population. On an average the outer zone sustained relatively higher population of fish eggs and larvae than the interior zone. The mean population density of larvae (334/100 m super(3)) was 3.5 times higher than fish eggs (93/100 m super(3)) suggesting the good survival rate and a congenial environment for larvae to thrive.

Reynolds number influence on turbulent blocking effects of a rigid plane boundary (3rd report, direct numerical simulation on wall blocking effects for anisotropic turbulence)

The Reynolds number influence on turbulent blocking effects by a rigid plane boundary is studied using direct numerical simulation (DNS). A new forcing method proposed in the second report using Townsend's "simple model eddies" for DNS was extended to generate axisymmetric anisotropic turbulence. A force field is obtained in real space by sprinkling many space-filling "simple model eddies" whose centers are randomly but uniformly distributed in space. The axes of rotation are controlled in this study to generate axisymmetric anisotropic turbulence. The method is applied to a shear-free turbulent boundary layer over a rigid plane boundary and the blocking effects for anisotropic turbulence are investigated. The results show that stationary axisymmetric anisotropic turbulence is generated using the present method. Turbulence intensities near the wall showed good agreements with the rapid distortion theory (RDT) for small t (t ≪ TL), where TL. is the eddy turnover time. The splat effect (i. e. turbulence intensities of the components parallel to the surface are amplified) occurs near the boundary and the viscous effect attenuates the splat effect at the quasi steady state at low Reynolds number as for Isotropic turbulence. Prandtl's secondary flow of the second kind does not occur for low Reynolds number flows, which qualitatively agrees with previous observetion in a mixing-box.

The biology, ecology, population parameters and the fishery of the Nile tilapia, Oreochromis niloticus (L)

Oreochromis niloticus (the Nile tilapia) and three other ti1apine species: Oreochromis leucostictus, Tilapia zi11ii and T. rendallii were introduced into Lakes Victoria, Kyoga and Nabugabo in 1950s and 1960s. The source and foci of the stockings are given by Welcomme (1966) but the origin of the stocked species was Lake Albert. The Nile tilapia was introduced as a management measure to relieve fishing pressure on the endemic tiapiines and, since it grows to a bigger size, to encourage a return to the use of larger mesh gill nets. Ti1apia zillii was introduced to fill a vacant ,niche of macrophytes which could not be utilised' by the other tilapiines. Tilapia rendallii, and possibly T. leucosticutus could been introduced into these lakes accidently as a consquence of one of the species being tried out for aquaculture. The Nile perch and Nile tilapia have since fully established themselves and presently dominate the commercial fisheries of Lakes Victoria and Kyoga. The original fisheries based on the endemic tilapiines O. escu1entus and o. variabilis have collapsed. It is hypothesized that the ecological and limnological changes that are observed in Lakes Victoria and Kyoga are due to a truncation of the original food webs of the two lakes. Under the changed conditions, O. niloticus to be either playing a stabilizing role or fuelling nutrient turnover in the lakes. Other testable hypotheses point to the possible role of predation by the Nile perch, change in regional climate and hydrology in the lake basins.

The evolution of a stratified turbulent cloud

Localized regions of turbulence, or turbulent clouds, in a stratified fluid are the subject of this study, which focuses on the edge dynamics occurring between the turbulence and the surrounding quiescent region. Through laboratory experiments and numerical simulations of stratified turbulent clouds, we confirm that the edge dynamics can be subdivided into materially driven intrusions and horizontally travelling internal wave-packets. Three-dimensional visualizations show that the internal gravity wave-packets are in fact large-scale pancake structures that grow out of the turbulent cloud into the adjacent quiescent region. The wave-packets were tracked in time, and it is found that their speed obeys the group speed relation for linear internal gravity waves. The energetics of the propagating waves, which include waveforms that are inclined with respect to the horizontal, are also considered and it is found that, after a period of two eddy turnover times, the internal gravity waves carry up to 16 % of the cloud kinetic energy into the initially quiescent region. Turbulent events in nature are often in the form of decaying turbulent clouds, and it is therefore suggested that internal gravity waves radiated from an initial cloud could play a significant role in the reorganization of energy and momentum in the atmosphere and oceans.©2013 Cambridge University Press.

Application of methyl parathion hydrolase (MPH) as a labeling enzyme

Methyl parathion hydrolase (MPH) is an enzyme that catalyzes the degradation of methyl parathion, generating a yellow product with specific absorption at 405 nm. The application of MPH as a new labeling enzyme was illustrated in this study. The key advantages of using MPH as a labeling enzyme are as follows: (1) unlike alkaline phosphatase (AP), horseradish peroxidase (HRP), and glucose oxidase (GOD), MPH is rarely found in animal cells, and it therefore produces less background noise; (2) its active form in solution is the monomer, with a molecular weight of 37 kDa; (3) its turnover number is 114.70 +/- 13.19 s(-1), which is sufficiently high to yield a significant signal for sensitive detection; and (4) its 3D structure is known and its C-terminal that is exposed to the surface can be easily subjected to the construction of genetic engineering monocloning antibody-enzyme fusion for enzyme-linked immunosorbent assay (ELISA). To demonstrate its utility, MPH was ligated to an single-chain variable fragment (scFv), known as A1E, against a white spot syndrome virus (WSSV) with the insertion of a [-(Gly-Ser)(5)-] linker peptide. The resulting fusion protein MPH-A1E possessed both the binding specificity of the scFv segment and the catalytic activity of the MPH segment. When MPH-A1E was used as an ELISA reagent, 25 ng purified WSSV was detected; this was similar to the detection sensitivity obtained using A1E scFv and the HRP/Anti-E Tag Conjugate protocol. The fusion protein also recognized the WSSV in 1 mu L hemolymph from an infected shrimp and differentiated it from a healthy shrimp.

Size-related shifts in reliance on benthic and pelagic food webs by lake anchovy

This paper reports large variations in stable carbon and nitrogen isotope ratios of lake anchovy (Coilia ectenes taihuensis) from Lake Chaohu, China. The lake anchovy exhibited a significant C-13- and N-15- enrichment in relation to increasing fish length, and the isotopic compositions of small lake anchovy (<= 130 mm) were significantly more enriched than those of large lake anchovy (> 130 mm). The significant differences in the isotopic compositions of small and large lake anchovy suggested that their assimilated diets differed over a period of time and reflected the size-related diet shift of this fish. Bellamya aeruginosa and Corbicula fluminea were used to establish the baseline carbon signal of benthic and pelagic food webs, and these data were used to parameterize a 2-source mixing model to estimate in consumers the contribution of carbon derived from benthic versus pelagic food webs. Mixing models showed that small lake anchovy derived only 37% of their carbon from benthic food web, indicating increased reliance on pelagic prey, whereas benthic prey contributed 71% of large lake anchovy diet, suggesting greater use of benthic sources. These data indicate that there was a change in lake anchovy feeding strategy related to their size, suggesting a role in dynamic coupling between pelagic and benthic food chains. The trophic position of small lake anchovy averaged 3.0, indicating a zooplankton-based diet, compared with 3.6 in large lake anchovy, indicative of an increase in piscivorous diet. Overlap in the isotopic compositions of small and large lake anchovy probably indicated that these fish occasionally shared common diets, as suggested by stomach content studies, and/or resulted from the differences in the rate of isotopic turnover depending on differences in growth rate and metabolic turnover between small and large anchovy during diet shift from pelagic to benthic food webs. This study presents the contributions of benthic and pelagic food webs supporting lake anchovy and indicates that the intraspecific isotopic dynamic should be considered when applying stable isotope analyses to infer trophic interactions in aquatic ecosystems.

Differential and spermatogenic cell-specific expression of DMRT1 during sex reversal in protogynous hermaphroditic groupers

DMRT1 has been suggested to play different roles in sex determination and gonad differentiation, because different expression patterns have been reported among different vertebrates. The groupers, since their gonads first develop as ovary and then reverse into testis, have been thought as good models to study sex differentiation and determination. In this study, we cloned the full-length cDNAs of DMRT] gene from orange-spotted grouper (Epinephelus coioides), and prepared corresponding anti-EcDMRT1] antiserum to study the relationship of DMRT] to sex reversal. One important finding is that the grouper DMRT] is not only differentially expressed in different stage gonads, but also restricted to specific stages and specific cells of spermatogenesis. Grouper DMRT1 protein exists only in spermatogonia, primary spermatocytes and secondary spermatocytes, but not in the supporting Sertoli cells. Moreover, we confirmed that EcSox3 is expressed not only in oogonia and different stage oocytes, but also in Sertoli cells and spermatogonia, and EcSox9 is expressed only in Sertoli cells. The data suggested that grouper DMRT1 might be a more specific sex differentiation gene for spermatogenesis, and play its role at the specific stages from spermatogonia to spermatocytes. In addition, no introns were found in the grouper DMRT1, and no duplicated DMRT1, genes were detected. The finding implicates that the intronless DMRT1 that is able to undergo rapid transcriptional turnover might be a significant gene for stimulating spermatogenesis in the protogynous hermaphroditic gonad. (c) 2006 Published by Elsevier Ireland Ltd.

Auxetic nuclei in embryonic stem cells exiting pluripotency.

Embryonic stem cells (ESCs) self-renew in a state of naïve pluripotency in which they are competent to generate all somatic cells. It has been hypothesized that, before irreversibly committing, ESCs pass through at least one metastable transition state. This transition would represent a gateway for differentiation and reprogramming of somatic cells. Here, we show that during the transition, the nuclei of ESCs are auxetic: they exhibit a cross-sectional expansion when stretched and a cross-sectional contraction when compressed, and their stiffness increases under compression. We also show that the auxetic phenotype of transition ESC nuclei is driven at least in part by global chromatin decondensation. Through the regulation of molecular turnover in the differentiating nucleus by external forces, auxeticity could be a key element in mechanotransduction. Our findings highlight the importance of nuclear structure in the regulation of differentiation and reprogramming.

Cell types, network homeostasis, and pathological compensation from a biologically plausible ion channel expression model.

How do neurons develop, control, and maintain their electrical signaling properties in spite of ongoing protein turnover and perturbations to activity? From generic assumptions about the molecular biology underlying channel expression, we derive a simple model and show how it encodes an "activity set point" in single neurons. The model generates diverse self-regulating cell types and relates correlations in conductance expression observed in vivo to underlying channel expression rates. Synaptic as well as intrinsic conductances can be regulated to make a self-assembling central pattern generator network; thus, network-level homeostasis can emerge from cell-autonomous regulation rules. Finally, we demonstrate that the outcome of homeostatic regulation depends on the complement of ion channels expressed in cells: in some cases, loss of specific ion channels can be compensated; in others, the homeostatic mechanism itself causes pathological loss of function.

ROLE OF PHOSPHORUS CYCLING IN ALGAL METABOLISM AND ALGAL SUCCESSION IN LAKE DONGHU, CHINA

The role of phosphorus cycling in algal metabolism was studied in a shallow lake, Donghu, in Wuhan using the methods of measuring cell quota C, N and P, and calculating nutrients uptake rate by algal photosynthesis. The mean daily phosphorus uptake rate of phytoplankton varied between 0.04-0.11 and 0.027-0.053 g/m2/d in station I and station II respectively. The turnover time of phosphorus in phytoplankton metabolism ranged from 0.75-5.0 days during 1979-1986. The available P was 0.176 (+/- 0.156) g/m3 (mean +/- SD) in 1982 and 0.591 (+/- 0.24) g/m3 in 1986. The relationship between P/B ratio (Y) and TP (X: mg/l) was described by the following regression equation Y = 1.163 + 0.512logX (r = 0.731, P < 0.001). The dynamics of algal biomass and algal species succession were monitored as the indicators of environmental enrichment. The small-sized algae have replaced the blue-green algae as the dominant species during 1979-1986. The small-sized algae include Merismopedia glauca, Cryptomonas ovata, Cryptomonas erosa, several species Cyclotella. There has been drastic decrease in algal biomass and an obvious increase in P/B ratio. A nutrient competition hypothesis is proposed to explain the reason of the disappearance of blue-green algae bloom. The drastic change in algal size and the results in high P/B ratio (reaching a maximum mean daily ratio of 1.09 in 1986) may suggest a transition of algal species from K-selection to r-selection in Lake Donghu.

Interplay between partial incoherence, partial inelasticity, resonance, and heterogeneity in long-range electron transfer and transport

A generalized scattering matrix formalism is constructed to elucidate the interplay of electron resonance, coherence, dephasing, inelastic scattering, and heterogeneity, which play important roles in the physics of long-range electron transfer/transport. The theory consists of an extension of the standard Buttiker phase-breaking model and an analytical expression of the electron transmission coefficient for donor-bridge-acceptor systems with arbitrary length and sequence. The theory incorporates the following features: Dephasing-assisted off-resonance enhancement, inelasticity-induced turnover, resonance enhancement and its dephasing-induced suppression, dephasing-induced smooth superexchange-hopping transition, and heterogeneity effects. (C) 2002 American Institute of Physics.

Scattering matrix approach to electronic dephasing in long-range electron transfer

Based on the Buttiker dephasing model, we propose an analytical scattering matrix approach to the long-range electron transfer phenomena. The present efficient scheme smoothly interpolates between the superexchange and the sequential hopping mechanisms. Various properties such as the drastic dephasing-assisted enhancement and turnover behaviors are demonstrated in good agreement with those obtained via the dynamical reduced density-matrix methods. These properties are further elucidated as results of the interplay among the dephasing strength, the tunneling parameter, and the bridge length of the electron transfer system. (C) 2001 American Institute of Physics.

基于任务的人力资源离职风险预测研究与实现

软件开发是智力密集型产业，人力资源在软件开发中扮演着极其重要的角色，不同的人在相同的设备上，可以生产出质量和功能完全不同的产品，其生产效率甚至可以相差数十倍，Boehm的COCOMO模型发现团队质量是目前项目成功最大的决定因素。在软件开发中，人力资源的离职是无法避免的，总会有人因为人为或非人为的原因而离职。不同的研究人员对人力资源离职进行统计率研究表明，人力资源的离职率高达33%～80%之间，平均雇员受雇时间仅为15～36个月，而且人力资源的离职往往会给公司带来很高的成本，使人力资源离职风险成为软件开发极其重要的一种风险。虽然现在软件开发过程比以前更成熟，人员的离职仍然会给项目带来严重的影响，甚至会给项目带来毁灭性的打击。 在人员高离职率的情况下，量化项目中的每个人在任一时间点的离职对项目造成的影响，对项目管理者来说是很有参考意义的，它可以帮助项目管理人员客观地了解目前项目的人力资源离职风险情况。本文在深入细致地研究了国内外研究现状的基础上，提出了一种基于任务的人力资源离职风险预测研究。 本文的主要内容包括： 第一、提出了基于任务的人力资源离职风险预测模型。通过建立项目计划任务模型、人力资源模型、任务分配模型，来对项目开发进行描述，使模型能够适用于大多数的软件开发项目； 第二、针对现有人力资源风险管理主要依靠主观判断和个人经验的弱点，将项目参与者离职对项目造成的影响（项目延迟时间和项目成本超支）量化，给项目风险管理者提供客观的数据支持，作为企业和项目进行人力资源风险管理的依据； 第三、对基于任务的人力资源离职风险研究进行实例化分析。通过一个实际的项目实例，来分析本研究的实际使用过程。并对实例的研究结果进行分析，给出了一些降低人力资源离职风险的切实可行的措施。 第四、设计和开发了一个基于任务的人力资源离职风险预测系统，提高人力资源风险管理的效率和准确性。

次生植被土壤碳、氮养分季节动态及凋落物输入与温度的影响

土壤微生物量、可溶性有机碳与氮虽然只占土壤有机碳、氮总量的较小部分，但可以在土壤全碳、氮变化之前反映土壤微小的变化，又直接参与土壤生物化学转化过程，因而在植被恢复过程中，较其它土壤理化性质等能够更好地指示土壤恢复情况。在青藏高原东缘存在大面积的次生人工林替代灌丛或采伐迹地，而关于这些人工林替代后的生态效果和生态过程的评估却十分缺乏，本研究通过评估岷江上游植被恢复重建过程中典型人工替代次生植被凋落物层与土壤碳、氮等养分大小，动态监测土壤微生物生物量、水溶性碳、氮等指标，结合温度与凋落物输入等影响土壤活性有机碳、氮因子的控制试验，系统分析不同人工替代次生植被土壤碳、氮等养分的差异原因，试图寻找低效人工林优化调控与持续管理技术，为区域生态公益林持续管理提供理论和技术依据。主要结论如下： 1. 通过对不同人工替代次生植被凋落物层和土壤碳、氮分析发现，油松和华山松人工林替代次生灌丛后土壤碳、氮含量较灌丛和阔叶人工林低，主要原因可能为凋落物质量(C/N)较差，而引起碳、氮等元素难以归还土壤。进而通过对不同人工替代次生植被凋落物层和土壤微生物生物量、水溶性有机碳、氮等指标的季节性动态模式的分析，发现各次生植被土壤微生物生物量C、N，P以及土壤水溶性碳、氮含量均呈明显季节性动态，呈现秋季明显大于其它季节，冬季最低，在表层土壤最为明显。 2. 油松、华山松人工林凋落物层和土壤水溶性有机碳(WDOC)、土壤水溶性有机氮(WDON)明显低于灌丛和连香树，土壤微生物生物量C、N也以油松和华山松人工林最低，而落叶类植被，如灌丛、连香树和落叶松之间没有明显差异，说明可利用底物的数量和质量差异是影响各次生植被凋落物分解和土壤微生物活性的主要原因。MBC/OC和MBN/ON能较好地指示土壤微生物活性的变化，MBC/OC凋落层总体以灌丛和连香树人工林最高，油松和华山松人工林最低；而土壤中MBC/OC连香树人工最高，华山松人工林最低。说明以油松和华山松为主的人工造林替代乡土阔叶灌丛造成土壤C、N等养分严重匮乏，微生物活性低下是影响其养分周转的主要原因。 3. 从各次生植被凋落物产生看，凋落物年归还量最大的为华山松人工林(5.1×103 kg ha-1)，其次为落叶松人工林(4.8×103 kg ha-1)，阔叶灌丛林地凋落物产生总量(4.4×103 kg ha-1)略大于油松人工林(4.2×103 kg ha-1)，最小的为连香树人工林(3.6×103 kg ha-1)；叶是凋落物的主体，落叶类树种月动态表现为单峰型，高峰主要在10-11月，如落叶松、连香树和灌丛林；常绿的松类月动态不明显，各月基本相同，最为明显地为油松林，华山松人工林略有二个小峰，分别出现在11月和5月。落叶阔叶灌丛的凋落物分解速率大于常绿针叶林，如油松和华山松。结合凋落物的产生量和分解速率，不同树种人工林替代次生阔叶灌丛后，人工油松和华山松林枯落物总贮量和厚度明显大于落叶松人工林、灌丛林和连香树人工林，说明以油松和华山松为主的人工造林替代乡土阔叶灌丛延缓了有机物向土壤的顺利归还，不利于土壤C、N等养分循环。 4. 通过控制地面凋落物和地下根系输入有机物对土壤碳、氮的影响研究发现，(1) 单独去除根系以及根系与地面凋落物同时去除处理1年后对表层(0-10cm)土壤WDOC均没有显著影响，而土壤WDON显著增加，油松人工林土壤微生物生物量C、N显著降低，人工落叶松林没有显著差异，说明油松人工林土壤微生物活性对地下碳输入的依赖大于其它次生植被，而落叶松土壤微生物活性对地下碳输入依赖性较小；去除地面凋落物，明显降低了落叶松人工林土壤WDOC，华山松和连香树土壤WDON均较对照显著减少，油松人工林土壤微生物量C较对照显著减少；双倍增加地面凋落物处理对土壤微生物生物量、WDOC和WDON没有明显地增加，相反，连香树、华山松和油松人工林土壤WDON较对照减少。说明油松人工林微生物活性不仅依赖于地下碳输入，而且对地上有机物输入的依赖性也较大；连香树、落叶松和华山松人工林土壤微生物生物量并没有因地面凋落物的去除减少可能与土壤总有机碳含量及活性均较高有关，而双倍增加地面凋落物反而降低了土壤微生物生物量，说明凋落物覆盖后改变了土壤微气候。 5. 碳矿化累积量与有机碳含量和活性有机碳含量之间存在显著地正相关关系。凋落物碳累积矿化量、矿化速率以连香树最高，油松和华山松人工林次之，落叶阔叶灌丛低于常绿针叶纯林，导致其差异的主要原因可能为凋落物产生的时间动态模式不一样，致使凋落物起始分解时间不一致。而土壤层有机碳矿化速率和矿化量以阔叶落叶灌丛和连香树最高，油松和华山松人工土壤最低，再次证实利用针叶纯林恢复植被阻碍了有机质周转与循环。 6. 凋落物累积矿化量与C/N值呈显著地相关关系，并随着温度的升高而明显增加，而土壤累积矿化量与C/N值没有显著相关关系，说明土壤有机碳质量(C/N)对温度的响应不十分明显。通过双指数模型对不同温度下碳矿化过程进行模拟和计算出活性有机碳与惰性有机碳比例，发现温度升高促进了惰性有机碳向活性有机碳的转化，增加了活性有机碳含量，说明温度升高可促进次生植被凋落物与土壤有机质的分解，进而可影响到林地碳源/汇关系的变化。 综上，通过对不同人工替代次生植被凋落物与土壤C、N大小、以及土壤微生物生物量、水溶性C、N等指标动态变化模式研究，结合温度与凋落物数量输入等影响土壤活性C、N因子的综合分析，以油松和华山松人工纯林对山地植被恢复，延缓或阻碍了有机质周转与循环，造成了土壤肥力退化。对现有低效人工纯林改造，应为地面大量有机物分解创造条件。 Although soil microbial biomass, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) are a small part of total soil organic carbon and nitrogen, they can directly participate in the process of soil biochemical translation and indicate the fine changes before changes of soil total organic carbon and nitrogen occur. So, they are good indexes to indicate soil restoration condition during the process of vegetation rehabilitation. There are large areas of secondary vegetations which substitute for indigenous shrubs in the eastern fringe of Qinghai-Tibet Plateau. However, it is not well known that the ecological effect and process after substitution by different secondary plantations. Based on comparison of soil organic and nitrogen contents in litter layer and soil under different secondary vegetations in upper reaches of Minjiang River, soil microbial biomass, DOC and DON in litter layer and soil were investigated in order to analyze the seasonal dynamic. Combining the effects of temperature, litter input and root exclusion on soil microbial biomass, DOC and DON, we also aim to understand the reason and mechanism of difference in soil carbon and nitrogen contents among different secondary vegetations. The study would contribute to comprehensively understanding C and N cycling processes and provide optimal control and sustainable technology of low-effect plantations in these regions. The results are as follows: (1) Organic carbon and nitrogen in litter layers and soil under different substitution plantations were investigated. The results showed that contents of soil organic carbon and nitrogen were lower in P. tabulaeformis (PT) and P. armandi Franch(PA) than those in native broad-leaf shrub and broad-leaf plantation. The low quality (C/N) of litter in PT and PA plantations caused carbon and nitrogen returning to soil difficultly. Seasonal dynamic of soil microbial carbon (MBC),-nitrogen (MBN),-phosphor (MBP), and WDOC and WDON showed similar pattern, which had the highest values in autumn and the lowest values in winter. (2) WDOC and WDON in litter layers and soil under PT and PA plantations were significantly lower than those in native broad-leaf shrub and Cercidiphyllum japonicum Sieb. et Zucc.(CJ). Soil MBC and MBN were also the lowest, while there were no significant differences among deciduous vegetations, i.e. native broad-leaf shrub, CJ and Larix kaempferi Lamb.(LK) plantation. The results suggested that difference in quantity and quality of available substance was main reason that affected the activity of microbe in soil and litter layer. MBC/OC and MBN/ON were good indexes to indicate the change of soil microbial activity. MBC/OC of litter had the highest value under native broad-leaf shrub and CJ plantation, and had the lowest value in PT and PA plantations, while MBC/OC of soil was the highest under CJ plantation, and was the lowest in PT and PA plantations. These results indicated that PT and PA plantations substituting for native broad-leaf shrub caused deficit of carbon and nitrogen in soil, low microbial activity was a main reason influencing the cycling and turnover of carbon and nitrogen in soil. (3) The annual litter fall production, composition, seasonal dynamic and decomposition of five typical secondary stands in upper reaches of Minjiang River were studied in this paper. The annual litter productions were: PA (5.1×103 kg ha-1), LK(4.8×103 kg ha-1), native broad-leaf shrub (4.4×103 kg ha-1), PT(4.2×103 kg ha-1)，CJ(3.6×103 kg ha-1). The litter production of leaves in five secondary vegetations occupied a higher percentage in the annual total litter production than those of other components. The litterfall was mostly producted in the cool and dry period (October-November) for deciduous vegetations and relatively equably producted in every season for evergreen coniferous vegetations. The decomposition rate of leaf litter in the broad-leaf stand was higher than those in evergreen coniferous stand. Combined with annual litter fall production and decomposition rate of leaf litter, we found that stock and depth of litter layer were significantly larger in PT and PA plantations than those in native broad-leaf shrub, LK and CJ plantations. The results confirmed that PT and PA plantations substituting for native broad-leaf shrub delayed organic matter returning to soil and hindered cycling of carbon and nitrogen again. (4) We explored plant litter removal, double litter addition, root trenching, and combining root trenching and litter removal treatments to examine the effects of above- and belowground carbon inputs on soil microbial biomass, WDOC and WDON in four secondary plantations. During the experimental period from June 2007 to July 2008, 1 year after initiation of the treatments, WDOC in soil did not vary in root trenching, and combining root trenching and litter removal treatments, while WDON in soil significantly increased compared with CK treatment. Root trenching reduced soil MBC and MBN in PT plantation, while MBC and MBN in soil did not vary in LK plantation. The rasults implied that soil microbial activity was more dependent on belowground carbon input in PT plantation than those in other secondary plantations, on the contrary, soil microbial activity in LK plantation was not dependent on belowground carbon input. Plant litter removal significantly decreased soil WDOC in LK plantation, decreased WDON in PA and CJ plantations, and also significantly reduced soil MBC in PT plantation. However, double litter addition did not increase soil microbial biomass, WDOC and WDON, on the contrary, soil WDON in CJ, PA and PT plantations were decreased. These suggested that soil microbial activity was not only dependent on belowground carbon input, but also on aboveground organic material input. Double litter addition could change the microclimate and result in the decrease of soil microbial activity in CJ, PA and PT plantations. (5) We measured carbon mineralization in a 107 days incubation experiment in 5℃,15℃ and 25℃. Carbon cumulative mineralization was positively correlated with organic matter and labile organic carbon in litter layer and soil. Cumulative carbon mineralization and mineralization rate of litter layers in PT and PA plantations were higher than that in native broad-leaf shrub. This difference between native broad-leaf shrub and coniferous plantations in cumulative carbon mineralization and mineralization rate of litter layers could be attributed to the initiating time of decomposition due to the difference in seasonal dynamic of litter fall production between two types of secondary plantations. However, cumulative carbon mineralization and mineralization rate in soil were the highest in native broad-leaf shrub and CJ plantation, and were the lowest in PT and PA plantations. This also confirmed that PT and PA plantations substituting for native broad-leaf shrub hindered the cycling and turnover of organic matter again. (6) Carbon cumulative mineralization was positively correlated with C/N in litter layer and increased with temperature increasing, while carbon cumulative mineralization was not correlated with C/N in soil. This indicated that soil organic matter quality (C/N) was insensitive to temperature. Applying bi-exponential model, we computed the percent of labile and stable carbon in different temperature incubation and found that temperature increasing would accelerate the transform from stable carbon to labile carbon and increase the percentage of labile organic carbon. This illuminated that temperature incraesing could facilitate the decomposition of litter and soil organic matter in secondary vegetations and hence affect the relationship between carbon source and sink.

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.