Flux and fate of Yangtze river sediment delivered to the East China Sea

Numerous cores and dating show the Yangtze River has accumulated about 1.16 x 10(12) t sediment in its delta plain and proximal subaqueous delta during Holocene. High-resolution seismic profiling and coring in the southern East China Sea during 2003 and 2004 cruises has revealed an elongated (similar to 800 km) distal subaqueous mud wedge extending from the Yangtze River mouth southward off the Zhejiang and Fujian coasts into the Taiwan Strait. Overlying what appears to be a transgressive sand layer, this distal clinoform thins offshore, from similar to 40 in thickness between the 20 and 30 m water depth to < 1-2 in between 60 and 90 m water depth, corresponding to an across shelf distance of less than 100 km. Total volume of this distal mud wedge is about 4.5 x 10(11) m(3), equivalent to similar to 5.4 x 10(11) t of sediment. Most of the sediment in this mud wedge comes from the Yangtze River, with some input presumably coming from local smaller rivers. Thus, the total Yangtze-derived sediments accumulated in its deltaic system and East China Sea inner shelf have amounted to about 1.7 x 10(12) t. Preliminary analyses suggest this longshore and across-shelf transported clinoform mainly formed in the past 7000 yrs after postglacial sea level reached its mid-Holocene highstand, and after re-intensification of the Chinese longshore current system. Sedimentation accumulation apparently increased around 2000 yrs BP, reflecting the evolution of the Yangtze estuary and increased land erosion due to human activities, such as fanning and deforestation. The southward-flowing China Coastal Current, the northward-flowing Taiwan Warm Current, and the Kuroshio Current appear to have played critical roles in transporting and trapping most of Yangtze-derived materials in the inner shelf, and hence preventing the sediment escape into the deep ocean. (c) 2006 Elsevier B.V. All rights reserved.

Recovery and fate of three species of marine dinoflagellates after yellow clay flocculation

The recovery and fate of three species of dinoflagellates, Alexandrium tamarense, Cochlodinium polykrikoides and Scrippsiella trochoidea, after having been sedimented by yellow clay, were investigated in the laboratory. The effect of burying period in yellow clay pellet and mixing on the recovery of settled algal cells were studied. The morphological changes of algal cells in yellow clay pellet were also tracked. Results showed that there was almost no recovery for A. tamarense and C. polykrikoides, and the cells decomposed after 2-3 days after visible changes in morphology and chloroplasts. There was some recovery for S. trochoidea. Moreover, S. trochoidea cysts were formed in clay pellet during the period of about 14 days, with the highest abundance of 87 000 cysts g(-1) clay and the incidence of cyst formation of 6.5%, which was considered as a potential threat for the further occurrence of algal blooms. S. trochoidea cysts were isolated from yellow clay and incubated to test their viability, and a germination ratio of more than 30% was obtained after incubation for 1 month. These results showed the species specificity of the mitigation effect of yellow clay. It is suggested that cautions be taken for some harmful species and thorough risk assessments be conducted before using this mitigation strategy in the field.

紫茎泽兰种子库及幼苗动态特征

紫茎泽兰（Eupatorium adenophorum）是臭名昭著的世界性恶草之一，目前已对全世界30多个国家和地区造成入侵危害，大约在20世纪30年代入侵我国，在我国西南地区造成了严重的危害。本文以四川省攀枝花市遭受紫茎泽兰入侵危害严重的生态系统为研究对象，分别对不同生境下的紫茎泽兰土壤种子库进行调查，以探究紫茎泽兰土壤种子库的结构，并分析人类干扰对土壤种子库结构的影响。并在种子库调查的基础上设计了两项盆栽实验，研究紫茎泽兰土壤种子库的结构的改变导致的紫茎泽兰种子环境因子的改变，从而影响紫茎泽兰种子的萌发、幼苗的命运，以期阐明人类干扰对紫茎泽兰入侵的影响。另外连续测定紫茎泽兰早期生长的生物量，研究紫茎泽兰生物量增长、分配规律，并与其它几种本地种相比较，说明紫茎泽兰能够入侵成功的原因。 在攀枝花紫茎泽兰入侵严重的地区，通过取样研究果园、放牧灌丛以及禁牧灌丛3种不同生境紫茎泽兰土壤种子库特征，发现这3种生境的土壤种子库大小分别为10422粒m-2，3522粒m-2和2889粒m-2 。果园、放牧灌丛和禁牧灌丛等3种干扰程度不同生境的深层种子量占总种子量的比例分别为56.44%，46.96%，24.86%（p=0.006）。从干扰程度上来说，由于果园>放牧灌丛>禁牧灌丛，这一结果表明土壤深层种子量大小与干扰成正比，干扰越大，深层次紫茎泽兰种子量占总种子量的比重越大。由此可以推测，人类的干扰使得紫茎泽兰土壤种子库结构发生了改变，一方面人类干扰导致生境植被覆盖不同，干扰越大，植被覆盖度越小，土壤种子库越大，另一方面人类活动对土壤的直接扰动，使土壤种子库结构发生变化，在放牧灌丛和果园2种生境中，由于人类活动的影响，促使了紫茎泽兰土壤种子库表层种子向下层转移，而且转移量与干扰程度成正相关。由于一定深度埋藏的紫茎泽兰种子萌发的幼苗具有较低的死亡率，进入土壤深层的紫茎泽兰种子越多，紫茎泽兰的长久性土壤种子库就越大，对紫茎泽兰幼苗的补充和定居越有利，入侵也就越难以治理。 初步研究了光照、水分和种子在土壤中的埋藏深度等对紫茎泽兰幼苗的影响，结果发现，1) 播种在0cm、2cm、5cm深度的种子萌发率分别为64.67%、22.67%、13.33%，即种子埋藏越深，萌发率越低，不同层次种子萌发率差异极显著(p=0.00)；幼苗死亡率分别为27.95%、0、0，表层种子萌发的幼苗有较高的死亡率，而由埋藏在深层种子萌发的幼苗没有死亡，土壤表层发芽的幼苗与不同埋藏深度种子萌发的幼苗之间死亡率差异极显著(p=0.00)；2) 在无遮蔽、半遮蔽、全遮蔽3种不同情况下，紫茎泽兰幼苗的死亡率分别为72.15%、30.38%、4.87%，定居率分别为6.66%、33.99%、46.67%，即遮蔽程度越高，死亡率越低，定居率越高，不同处理之间死亡率和定居率差异均极显著（p=0.00）；3) 在浇水、不浇水这2种水分条件下紫茎泽兰的萌发率分别为41.56%、32% (p=0.021)；死亡率分别为35.8%、35.23% (p=0.934)；定居率分别为29.11%、22.66% (p=0.083)，说明水分因子对萌发率的影响显著，对死亡率、定居率的影响不显著。上述结果表明，土壤埋藏深度、光照和水分都是影响紫茎泽兰幼苗萌发的重要因素：一定深度的土壤埋藏能够有效降低紫茎泽兰幼苗的死亡率；光照强度与紫茎泽兰幼苗死亡率成正相关；而水分对紫茎泽兰幼苗的存活影响不显著。 通过跟踪调查紫茎泽兰的早期生长的生物量，发现紫茎泽兰生物量和高度增加迅速,且生物量的增加主要来自地上部分量的增加，而本地灌木却生长缓慢。与本地种相比，紫茎泽兰的根冠比很小，在生殖分配上，紫茎泽兰与本地灌木相比又比较大。另一方面，在生长季到来的时候，紫茎泽兰能够迅速生长，并将大部分生物量分配到地上部分；而在旱季，当许多本地本植物由于枯死、休眠进入休眠状态时，紫茎泽兰却能继续生长，从而确保其在竞争中的空间优势。 综上所述，人类活动的干扰可能导致更多的紫茎泽兰种子进入土壤深层，从而改变了紫茎泽兰土壤种子库的结构；种子萌发后强光直射可能是导致紫茎泽兰幼苗死亡的重要原因；由于土壤深层种子比表层种子具有更强的抵抗强光照射等不良环境因子影响的能力，所萌发的幼苗成活率高，表明其具有更高的繁殖效率。因此可以说是人类活动的干扰不但加剧了紫茎泽兰的入侵，也使得紫茎泽兰入侵后难以根除。

Stepwise loss of motilin and its specific receptor genes in rodents

Specific interactions among biomolecules drive virtually all cellular functions and underlie phenotypic complexity and diversity. Biomolecules are not isolated particles, but are elements of integrated interaction networks, and play their roles through specific interactions. Simultaneous emergence or loss of multiple interacting partners is unlikely. If one of the interacting partners is lost, then what are the evolutionary consequences for the retained partner? Taking advantages of the availability of the large number of mammalian genome sequences and knowledge of phylogenetic relationships of the species, we examined the evolutionary fate of the motilin (MLN) hormone gene, after the pseudogenization of its specific receptor, MLN receptor (MLNR), on the rodent lineage. We speculate that the MLNR gene became a pseudogene before the divergence of the squirrel and other rodents about 75 mya. The evolutionary consequences for the MLN gene were diverse. While an intact open reading frame for the MLN gene, which appears functional, was preserved in the kangaroo rat, the MLN gene became inactivated independently on the lineages leading to the guinea pig and the common ancestor of the mouse and rat. Gain and loss of specific interactions among biomolecules through the birth and death of genes for biomolecules point to a general evolutionary dynamic: gene birth and death are widespread phenomena in genome evolution, at the genetic level; thus, once mutations arise, a stepwise process of elaboration and optimization ensues, which gradually integrates and orders mutations into a coherent pattern.

Duplication and independent selection of cell-wall invertase genes GIF1 and OsCIN1 during rice evolution and domestication

Background: Various evolutionary models have been proposed to interpret the fate of paralogous duplicates, which provides substrates on which evolution selection could act. In particular, domestication, as a special selection, has played important role in crop cultivation with divergence of many genes controlling important agronomic traits. Recent studies have indicated that a pair of duplicate genes was often sub-functionalized from their ancestral functions held by the parental genes. We previously demonstrated that the rice cell-wall invertase (CWI) gene GIF1 that plays an important role in the grain-filling process was most likely subjected to domestication selection in the promoter region. Here, we report that GIF1 and another CWI gene OsCIN1 constitute a pair of duplicate genes with differentiated expression and function through independent selection. Results: Through synteny analysis, we show that GIF1 and another cell-wall invertase gene OsCIN1 were paralogues derived from a segmental duplication originated during genome duplication of grasses. Results based on analyses of population genetics and gene phylogenetic tree of 25 cultivars and 25 wild rice sequences demonstrated that OsCIN1 was also artificially selected during rice domestication with a fixed mutation in the coding region, in contrast to GIF1 that was selected in the promoter region. GIF1 and OsCIN1 have evolved into different expression patterns and probable different kinetics parameters of enzymatic activity with the latter displaying less enzymatic activity. Overexpression of GIF1 and OsCIN1 also resulted in different phenotypes, suggesting that OsCIN1 might regulate other unrecognized biological process. Conclusion: How gene duplication and divergence contribute to genetic novelty and morphological adaptation has been an interesting issue to geneticists and biologists. Our discovery that the duplicated pair of GIF1 and OsCIN1 has experiencedsub-functionalization implies that selection could act independently on each duplicate towards different functional specificity, which provides a vivid example for evolution of genetic novelties in a model crop. Our results also further support the established hypothesis that gene duplication with sub-functionalization could be one solution for genetic adaptive conflict.

Sorptive interaction between goethite and strongly reducing organic substances from anaerobic decomposition of green manures

Strongly reducing organic substances (SROS) and iron oxides exist widely in soils and sediments and have been implicated in many soil and sediment processes. In the present work, the sorptive interaction between goethite and SROS derived from anaerobic decomposition of green manures was investigated by differential pulse voltammetry (DPV). Both green manures, Astragaltus sinicus (Astragalus) and Vicia varia (Vicia) were chosen to be anaerobically decomposed by the mixed microorganisms isolated from paddy soils for 30 d to prepare different SROS. Goethite used in experiments was synthesized in laboratory. The anaerobic incubation solutions from green manures at different incubation time were arranged to react with goethite, in which SROS concentration and Fe(II) species were analyzed. The anaerobic decomposition of Astragalus generally produced SROS more in amount but weaker in reducibility than that of Vicia in the same incubation time. The available SROS from Astragalus that could interact with goethite was 0.69 +/- 0.04, 0.84 +/- 0.04 and 1.09 +/- 0.03 cmol kg(-1) as incubated for 10, 15 and 30 d, respectively, for Vicia, it was 0.12 +/- 0.03, 0.46 +/- 0.02 and 0.70 +/- 0.02 cmol kg(-1). One of the fates of SROS as they interacted with goethite was oxidation. The amounts of oxidizable SROS from Astragalus decreased over increasing incubation time from 0.51 +/- 0.05 cmol kg(-1) at day 10 to 0.39 +/- 0.04 cmol kg(-1) at day 30, but for Vicia, it increased with the highest reaching to 0.58 +/- 0.04 cmol kg(-1) at day 30. Another fate of these substances was sorption by goethite. The SROS from Astragalus were sorbed more readily than those from Vicia, and closely depended upon the incubation time, whereas for those from Vicia, the corresponding values were remarkably less and apparently unchangeable with incubation time. The extent of goethite dissolution induced by the anaerobic solution from Vicia was greater than that from Astragalus, showing its higher reactivity. (c) 2008 Published by Elsevier Ltd.

Reduction in microcystin concentrations in large and shallow lakes: Water and sediment-interface contributions

Blooms of cyanobacteria, or blue-greens, are known to produce chemicals, such as microcystins, which can be toxic to aquatic and terrestrial organisms. Although previous studies have examined the fate of microcystins in freshwater lakes, primary elimination pathways and factors affecting degradation and loss have not been fully explained. The goal of the present study was to explore sources of algal toxins and investigate the distribution and biodegradation of microcystins in water and sediment through laboratory and field analyses. Water and sediment samples were collected monthly from several locations in Lake Taihu from February 2005 to January 2006. Samples were analyzed for the presence of microcystin. Water and sediment were also used in laboratory studies to determine microcystin degradation rates by spiking environmental samples with known concentrations of the chemical and observing concentration changes over time. Some water samples were found to efficiently degrade microcystins. Microcystin concentrations dropped faster in water collected immediately above lake sediment (overlying water). Degradation in sediments was higher than in water. Based on spatial distribution analyses of microcystin in Lake Taihu, higher concentrations (relative to water concentrations) of the chemical were found in lake sediments. These data suggest that sediments play a critical role in microcystin degradation in aquatic systems. The relatively low levels of microcystins found in the environment are most likely due to bacterial biodegradation. Sediments play a crucial role as a source (to the water column) of bio-degrading bacteria and as a carbon-rich environment for bacteria to proliferate and metabolize microcystin and other biogenic toxins produced by cyanobacteria. These, and other, data provide important information that may be applied to management strategies for improvement of water quality in lakes, reservoirs and other water bodies. (C) 2007 Elsevier Ltd. All rights reserved.

Antioxidant enzyme activities of Microcystis aeruginosa in response to nonylphenols and degradation of nonylphenols by M-aeruginosa

The aim of this study was to examine the effects of chemical nonylphenols (NPs) on the antioxidant system of Microcystis aeruginosa strains. The degradation and sorption of NPs by M. aeruginosa were also evaluated. High concentrations of NPs (1 and 2 mg/l) were found to cause increases in superoxidase dismutase (SOD) and glutathione-S-transferase (GST) activities and in glutathione (GSH) levels. These results suggest that toxic stress manifested by elevated SOD and GST levels and GSH contents may be responsible for the toxicity of NPs to M. aeruginosa and that the algal cells could improve their antioxidant and detoxification ability through the enhancement of enzymatic and nonenzymatic prevention substances. The observed elevations in GSH levels and GST activities were relatively higher than those in SOD activities, indicating that GSH and GST contributed more in eliminating toxic effects than SOD. Low concentrations of NPs (0.05-0.2 mg/l) enhanced cell growth and decreased GST activity in algal cells of M. aeruginosa, suggesting that NPs may have acted as a protecting factor, such as an antioxidant. The larger portion of the NPs (> 60%) disappeared after 12 days of incubation, indicating the strong ability of M. aeruginosa to degrade the moderate persistent NP compounds. The sorption ratio of M. aeruginosa after a 12-day exposure to low nominal concentrations of NPs (0.02-0.5 mg/l) was relatively high (> 30%). The fact that M. aeruginosa effectively resisted the toxic effects of NPs and strongly degraded these pollutants indicate that M. aeruginosa cells have a strong ability to adapt to variations in environmental conditions and that low and moderate concentrations of organic compounds may favor its survival. Further studies are needed to provide detailed information on the fate of persistent organic pollutants and the survival of algae and to determine the possible role of organic pollutants in the occurrence of water blooms in eutrophic lakes.

Applicability of the MTT assay for measuring viability of cyanobacteria and algae, specifically for Microcystis aeruginosa (Chroococcales, Cyanobacteria)

Several assay methods were screened for viability assessment in cyanobacteria using Microcystis aeruginosa FACHB 905. Compared with fluorescent diacetate (FDA), Evan's Blue and autofluorescence, the 3-[4,5-dimethylthiazol-2-yl]2,5-diphenyl tetrazolium bromide (MTT) assay, which was based on the ability of viable cells to reduce MTT to formazan, was found to be reliable and was selected for further study. MTT concentration, incubation time and temperature were optimized for M. aeruginosa. Improvements to the sensitivity and reproducibility of the MTT assay included performing it in the dark to reduce the effects of formazan light sensitivity when extracted in DMSO. Another improvement involved collecting viability data by cell by counting rather than colourimetrically, which was concluded from the fact that oxidoreductase activity, responsible for MTT reduction, would elevate or decrease under stress conditions. Half-life of oxidoreductase in dead cell was calculated to be 3 h. The MTT assay was also found to be applicable to other cyanobacteria and diatoms, including field samples, but not for algae belonging to Chlorophyta, Euglenophyta, Pyrrophyta or Chrysophyta. Based on the above results, we proposed an optimized procedure for the MTT method on Microcystis strains. The use of this assay may be of importance to better understand the dynamics of bloom and the fate of Microcystis under natural or disturbed conditions.

Mitochondrion-mediated apoptosis induced by Rana grylio virus infection in fish cells

A fish cell line, fathead minnow (FHM) cell, was used to investigate the alteration of mitochondrial dynamics and the mechanism of apoptosis under Rana grylio virus (RGV) infection. Microscopy observations, flow-cytometry analysis and molecular marker detection revealed the apoptotic fate of the RGV-infected cells. Some typical apoptotic characteristics, such as chromatin condensation, DNA fragmentation and mitochondrial fragmentation, were observed, and significantly morphological changes of mitochondria, including size, shape, internal structure and distribution, were revealed. The mitochondria in RGV-infected cells were aggregated around the viromatrix, and the aggregation could be blocked by colchicine. Moreover, the Delta psi m collapse was induced, and caspase-9 and caspase-3 were activated in the RGV-infected cells. In addition, NF-kappa B activation and intracellular Ca2+ increase were also detected at different times after infection. The data revealed the detailed dynamics of mitochondrion-mediated apoptosis induced by an iridovirus, and provided the first report on mitochondrial fragmentation during virus-induced apoptosis in fish cells.