林火干扰对广东省桉树林生态系统碳密度的影响

林火作为森林非连续的生态因子,引起森林生态系统碳库碳储量与碳分配的变化,影响森林演替进程及固碳能力。以桉树林不同林火干扰强度的火烧迹地为对象,采用相邻样地比较法,以野外调查采样与室内试验分析相结合为主要手段,研究不同林火干扰强度对森林生态系统各碳库及生态系统碳密度变化和空间分布格局的影响,探讨林火干扰对生态系统碳密度与碳分布格局的影响机制。结果表明:林火干扰降低了植被碳密度(P<0.05),轻度、中度和重度林火干扰样地植被碳密度依次为67.88、35.68和15.50 t·hm^-2,相比对照分别下降了15.86%、55.78%和80.79%;在轻度、中度和重度林火干扰样地中,凋落物碳密度分别为1.43、0.94和0.81 t·hm^-2,相比对照分别降低了28.14%、52.76%和59.30%;不同林火干扰强度样地土壤有机碳密度均低于对照,且减少幅度随土壤剖面深度增加而逐渐变小,轻度、中度和重度林火干扰样地土壤有机碳密度分别为103.30、84.33和70.04 t·hm^-2,相比对照分别下降了11.67%、27.89%和40.11%;轻度、中度和重度林火干扰后桉树林生态系统碳密度分别为172.61、120.95和86.35 t·hm^-2,相比对照依次下降了13.53%、39.41%和56.74%;林火干扰降低了桉树林的碳密度,表现为随林火干扰强度增加,碳密度呈递减的规律;与对照相比,轻度林火干扰强度对桉树林碳密度的影响不显著(P>0.05),而中度和重度林火干扰强度对桉树林碳密度的影响差异显著(P<0.05)。     

有机物料还田对双季稻田土壤有机碳及其活性组分的影响

有机物料还田是提升农田土壤有机碳、培肥土壤的重要措施。为探讨不同有机物料的还田效果,采用室外培养方法,研究了在等碳输入条件下,施用水稻秸秆、紫云英、生物有机肥、猪粪和水稻秸秆生物炭对洞庭湖双季稻区潮土有机碳和活性有机碳组分含量的影响。结果表明: 经过180 d的培养试验,与不施用有机物料相比,施用有机物料提高了土壤活性有机碳含量。生物有机肥、猪粪和水稻秸秆生物炭处理分别使土壤有机碳含量显著提升了26.1%、9.7%和30.7%,水稻秸秆和紫云英对土壤有机碳含量的提升效应在试验期间并不显著。水稻秸秆和紫云英还田更有利于土壤可溶性有机碳和微生物生物量碳的积累,猪粪更有利于土壤可溶性有机碳的积累,生物有机肥更有利于土壤微生物生物量碳和易氧化有机碳的积累,水稻秸秆生物炭则更有利于土壤微生物生物量碳和轻组有机碳的积累。与水稻秸秆还田相比,紫云英、生物有机肥、猪粪和水稻秸秆生物炭还田使土壤碳库管理指数分别提高了31.8%、111.6%、62.2%和50.7%。从土壤固碳和土壤碳库管理指数来看,生物有机肥、猪粪和水稻秸秆生物炭的还田效果优于水稻秸秆和紫云英还田。     

长期氮添加对草甸草原生态系统氮库的影响

大气氮沉降增加深刻影响生态系统物种多样性、生产力及其稳定性,研究草原生态系统N库如何响应不断增加的大气氮沉降至关重要。本研究在内蒙古额尔古纳草甸草原开展刈割和不同水平外源氮添加试验,设置6个氮添加水平: 0、2、5、10、20和50 g·m^-2·a^-1,同时设置刈割处理,分为刈割和不刈割2个水平。在连续处理的第7年,采集群落中优势植物地上部分、群落根、地表凋落物和0～100 cm分层土壤样品,测定N含量并计算N库储量。结果表明: 氮添加显著增加植物地上部分和凋落物N含量,以及羊草、植物群落和凋落物的N库及生态系统N库总量。刈割处理显著增加羊草叶片和凋落物N含量,降低羊草、植物群落和凋落物N库,但并不改变它们对氮添加的响应格局。此外,刈割和氮添加对植物群落N库存在显著的交互作用。在不刈割处理下,高水平氮添加使更多的氮储存在凋落物中等待分解,植物群落N库的饱和阈值出现在10 g·m^-2·a^-1;在刈割处理下,植物群落N库表现为随氮添加量增加而不断增加,并且在相同水平氮添加条件下刈割后进入到植物群落N库中的氮更多。刈割可以缓解氮沉降不断增加对生物多样性和生态系统稳定性造成的不利影响,并可以在一定程度上推迟氮沉降增加引起的生态系统氮饱和的发生。     

Temperature stress and survival ability of Mediterranean sclerophyllous plants

ABSTRACT

The Mediterranean climate with hot and dry summer periods, and low winter temperatures and episodic frosts in northern, altitudinal and continental districts, demands from evergreen broadleaved woody plants an adequate and flexible acclimation to the climatic constraints.

In this brief survey on some responses of Mediterranean sclerophylls to temperature stress, the following is presented and discussed: criteria for cold and heat limits of photosynthetic function; winter depression and summer photoinactivation of photosynthesis; peculiar patterns of tissue freezing of scleromorphous leaves and limits of frost resistance of various plant parts and ontogenetic stages; heat impairment of chloroplasts and thermotolerance of sclerophyllous species; survival capacity and recovery after damage. Risks of damage to plants in relation to stressful temperatures in Mediterranean regions are estimated. Cold stress and drought stress indices, according to Mitrakos (1980), have been applied to characterise different localities in Italy. Additionally, a heat stress index for the Mediterranean region is proposed. Future research topics are suggested.     

Flow cytometric estimation of ‘labile iron pool’ in human white blood cells reveals a positive association with ageing

A small part of cellular iron, usually called ‘labile iron pool’ (LIP), is not securely stored and has the potential to catalyse the formation of highly reactive oxygen species. The present work estimated LIP levels in human white cells by using the analytical power of flow cytometry. The method relies essentially on already established principles but has the added value of monitoring LIP in different subpopulations of human blood cells concurrently in a single sample. Examination of 41 apparently healthy individuals revealed a positive correlation between LIP levels and the age of the donors (r=0.656, 0.572 and 0.702 for granulocytes, lymphocytes and monocytes, respectively, p<0.0001), indicating that cells of older individuals are prone to oxidations in conditions of oxidative stress. It is suggested that LIP estimation may represent a valuable tool in examinations searching for links between iron and a variety of oxidative stress-related pathological conditions.     

Effects of overexpression of NAPRTase,NAMNAT, and NAD synthetase in the NAD(H) biosynthetic pathways on the NAD(H) pool,NADH/NAD+ ratio,and succinic acid production with different carbon sources by metabolically engineered Escherichia coli

Escherichia coli BA002, the ldhA and pflB deletion strain, cannot utilize glucose anaerobically due to the inability to regenerate NAD⁺. To regulate NAD(H) pool size and NADH/NAD⁺ ratio, overexpression of the enzymes in the NAD(H) biosynthetic pathways in BA002 was investigated. The results clearly demonstrate that the increased NAD(H) pool size and the decreased NADH/NAD⁺ ratio improved the glucose consumption and cell growth, which improved succinic acid production. When the pncB and the nadD genes were co-overexpressed in CA102, the ratio of NADH/NAD⁺ was decreased from 0.60 to 0.12, and the concentration of NAD(H) was the highest among that of all the strains. Moreover, the dry cell weight (DCW), glucose consumption, and the concentration of succinic acid in CA102 were also the highest. Based on the sufficient NAD⁺ supply after gene modification in the NAD(H) biosynthetic pathways, reductive carbon sources with different amounts of NADH can further change the distribution of metabolites. When sorbitol was used as a carbon source in CA102, the byproducts were lower than those of glucose fermentation, and the yield of succinic acid was increased.     

Beta‐diversity in temperate and tropical forests reflects dissimilar mechanisms of community assembly

Site‐to‐site variation in species composition (β‐diversity) generally increases from low‐ to high‐diversity regions. Although biogeographical differences in community assembly mechanisms may explain this pattern, random sampling effects can create this pattern through differences in regional species pools. Here, we compared assembly mechanisms between spatially extensive networks of temperate and tropical forest plots with highly divergent species pools (46 vs. 607 species). After controlling for sampling effects, β‐diversity of woody plants was similar and higher than expected by chance in both forests, reflecting strong intraspecific aggregation. However, different mechanisms appeared to explain aggregation in the two forests. In the temperate forest, aggregation reflected stronger environmental correlations, suggesting an important role for species‐sorting (e.g. environmental filtering) processes, whereas in the tropics, aggregation reflected stronger spatial correlations, more likely reflecting dispersal limitation. We suggest that biogeographical differences in the relative importance of different community assembly mechanisms contribute to these striking gradients in global biodiversity.     

Liposomes and Micelles to Target the Blood Pool for Imaging Purposes

Abstract

The blood pool is among body compartments of a special interest for imaging using magnetic resonance (MR) and computed tomography (CT), since with the help of selective blood-pool contrast agents blood perfusion and various cardiac parameters as well as a status of the blood flow and vascular system in any organ can be evaluated. Blood pool-specific imaging agents can also provide minimally invasive angiography, image guidance of minimally invasive procedures, oncologic imaging of angiogenesis, ascertaining organ blood volume, and identifying hemorrhage. Particulate contrast agents (such as liposomes and micelles) whose distribution is limited to the blood pool, should have a size larger than fenestrated capillaries (> 10 nm), contain the reporter (paramagnetic or radiopaque) moiety structurally incorporated within the particulate, and be able to stay in the blood long enough to obtain clinically useful images. We describe here a new generation of long-circulating Gd-loaded liposomes and iodine-loaded micelles to provide an efficient blood pool MR and CT imaging, respectively. In this study, we developed the optimized protocol to prepare a liposomal MR contrast agent with high relaxivity and narrow size distribution. Liposomes were loaded with Gadolinium (Gd) via so called polychelating amphiphilic polymer (PAP) that represents a low-molecular-weight DTPA-polylysine linked via its N-terminus to a lipid anchor, NGPE-PE. Gd-containing liposomes were additionally modified with PEG to provide the longevity in vivo. We demonstrated also that upon the intravenous administration in rabbits and dogs, a new preparation causes prolonged decrease in the blood Tl value, permits to obtain sharp and clear MR images of the vasculature, and may be considered as a potential contrast agent for MRI of the blood pool. In addition, to prepare micellar contrast agents for CT blood-pool imaging, we synthesized an iodine-containing amphiphilic block-copolymer consisting of methoxypoly(ethyleneglycol) and polyl?,N-(triiodobenzoyl)]-L-lysine. In aqueous solutions, it forms stable micelles with an average diameter of 80 nm and an iodine content of 35–40% wt. Iodine-containing micelles were intravenously injected into rats and rabbits at a dose of 170 mg I/kg and produced significant and sustained enhancement of the blood pool (aorta and heart), liver and spleen for a period of at least 3 hours providing clear and informative CT images.     

Multifaceted applications of nanomaterials in cell engineering and therapy

Nanomaterials with superior physiochemical properties have been rapidly developed and integrated in every aspect of cell engineering and therapy for translating their great promise to clinical success. Here we demonstrate the multifaceted roles played by innovatively-designed nanomaterials in addressing key challenges in cell engineering and therapy such as cell isolation from heterogeneous cell population, cell instruction in vitro to enable desired functionalities, and targeted cell delivery to therapeutic sites for prompting tissue repair. The emerging trends in this interdisciplinary and dynamic field are also highlighted, where the nanomaterial-engineered cells constitute the basis for establishing in vitro disease model; and nanomaterial-based in situ cell engineering are accomplished directly within the native tissue in vivo. We will witness the increasing importance of nanomaterials in revolutionizing the concept and toolset of cell engineering and therapy which will enrich our scientific understanding of diseases and ultimately fulfill the therapeutic demand in clinical medicine.     

Multiple C-Terminal Tails within a Single E. coli SSB Homotetramer Coordinate DNA Replication and Repair

Escherichia coli single-stranded DNA binding protein (SSB) plays essential roles in DNA replication, recombination and repair. SSB functions as a homotetramer with each subunit possessing a DNA binding domain (OB-fold) and an intrinsically disordered C-terminus, of which the last nine amino acids provide the site for interaction with at least a dozen other proteins that function in DNA metabolism. To examine how many C-termini are needed for SSB function, we engineered covalently linked forms of SSB that possess only one or two C-termini within a four-OB-fold “tetramer”. Whereas E. coli expressing SSB with only two tails can survive, expression of a single-tailed SSB is dominant lethal. E. coli expressing only the two-tailed SSB recovers faster from exposure to DNA damaging agents but accumulates more mutations. A single-tailed SSB shows defects in coupled leading and lagging strand DNA replication and does not support replication restart in vitro. These deficiencies in vitro provide a plausible explanation for the lethality observed in vivo. These results indicate that a single SSB tetramer must interact simultaneously with multiple protein partners during some essential roles in genome maintenance.