基于“源-汇”景观的典型半城市化小流域非点源污染风险评价

小流域的水质恶化主要由点源污染和非点源污染引起，随着点源污染控制水平达到一定程度后，非点源污染已成为首要污染源。当前对非点源污染的管控仍存在难监测和难治理的问题，明晰非点源污染发生风险以及背后的原因是亟需解决的问题，因此开展非点源污染风险分析和评价具有重要意义。采用高分辨率影像解译了2010年、2015年和2020年三期厦门市后溪流域土地利用数据；基于"源-汇"景观格局方法计算研究区网格单元的网格污染指数（GPI）；结合土地利用变化数据分析非点源污染风险的时空变异，对风险区成因进行了分析。研究结果表明：当前，"汇"景观占流域面积的67.86%，非点源污染发生风险分布呈现北低南高；十年中，非点源污染风险呈现上升趋势，目前非点源污染发生风险处于低风险水平（GPI=0.27）。通过分析风险区的土地利用构成发现耕地面积的缩减（减少67.08%）和建设用地面积扩张（增加43.02%）是污染风险发生变动的主要原因。计算了风险区转移矩阵，发现非点源污染发生风险区呈现出中高风险区向低风险区和"汇"景观区域转移的趋势。基于"源-汇"景观格局理论计算的网格污染指数（GPI）可以有效地对流域非点源污染风险值进行表征，是评价和分析流域非点源污染发生风险的可用方法。     

Optimal Design of River Monitoring Network in Taizihe River by Matter Element Analysis

The objective of this study is to optimize the river monitoring network in Taizihe River, Northeast China. The situation of the network and water characteristics were studied in this work. During this study, water samples were collected once a month during January 2009 - December 2010 from seventeen sites. Futhermore, the 16 monitoring indexes were analyzed in the field and laboratory. The pH value of surface water sample was found to be in the range of 6.83 to 9.31, and the average concentrations of NH₄⁺-N, chemical oxygen demand (COD), volatile phenol and total phosphorus (TP) were found decreasing significantly. The water quality of the river has been improved from 2009 to 2010. Through the calculation of the data availability and the correlation between adjacent sections, it was found that the present monitoring network was inefficient as well as the optimization was indispensable. In order to improve the situation, the matter element analysis and gravity distance were applied in the optimization of river monitoring network, which were proved to be a useful method to optimize river quality monitoring network. The amount of monitoring sections were cut from 17 to 13 for the monitoring network was more cost-effective after being optimized. The results of this study could be used in developing effective management strategies to improve the environmental quality of Taizihe River. Also, the results show that the proposed model can be effectively used for the optimal design of monitoring networks in river systems.     

长江口滨岸带河蚬的时空分布特征及其指示作用

以长江口滨岸湿地生态系统习见的大型底栖动物河蚬为对象,研究了河蚬种群密度、生物量的时空分布特征,分析了河蚬及环境中悬浮颗粒物和沉积物中的重金属含量.结果表明,不同季节、不同采样点以及相同采样点的不同断面河蚬的分布都有差异.河蚬种群密度、生物量的季节分布趋势是春、秋两季＞夏季;其中,浒浦河蚬的年度平均种群密度与平均生物量最高;河蚬在崇明中潮滩的种群密度、生物量高于低潮滩和高潮滩.研究表明,河蚬对沉积物中的重金属元素Cu、Zn富集能力强,对Pb、Cr的富集能力弱,其中,河蚬体内Pb含量与沉积物中Pb含量呈显著负相关(R=-0.924,P<0.01).     

Grazing response patterns indicate isolation of semi‐natural European grasslands

Identifying drivers of species diversity is a major challenge in understanding and predicting the dynamics of species‐rich semi‐natural grasslands. In particular in temperate grasslands changes in land use and its consequences, i.e. increasing fragmentation, the on‐going loss of habitat and the declining importance of regional processes such as seed dispersal by livestock, are considered key drivers of the diversity loss witnessed within the last decades. It is a largely unresolved question to what degree current temperate grassland communities already reflect a decline of regional processes such as longer distance seed dispersal. Answering this question is challenging since it requires both a mechanistic approach to community dynamics and a sufficient data basis that allows identifying general patterns. Here, we present results of a local individual‐ and trait‐based community model that was initialized with plant functional types (PFTs) derived from an extensive empirical data set of species‐rich grasslands within the ‘Biodiversity Exploratories’ in Germany. Driving model processes included above‐ and belowground competition, dynamic resource allocation to shoots and roots, clonal growth, grazing, and local seed dispersal. To test for the impact of regional processes we also simulated seed input from a regional species pool. Model output, with and without regional seed input, was compared with empirical community response patterns along a grazing gradient. Simulated response patterns of changes in PFT richness, Shannon diversity, and biomass production matched observed grazing response patterns surprisingly well if only local processes were considered. Already low levels of additional regional seed input led to stronger deviations from empirical community pattern. While these findings cannot rule out that regional processes other than those considered in the modeling study potentially play a role in shaping the local grassland communities, our comparison indicates that European grasslands are largely isolated, i.e. local mechanisms explain observed community patterns to a large extent.     

Maintenance of Chloroplast Structure and Function by Overexpression of the Rice MONOGALACTOSYLDIACYLGLYCEROL SYNTHASE Gene Leads to Enhanced Salt Tolerance in Tobacco

In plants, the galactolipids monogalactosyldiacylglycerol (MGDG) and digalactodiacylglycerol (DGDG) are major constituents of photosynthetic membranes in chloroplasts. One of the key enzymes for the biosynthesis of these galactolipids is MGDG synthase (MGD). To investigate the role of MGD in the plant’s response to salt stress, we cloned an MGD gene from rice (Oryza sativa) and generated tobacco (Nicotiana tabacum) plants overexpressing OsMGD. The MGD activity in OsMGD transgenic plants was confirmed to be higher than that in the wild-type tobacco cultivar SR1. Immunoblot analysis indicated that OsMGD was enriched in the outer envelope membrane of the tobacco chloroplast. Under salt stress, the transgenic plants exhibited rapid shoot growth and high photosynthetic rate as compared with the wild type. Transmission electron microscopy observation showed that the chloroplasts from salt-stressed transgenic plants had well-developed thylakoid membranes and properly stacked grana lamellae, whereas the chloroplasts from salt-stressed wild-type plants were fairly disorganized and had large membrane-free areas. Under salt stress, the transgenic plants also maintained higher chlorophyll levels. Lipid composition analysis showed that leaves of transgenic plants consistently contained significantly higher MGDG (including 18:3-16:3 and 18:3-18:3 species) and DGDG (including 18:3-16:3, 18:3-16:0, and 18:3-18:3 species) contents and higher DGDG-MGDG ratios than the wild type did under both control and salt stress conditions. These results show that overexpression of OsMGD improves salt tolerance in tobacco and that the galactolipids MGDG and DGDG play an important role in the regulation of chloroplast structure and function in the plant salt stress response.Salt stress is a major environmental factor that poses a serious threat to crop yield and future food production (Møller and Tester, 2007). When plants are exposed to salinity, they suffer two primary obstacles: low external water potentials and high concentrations of toxic ions (Hirayama and Mihara, 1987). These obstacles generally lead to the disruption of various enzymatic processes, changes in membrane lipid composition, alteration in chloroplast structure and function, impairment of photosynthetic capacity, and inhibition of plant growth (Brown and Dupont, 1989; Elkahoui et al., 2004; Munns and Tester, 2008; Sui et al., 2010; Shu et al., 2012).Membranes are the primary matrix for numerous physiological and biochemical activities, and plants easily change their membrane lipid compositions in response to environmental stresses (Harwood, 1996). A number of studies have proved that salt stress can induce changes in plant membrane lipids (Huflejt et al., 1990; Elkahoui et al., 2004; Sui et al., 2010). Sui et al. (2010) found that, in Suaeda salsa, salt stress increased the proportion of phosphatidylglycerol and reduced the proportion of galactolipids. Similar results were observed in Catharanthus roseus cultured cell suspensions, which showed an increase in phospholipid content and a decrease in galactolipid content that were more obvious under 100 mm NaCl than under 50 mm (Elkahoui et al., 2004). Meanwhile, it was shown that salt tolerance in plants is strongly linked with their membrane lipid composition and especially with their galactolipid content, which is positively related to salt tolerance (Hirayama and Mihara, 1987).In plants, galactolipids are major constituents of the photosynthetic membrane, which is the most abundant membrane in nature (Lee, 2000). Two galactolipids, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), are the predominant photosynthetic membrane lipid building blocks, accounting for about 52 mol % and 26 mol % of thylakoid membrane lipids, respectively (Block et al., 1983). These galactolipids are also the major lipids in cyanobacteria, suggesting that MGDG and DGDG are important for all oxygenic photosynthetic organisms (Hölzl and Dörmann, 2007). They are components of PSII and are the indispensable matrix for photosynthesis (Mizusawa and Wada, 2012). Their unique characteristics also give them distinctive packing properties that are important for the organization of thylakoid membranes (Lee, 2000). MGDG has a conical shape due to its smaller head group and a high content of unsaturated fatty acids, giving it nonbilayer-forming characteristics (Webb and Green, 1991; Aronsson et al., 2008); this feature is assumed to play an important structural role in the dense packing of proteins in the membrane (Williams, 1998; Garab et al., 2000). In contrast to MGDG, DGDG has a cylindrical shape that is typical for most plastid lipids and is considered a bilayer-prone lipid (Aronsson et al., 2008); this feature is involved in lipid-mediated contacts between adjacent trimers of light-harvesting complex II (LHCII) when they are packed into two-dimensional crystalline arrays (Lee, 2000). In addition to forming important membrane structures in the thylakoids, MGDG and DGDG are also present in extraplastidic membranes, including the plasma membrane, tonoplasts, endoplasmic reticulum, and Golgi membranes, indicating the crucial role of these galactoglycerolipids in higher plant membrane systems (Yoshida and Uemura, 1986; Brown and Dupont, 1989; Härtel et al., 2000).Two enzymes are involved in the biosynthesis of these galactoglycerolipids: MGDG synthase (MGD), which transfers a galactosyl residue from UDP-Gal to diacylglycerol, and DGDG synthase, which catalyzes the further galactosylation of MGDG to form DGDG (Shimojima et al., 1997; Dörmann et al., 1999; Shimojima and Ohta, 2011). Thus, MGD is the key enzyme in the biosynthesis of both galactolipids and, consequently, also in the formation of photosynthetic membranes (Nakamura et al., 2010). A number of studies have revealed that MGD is vital for plant growth and development. The loss of MGD function in plants leads to a pale-green phenotype, defects in the chloroplast ultrastructure, disruption in the photosynthetic membranes, and complete impairment of photosynthetic ability and photoautotrophic growth, suggesting a unique role for MGD in chlorophyll formation, the structural organization of the plastidic membranes, and photosynthetic growth (Jarvis et al., 2000; Kobayashi et al., 2007; Botté et al., 2011; Myers et al., 2011). The crucial role of MGD under environmental stresses, including phosphorus deficiency and wounding, is also well studied (Kobayashi et al., 2004, 2009a, 2009b; Moellering and Benning, 2011). However, although a number of studies have proved that salt stress can induce changes in plant membrane lipids (Huflejt et al., 1990; Elkahoui et al., 2004; Sui et al., 2010), little is known about the role of MGD and the involvement of galactolipids in response to salt stress.To investigate the function of MGD in plant salt tolerance, we cloned the relevant gene, which is called OsMGD (Qi et al., 2004), from rice (Oryza sativa ‘FR13A’). This gene has a high similarity to Arabidopsis (Arabidopsis thaliana) MGD2 and MGD3, and its expression is induced by several environmental stresses, including salt, drought, and submergence (Qi et al., 2004; Benning and Ohta, 2005). We then generated tobacco (Nicotiana tabacum) plants overexpressing OsMGD and investigated the salt tolerance ability in the transgenic lines and wild-type plants. The results of this study demonstrate that an increase in galactolipid content in leaves is beneficial for maintaining chloroplast structure and function and leads to enhanced salt tolerance in tobacco.     

Focus Issue on Roots: Beyond the Barrier: Communication in the Root through the Endodermis

The root endodermis is characterized by the Casparian strip and by the suberin lamellae, two hydrophobic barriers that restrict the free diffusion of molecules between the inner cell layers of the root and the outer environment. The presence of these barriers and the position of the endodermis between the inner and outer parts of the root require that communication between these two domains acts through the endodermis. Recent work on hormone signaling, propagation of calcium waves, and plant-fungal symbiosis has provided evidence in support of the hypothesis that the endodermis acts as a signaling center. The endodermis is also a unique mechanical barrier to organogenesis, which must be overcome through chemical and mechanical cross talk between cell layers to allow for development of new lateral organs while maintaining its barrier functions. In this review, we discuss recent findings regarding these two important aspects of the endodermis.Soil contains water and dissolved nutrients needed for plant growth, but also holds pathogens and toxic compounds that can be detrimental to the plant. The root system, which is directly in contact with soil particles, can integrate environmental cues to adjust its development in order to optimize nutrient (Péret et al., 2011; Lynch, 2013) and water uptake (Cassab et al., 2013; Lynch, 2013; Bao et al., 2014) or avoid regions of high salinity (Galvan-Ampudia et al., 2013). Once anchored in the soil, roots must deal with the constraints of their local environment and develop specific barriers to balance uptake of nutrients, water, and interactions with symbionts with protection against detrimental biotic and abiotic factors.In young roots, these barriers are mainly formed by the deposition of hydrophobic polymers such as lignin and suberin within the primary cell wall of the endodermis, which separates the pericycle from the cortex (Fig. 1), and of the exodermis, which lies between the cortex and the epidermis (Nawrath et al., 2013). Although formation of an exodermis is species dependent, the endodermis is a distinguishing figure of extant vascular plants (Raven and Edwards, 2001). Within this layer, two barriers (i.e. the Casparian strip and the suberin lamellae) are sequentially deposited and regulate water and nutrient movements between the inner and outer parts of the root. In this review, we discuss how the presence of these two major endodermal barriers affects communication between the different cell layers of the root. We focus on recent articles highlighting the importance of the endodermis in this communication during various biological and developmental processes.Open in a separate windowFigure 1.Endodermal barriers affect radial movement of water and solutes through the root. A, At the root tip, to move from the soil to the outer tissues of the root and then into the stele, water and solute molecules can use either the apoplastic (black lines), symplastic (dotted lines), or transcellular (dashed lines) pathways. B, The deposition of the Casparian strip in the endodermis prevents the free apoplastic diffusion of molecules between the outer part and the inner part of the root forcing molecules to pass through the symplast of endodermal cells. C, The deposition of suberin lamellae prevents the uptake of molecules from the apoplast directly into the endodermis forcing molecules to enter the symplast from more outer tissue layers. Suberin deposition is also likely to prevent the backflow of water and ions out of the stele. Passage cells are unsuberized and may facilitate the uptake of water and nutrients in older parts of the root. Cor, Cortex; End, endodermis; Epi, epidermis; Peri, pericycle; Vasc, vasculature. Figure redrawn and modified from Geldner et al. (2013).     

Prokaryotic Expression, Identification and Bioinformatics Analysis of the Mycobacterium tuberculosis Rv3807c Gene Encoding the Putative Enzyme Committed to Decaprenylphosphoryl-d-arabinose Synthesis

Decaprenylphosphoryl-d-arabinofuranosyl (DPA), the immediate donor for the polymerized d-Araf residues of mycobacterial arabinan, is synthesized from 5-phosphoribose-1-diphosphate (PRPP) in three-step reactions. (i) PRPP is transferred to decaprenyl-phosphate (DP) to form decaprenylphosphoryl-d-5-phosphoribose (DPPR). (ii) DPPR is dephosphorylated to form decaprenylphosphoryl-d-ribose (DPR). (iii) DPR is formed to DPA by the epimerase. Mycobacterium tuberculosis Rv3806c and heteromeric Rv3790/Rv3791 have been identified as the PRPP: decaprenyl-phosphate 5-phosphoribosyltransferase and the epimerase respectively. Rv3807c, however, as the candidate of phospholipid phosphatase, catalyzing the biosynthesis of decapreny-l-phosphoryl-ribose (DPR) from decaprenylphosphoryl-β-d-5-phosphoribose by dephosphorylating, has no direct experimental evidence of its essentiality in any species of mycobacterium. In this study, Rv3807c gene was amplified from the genome of M. tuberculosis H37Rv by PCR, and was successfully expressed in Escherichia coli BL21 (DE3) via the recombinant plasmid pColdII-Rv3807c. The resulting protein with the 6× His-tag was identified by SDS-PAGE and Western blotting. The protein was predicted through bioinformatics to contain three transmembrane domains, the N-terminal peptide, and a core structure with phosphatidic acid phosphatase type2/haloperoxidase. This study provides biochemical and bioinformatics evidence for the importance of Rv3807c in mycobacteria, and further functional studies will be conducted for validating Rv3807c as a promising phospholipid phosphatase in the synthetic pathway of DPA.     

Nonredundant Roles for Cytochrome c2 and Two High-Potential Iron-Sulfur Proteins in the Photoferrotroph Rhodopseudomonas palustris TIE-1

The purple bacterium Rhodopseudomonas palustris TIE-1 expresses multiple small high-potential redox proteins during photoautotrophic growth, including two high-potential iron-sulfur proteins (HiPIPs) (PioC and Rpal_4085) and a cytochrome c₂. We evaluated the role of these proteins in TIE-1 through genetic, physiological, and biochemical analyses. Deleting the gene encoding cytochrome c₂ resulted in a loss of photosynthetic ability by TIE-1, indicating that this protein cannot be replaced by either HiPIP in cyclic electron flow. PioC was previously implicated in photoferrotrophy, an unusual form of photosynthesis in which reducing power is provided through ferrous iron oxidation. Using cyclic voltammetry (CV), electron paramagnetic resonance (EPR) spectroscopy, and flash-induced spectrometry, we show that PioC has a midpoint potential of 450 mV, contains all the typical features of a HiPIP, and can reduce the reaction centers of membrane suspensions in a light-dependent manner at a much lower rate than cytochrome c₂. These data support the hypothesis that PioC linearly transfers electrons from iron, while cytochrome c₂ is required for cyclic electron flow. Rpal_4085, despite having spectroscopic characteristics and a reduction potential similar to those of PioC, is unable to reduce the reaction center. Rpal_4085 is upregulated by the divalent metals Fe(II), Ni(II), and Co(II), suggesting that it might play a role in sensing or oxidizing metals in the periplasm. Taken together, our results suggest that these three small electron transfer proteins perform different functions in the cell.