Interaction between Heracleum laciniatum and some other plants

The aim of this study was to find out whether the low plant production under a canopy of Heracleum laciniatum Horn was due to competition for water, nutrients or light or to chemical inhibitors produced by H. laciniatum .
The main conclusion is that the low plant production observed under the canopy is due to competition for light. There were also indications that the competition for nutrition was larger in the soil under H. laciniatum than in the meadow outside the stand, but it has not been shown that nutrient supply limits the plant growth under the canopy. There were no indications that competition for water was a limiting factor. Water percolated through pots with H. laciniatum plants slightly inhibited growth of Poa pratensis and Phleum pratense , but had no effect on H. laciniatum . In soil samples collected from mid of June to late October seeds of Phleum pratense germinated better in meadow-soil than in soil collected under H. laciniatum . Allelopathy is suggested to account for a minor part only of the suppressed plant production under a H. laciniatum canopy.     

Rhizobial Association with Non-Legumes: Mechanisms and Applications

It has been known for more than a century that rhizobia can promote the growth of legumes through the formation of nitrogen-fixing nodules, but the interaction of rhizobia with non-legumes has been neglected as an experimental system. During the last couple of decades, work on rhizobial interaction with non-legumes has been done progressively and it has been demonstrated that rhizobia can associate with roots of non-legumes also, without forming true nodules, and can promote their growth by using one or more of the direct or indirect mechanisms of actions. Phytohormone production, secretion of other chemicals like lipo-chito-oligosaccharides (LCOs) and lumichrome, solubilization of precipitated phosphorus and mineralization of organic P, improvement in uptake of plant nutrients by altering root morphology, production of siderophores to meet the iron requirements of the plant under iron-stressed conditions and lowering of ethylene level through ACC deaminase enzyme, are some examples of the rhizobial mechanisms with direct positive effects on non-leguminous plant growth. Indirectly, rhizobia improve the growth of non-legumes through biocontrol of pathogens via antibiosis, parasitism or competition with pathogens for nutrients and space, by inducing systemic resistance in the host plant and through increasing root adhering soil by releasing exopolysaccarides which regulate the water movement and facilitate the root growth. However, no influence or even inhibitory effects of rhizobial inoculation on non-legumes has also been demonstrated in some cases. Plant growth promoting mechanisms of rhizobia and its practical application in non-legumes are the major focus of this review.     

基于非点源污染控制的景观格局优化方法与原则

对目前国内外较为常用的基于非点源污染控制的景观格局优化方法及其设计原则进行了系统的评述 ,以促进其推广应用并提高其污染控制效果。还通过分析这些方法在我国的应用前景 ,强调了探索适合我国国情的景观格局优化方法对于控制非点源污染的重要意义。     

Development of toxicity tolerant water hyacinth (Eichhornea crassipes) for effective treatment of raw sewage

Pioneering research efforts in the handling of municipal sewage in developing countries have involved the use of water hyacinth (Eichhornea crassipes) to purify sewage for possible re-use of the effluent water for domestic purposes. The ability of water hyacinth to remove pollution from raw sewage has been found to be impaired by sewage toxicity. Trials were therefore carried out to adapt water hyacinth to toxicity and thereby increase its ability to remove pollutants from raw sewage. The plants were adapted using an active bio-degrader consisting of Pseudomonas aeruginosa, Escherichia coli, Klebsiella ozaenae, Klebsiella edwardsiella and Baccillus subtilis. The adaptation progressed through 20, 40, 60 and 80% sewage dilution until plants capable of growth in 100% raw sewage were obtained. Plants were observed for morphological growth and at four weeks, samples were collected for tissue analysis. The plants progressively absorbed nutrients from sewage up to the fourth week, when signs of toxicity were obsereved through wilting, loss of turgidity and reduction in leaf number. However, plants that survived through a series of adaptations under various sewage dilutions exhibited luxuriant growth on raw sewage. In synergy with the active bio-degrader, the efficiency of the adapted water hyacinth to remove pollutants (nutrients) from raw sewage was enhanced by 93%.     

用光合-蒸散耦合模型模拟冬小麦CO2通量的日变化

根据SPAC理论建立了一个冬小麦光合和蒸散的耦合模型.冬小麦CO2通量包括冠层光合、呼吸和土壤呼吸.冠层光合采用了Farquhar光合作用生化模型,并通过冠层阻力的参数化将光合作用与蒸腾作用耦合起来.用涡度相关方法观测了CO2通量,对模型进行了验证,结果显示模型可以较好地模拟CO2通量日变化过程.对模型的敏感性分析发现日间CO2通量最敏感的参数是初始量子效率.其次,CO2通量对光响应曲线凸度、CO2补偿点、凋萎点和叶面积指数的变化也有着较强的敏感性;夜间CO2通量敏感的参数是最适温度下Rubisco催化能力和暗呼吸参数.     

用光合-蒸散耦合模型模拟冬小麦CO2通量的日变化

根据 SPAC理论建立了一个冬小麦光合和蒸散的耦合模型。冬小麦 CO2 通量包括冠层光合、呼吸和土壤呼吸。冠层光合采用了 Farquhar光合作用生化模型 ,并通过冠层阻力的参数化将光合作用与蒸腾作用耦合起来。用涡度相关方法观测了 CO2通量 ,对模型进行了验证 ,结果显示模型可以较好地模拟 CO2 通量日变化过程。对模型的敏感性分析发现日间 CO2 通量最敏感的参数是初始量子效率。其次 ,CO2 通量对光响应曲线凸度、CO2 补偿点、凋萎点和叶面积指数的变化也有着较强的敏感性 ;夜间 CO2 通量敏感的参数是最适温度下 Rubisco催化能力和暗呼吸参数     

Intercropping Competition between Apple Trees and Crops in Agroforestry Systems on the Loess Plateau of China

Agroforestry has been widely practiced in the Loess Plateau region of China because of its prominent effects in reducing soil and water losses, improving land-use efficiency and increasing economic returns. However, the agroforestry practices may lead to competition between crops and trees for underground soil moisture and nutrients, and the trees on the canopy layer may also lead to shortage of light for crops. In order to minimize interspecific competition and maximize the benefits of tree-based intercropping systems, we studied photosynthesis, growth and yield of soybean (Glycine max L. Merr.) and peanut (Arachis hypogaea L.) by measuring photosynthetically active radiation, net photosynthetic rate, soil moisture and soil nutrients in a plantation of apple (Malus pumila M.) at a spacing of 4 m × 5 m on the Loess Plateau of China. The results showed that for both intercropping systems in the study region, soil moisture was the primary factor affecting the crop yields followed by light. Deficiency of the soil nutrients also had a significant impact on crop yields. Compared with soybean, peanut was more suitable for intercropping with apple trees to obtain economic benefits in the region. We concluded that apple-soybean and apple-peanut intercropping systems can be practical and beneficial in the region. However, the distance between crops and tree rows should be adjusted to minimize interspecies competition. Agronomic measures such as regular canopy pruning, root barriers, additional irrigation and fertilization also should be applied in the intercropping systems.     

soil-root-canopy interactions

When supplies of water and mineral nutrients are adequate, crop growth is determined by the amount of solar radiation intercepted over the season and the efficiency of its conversion into dry matter. Soil factors such as drought, nutrient availability, salinity, waterlogging, mechanical impedance and root‐infecting pathogens can be a serious constraint to yield and operate through effects on the growth, photosynthetic activity and duration of the canopy, and on the partitioning of biomass to harvested parts. One approach to overcome restrictions on the canopy and enhance yield is to modify root systems so that they are better suited to the prevailing soil conditions. This might be achieved through genetic improvement or by cultural practices. A better understanding of the physiology of root systems is required to identify appropriate root traits for selection or management. Not only should this encompass considerations of the function of roots in the capture of water and nutrients and the provision of anchorage, but also new concepts about the role of chemical signals in the regulation of the canopy. Greater emphasis must be placed on field‐based research. The growth, development and activity of roots in the field can differ markedly from those in most laboratory experiments, because field soils are more complex in structure and differ in their biological, chemical and physical properties. It is argued that a decline in field‐based research of crop root systems, as seen in the UK over the last 15–20 years, could, if allowed to continue, generate a skills gap which may undermine future exploitation of discoveries made at the cell and molecular level.     

Strategies for the engineered phytoremediation of toxic element pollution: mercury and arsenic

Plants have many natural properties that make them ideally suited to clean up polluted soil, water, and air, in a process called phytoremediation. We are in the early stages of testing genetic engineering-based phytoremediation strategies for elemental pollutants like mercury and arsenic using the model plant Arabidopsis. The long-term goal is to develop and test vigorous, field-adapted plant species that can prevent elemental pollutants from entering the food-chain by extracting them to aboveground tissues, where they can be managed. To achieve this goal for arsenic and mercury, and pave the way for the remediation of other challenging elemental pollutants like lead or radionucleides, research and development on native hyperaccumulators and engineered model plants needs to proceed in at least eight focus areas: (1) Plant tolerance to toxic elementals is essential if plant roots are to penetrate and extract pollutants efficiently from heterogeneous contaminated soils. Only the roots of mercury- and arsenic-tolerant plants efficiently contact substrates heavily contaminated with these elements. (2) Plants alter their rhizosphere by secreting various enzymes and small molecules, and by adjusting pH in order to enhance extraction of both essential nutrients and toxic elements. Acidification favors greater mobility and uptake of mercury and arsenic. (3) Short distance transport systems for nutrients in roots and root hairs requires numerous endogenous transporters. It is likely that root plasma membrane transporters for iron, copper, zinc, and phosphate take up ionic mercuric ions and arsenate. (4) The electrochemical state and chemical speciation of elemental pollutants can enhance their mobility from roots up to shoots. Initial data suggest that elemental and ionic mercury and the oxyanion arsenate will be the most mobile species of these two toxic elements. (5) The long-distance transport of nutrients requires efficient xylem loading in roots, movement through the xylem up to leaves, and efficient xylem unloading aboveground. These systems can be enhanced for the movement of arsenic and mercury. (6) Aboveground control over the electrochemical state and chemical speciation of elemental pollutants will maximize their storage in leaves, stems, and vascular tissues. Our research suggests ionic Hg(II) and arsenite will be the best chemical species to trap aboveground. (7) Chemical sinks can increase the storage capacity for essential nutrients like iron, zinc, copper, sulfate, and phosphate. Organic acids and thiol-rich chelators are among the important chemical sinks that could trap maximal levels of mercury and arsenic aboveground. (8) Physical sinks such as subcellular vacuoles, epidermal trichome cells, and dead vascular elements have shown the evolutionary capacity to store large quantities of a few toxic pollutants aboveground in various native hyperaccumulators. Specific plant transporters may already recognize gluthione conjugates of Hg(II) or arsenite and pump them into vacuole.     

Strategies for the engineered phytoremediation of toxic element pollution: mercury and arsenic

Plants have many natural properties that make them ideally suited to clean up polluted soil, water, and air, in a process called phytoremediation. We are in the early stages of testing genetic engineering-based phytoremediation strategies for elemental pollutants like mercury and arsenic using the model plant Arabidopsis. The long-term goal is to develop and test vigorous, field-adapted plant species that can prevent elemental pollutants from entering the food-chain by extracting them to aboveground tissues, where they can be managed. To achieve this goal for arsenic and mercury, and pave the way for the remediation of other challenging elemental pollutants like lead or radionucleides, research and development on native hyperaccumulators and engineered model plants needs to proceed in at least eight focus areas: (1) Plant tolerance to toxic elementals is essential if plant roots are to penetrate and extract pollutants efficiently from heterogeneous contaminated soils. Only the roots of mercury- and arsenic-tolerant plants efficiently contact substrates heavily contaminated with these elements. (2) Plants alter their rhizosphere by secreting various enzymes and small molecules, and by adjusting pH in order to enhance extraction of both essential nutrients and toxic elements. Acidification favors greater mobility and uptake of mercury and arsenic. (3) Short distance transport systems for nutrients in roots and root hairs requires numerous endogenous transporters. It is likely that root plasma membrane transporters for iron, copper, zinc, and phosphate take up ionic mercuric ions and arsenate. (4) The electrochemical state and chemical speciation of elemental pollutants can enhance their mobility from roots up to shoots. Initial data suggest that elemental and ionic mercury and the oxyanion arsenate will be the most mobile species of these two toxic elements. (5) The long-distance transport of nutrients requires efficient xylem loading in roots, movement through the xylem up to leaves, and efficient xylem unloading aboveground. These systems can be enhanced for the movement of arsenic and mercury. (6) Aboveground control over the electrochemical state and chemical speciation of elemental pollutants will maximize their storage in leaves, stems, and vascular tissues. Our research suggests ionic Hg(II) and arsenite will be the best chemical species to trap aboveground. (7) Chemical sinks can increase the storage capacity for essential nutrients like iron, zinc, copper, sulfate, and phosphate. Organic acids and thiol-rich chelators are among the important chemical sinks that could trap maximal levels of mercury and arsenic aboveground. (8) Physical sinks such as subcellular vacuoles, epidermal trichome cells, and dead vascular elements have shown the evolutionary capacity to store large quantities of a few toxic pollutants aboveground in various native hyperaccumulators. Specific plant transporters may already recognize gluthione conjugates of Hg(II) or arsenite and pump them into vacuole.

     

Impact of urbanization on coastal wetland structure and function

Abstract Urbanization is a major cause of loss of coastal wetlands. Urbanization also exerts significant influences on the structure and function of coastal wetlands, mainly through modifying the hydrological and sedimentation regimes, and the dynamics of nutrients and chemical pollutants. Natural coastal wetlands are characterized by a hydrological regime comprising concentrated flow to estuarine and coastal areas during flood events, and diffused discharge into groundwater and waterways during the non‐flood periods. Urbanization, through increasing the amount of impervious areas in the catchment, results in a replacement of this regime by concentrating rain run‐off. Quality of run‐off is also modified in urban areas, as loadings of sediment, nutrients and pollutants are increased in urban areas. While the effects of such modifications on the biota and the physical environment have been relatively well studied, there is to date little information on their impact at the ecosystem level. Methodological issues, such as a lack of sufficient replication at the whole‐habitat level, the lack of suitable indices of urbanization and tools for assessing hydrological connectivity, have to be overcome to allow the effects of urbanization to be assessed at the ecosystem level. A functional model is presented to demonstrate the impact of urbanization on coastal wetland structure and function.     

光衰减及其相关环境因子对沉水植物生长影响研究进展

光衰减对沉水植物的生长具有至关重要的影响。系统归纳总结了光衰减及其相关环境因子对沉水植物生长的影响,指出:光因子是沉水植物生长的第一环境要素,水体中的有色可溶性有机质、浮游植物叶片细胞中的叶绿素和悬浮颗粒物以及水体本身,对光穿透水体时光强的衰减有着直接的影响,是影响沉水植物最重要的光衰减水质参数。其他环境因子如营养盐、沉积物和流水动力学等因素,则会直接或间接影响光衰减水质参数,进而影响水体透明度和浑浊度,影响沉水植物的光合作用,是影响沉水植物光衰减的间接环境因子。提出了研究中重点关注的几个问题。     

洪灾后的反思：湿地管理和洪水灾害的生态关系浅析

湿地是水陆相互作用形成的独特生态系统类型,广泛分布于世界各地,是自然界最富生物多样性的生态景观和人类最重要的生存环境之一。在世界自然保护联盟（ＩＵＣＮ）、联合国环境规划署（ＵＮＥＰ）、世界自然基金会（ＷＷＦ）编制的世界自然保护大纲中,湿地与森林、海洋...     

The nutrient-toxin dosage continuum in human evolution and modern health.

Recent findings support the long-recognized principle that nutritive and toxic effects of an ingested material depend not only on its nature but very much on its quantity. The well known observation that essential nutrients can be toxic at high dosages suggests that the same reversal of effect may be true of many substances that could be beneficial but not essential at low dosages (the phenomenon of hormesis). This has been demonstrated for many well known toxins. We suggest a mathematical model that describes these dosage effects as an expected result of the evolution of human metabolic and dietary adaptations for maximizing benefits and minimizing costs of the ingestion or other intake of any substance. Evolved mechanisms for achieving benefits may be unrelated to those for reducing costs. These evolutionary considerations suggest important consequences demonstrable by experimental or epidemiological studies. They also suggest ways in which our evolved dietary adaptations may be currently maladaptive, and individual development of taste preferences poorly calibrated by early experience in modern environments. The apparent reality of hormesis raises the possibility of counterproductive effects of current dosage recommendations and limits for nutrients and pollutants. We propose that some conceptual and factual problems are urgently in need of resolution. Fundamental to evolutionary biology is the tendency for organisms to become increasingly adapted to those environments to which they are most commonly exposed (Parsons 1990).     

Spatial Variability of Plant Litter Decomposition in Stream Networks: from Litter Bags to Watersheds

The decomposition of plant litter plays a fundamental role in the cycling of carbon and nutrients and is driven by complex interactions of biological and physical controls, yet little is known about its variability and controls across spatial scales. Here we address the indirect effects of riparian canopy cover on litter decomposition and decomposers and their variability within a set of hierarchical scales (watershed, stream segments and reaches) controlling for confounding factors that could co-vary with canopy cover (for example, temperature and nutrients), in high-altitude subtropical streams. Total, microbial and invertebrate-driven decomposition rates were approximately 1.4–6.6 times higher in closed-canopy than in open-canopy watersheds. Riparian canopy cover accounted for 62–69% of total variability of decomposition rates and indirectly (via light availability and litter inputs) promoted fungal facilitation of shredders through leaf litter conditioning. In contrast to what we expected, much of the spatial variability in the decomposition occurred at smaller scale (4–20% of total variability among reaches versus <1% among watersheds) and coincided with the greatest variability in shredder abundance and fungal biomass (70 and 17% among reaches, respectively). We conclude that riparian canopy cover may be an important control of natural variability of litter decomposition at the watershed scale through its effects on fungal decomposers and shredder consumption. We also provide evidence of higher reach and minor watershed variability of litter decomposition in stream networks. Our results point to the importance of identifying the sources of natural variability of decomposition and how they interact within and among spatial scales.     

Hydraulic lift: consequences of water efflux from the roots of plants

Hydraulic lift is the passive movement of water from roots into soil layers with lower water potential, while other parts of the root system in moister soil layers, usually at depth, are absorbing water. Here, we review the brief history of laboratory and field evidence supporting this phenomenon and discuss some of the consequences of this below-ground behavior for the ecology of plants. Hydraulic lift has been shown in a relatively small number of species (27 species of herbs, grasses, shrubs, and trees), but there is no fundamental reason why it should not be more common as long as active root systems are spanning a gradient in soil water potential (Ψ_s) and that the resistance to water loss from roots is low. While the majority of documented cases of hydraulic lift in the field are for semiarid and arid land species inhabiting desert and steppe environments, recent studies indicate that hydraulic lift is not restricted to these species or regions. Large quantities of water, amounting to an appreciable fraction of daily transpiration, are lifted at night. This temporary partial rehydration of upper soil layers provides a source of water, along with soil moisture deeper in the profile, for transpiration the following day and, under conditions of high atmospheric demand, can substantially facilitate water movement through the soil-plant-atmosphere system. Release of water into the upper soil layers has been shown to afford the opportunity for neighboring plants to utilize this source of water. Also, because soils tend to dry from the surface downward and nutrients are usually most plentiful in the upper soil layers, lifted water may provide moisture that facilitates favorable biogeochemical conditions for enhancing mineral nutrient availability, microbial processes, and the acquisition of nutrients by roots. Hydraulic lift may also prolong or enhance fine-root activity by keeping them hydrated. Such indirect benefits of hydraulic lift may have been the primary selective force in the evolution of this process. Alternatively, hydraulic lift may simply be the consequence of roots not possessing true rectifying properties (i.e., roots are leaky to water). Finally, the direction of water movement may also be downward or horizontal if the prevailing Ψ_s gradient so dictates, i.e., inverse, or lateral, hydraulic lift. Such downward movement through the root system may allow growth of roots in otherwise dry soil at depth, permitting the establishment of many phreatophytic species. Received: 2 June 1997 / Accepted: 24 September 1997     

红砂灌丛对土壤和草本植物特征的影响

研究了黄土高原西部荒漠草原区天然红砂灌丛内外土壤水分、养分的差异及植物萌动期红砂灌丛对草本植物生长和植被组成的影响.结果表明:红砂灌丛下土壤水分状况明显好于灌丛外空地,尤其是在30～110 cm土层最为显著;灌丛内土壤粘粒和粉粒含量明显高于灌丛外,而沙粒含量低于灌丛外,尤其是0～10 cm土层;土壤有机质、全效氮、磷、钾及速效氮、磷、钾均在灌丛下富集,富集率分别达到1.40、1.25、1.04、1.05、1.37、1.77和1.49;从灌丛内到灌丛外草本植物的盖度和高度逐渐减小,而植物丰富度增大;红砂灌丛对草本植物密度、盖度和高度的相互作用强度均呈现正值,而植物丰富度的相互作用强度为负值.说明红砂灌丛具有明显的沃岛效应,并对草本植物的生长有促进作用.     

台风对森林的影响

台风通过树枝折断、吹落叶果、产生倒木和折干等许多途径影响林分结构和动态。森林受害程度随树种、林龄、森林类型、树高和地形而异。高密度的森林通常具有较差的根系和较大的树高/胸径比值,在台风袭击下,往往具有较高的受损和死亡的风险。台风疏开郁闭的林冠层,促进了先锋树种的大量增加、生长和成熟,形成的林隙也为个体更新提供了机会。强风造成了土壤基质的多样化,从而促进了实生苗和幼树的更新和生物多样性的增加。台风也通过改变粗木质残体,枯枝落叶层,地洞和土墩,以及繁殖可用性来影响生物多样性。台风产生的粗死木和枯枝落叶使森林的碳储量迅速归还土壤,并影响土壤的养分分布。台风减少了动物的食物供应和恶化栖息地的环境,减少鸟的数量,促进昆虫扩散。受害森林给害虫滋生提供了场所。今后的研究热点是受台风干扰森林的长期监测,不同森林土壤的有机碳贮藏,土壤和养分流失规律,台风和其他自然灾害的交叉影响,改进数学模型以准确预测台风损害。     

Stomatal closure with soil water depletion not associated with changes in Bulk leaf water status

Summary It has previously been reported that canopy water loss by cowpea (Vigna unguiculata) decreases with small depletions in soil water. In these studies, under field conditions, it was demonstrated that with small changes in soil water status leaf conductance of cowpea decreases in a manner which is consistent with the sensitive regulation of canopy water loss.However, treatments which differed in leaf conductance, and presumably stomatal aperture, had similar leaf water potentials. It is hypothesized that the stomatal closure which results from soil water depletion is mediated by changes in root water status through effects on the flow of information from root to shoot. An efficient mechanism of this type could be partially responsible for the extreme drought avoidance exhibited by this plant.Dedicated to Dr. K. Springer     

Fungi in the Canopy: How Soil Fungi and Extracellular Enzymes Differ Between Canopy and Ground Soils

Ecosystems - Tropical montane cloud forests contain a large abundance and diversity of canopy epiphytes, which depend on canopy soil to retain water and nutrients. We lack an in depth understanding...