The effects of nutrient pulsing on the threatened,floodplain species,Boltonia decurrens

Prior to anthropogenic disturbance, the floodplains of the Illinois River (USA) experienced moderate, cyclical flooding; a phenomenon termed a 'flood pulse'. Significant changes in the hydrology of the Illinois River caused by human alteration of the river channel resulted in a decline in populations of Boltonia decurrens, a native, herbaceous floodplain species of the Illinois River Valley and the demography of the species and underlying mechanisms causing the severe decline of B. decurrens are currently being studied. One component of the river flood pulse is the increased availability of nutrients in floodplain soils. We studied the effects of increased nutrient availability on growth and reproduction of B. decurrens and Aster pilosus, a species replacing B. decurrens in the floodplain. In this study, we examined the effects of a spring nutrient pulse and a late summer nutrient pulse, as compared to a control treatment, on rosettes of B. decurrens and A. pilosus grown in three soil types: sandy loam, silty loam and clay. Biomass, plant height, inflorescences per plant, seed production, and seed mass were measured and compared. Individuals of B. decurrens grown in sandy loam, the predominant soil type of the Illinois River Valley, had thegreatest increase in growth and fecundity in response to nutrient pulsing. Total biomass and inflorescences per plant were significantly greater than the control regardless of the timing of the nutrient pulse. Aster pilosus did not exhibit a clear pattern of increased growth and fecundity in a specific soil type or pulse treatment. The early pulse treatment appeared to have a greater effect across the range of soil types than the late pulse treatment; however, it did not seem to influence any particular variable(s) that we measured. A pulse of nutrients benefits B. decurrens more than A. pilosus, particularly in sandy loam. The increased vigor and fecundity of B. decurrens with a nutrient pulse could be a factor contributing to population survival during the period between disturbance events.     

Dynamics of patchy stomatal movements, and their contribution to steady-state and oscillating stomatal conductance calculated using gas-exchange techniques

Patchy stomatal movements were induced in leaves of Helianthus annuus L. and Xanthium strumarium L. by increasing Δw and decreasing light in a gas-exchange cuvette. The dynamics of the patchy movements were recorded and analysed using images of chlorophyll fluorescence, and the influence of heterogeneous stomatal activity on gas-exchange measurements of whole-leaf stomatal conductance was explored. Image series and gas-exchange measurements from two contrasting 100 min experiments are presented. One series of images, taken using Helianthus annuus, was characterized by strongly oscillating stomatal conductance induced by a decrease in light at high Δw. Fluorescence analysis revealed that individual patches of the leaf displayed a variety of behaviours (from static to strongly oscillating fluorescence), which, when averaged, matched the time dependence of the oscillating stomatal conductance measured by gas-exchange techniques. During the second series of images, taken using Xanthium strumarium, stomatal conductance (measured with gas exchange) declined slightly after an increase in Δw, and then maintained a steady state. Again, some patches in this leaf showed highly dynamic q_NP, although on the whole q_NP varied without any obvious pattern or frequency. When all patch activity in this series was averaged, it paralleled the steady whole-leaf stomatal conductance determined by gas-exchange measurements. It is clear from this work that coordinated patchy stomatal movements can contribute significantly to the dynamics of whole-leaf stomatal conductance, and, in contrast, that dynamic but uncoordinated patchy movements can average to produce a steady gas-exchange trace.     

短期环割对骆驼刺气孔导度及叶绿素荧光的影响

为研究骆驼刺对不同环割的生理响应,以塔克拉玛干沙漠南缘策勒绿洲外围骆驼刺为试验材料,设置了对照(CK),韧皮部半割(PS),韧皮部全割(PF),木质部半割(XS)4种处理,研究了骆驼刺的气孔导度、光合色素含量、Chl a/b、叶绿素荧光参数和曲线在不同环割处理下的变化特征。结果表明:短期韧皮部半割对骆驼刺各项生理指标影响不明显;韧皮部全割下,骆驼刺气孔导度、光合色素含量、叶绿素荧光参数有了不同程度的下降;木质部半割显著降低了骆驼刺气孔导度但光合色素含量和大部分荧光参数没有发生变化。处理后第5天和第10天各项参数相差不大,短期内环割对骆驼刺的伤害程度随时间推移变化较小。总体来看,短期环割处理对骆驼刺伤害程度是PFXSPSCK。在荒漠化防治过程中,应尽量避免骆驼刺的韧皮部被全部剥蚀。     

Measurement of cystic fibrosis transmembrane conductance regulator activity using fluorescence spectrophotometry

Cystic fibrosis (CF) is a frequent autosomal recessive disease caused by mutations that impair the CF transmembrane conductance regulator (CFTR) protein function. CFTR is a chloride channel activated by cyclic AMP (cAMP) via protein kinase A (PKA) and ATP hydrolysis. We describe here a method to measure CFTR activity in a monolayer of cultured cells using a fluorescence spectrophotometer and the chloride-sensitive probe 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ). Modifying a slice holder, the spectrophotometer quartz cuvette was converted in a perfusion chamber, allowing measurement of CFTR activity in real time, in a monolayer of T84 colon carcinoma cells. The SPQ Stern–Volmer constant (K_Cl^-) for chloride in water solution was 115.0 ± 2.8 M⁻¹, whereas the intracellular K_Cl^- was 17.8 ± 0.8 M⁻¹, for T84 cells. A functional analysis was performed by measuring CFTR activity in T84 cells. The CFTR transport inhibitors CFTR(inh)-172 (5 μM) and glibenclamide (100 μM) showed a significant reduction (P < 0.05) in CFTR activity. This simple method allows measuring CFTR activity in a very simple, reproducible, and sensitive way.     

Genetic variation of stomatal conductance, blue light sensitivity and zeaxanthin content in guard cells of Pima cotton (Gossypium barbadense)

Pima S‐6 ( Gossypium barbadense L.) is a modern line with high stomatal conductance, while B368 is a primitive cotton with low conductance. The blue light sensitivity of adaxial guard cells, probed as the blue light‐dependent enhancement of the red light‐induced chlorophyll a fluorescence quenching, was investigated in these two cotton lines with contrasting stomatal conductance. Adaxial guard cells isolated from Pima S‐6 cotton plants had a significantly higher carotenoid content and a higher blue light sensitivity than those isolated from B368 plants. In a growth chamber‐grown F₂ population of a cross between these two lines, adaxial stomatal conductances of individual plants segregated over a range exceeding the average conductances of the parents. Carotenoid content and the blue light sensitivity of adaxial guard cells also segregated. The concentrations of xanthophylls and β‐carotene in the adaxial guard cells were poorly correlated with the blue light response, except for zeaxanthin. The co‐segregation of stomatal conductance and blue light sensitivity suggested that the stomatal response to blue light may play a role in the regulation of stomatal conductance in the intact leaf. Zeaxanthin content and blue light sensitivity also co‐segregated, suggesting that both parameters are under genetic control. The co‐segregation of zeaxanthin content, blue light sensitivity and stomatal conductance provides further evidence for a role of zeaxanthin in the blue light photoreception of guard cells.     

Diurnal patterns of chlorophyll a fluorescence and stomatal conductance in species of two types of coastal tree vegetation in southeastern Brazil

 Diurnal measurements of chlorophyll fluorescence parameters and stomatal conductance to water vapour were carried out in five woody species and a bromeliad from two coastal vegetation types in Brazil, the rock outcrop of Pao de Acúcar and the sand dunes of Macaé. The environmental conditions of both study sites are characterized by high temperatures and light levels. The studied species comprised C₃ plants with different degrees of stomatal closure during the day, overall daily stomatal conductance and a plant with a typical CAM pattern. Plants on Pao de Acúcar exhibited only a small decline in potential quantum yield throughout the day. The non-photochemical quenching and the approximate photosynthetic electron transport rates were maximal during the peak of irradiance. In Macaé, light response curves of fluorescence parameters in the CAM-tree Clusia hilariana showed a clear differentiation between phases III and IV of CAM. In phase III, decarboxylation of organic acids probably maintained high internal CO₂ levels and there was only a small decrease in photochemical quenching with saturating light levels. In phase IV, the depletion of the organic acid pool and low stomatal conductances resulted in much lower levels of effective quantum yield and a substantial increase in both 1-q_P and non-photochemical quenching with increasing light levels. This behaviour during phase IV in the CAM-tree C. hilariana was comparable to the performance of the C₃-Clusia C. aff parviflora at Pao de Acúcar. It is seen that both the C₃ species and the CAM tree occurring in the two coastal communities effectively adjust their photochemical efficiency to environmental conditions and especially to diurnal variations of stress. Received: 29 April 1996 / Accepted: 14 November 1996     

An overview of models of stomatal conductance at the leaf level

Stomata play a key role in plant adaptation to changing environmental conditions as they control both water losses and CO₂ uptake. Particularly, in the context of global change, simulations of the consequences of drought on crop plants are needed to design more efficient and water‐saving cropping systems. However, most of the models of stomatal conductance (g_s) developed at the leaf level link g_s to environmental factors or net photosynthesis (A_net), but do not include satisfactorily the effects of drought, impairing our capacity to simulate plant functioning in conditions of limited water supply. The objective of this review was to draw an up‐to‐date picture of the g_s models, from the empirical to the process‐based ones, along with their mechanistic or deterministic bases. It focuses on models capable to account for multiple environmental influences with emphasis on drought conditions. We examine how models that have been proposed for well‐watered conditions can be combined with those specifically designed to deal with drought conditions. Ideas for future improvements of g_s models are discussed: the issue of co‐regulation of g_s and A_net; the roles of CO₂, absissic acid and H₂O₂; and finally, how to better address the new challenges arising from the issue of global change.     

三种植被恢复树种的冠层气孔导度特征及其对环境因子的敏感性

应用Granier热消散探针,长期监测华南地区荷木、大叶相思和柠檬桉林不同径级样树的树干液流,结合同步观测的气象数据,求算冠层气孔导度(g_c),并分析其对环境因子的响应方式及敏感性.结果表明: 不同季节荷木林日间平均g_c显著高于大叶相思和柠檬桉(P<0.05)（除3月外）.在干季和湿季,g_c与光合有效辐射(PAR)呈现对数正相关关系(P<0.001),湿季g_c对PAR响应比干季更敏感.g_c与水汽压亏缺(VPD)在干湿季均呈现对数负相关关系(P<0.001),同样在湿季表现出更高的敏感性.湿季g_c与VPD的偏相关系数高于干季,VPD对气孔行为的调控作用在湿季更为明显.随着土壤含水量的降低,g_c对VPD的敏感性下降,荷木和柠檬桉林下降的幅度大于大叶相思林,荷木和柠檬桉林下降的幅度相当.通过综合分析g_c对环境因子(PAR和VPD)的敏感性及其对土壤含水量变化的响应规律,发现乡土树种荷木作为植被恢复树种比外来引种的大叶相思和柠檬桉更为适宜.     

Strategies for establishing and using genome resource banks to protect genetic diversity in conservation breeding programs

Genome resource banks (GRBs) have the potential to preserve the genetic diversity of a species over time, yet they are rarely utilized as effective components of conservation breeding programs. Advances have been made in reproductive biology, collection and storage techniques, and use of stored gametes for achieving successful reproduction, but there are few guidelines for integrating GRBs into established breeding programs. Here we present basic guidelines, focusing on strategies for the collection, maintenance, and use of semen GRBs for protecting genetic diversity. These guidelines should be applied in the context of the specific purposes and roles of a breeding program's GRB, which will differ among species depending on vulnerability to loss and the status of rescue and conservation efforts. We recommend establishing up to three types of collections: (1) a National Reserve to preserve a species' genetic diversity, to be used only as a last resort; (2) a Savings Account to be used periodically to invigorate a genetically depauperate population; and (3) a Checking Account to be used as a regular part of the breeding program. We present methods for identifying donors to maximize genetic diversity in a GRB, as well as strategies for maintaining and optimally using GRBs.     

Influence of environmental conditions on sex allocation in the black rhinoceros population of Mkhuze Game Reserve,South Africa

According to the Trivers–Willard and local resource competition (LRC) hypotheses, for species where reproductive success is more variable in one sex, natural selection may lead to a bias in sex allocation of a female’s offspring according to her body condition. The extrinsic modification hypothesis (EMH) suggests that offspring sex can also be influenced by environmental conditions experienced by mothers. We investigated the influence of rainfall, El Niño‐Southern Oscillation (ENSO), population size and burning, in the year before conception and during pregnancy, on sex allocation in the black rhinoceros population of Mkhuze Game Reserve, South Africa, during 1970–2007. Females were more likely to have a male calf as rainfall during pregnancy increased, supporting the Trivers–Willard hypothesis. Also, the probability of having a male calf increased with population size, supporting the LRC hypothesis. Calf sex allocation was not influenced by ENSO. In conclusion, local environmental conditions may influence sex allocation in black rhinoceros, thereby supporting the EMH. Burning and population size may influence sex allocation in black rhinoceros, and yet can be manipulated by managers. Thus, this knowledge can be applied to improve population structure assessments and management regimes, especially in enclosed reserves, which is essential to maintain endangered species’ productivity.     

Evolutionary rescue and the coexistence of generalist and specialist competitors: an experimental test

Competition for resources is thought to play a critical role in both the origins and maintenance of biodiversity. Although numerous laboratory evolution experiments have confirmed that competition can be a key driver of adaptive diversification, few have demonstrated its role in the maintenance of the resulting diversity. We investigate the conditions that favour the origin and maintenance of alternative generalist and specialist resource-use phenotypes within the same population. Previously, we confirmed that competition for hosts among φ6 bacteriophage in a mixed novel (non-permissive) and ancestral (permissive) host microcosm triggered the evolution of a generalist phenotype capable of infecting both hosts. However, because the newly evolved generalists tended to competitively exclude the ancestral specialists, coexistence between the two phenotypes was rare. Here, we show that reducing the relative abundance of the novel host slowed the increase in frequency of the generalist phenotype, allowing sufficient time for the specialist to further adapt to the ancestral host. This adaptation resulted in ‘evolutionary rescue’ of the specialists, preventing their competitive exclusion by the generalists. Thus, our results suggest that competition promotes both the origin and maintenance of biodiversity when it is strong enough to favour a novel resource-use phenotype, but weak enough to allow adaptation of both the novel and ancestral phenotypes to their respective niches.     

Assessing photosynthetic efficiency in an experimental mangrove canopy using remote sensing and chlorophyll fluorescence

This study examined the ability of the photochemical reflectance index (PRI) to track changes in effective quantum yield (Δ F/F _m ′), non-photochemical quenching (NPQ), and the xanthophyll cycle de-epoxidation (DPS) in an experimental mangrove canopy. PRI was correlated with (Δ F/F _m ′) and NPQ over the 4-week measurement period and over the diurnal cycle. The normalised difference vegetation index (NDVI) was not correlated with any aspect of photochemical efficiency measured using chlorophyll fluorescence or xanthophyll pigments. This study demonstrated that photochemical adjustments were responsible for controlling the flow of energy through the photosynthetic apparatus in this mangrove forest canopy rather than canopy structural or chlorophyll adjustments.     

Diel patterns of larval drift of honmoroko Gnathopogon caerulescens in an inlet of Ibanaiko Lagoon,Lake Biwa,Japan

Diel drift patterns of larvae of the endangered cyprinid Gnathopogon caerelescens in an inlet of the Ibanaiko Lagoon, connected to Lake Biwa in Japan, were assessed in April 2012. Peak occurrence of yolk‐sac larvae was within a few hours after dark. Drift of newly hatched larvae is considered to be an important biological mechanism that ensures larval dispersal and recruitment from the inlets (spawning grounds) to the lagoon which functions as a nursery ground.     

气孔导度对CO2浓度变化的模拟及其生理机制

基于气孔运动的生理生化机制重点进行了气孔导度(gs)对CO2浓度变化的响应机制分析,并推导得到气孔导度(gs)对CO2浓度变化响应模型,并以9种植物进行了模型验证。结果表明:随着CO2浓度的升高,气孔导度会逐渐降低,且下降的幅度会随着CO2浓度的升高而逐渐减弱。气孔导度对CO2浓度(Cs)变化的响应模型可以表达为gs=gmax/(1+Cs/Cs0),其中式中gmax是最大气孔导度和Cs0是实验常数。该模型较好地模拟了气孔导度随CO2浓度变化的规律,模型参数具有明确的生理意义,与Jarvis模型和Ball-Berry模型相比,该模型如何实现多种环境因子的耦合有待进一步突破。另外,模型是在短期改变叶片CO2浓度的条件下得出的,在CO2浓度长期胁迫下的适用性也有待进一步确认。     

Epidermal conductance, stomatal density and stomatal size among genotypes of Sorghum bicolor (L.) Moench

Abstract. The ability of a plant to survive severe water deficits depends on its ability to restrict water loss through the leaf epidermis after stomata attain minimum aperture. At this stage, the rate of water loss is regulated by the epidermal conductance (g_c). Low g_c would be a useful selection criterion to identify genotypes with enhanced survival capability. Consequently, variation in g_c among Sorghum bicolor (L.) Moench genotypes was evaluated. Since there is little conclusive evidence linking g _c with leaf waxiness, alternative hypotheses relating g _c to stomatal trails were also examined. Epidermal conductance varied from 6.3 to 17.6mmol m⁻² s⁻¹ among sorghum genotypes. It was unrelated to stomatal pore length which varied with genotype and to pore depth which was similar for all genotypes measured. However, g _c, increased with increasing stomatal density. This indicates that stomatal density plays a direct role in water loss even at very low conductances. The association of low stomatal density with low g _c is consistent with the hypothesis that at the smallest stomata aperture, water loss from the epidermis above guard cell teichodes becomes a significant source of leaf water loss. Since low g _c is directly related to crop survival under severe water deficits, it is recommended that genotypes with low g _c. be selected using the selection criterion of stomatal density.     

The ecology, behavior, and conservation of the tidewater goby, Eucyclogobius newberryi

Understanding the ecology and behavior of endangered species, such as the tidewater goby, Eucyclogobius newberryi, is important for identifying problems and formulating solutions for species recovery. The tidewater goby forms isolated populations in California's coastal lagoons, creeks, and marshes. Rapid declines in the number of populations led to its listing as an endangered species in 1994. This benthic fish prefers stillwater habitats and feeds on small invertebrates. It is an annual species with an extended breeding season. Fish are larger in marsh habitats than in lagoon or creek habitats. The male digs a spawning burrow, preferably in sand, where he provides care for a single clutch. The tidewater goby is sex-role reversed: females compete more intensely than males for access to mates. The tidewater goby is a species at risk, in part due to narrow habitat preferences, isolation of populations, short lifespan, lack of marine dispersal, and vulnerability to introduced predatory fishes. Attributes that favor its recovery include euryhaline tolerances, rapid reproductive rate, its potential for opportunistic feeding, and the possibility of natural recolonization under certain circumstances. Potential conservation measures include protecting coastal marshes that adjoin creeks and lagoons, maintaining natural hydrologic regimes, preventing artificial breaching of the sandbar at the estuary's mouth, and preventing introductions of predatory fishes. Captive breeding and reintroduction of tidewater gobies are potential tools for recovery, provided that underlying problems of habitat availability and suitability and issues of genetic integrity and disease transmission are addressed. Further research into the tidewater goby's utilization of marsh habitats, dispersal mechanisms, response to artificial breaching events, and metapopulation genetics would provide additional information for management.     

植物气孔导度的环境响应模拟及其尺度扩展

气孔导度是衡量植物和大气间水分、能量及CO2平衡和循环的重要指标,探讨气孔导度与环境因子的关系及其模拟,以及气孔导度在叶片、冠层及区域尺度间的尺度转换及累积效应,对更好地认识植被与大气间的水热运移过程,合理评价植被在陆面过程中的地位和作用都具有重要意义。从植物气孔导度与环境因子的关系、气孔导度模拟以及尺度扩展三个方面,对前人的研究成果进行了概括总结。从叶片和冠层两个尺度出发,归纳总结了前人对于不同植物气孔导度与环境因子关系的研究成果,发现由于不同植物的遗传特性、测定时的环境、时间尺度的不同,以及未考虑各个环境因子的相互作用对气孔导度的影响,由此得到的气孔导度与环境因子之间的关系也不尽一致。对各单一环境因子与气孔导度的关系,给出了生理学解释,从根本上说明了环境因子变化对气孔导度的影响,而研究环境因子对气孔导度的综合影响时,应对各环境因子进行系统控制与同步观测。模拟计算植物气孔导度的模型主要有Jarvis模型和BWB模型两类,这些模型的模拟能力随着研究对象、试验区域、环境条件的改变而存在一定的差异,在具体使用时应结合实际情况选择最优模型进行模拟。除上述常用模型外,还总结了其他学者分别从不同角度提出的新的模型,对现有气孔导度模型进行了全面的总结。从叶片-冠层、冠层-区域两个方面归纳总结了前人关于气孔导度尺度扩展的研究成果,发现叶片-冠层的尺度扩展研究较成熟而冠层-区域的尺度扩展在模拟精度的验证方面存在困难。针对以下几个方面提出了今后气孔导度的研究重点:(1)结合研究对象所在的区域及环境条件,选择最优模型进行模拟;(2)综合考虑环境因子之间的相互作用及其对气孔导度的累积影响;(3)BWB模型与光合模型的耦合;(4)提高大尺度范围内的气孔导度模拟精度。     

Allozymic variation and relationships of the endangered cyprinodontid genus Valencia and its implications for conservation

Allozyme analysis was used to determine patterns of genetic variation and relationships within the genus Valencia , a group with two allopatric species, V. letourneuxi inhabiting the Balkan Peninsula, and V. hispanica which is endemic to the Iberian Peninsula. Products of 25 gene loci were analysed with AK *, FH *, LDH -1* and LDH -2* monomorphic when Fundulus heteroclitus macrolepidotus was not taken into account. Nine loci were diagnostic for both species of the genus Valencia . Levels of genetic variation of V. hispanica ( P =0·416, H ^e=0·118) and V. letourneuxi ( P =0·160, H _e=0·040) were higher than values reported previously. High population subdivision ( F _st=0·321) among V. hispanica populations indicates a clear interruption of genetic exchange among populations. High genetic variation and differentiation exhibited by populations of V. hispanica suggest that a recovery program should be carried out with natural stocks from the same localities.