Copepod photobehavior in a simulated natural light environment and its relation to nocturnal vertical migration

To investigate the roles of light in initiating, controlling and directing nocturnal vertical migration, photoresponses of the adult, female copepod Acartia tonsa Dana were measured under simulated natural underwater light conditions using a video system. Copepods were adapted to a range of background light levels and tested with the following stimuli: absolute quantal intensity, absolute change in quantal intensity and relative (%) change in quantal intensity. The stimulus initiating vertical movements was relative change in quantal intensity, while responsiveness was controlled by the level of light adaptation. A. tonsa swam upward in response to decreases. Response with minimal stimulation occurred at an adaptation intensity close to that in the copepod's natural habitat at the time of the migratory ascent (near the bottom of the Newport River estuary, North Carolina, near sunset). Analysis of the angles of upward movement showed that light is not a directional cue. Relative increases in intensity resulted in sinking, with minimal stimulation required at an adaptation intensity close to that in the field when the migratory descent occurs near sunrise. These results offer a reasonable explanation of how light cues may shape nocturnal vertical migratory patterns.     

Does the Harvard/U.S. Environmental Protection Agency Ambient Particle Concentrator Change the Toxic Potential of Particles?

Abstract

Inhalation exposure to urban air particles is known to increase morbidity in humans and animals. Our group utilizes the Harvard/U.S. Environmental Protection Agency Ambient Particle Concentrator (HAPC) to generate concentrated aerosols of outdoor air particles for experimental exposures. We have reported increased pathologic responses to inhalation of concentrated urban air particles and identified silicon (as silicate) as an element associated with many of these responses. Using silicate-rich Mt. St. Helen’s volcanic ash (MSHA), we exposed three groups of Sprague-Dawley rats by inhalation for 6 hr to filtered air, MSHA, or MSHA passed though the HAPC. Twenty-four hours following exposure, bronchoalveolar lavage was performed to assess total cell count, differential cell count, protein, lactate dehydrogenase, and n-β[notdef]glucosaminidase levels. Peripheral blood was examined for packed cell volume, total protein, total white cells, and differential cell count. Morphologic studies localized particles in the lung and assessed pulmonary vasculature. No significant differences were observed among any of the groups in any parameter measured including morpho-metric analysis of pulmonary vasoconstriction. Scanning electron microscopy and X-ray analysis identified particles as silicates typical of MSHA throughout the lung. These findings suggest that particles passing through the HAPC have no change in their toxic potential in an exposure setting where particle deposition in the lung has occurred.     

Fuzzy综合评判在森林水文效应研究中的应用

本文应用多层次、二型Fuzzy综台评判方法,对祁连山水源涵养林区的青海云杉林、祁连圆柏林、灌木林和牧坡草地4个不同植被类型进行了森林水文效应的多因子综合评判。结果表明:青海云杉林是该林区涵养水源效应最佳的林型,祁连圆柏林和灌木林次之,牧坡草地不仅蓄水能力差,且有水土流失发生;并提出了各植被类型合理经营的对策,为祁连山水源涵养林的保护、发展和综合利用提供科学依据。     

Ecological Benefits of the Conservation Reserve Program

The Conservation Reserve Program was initiated in 1985 to reduce soil loss on highly erodible agricultural land. This stated objective of the program has been quite successful. However, there are other unintentional yet significant ecological benefits to the program that merit evaluation. These benefits include the reversal of landscape fragmentation, maintenance of regional biodiversity, creation of wildlife habitat, and favorable changes in regional carbon flux. These and other benefits should be used by policy makers and federal officials to maintain the program even after enrollment expectations have been achieved.     

Life history evolution: successes, limitations, and prospects

Life history theory tries to explain how evolution designs organisms to achieve reproductive success. The design is a solution to an ecological problem posed by the environment and subject to constraints intrinsic to the organism. Work on life histories has expanded the role of phenotypes in evolutionary theory, extending the range of predictions from genetic patterns to whole-organism traits directly connected to fitness. Among the questions answered are the following: Why are organisms small or large? Why do they mature early or late? Why do they have few or many offspring? Why do they have a short or a long life? Why must they grow old and die? The classical approach to life histories was optimization; it has had some convincing empirical success. Recently non-equilibrium approaches involving frequency-dependence, density-dependence, evolutionary game theory, adaptive dynamics, and explicit population dynamics have supplanted optimization as the preferred approach. They have not yet had as much empirical success, but there are logical reasons to prefer them, and they may soon extend the impact of life history theory into population dynamics and interspecific interactions in coevolving communities.     

施肥对落叶松人工林植物养分及生理特性的影响

以东北林业大学帽儿山实验林场的14年生落叶松人工幼龄林为研究对象，对白浆化的暗棕壤林地进行了施肥试验。采用完全随机排列的方法，在林分内设置了9个施肥处理和1个无肥对照。在生长旺盛期测定了叶片和根系的全N和全P质量分数以及光合速率、呼吸速率、叶绿素质量分数等指标。结果表明，单施520kg/hm^2尿素，在提高全N、全P质量分数的同时，还能促进根系对磷素的吸收和利用，增加光合速率和叶绿素质量分数；单施314kg／hm^2磷酸二铵，能加快根系对养分的转移速度，提高光合系数(光合速率／呼吸速率)，且是这些施肥处理中效果最好的施肥水平，这说明此林龄的落叶松林容易缺磷，应适量多施磷肥；处理436kg／hm^2尿素 236kg／hm^2磷酸二铵 133kg／hm^2氯化钾，由于K肥的混入，加快了根系对N、P的转移，使叶片中的质量分数增加，有利于光合作用的进行。因此，合理的施肥措施，不仅能提高落叶松人工林叶片与根系的养分质量分数，还能提高叶片的光合能力。对于此幼龄林，少N多P或N、P、K混合施肥效果最佳。     

Potential site productivity influences the rate of forest structural development

Development and maintenance of structurally complex forests in landscapes formerly managed for timber production is an increasingly common management objective. It has been postulated that the rate of forest structural development increases with site productivity. We tested this hypothesis for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests using a network of permanent study plots established following complete timber harvest of the original old-growth forests. Forest structural development was assessed by comparing empirical measures of live tree structure to published values for Douglas-fir forests spanning a range of ages and structural conditions. The rate of forest structural development--resilience--exhibited a positive relationship with site index, a measure of potential site productivity. Density of shade-intolerant conifers declined in all study stands from an initial range of 336-4068 trees/ha to a range of 168-642 trees/ha at the most recent measurement. Angiosperm tree species declined from an initial range of 40-371 trees/ha to zero in seven of the nine plots in which they were present. Trends in shade-tolerant tree density were complex: density ranged from 0 to 575 trees/ha at the first measurement and was still highly variable (25-389 trees/ha) at the most recent measurement. Multivariate analysis identified the abundance of hardwood tree species as the strongest compositional trend apparent over the study period. However, structural variables showed a strong positive association with increasing shade-tolerant basal area and little or no association with abundance of hardwood species. Thus, while tree species succession and forest structural development occur contemporaneously, they are not equivalent processes, and their respective rates are not necessarily linearly related. The results of this study support the idea that silvicultural treatments to accelerate forest structural development should be concentrated on lower productivity sites when the management objective is reserve-wide coverage of structurally complex forests. Alternatively, high-productivity sites should be prioritized for restoration treatments when the management objective is to develop structurally complex forests on a portion of the landscape.     

Mechanistic aspects regarding the direct aqueous environmental photochemistry of phenol and its simple halogenated derivatives. A review

We have reviewed the mechanistic aspects regarding the direct aqueous phase environmental photochemistry of phenol and its simple halogenated derivatives. These compounds are important industrial and natural products, are ubiquitous in aquatic systems, and their acute and chronic toxicity makes their environmental fate of interest. Work over the past two decades has unified the photochemistry of phenol and its simple halogenated derivatives. In general, three photochemical pathways dominate in aqueous solution depending on the nature of the substrate: (1) photoionization, (2) photochemical aryl-halogen bond homolysis, and (3) photochemical aryl-halogen bond heterolysis. Photoionization typically results in an array of biaryl radical coupling products which are only relevant for highly concentrated waste streams. Photolytic aryl-halogen bond homolysis will primarily give photoreduction products where reducing agents such as dissolved organic matter or reduced metal cations are present, and radical coupling products in highly concentrated waste streams. The 2- and 4-substituted halophenols may undergo photochemical aryl-halogen bond heterolysis upon irradiation to give an aryl cation. The aryl cation can be attacked by water to give the corresponding hydroxylated derivative, or may deprotonate to generate alpha- and gamma-ketocarbenes, respectively. Following their formation, the singlet alpha-ketocarbenes may undergo Wolff rearrangements to cyclopentadiene-ketenes that are subsequently hydrolyzed to cyclopentadiene carboxylic acids. The triplet alpha- and gamma-ketocarbenes are attacked by oxygen and hydrolyzed to give benzoquinones, directly hydrolyzed to yield hydroquinones, reduced to give phenols, or could take part in coupling reactions in highly concentrated waste streams to give dimers and hydroxybiaryl complexes. Additional studies in natural water samples are required to assess the relative importance of these direct irradiation mechanisms relative to indirect photolysis and other abiotic and biotic degradation and environmental partitioning pathways across the continuum of marine, freshwater, and wastewater biogeochemical signatures.