Factors Regulating Nitrogen Retention During the Early Stages of Recovery from Fire in Coastal Chaparral Ecosystems

Fire is a fundamental reorganizing force in chaparral and other Mediterranean-type ecosystems. Postfire nutrient redistribution and cycling are frequently invoked as drivers of ecosystem recovery. The extent to which N is transported from slopes to streams following fire is a function of the balance between the rate at which soil microbes retain and metabolize N into forms that readily dissolve or leach, and how rapidly recovering plants sequester this mobilized N. To better understand how fire impacts this balance, we sampled soil and plant N dynamics in 17 plots distributed across two burned, chaparral-dominated watersheds in Santa Barbara County, California. We measured a variety of ecosystem properties in both burned and unburned plots on a periodic basis for 2 years, including soil water content, pH, soil and plant carbon and nitrogen, extractable inorganic nitrogen, dissolved organic nitrogen, and microbial biomass. In burned plots, nitrification was significantly enhanced relative to rates measured in unburned plots. Ephemeral herbs established quickly following the first postfire rain events. Aboveground plant biomass assimilated N commensurate with soil net mineralization, implying tight N cycling during the early stages of recovery. Microbial biomass N, on the other hand, remained low throughout the study. These findings highlight the importance of herbaceous species in conserving ecosystem nutrients as shrubs gradually recover.     

Diversity of Species and Interactions in the Upper Tree Canopy of Forest Ecosystems

SYNOPSIS. The importance of the organisms and processes thatoccur in forest canopies is becoming increasingly recognizedin relation to understanding biodiversity. The upper tree canopyof many forest ecosystems fosters extremely diverse communities,particularly of vascular epiphytes and arthropods. Epiphytesalso contribute to the diversity of birds because they add tothe total amounts of resources, provide opportunities for resourcespecialization, and temporally spread available resources inthe canopy throughout the year. Epiphytes also contribute toecosystem processes such as nutrient cycling because they gainaccess to nutrient sources originating outside the ecosystemand transfer them to other members of the forest, thus functioningas a "keystone" resource.     

Ultrastructure of the Pro-adenohypophysis of the River Lamprey,Lampetra fluviatilis,During Gonad Maturation

Abstract The pro-adenohypophysis (pro-AH) of migrating adult river lamprey, Lampetra fluviatilis, has been examined from October, when the gonads are developing slowly, until May, when the sexual maturation is completed. Two granulated cell types are dominating. One is chromophobic (C2, 95 nm), the other is basophilic (B1-B3) and probably gonadotropic. The mean diameter of the basophil secretory granules increases from 150 nm in October to 220 nm in April and May. The staining affinity of a rare, granulated cell type (D, 115 nm) has not been established. No acidophil cells are found in the pro-AH. The ultrastructural characteristics of the lead hematoxylin positive cells found sometimes in paraffin sections are unknown. Non-glandular stellate cells are common. They contain microfilaments, are probably contractile, and transform to phagocytes during the last months before spawning. This phagocytosis involves only the basophil cells. It is suggested that the stellate cells in this way destroy excess hormone. All cell types in the pituitary accumulate large irregular lipid droplets during the last month before spawning. These lipid droplets seem to be expelled from residual bodies as an end product of autolysis and phagocytosis.     

中国不同气候带植被挥发性有机化合物通量与生态系统演替的相关性

从群落水平和生态系统演替的角度对中国热带,亚热带和温带生态系统植物挥发性有机化合物（VOC）通量的研究表明,异戊二烯通量呈现出在生态系统演替的早期到中期阶段随着演替的的进行而升高,在先锋性灌木和乔木阶段达到高峰,然后又随着演替的发展而逐渐下降的演替格局,而其他VOC通量则有随着演替的进行而上升的趋势。生态系统不同演替阶段异戊二烯通量的变化可能与植物获取养分氮有关,根据植物VOC释放通量的生态演替格局,可以建立全球陆地生态系统的VOC模型,对大气化学过程中的VOC时空动态进行很好的模拟。     

Response of Soybean Canopy Photosynthesis to CO2 Concentration, Light, and Temperature

Photosynthetic rates of outdoor-grown soybean (Glycine max L.Merr. cv. Bragg) canopies increased with increasing CO₂ concentrationduring growth, before and after canopy closure (complete lightinterception), when measured over a wide range of solar irradiancevalues. Total canopy leaf area was greater as the CO₂ concentrationduring growth was increased from 160 to 990 mm³ dm^–3.Photosynthetic rates of canopies grown at 330 and 660 mm³ CO₂dm^–3 were similar when measured at the same CO₂ concentrationsand high irradiance. There was no difference in ribulose bisphosphatecarboxylase/oxygenase (rubisco) activity or ribulose 1,5-bisphosphate(RuBP) concentration between plants grown at the two CO₂ concentrations.However, photosynthetic rates averaged 87% greater for the canopiesgrown and measured at 660 mm³ CO₂ dm^–3. A 10°C differencein air temperature during growth resulted in only a 4°Cleaf temperature difference, which was insufficient to changethe photosynthetic rate or rubisco activity in canopies grownand measured at either 330 or 660 mm³ CO₂ dm^–3. RuBP concentrationsdecreased as air temperature during growth was increased atboth CO₂ concentrations. These data indicate that the increasedphotosynthetic rates of soybean canopies at elevated CO₂ aredue to several factors, including: more rapid development ofthe leaf area index; a reduction in substrate CO₂ limitation;and no downward acclimation in photosynthetic capacity, as occurin some other species. Key words: CO₂ concentration, soybean, canopy photosynthesis     

Electrical Properties of Toad Oocytes During Maturation and Activation

The full-grown oocytes of the toad Bufo bufo japonicus , whether in follicular layer or not, had a membrane potential of about -50 mV in De Boer's solution (DB), but underwent a deep hyper-polarization of up to -90 mV when pretreated with Ca, Mg-free EDTA-solution. Regardless of the magnitude of their resting potentials, the defolliculated oocytes exposed to progesterone underwent a gradual depolarization before the germinal vesicle breakdown and retained membrane potential at a level of -10 mV until 18 hr post hormone treatment (PHT), the stage of the second meiotic metaphase. A positive-going activation potential of a magnitude of 70 mV was recorded in the oocytes when pricked at 18 hr PHT as well as in uterine eggs 3–5 min after insemination. A low magnitude of activation potential in response to pricking was recorded in 63% of the oocytes at 13 hr PHT, and premature oocytes exhibiting the activation potential always underwent cortical granule breakdown (CGBD) and perivitelline space formatión. Oocytes where the germinal vesicle had been removed before the hormone treatment exhibited an activation potential and underwent CGBD in response to pricking at 18 hr PHT, whereas those pulse-treated with cycloheximide (10 μg/ml) during the 8–11 hr PHT exhibited neither of these cortical responses. These results indicate that the syntheses of proteins independent of germinal vesicle taking place at 9–11 hr PHT enable the oocytes to undergo cortical responses.     

小麦种子成熟和萌发过程中的假萌发素活性

用SDS-PAGE方法研究了假萌发素(ψG)在小麦种子成熟和萌发过程中活性的变化.结果表明:在种子成熟过程中只有ψG表达,扬花后10 d,在颖壳、内外桴、种皮和果皮中皆可检测到ψG的草酸氧化酶活性,随着发育进程的推进,ψG的活性增大.在种子萌发过程中,在小麦品种中育5号的维管束过渡区中除了萌发素G和G'外,还可检测到ψG的草酸氧化酶活性.由于ψG在种子成熟过程中主要存在于颖壳、内外桴、果皮及种皮这些保护组织中,且开始大量表达的时间正是生长接近停止时,于是推测ψG很可能通过降解草酸产生H2O2而推动这些组织细胞壁的木质化.     

Survival, Gap Formation, and Recovery Dynamics in Grassland Ecosystems Exposed to Heat Extremes: The Role of Species Richness

A field experiment was performed in which the richness of perennial grasses (S) was varied in model ecosystems exposed to a simulated heat wave (free air temperature increase and drought). The proportion of individuals that survived the heat wave decreased with S, which could be ascribed to higher water consumption in the species-rich systems. Higher transpiration at high diversity was also observed in other studies using functional groups and could have originated from increased leaf area, less intense stomatal closure, or a combination of both. The increased tiller number per plant that we observed, while leaf area per tiller remained constant, suggests that an enhanced leaf area index was most likely responsible. However, competitive interactions also seemed to play a role in the influence of S on survival. Regrowth of the surviving individuals, expressed as leaf area per living plant after a recovery period following the heat wave, increased with S, most likely due to the dominance of productive species, which was facilitated by the additional space yielded by more intense gap formation at higher S (due to higher plant mortality). Species richness affected both the size and density of the gaps. Mean size increased exponentially with S, while density increased at low S but decreased at higher S when connectance of the gaps occurred. Size distribution of the gaps was not affected. Received 18 January 2000; accepted 31 May 2001.     

Orthophosphate Absorption by the Sporophyte of Funaria Hygrometrica During Maturation

The absorption of phosphate by the sporophyte of Funaria hygrometrica,during its maturation, has been studied using ³²P. More radioactivitywas found in the capsule when the absorption occured throughthe seta alone than when it look place through the leaves ofthe gametophyte. Each stage of capsule development studied isdescribed from transverse sections and electron micrographs.Phosphate is accumulated very actively by the capsule in theyoungest stage when the spores are being formed. The exchangesbetween the capsular tissues and the spores are low.     

A Cell-based Model of Endothelial Cell Migration,Proliferation and Maturation During Corneal Angiogenesis

The motivation of this work stems from two critical experimental observations associated with corneal angiogenesis: (1) angiogenesis will not succeed without endothelial cell proliferation, and (2) proliferation mainly occurs at the leading edge of developing sprouts (Sholley et al., Lab. Invest. 51:624–634, 1984). To discover the underlying mechanisms of these phenomena, we develop a cell-based mathematical model that integrates a mechanical model of elongation with a biochemical model of cell phenotype variation regulated by angiopoietins within a developing sprout. This model allows for a detailed study of the relative roles of endothelial cell migration, proliferation, and maturation. The model is validated by quantitatively comparing its predictions with data derived from corneal angiogenesis experiments. We conclude that cell elasticity and cell-to-cell adhesion allow only limited sprout extension in the absence of proliferation, and the maturation process combined with bioavailability of VEGF can explain the localization of proliferation to the leading edge. We also use this model to investigate the effects of X-ray irradiation, Ang-2 inhibition, and extracellular matrix anisotropy on sprout morphology and extension.     

Photosynthesis of White Clover Leaves as Influenced by Canopy Position, Leaf Age, and Temperature

Microswards of white clover (Trifolium repens L.) were grownin controlled environments at 10/7, 18/13 and 26/21 °C day/nighttemperatures. The vertical distribution of leaves of differentages and their rates of ¹⁴CO₂-uptake in situ were studied. Extending petioles carried the laminae of young leaves throughthe existing foliage. A final position was reached within 1/4to 1/3 of the time between unfolding and death. Newly unfoldedleaves had higher rates of ¹⁴CO₂-uptake per leaf area than olderones at the same height in the canopy. At higher temperatures,the decrease with age was faster. However, the light-photosynthesisresponse of leaves which were removed from different heightsin the canopy varied much less with leaf age than did the ratesof ¹⁴CO₂-uptake in situ. The comparison of the rates of ¹⁴CO₂-uptake in situ with thelight-photosynthesis response curves suggests that young leavesreceive more light than older ones at the same height in thecanopy. This would imply that young white clover leaves havethe ability to reach canopy positions having a favourable lightenvironment. This ability may improve the chances of survivalof white clover in competition with other species. Trifolium repens L., white clover, photosynthesis, canopy, leaf age, ¹⁴CO₂-uptake, ecotypes, temperature     

Changes in the Uptake of GABA and Taurine During Neuronal and Glial Maturation

Abstract: The influence of the time of culture on GABA and taurine uptake was investigated in spontaneously matured cultures of glial and neuronal origins and in cultures treated with cyclic nucleotides. In the spontaneously matured cultures the capacity of the high-affinity neuronal GABA transport system increased with time in culture. Essentially opposite results were found for the uptake of GABA by glial cultures. In contrast with the neuronal uptake of GABA, the capacity of the taurine transport system was significantly decreased. Uptake of taurine into glia, however, exhibited a progressive increase with the period of culture. The values of Km, for the high-affinity systems were always found to range around 10 μM. It is suggested that, in mature cells, neuronal uptake sites are of prime importance for GABA transport, while taurine uptake may be more specifically directed towards glial cells. When cultures were treated with cyclic nucleotide derivatives, a morphological differentiation was induced, which could not be linked to a stimulation of GABA or taurine uptake systems as compared with the non-treated cultures.     

Shaping of Receptive Fields in the Visual Cortex During Retinal Maturation

We present a computational study of the formation of simple-cell receptive field patterns in the primary visual cortex. Based on the observation that the spatial frequency of the retinal filter increases postnatally, our results explain differences in the time course of the development of orientation selectivity in binocularly deprived and normally reared kittens. Development after eye-opening in normal animals is modelled by training with natural images, whereas in the case of binocular deprivation noise-like stimulation continues. Further, it is shown that different orientation selectivities are obtained for network models trained with natural images in contrast to random phase images of identical second order statistics. The latter finding suggests that higher-order statistics of the inputs influences development of primary visual cortex. Finally, we search for quantities that identify possible signatures of natural image statistics in order to specify the amount of constructiveness that visual experience has on the formation of receptive fields.     

Polysaccharide Complexes in Full-Grown Oocytes of the Newt, Pleurodeles, and Changes in their Distribution During Progesterone-Induced Maturation

Immature full-grown oocytes of Pleurodeles waltlii contain large amounts of small electron-dense polysaccharidic granules. These granules lack a limiting membrane, and have a dense but heterogeneous matrix and an apparent diameter of 24–36 nm. Their structure, organization and distribution strongly suggest that they are glycogen granules. On the other hand, mature oocytes both after oviposition or 22–24 hr after in vitro progesterone stimulation contain no polysaccharide granules or complexes. During the first 9–10 hr after hormonal stimulation, granules were abundant and present both individually and as large strands occupying most of the space between the organelles. Granules were frequently found packed together and arranged in regularly arrayed stacks within large subcortical ant cortical vacuoles. Between 4 and 6 hr after progesterone addition, oocytes released the contents of vacuoles to the outside. Between about 11 and 14 hr after progesterone addition, oocytes still contained large amounts of polysaccharide complexes, but the vacuoles were empty. From about 15 hr after progesterone treatment until the end of maturation, the complexes progressively disappeared from the cytoplasm, coincident with the detachment of the follicle cell layer from the oocytes and a reduction in the number and size of microvilli.     

Effects of Zinc Supplementation During In Vitro Maturation on Meiotic Maturation of Oocytes and Developmental Capacity in Yak

Zinc (Zn) is an essential trace element that is required during mammalian developmental processes. The objective of this study was to investigate the effects of Zn supplementation during in vitro maturation (IVM) on the developmental capacity of yak (Bos grunniens) oocytes. Cumulus expansion, nuclear maturation, intracellular glutathione (GSH), reactive oxygen species (ROS) levels, superoxide dismutase (SOD) activity, subsequent embryonic development, and the expression of Zn transporters (ZnTs) and Zrt and Irt-like proteins (ZiPs) were evaluated. The Zn concentrations in yak plasma and follicular fluid were 0.740?±?0.012 and 0.382?±?0.009 μg/mL, respectively. The cumulus expansion did not show significant differences in COCs after matured with or without Zn supplementation (P?>?0.05). The intracellular GSH was higher in oocytes matured with 1 or 2 mg/L Zn than in control group (0 mg/L) (P?<?0.05). However, ROS levels of oocytes matured with 1 or 2 mg/L Zn were reduced significantly compared with the control and 0.5 mg/L groups (P?<?0.05). The SOD activity was increased significantly after Zn supplementation. The cleavage rate was not significantly different after Zn supplementation (P?>?0.05). Percentages of matured oocytes that developed into the blastocyst stage after IVF were 47.9, 50.5, 60.4, and 58.9% for 0, 0.5, 1, and 2 mg/L Zn groups, respectively. Gene expression analysis revealed that the expression patterns associated with Zn were changed after Zn supplementation. In conclusion, Zn supplementation to IVM improved yak oocyte maturation and subsequent development by increasing GSH and SOD activity, decreasing ROS in oocytes.     

The Development of Desiccation-tolerance and Maximum Seed Quality During Seed Maturation in Six Grain Legumes

‘Physiological maturity’, i.e. the time when seedsreach their maximum dry weight during development, occurredwhen maturation drying on the parent plant in the field hadreduced seed moisture content to approximately 60 per cent infaba bean (Vicia faba L.), lentil (Lens culinaris Medic.), chickpea(Cicer arietinum L.), white lupin (Lupinus albus L.), soya bean(Glycine max [L.] Merr.) and pea (Pisum sativum L.) The onsetof desiccation-tolerance, i.e. the ability of seeds to germinatefollowing harvest and rapid artificial drying, coincided withphysiological maturity, except in pea where it occurred a littleearlier at about 70 per cent moisture content. Maximum seedquality as determined by maximum viability, minimum seedlingabnormalities and maximum seedling size occurred in pea, chickpeaand lupin when seeds were harvested for rapid drying at physiologicalmaturity; but for maximum seed quality in the other speciesmaturation drying had to proceed further - to about 45 per centmoisture content in soya bean and to about 30 per cent moisturecontent in lentil and faba bean seed crops. Much of this variationamongst the six species, however, was due to differences inthe variation in maturity within each seed crop. Results forindividual pods showed that peak maturity, i.e. maximum seedquality following harvest and rapid artificial drying, was achievedin all six species once maturation drying had reduced the moisturecontent of the seeds to 45–50 per cent. In pea, faba beanand soya bean there was a substantial decline in viability andan increase in seedling abnormalities when harvest was delayedbeyond the optimal moisture content for harvest.     

Honeybees, Communicative Order, and the Collapse of Ecosystems

The paper examines the sudden disappearance in the United States of millions of honeybees in managed bee colonies. The major research undertaken in the U.S. concentrates on finding the pathogens responsible. This paper suggests an alternative avenue of research a) that as a result of global warming there is a disjunction between bees pollinating cycles and the life cycle of plants b) that understanding changes in “timing cycles” as a result of global warming is the key to understanding the disappearance of the bees. It notes that Gregory Bateson argued that any condition of ecosystem collapse would be characterized first by a collapse in its communicative order rather, than from changed physical states. The collapse of bee colonies and demise of other pollinators is a seeming confirmation of Gregory Bateson argument. Honeybees are ‘go betweens’ in ecosystemic order. It also argues that an appropriate topology of timing cycles and their recursions would enable better visual comprehension of the heterarchical ‘pattern which connects’, in Bateson’s phrase, and prompt awareness of possible catastrophe in human food supplies.

Tracking the Rates and Mechanisms of Canopy Damage and Recovery Following Hurricane Maria Using Multitemporal Lidar Data

Ecosystems - Hurricane Maria, a Category 4 storm, snapped and uprooted canopy trees, removed large branches, and defoliated vegetation across Puerto Rico. The magnitude of forest damages and the...