Can genetic variability for nitrogen metabolism in the developing ear of maize be exploited to improve yield?

Quantitative trait loci (QTLs) for the main steps of nitrogen (N) metabolism in the developing ear of maize (Zea mays L.) and their co-localization with QTLs for kernel yield and putative candidate genes were searched in order to identify chromosomal regions putatively involved in the determination of yield. During the grain-filling period, the changes in physiological traits were monitored in the cob and in the developing kernels, representative of carbon and N metabolism in the developing ear. The correlations between these physiological traits and traits related to yield were examined and localized with the corresponding QTLs on a genetic map. Glycine and serine metabolism in developing kernels and the cognate genes appeared to be of major importance for kernel production. The importance of kernel glutamine synthesis in the determination of yield was also confirmed. The genetic and physiological bases of N metabolism in the developing ear can be studied in an integrated manner by means of a quantitative genetic approach using molecular markers and genomics, and combining agronomic, physiological and correlation studies. Such an approach leads to the identification of possible new regulatory metabolic and developmental networks specific to the ear that may be of major importance for maize productivity.     

Can classifications of functional gender be extended to all land plants?

Land plants (bryophytes, seedless vascular plants and seed plants) may have combined or separate sexes, and this variation also may occur at two life-cycle stages. Thus plants show variation in individuals’ attainment of fitness via sperms versus eggs (functional gender) and the diversity of gender morphs found in populations. We extend D.G. Lloyd's classification of flowering plant gender to all land plants, with three main functional classes according to whether populations are dimorphic or monomorphic for gender (i.e., populations consist of either one or two distinct sex classes), and at which life cycle stages this occurs: (1) sporophyte-dimorphic, (2) sporophyte-cosexual and gametophyte-dimorphic, and (3) gametophyte-cosexual. In dimorphic sporophytes and gametophytes, morphs that reproduce mostly as females and males may be constant (dioecy) or inconstant (gynodioecy, androdioecy, trioecy). We suggest that examining the sex conditions of seedless plants using a functional perspective will reveal a diversity of sexual systems largely analogous to those found in seed plants. An extended suite of model plants with different biological attributes will allow new tests of existing models of mechanisms that select for different sexual systems, and may lead to important new questions in the field, some of which we suggest here.     

Can the scaling of plant nitrogen to phosphorus be altered by global change? An empirical test

全球变化可能引起土壤中各种养分的供应失衡,进而导致陆地植物中氮(N)和磷(P)元素化学计量学的不平衡。前人的研究报道了全球变化因子对植物N、P含量和N:P的影响,但鲜有研究探讨全球变化因子是否影响以及如何影响这两种元素之间的异速关系。本研究利用改变降水(增雨和干旱)、增温和N添加处理的野外控制试验,结合异速函数 N = βP^α (或对数转换后的线性关系：Log N = Log β + α Log P),检验了中国西北地区黄土高原半干旱草原植物N和P化学计量特征及N和P之间的异速关系对这些全球变化因子的响应。研究结果表明,干旱和增温均降低了植物P浓度,N添加增加了植物N浓度,这些都导致植物N:P增加。干旱、增温和N添加没有显著改变植物N和P浓度之间异速关系的斜率(即N和P浓度对数转换后的线性关系斜率α),但是显著增加了其截距(Log β)。这些结果表明,全球变化因子可能不会影响植物N和P之间的协同变化关系,植物中N和P之间可能存在着紧密的耦合关系。这些结果将有助于我们更好地理解全球变化背景下的植物养分动态和元素平衡。     

Do competition and herbivory alter the internal nitrogen dynamics of birch saplings?

Deciduous trees recycle nitrogen within their tissues. The aim of this study was to test the hypothesis that reductions in plant growth, caused by competition and herbivory, reduce the sink strength for N during autumn nutrient withdrawal, and reduce the storage capacity and hence the amount of N remobilized in the following spring. We used (15)N-labelled fertilizer to quantify N uptake, leaf N withdrawal and remobilization. Betula pubescens saplings were grown with either Molinia caerulea or Calluna vulgaris, and subjected to simulated browsing damage. Competition reduced B. pubescens leaf N withdrawal and remobilization, with C. vulgaris having a greater effect than M. caerulea. However, simulated browsing had no significant effect on sapling N dynamics. The patterns of leaf N withdrawal and remobilization closely followed sapling dry mass. We conclude that the effect of competition on sapling mass reduces their N-storage capacity. This reduces sink strength for leaf N withdrawal and the source strength for remobilized N. The ability of saplings to compensate for browsing damage removed any potential effect of browsing on N dynamics.     

How does a mistletoe affect the water,nitrogen and carbon balance of two mangrove ecosystem species?

Abstract. The effect of a mistletoe, Phthirusa maritima , on the water, nitrogen and carbon balance of two mangrove host species, Conocarpus erectus and Coccoloba uvifera , was studied. Several daily cycles of water potential and its components (pressure-volume curves); leaf nitrogen content (Kjeldahl method); leaf conductance, transpiration rates and carbon assimilation (portable gas exchange system) were measured on mistletoe, infested and uninfested plants in the Caribbean coast of Venezuela. The mistletoe on both host species showed higher transpiration rates and lower CO₂ assimilation rates, and therefore lower water use efficiencies. With respect to infested and uninfested plants, C. erectus did not show large differences in the parameters measured with the exception of assimilation rates which were significantly lower in the infested plants. On the other hand, C. uvifera did show differences in all parameters and, therefore, was affected to a greater degree by the mistletoe. The behaviour of mistletoeinfested and uninfested plants, with respect to habitats with different degrees of water stress and with respect to the salinity gradient in which these mangroves grow, is discussed.     

Can antioxidants be beneficial in the treatment of lead poisoning?

Recent studies have shown that lead causes oxidative stress by inducing the generation of reactive oxygen species, reducing the antioxidant defense system of cells via depleting glutathione, inhibiting sulfhydryl-dependent enzymes, interfering with some essential metals needed for antioxidant enzyme activities, and/or increasing susceptibility of cells to oxidative attack by altering the membrane integrity and fatty acid composition. Consequently, it is plausible that impaired oxidant/antioxidant balance can be partially responsible for the toxic effects of lead. Where enhanced oxidative stress contributes to lead-induced toxicity, restoration of a cell's antioxidant capacity appears to provide a partial remedy. Several studies are underway to determine the effect of antioxidant supplementation following lead exposure. Data suggest that antioxidants may play an important role in abating some hazards of lead. To explain the importance of using antioxidants in treating lead poisoning the following topics are addressed: (i) Oxidative damage caused by lead poisoning; (ii) conventional treatment of lead poisoning and its side effects; and (iii) possible protective effects of antioxidants in lead toxicity.     

Can the functional response to prey predict invasiveness? A comparison of native fishes and alien poeciliids in Hong Kong

Biological invasion is globally pervasive and an increasing threat to biodiversity. We need to be able to predict the ecological impacts of alien species, in order to prioritize management of those expected to be most damaging. Comparisons of functional response (FR) between invaders and trophically similar natives has been proposed as useful for predicting invader impacts, as interaction intensity tends to be reflected in higher FRs. We undertook feeding trials comparing FRs of four invasive poeciliids (mosquitofish [Gambusia affinis], guppy [Poecilia reticulata], liberty molly [P. salvatoris] and swordtail [Xiphophorus hellerii]) in Hong Kong with three similar-sized native fishes (ricefish [Oryzias curvinotus: Adrianichthyidae]; predaceous chub [Parazacco spilurus] and half-banded barb [Puntius semifasciolatus: Cyprinidae]). We tested whether FRs correctly reflected known impacts of the mosquitofish and guppy locally, and used FRs to forecast potential impacts of the molly and swordtail. Overall, the swordtail and molly consumed more prey and had higher FRs than the other five fishes, owing to their shorter prey handling time and/or higher attack rate. Mosquitofish and guppy had similar FRs to native fishes. All fishes showed type-II FRs, and had some potential to destabilize prey populations. Such results predict that the molly and swordtail could have strong ecological effects in Hong Kong freshwaters. However, FR alone was not highly predictive of known impacts of mosquitofish and guppy. It is suggested a more holistic approach incorporating estimates of field abundance and parameterization of other niche dimensions of the invader will be needed.

     

Can export of organic matter from estuaries support zooplankton in nearshore,marine plumes?

Marine and terrestrial ecosystems are connected via transfers of nutrients and organic matter in river discharges. In coastal seas, such freshwater outflows create prominent turbidity plumes. These plumes are areas of high biological activity in the pelagos, of which zooplankton is a key element. Conceptually, the increased biomass of zooplankton consumers in plumes can be supported by two alternative trophic pathways—consumption of fresh marine phytoplankton production stimulated by riverine nutrients, or direct trophic subsidies through the uptake of terrestrial and estuarine organic matter flushed to sea. The relative importance of these two pathways has not been established previously. Isotopic tracing (carbon and nitrogen) was used to measure the extent of incorporation of marine versus terrestrial matter into mesozooplankton consumers in the plumes off a small estuary in eastern Australia. Replicate zooplankton samples were taken during baseflow conditions with minimal freshwater influence to the sea, and during pulsed discharge events that generated turbidity plumes in coastal waters. Food sources utilized by zooplankton differed among locations and with the strength of freshwater flow. Terrestrial and estuarine carbon only made a sizeable contribution (47%) to the carbon demands of zooplankton in the lower estuary during pulsed freshwater flows. By contrast, in plumes that developed in nearshore marine waters, phytoplankton supplied up to 90% of the dietary carbon of zooplankton feeding in the plumes. Overall, it was “fresh” carbon, fixed by marine phytoplankton, the growth of which became stimulated by fluvial nutrient exports, that dominated energy flows in plume regions. The trophic role of terrestrial and estuarine organic exports was comparatively minor. The trophic dynamics of plankton in small coastal plumes is closely linked to variations in freshwater flow, but this coupling operates mainly through the enhancement of in-situ phytoplankton production rather than cross-boundary transfers of organic matter to marine food webs in the pelagos.     

Can Coral Cover be Restored in the Absence of Natural Recruitment and Reef Recovery?

With many coral reef areas being degraded whether by anthropogenic or natural causes, a search is on for resilient species of corals that can restore coral cover where needed, if coral reefs are to continue to provide adequate ecosystem services. A series of experiments were undertaken in two sites with different environmental attributes and substrates in a lagoonal area in the northwestern Philippines to test the potentials of a local species, Porites cylindrica, for reef rehabilitation. With the use of asexual fragmentation of donor colonies, different treatments were tested, particularly to determine if the species would survive on different substrates, that is, solid, massive versus digitate/anastomosing, dead colonies. The results after nearly 2 years of the experiment were extraordinarily successful, with survival of transplants ranging from a high of 98% to a low of 80% of colonies, resulting in extensive coral cover on both original and new or different substrate from the original. A subsequent observation after another 16 months showed the coral cover to have been complete or nearly complete in the experimental plots, with the transplanted colonies fusing, and with evident reef fish communities where there were none before. Had there been no intervention, it is highly likely that the reefs would have remained in a degraded state .     

Can periods of static loading be used to enhance the resistance of the spine to cumulative compression?

Results of in vitro studies conducted on isolated bone specimens have indicated a higher tolerance to static load than exists when exposed to cyclic loading, when controlled for creep rate. If this difference in load tolerance exists, it may be exploited to extend the life of vertebral bone exposed to repetitive compression, and potentially alter the development of spinal injury. However, little work has been conducted on functional spinal units to determine if bone displays this characteristic within an intact joint. Additionally, static loading may result in load redistribution within the intervertebral disc forcing more of the compressive load towards the periphery of the endplate away from the nucleus. In order to examine these potential mechanisms, 218 osteoligamentous porcine functional spinal units were assigned to one of 15 loading scenarios. This involved one of three normalized peak load magnitudes (50%, 70% and 90% of estimated compressive tolerance) and one of five normalized static load applications (0%, 50%, 100%, 200% and 1000% of the total dynamic work duration). Load magnitude significantly altered the resistance to cumulative compression with decreased peak magnitudes corresponding to both increased cumulative load tolerance and increased height loss. Static load periods did not alter the resistance of the spinal unit to cumulative compression or impact the number of cycles tolerated to failure. The insertion of static load periods impacted the total survival time to failure, but only for the 1000% static load group, an exposure unlikely to occur for most in vivo exposures. The insertion of static load periods decreased the amount of height loss during testing which may play a protective role by allowing load redistribution within the vertebral bone and intervertebral disc.     

Can atmospheric input of nitrogen affect seed bank dynamics in habitats of conservation interest? The case of dune slacks

Questions: Does the increased atmospheric deposition of nitrogen, which can have major effects on the established vegetation of nutrient‐poor habitats, also impact germination from the soil seed bank? Location: Coastal dune slacks at Newborough Warren, Wales, UK. Methods: The effects of nitrogen addition (15 kg.ha^‐1.a^‐1) on seed germination from the soil seed bank were investigated using the seedling emergence method between September 2004 and February 2005. Results: More seedlings emerged from fertilised samples than unfertilised controls. Most species showed enhanced germination after fertilisation with nitrogen, with seedling numbers statistically significantly greater in nitrogen addition samples in a quarter of species abundant enough for analysis. Species that responded positively to fertilisation were species with low Ellenberg indicator values indicative of infertile sites. Conclusions: Most species showed increased germination after fertilisation with nitrogen, including early successional species normally growing in nutrient‐poor conditions. This suggests that the increased atmospheric deposition of nitrogen probably not only impacts on established vegetation, but also has the potential to alter seed bank dynamics.     

Can changes in the distributions of resident birds in China over the past 50?years be attributed to climate change?

The distributions of bird species have changed over the past 50 years in China. To evaluate whether the changes can be attributed to the changing climate, we analyzed the distributions of 20 subspecies of resident birds in relation to climate change. Long‐term records of bird distributions, gray relational analysis, fuzzy‐set classification techniques, and attribution methods were used. Among the 20 subspecies of resident birds, the northern limits of over half of the subspecies have shifted northward since the 1960s, and most changes have been related to the thermal index. Driven by climate change over the past 50 years, the suitable range and latitude or longitude of the distribution centers of certain birds have exhibited increased fluctuations. The northern boundaries of over half of the subspecies have shifted northward compared with those in the 1960s. The consistency between the observed and predicted changes in the range limits was quite high for some subspecies. The changes in the northern boundaries or the latitudes of the centers of distribution of nearly half of the subspecies can be attributed to climate change. The results suggest that climate change has affected the distributions of particular birds. The method used to attribute changes in bird distributions to climate change may also be effective for other animals.     

Can model species be used to advance the field of invasion ecology?

Hypotheses for explaining plant invasions have focused on a variety of factors that may influence invasion success, including propagule pressure, interactions of the introduced species with the biotic, abiotic, or disturbance properties of the new ecosystem, or the genetic characteristics of the invader itself. Evaluating the relative importance of these factors has been difficult because for most invaders key information about the introduced population or the introduction event is not available. We propose that natural experiments using model species is an important tool to test multiple invasion hypotheses at the same time, providing a complementary approach to meta-analysis and literature review. By focusing on a single candidate species, Pinus contorta, we explore several attributes that we propose constitute a good model, including: (a) intentional and relatively well documented introduction into a wide range of environments and countries across the world during the past century, where invasion success or failure has already occurred, (b) conspicuous growth form that simplifies assessment of growth rates, and comparisons across native and introduced ecosystems around the world, and, (c) documented and replicated variability of introduction intensity, genetic characteristics of the introduced populations, contrasting biotic communities present at sites of introduction, and abiotic conditions within and across introduced ecosystems. We propose that identifying model species with these characteristics will provide opportunities to disentangle the relative importance of different mechanisms hypothesized to influence invasion success, and thereby advance the field of invasion ecology.     

Can the resurgence of malaria be partially attributed to structural adjustment programmes?

Structural Adjustment Programmes (SAPs) (restrictive fiscal and monetary policies and extensive public sector reforms) were implemented in many developing countries during the 1980s. Their socio-economic impact on the poor has been widely discussed. Antimalarial efforts could have been affected by this economic reform process, and the resurgence of malaria during the past twenty years could be partially attributed to the socio-economic hardship generated by these programmes.     

Can morphological and behavioral traits predict the foraging and feeding dynamics of social arachnids?

Complex social insect species exhibit task specialization mediated by morphological and behavioral traits. However, evidence of such traits is scarce for other social arthropods. We investigated whether the social pseudoscorpion Paratemnoides nidificator exhibits morphologically and behaviorally specialized individuals in prey capture. We measured body and chela sizes of adult pseudoscorpions and analyzed predation processes. Larger individuals spent more time moving through the colony and foraging than smaller pseudoscorpions. Individuals that captured prey had increased body and absolute chelae sizes. Although larger individuals had relatively small chelae size, they showed a higher probability of prey capture. Larger individuals manipulated prey often, although they fed less than smaller pseudoscorpions. Individuals that initiated captures fed more frequently and for more time than the others. Natural selection might be favoring individuals specialized in foraging and colony protection, allowing smaller and less efficient adults to avoid contact with dangerous prey. To our knowledge, there is incipient information regarding specialized individuals in arachnids, and our results might indicate the emergence of a morphologically specialized group in this species.     

Can sleep quality and wellbeing be improved by changing the indoor lighting in the homes of healthy,elderly citizens?

The study investigated the effect of bright blue-enriched versus blue-suppressed indoor light on sleep and wellbeing of healthy participants over 65 years. Twenty-nine participants in 20 private houses in a uniform settlement in Copenhagen were exposed to two light epochs of 3 weeks with blue-enriched (280 lux) and 3 weeks blue-suppressed (240 lux) indoor light or vice versa from 8 to 13 pm in a randomized cross-over design. The first light epoch was in October, the second in November and the two light epochs were separated by one week. Participants were examined at baseline and at the end of each light epoch. The experimental indoor light was well tolerated by the majority of the participants. Sleep duration was 7.44 (95% CI 7.14–7.74) hours during blue-enriched conditions and 7.31 (95% CI 7.01–7.62) hours during blue-suppressed conditions (p?=?0.289). Neither rest hours, chromatic pupillometry, nor saliva melatonin profile showed significant changes between blue-enriched and blue-suppressed epochs. Baseline Pittsburgh Sleep Quality Index (PSQI) was significantly worse in females; 7.62 (95% CI 5.13–10.0) versus 4.06 (95% CI 2.64–5.49) in males, p?=?0.009. For females, PSQI improved significantly during blue-enriched light exposure (p?=?0.007); no significant changes were found for males. The subjective grading of indoor light quality doubled from participants habitual indoor light to the bright experimental light, while it was stable between light epochs, although there were clear differences between blue-enriched and blue-suppressed electrical light conditions imposed. Even though the study was carried out in the late autumn at northern latitude, the only significant difference in Actiwatch-measured total blue light exposure was from 8 to 9 am, because contributions from blue-enriched, bright indoor light were superseded by contributions from daylight.     

Can alloethism in workers of the bumblebee, Bombus terrestris, be explained in terms of foraging efficiency?

Bumblebee workers vary greatly in size, unlike workers of most other social bees. This variability has not been adequately explained. In many social insects, size variation is adaptive, with different-sized workers performing different tasks (alloethism). Here we established whether workers of the bumblebee, Bombus terrestris (L.) (Hymenoptera; Apidae), exhibit alloethism. We quantified the size of workers engaging in foraging compared to those that remain in the nest, and confirmed that it is the larger bees that tend to forage (X±SE thorax widths 4.34±0.01 mm for nest bees and 4.93±0.02 mm for foragers). We then investigated whether large bees are better suited to foraging because they are able to transport heavier loads of food back to the nest. Both pollen and nectar loads of returning foragers were measured, demonstrating that larger bees do return with a heavier mass of forage. Foraging trip times were inversely related to bee size when collecting nectar, but were unrelated to bee size for bees collecting pollen. Overall, large bees brought back more nectar per unit time than small bees, but the rate of pollen collection appeared to be unrelated to size. The smallest foragers had a nectar foraging rate close to zero, presumably explaining why foragers tend to be large. Why might larger bees be better at foraging? Various explanations are considered: larger bees are able to forage in cooler conditions, may be able to forage over larger distances, and are perhaps also less vulnerable to predation. Conversely, small workers are presumably cheaper to produce and may be more nimble at within-nest tasks. Further research is needed to assess these possibilities. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Litter decomposition of woody species in shrublands of NW Patagonia: how much do functional groups and microsite conditions influence decomposition?

The study examined the effects of leaf traits, soil microsite, and microclimate characteristics on litter decomposition of the dominant species in two functional groups (FG), deciduous and evergreen, in shrublands in NW Patagonia, Argentina. Leaf traits considered were nutrient concentration (C, N, P, C/N, and N/P) and physical characteristics (area, strength, specific leaf area, and dry matter content). Soil microsite characteristics measured were pH, C, N, P, C/N and water retention capacity, while soil microclimate characteristics recorded were soil and air, temperature and moisture, and solar radiation. Five evergreen and five deciduous woody shrub species were selected. During 1 year, litter and microsite properties were measured below canopy: (i) senescent leaf chemical and physical properties, and the quantity as well as field decomposition of litter and (ii) soil chemistry, and soil and air physical properties. The factors controlling litter decomposition were different for each FG. In deciduous species, C/N ratio had a negative effect on decomposition. In evergreen species, decomposition was affected negatively by leaf carbon and dry matter content. Litter decomposition depended exclusively on the inherent senescent leaves traits. The common decomposition pattern between species of both FG could be attributed to similar leaf traits and the correlation between variables that control decomposition in both groups. Plant nutrient inputs associated with the litter decomposition process did not explain the soil nutrient content. These results suggest that other organic matter sources (roots, branches, and fruits) are more important than leaves on soil fertility.     

Can the restoration of natural vegetation be accelerated on the Chinese Loess Plateau? A study of the response of the leaf carbon isotope ratio of dominant species to changing soil carbon and nitrogen levels

For the heavily degraded ecosystem on the Chinese Loess Plateau, it would be of great significance if vegetation restoration could be accelerated anthropogenically. However, one major concern is that if the late successional species were planted or sown in degraded habitats, would they still be competitive in terms of some critical plant traits associated with specific habitats? Water use efficiency (WUE) is a major plant trait shaping the pattern of species turnover in vegetation secondary succession on the Loess Plateau. We hypothesized that if late successional stage plants could still hold a competitive advantage in terms of WUE, the prospects for an acceleration of succession by sowing these species in newly abandoned fields would be good. We tested this hypothesis by comparing the leaf C isotope ratio (δ¹³C) value (a surrogate of WUE) of dominant species from different successional stages at given soil C and N levels. Results indicated that leaf δ¹³C of the two dominant species that co-dominated in the second and third stages were significantly more positive than that of the dominant species from the first stage regardless of changing soil C and N. Yet the dominant species from the climax stage is a C₄ grass assumed to have the highest WUE. In addition, increasing soil nutrition had no effects on leaf δ¹³C of two dominant species in the late successional stage, indicating that dominant species from the late successional stages could still have a competitive advantage in terms of WUE in soil C- and N-poor habitats. Therefore, from the perspective of plant WUE, there are great opportunities for ecosystem restoration by sowing both dominant species and other species that co-occur in late successional stages in newly abandoned fields, for the purpose of enhancing species diversity and optimising species composition.     

Territoriality and Survivorship of the Sierra Madre Sparrow in La Cima,México

We studied the life-history of the Sierra Madre sparrow (Xenospiza baileyi) in a subalpine grassland-agriculture mosaic south of Mexico City. From March to early September 1999 we captured and color-banded 53 adults with mist-nets and mapped the breeding territories of 21 males. We again mapped territories in the same spot in April and May 2000. The number of breeding territories was found to be the same in the two consecutive years and interannual survivorship was found to be relatively high. Breeding territories were restricted to the bunchgrass-covered areas. We used the density of territories and the amount of remaining habitat to estimate a total population size of 5,380–6,150 adults for this species. Using this and other recent data, we recommend raising the Sierra Madre sparrow to the status of critically endangered using BirdLife International criteria.