Do radial oxygen loss and external aeration affect iron plaque formation and arsenic accumulation and speciation in rice?

Hydroponic experiments were conducted to investigate the effect of radial oxygen loss (ROL) and external aeration on iron (Fe) plaque formation, and arsenic (As) accumulation and speciation in rice (Oryza sativa L.). The data showed that there were significant correlations between ROL and Fe concentrations in Fe plaque produced on different genotypes of rice. There were also significant differences in the amounts of Fe plaque formed between different genotypes in different positions of roots and under different aeration conditions (aerated, normal, and stagnant treatments). In aerated treatments, rice tended to have a higher Fe plaque formation than in a stagnant solution, with the greatest formation at the root tip decreasing with increasing distances away, in accordance with a trend of spatial ROL. Genotypes with higher rates of ROL induced higher degrees of Fe plaque formation. Plaques sequestered As on rice roots, with arsenate almost double that with arsenite, leading to decreased As accumulation in both roots and shoots. The major As species detected in roots and shoots was arsenite, ranging from 34 to 78% of the total As in the different treatments and genotypes. These results contribute to our understanding of genotypic differences in As uptake by rice and the mechanisms causing rice genotypes with higher ROL to show lower overall As accumulation.     

Do plants and animals differ in phenotypic plasticity?

This paper compares the flexibility in the nexus between phenotype and genotype in plants and animals. These taxa although considered to be fundamentally different are found to be surprisingly similar in the mechanisms used to achieve plasticity. Although non-cognitive behaviour occurs in plants, its range is limited, while morphological and developmental plasticity also occur to a considerable extent in animals. Yet both plants and animals are subject to unique constraints and thus need to find unique solutions to functional problems. A true comparison between the plant and animal phenotype would be a comparison between plants and sessile photosynthesizing colonial invertebrates. Such comparisons are lacking. However, they would provide important insights into the adaptive significance of plasticity in these groups. It is also suggested that a comparison of inflexible traits in these groups would provide an understanding of the constraints, as well as the costs and benefits, of a plastic versus non-plastic phenotype in plants and animals.     

Does the different photosynthetic pathway of plants affect soil respiration in a subtropical wetland?

Plants with different photosynthetic pathways could produce different amounts and types of root exudates and debris which may affect soil respiration rates. Therefore, wetland vegetation succession between plants with different photosynthetic pathways may ultimately influence the wetland carbon budget. The middle and lower reaches of the Yangtze River has the largest floodplain wetland group in China. Tian'e Zhou wetland reserve (29°48'N, 112°33′E) is located in Shishou city, Hubei province and covers about 77.5 square kilometers. Hemathria altissima (C4) was found gradually being replaced by Carex argyi (C3) for several years in this place. An in situ experiment was conducted in Tian'e Zhou wetland to determine the change of soil respiration as the succession proceeds. Soil respiration, substrate‐induced respiration, and bacterial respiration of the C4 species was greater than those of the C3 species, but below‐ground biomass and fungal respiration of the C4 species was less than that of the C3 species. There were no significant differences in above‐ground biomass between the two species. Due to the higher photosynthesis capability, higher soil respiration and lower total plant biomass, we inferred that the C4 species, H. altissima, may transport more photosynthate below‐ground as a substrate for respiration. The photosynthetic pathway of plants might therefore play an important role in regulating soil respiration. As C. argyi replaces H. altissima, the larger plant biomass and lower soil respiration would indicate that the wetland in this area could fix more carbon in the soil than before.     

Do soil organisms affect aboveground litter decomposition in the semiarid Patagonian steppe, Argentina?

Surface litter decomposition in arid and semiarid ecosystems is often faster than predicted by climatic parameters such as annual precipitation or evapotranspiration, or based on standard indices of litter quality such as lignin or nitrogen concentrations. Abiotic photodegradation has been demonstrated to be an important factor controlling aboveground litter decomposition in aridland ecosystems, but soil fauna, particularly macrofauna such as termites and ants, have also been identified as key players affecting litter mass loss in warm deserts. Our objective was to quantify the importance of soil organisms on surface litter decomposition in the Patagonian steppe in the absence of photodegradative effects, to establish the relative importance of soil organisms on rates of mass loss and nitrogen release. We estimated the relative contribution of soil fauna and microbes to litter decomposition of a dominant grass using litterboxes with variable mesh sizes that excluded groups of soil fauna based on size class (10, 2, and 0.01 mm), which were placed beneath shrub canopies. We also employed chemical repellents (naphthalene and fungicide). The exclusion of macro- and mesofauna had no effect on litter mass loss over 3 years (P = 0.36), as litter decomposition was similar in all soil fauna exclusions and naphthalene-treated litter. In contrast, reduction of fungal activity significantly inhibited litter decomposition (P < 0.001). Although soil fauna have been mentioned as a key control of litter decomposition in warm deserts, biogeographic legacies and temperature limitation may constrain the importance of these organisms in temperate aridlands, particularly in the southern hemisphere.     

Do mesocosms influence photosynthesis and soil respiration?

Mesocosms, enclosed outdoor experimental systems, are commonly used in terrestrial ecology. They are frequently used to study the effects of elevated CO₂ and temperature on terrestrial ecosystem processes. Despite their advantages and frequent use it is important to verify, through explicit measures, that mesocosms reliably model the larger system. In this study, fully-coupled, soil–litter–plant mesocosms were constructed in Corvallis using native soil and litter, and planted with Douglas-fir (Pseudotsuga menziesii Mirb. Franco) seedlings. Needle photosynthesis and soil respiration were measured repeatedly over a 21-month period in mesocosms and compared to measurements made at two field sites (Toad Creek and Falls Creek) planted at the same density as the mesocosms. Under the temperature and soil moisture conditions, photosynthetic and soil respiration rates in the mesocosms were not significantly different than the rates at Toad Creek, where the soil and litter in the mesocosms were collected. In contrast, the soil at Falls Creek was different than the soil in the mesocosms and at Toad Creek and photosynthetic and soil respiration rates at Falls Creek were significantly different than at the other two sites. The lack of significant differences between rates measured in the mesocosms in Corvallis and at the Toad Creek field site indicate that the mesocosms did not cause significant artifacts in the data and that the results for these rates in the mesocosms can be extrapolated to field settings with comparable edaphic conditions.     

Do litter manipulations affect leaf functional traits of savanna woody plants?

Plant litter is the layer composed of dead plant material that covers soil surfaces in terrestrial ecosystems. It is an important pool of essential nutrients for soil and plants, serving also as a protective layer on the soil surface. In this study, we investigated the effects of litter addition and removal on leaf functional traits of woody Neotropical savanna trees. We measured maximum photosynthesis (A _max), stomatal conductance (g _s), leaf transpiration (E), intrinsic water use efficiency (IWUE), specific leaf area (SLA), and chlorophyll content (CCI) in 15 species belonging to three different phenological groups (evergreen, briefly deciduous, and deciduous species) that were subjected to three distinct litter availability treatments (addition, removal, and control plots) in a Neotropical Savanna site in Brazil. Although SLA and CCI differed among phenology groups, they were not affected by the litter treatments. In contrast, when considered at the community level, we found that the availability of litter affected the leaf traits linked with the water status of the plants (E, g _s and IWUE). Plants in the litter removal plots exhibited lower g _s and E (25 % of reduction in comparison with control group) but higher IWUE, while plants in the litter addition plots had a 10 % decrease in IWUE but a 12 % increase in g _s and E compared with plants in control plots. Savanna woody plants responded promptly to litter manipulation by adjusting leaf water loss, which suggests that in the short term, changes in the amount of litter in Cerrado ecosystems can affect the soil water availability to the plant community.     

Do different irrigation techniques affect the small-scale patterns of plant diversity and soil characteristics in mountain hay meadows?

Traditional management practices are suggested to maintain species-rich grasslands. In the Valais, an arid region of Switzerland, hay meadows are traditionally irrigated using open water channels. However, in the past decades this irrigation technique has been increasingly replaced by sprinkler irrigation, which is assumed to result in a more homogeneous water distribution than open water channels. This study examined whether the change in irrigation technique affected the small-scale distribution of plants and soil characteristics in hay meadows in the Valais. Three plots consisting of 13 subplots of increasing size (0.1 × 0.1 to 6.4 × 6.4 m) were installed in six traditionally and six sprinkler-irrigated meadows. In all subplots, plant species richness and soil characteristics [moisture, pH, total organic nitrogen, organic matter content (SOM), total and plant available phosphorus] were recorded. The type of irrigation technique did not affect the shape of the plant species–area relationship. In none of the meadows did the species area–curves reach the asymptote within the range of plot sizes examined. Mantel r statistics showed that spatial autocorrelation in the soil characteristics examined was low and their small-scale distributions were not influenced by the irrigation technique except for soil pH and SOM. Our results indicate a pronounced small-scale heterogeneity in the distribution of plant species and soil characteristics for both types of irrigation technique. This can partly be explained by the fact that sprinklers distribute the water less homogeneously than commonly assumed. As applied in the Valais, sprinkler irrigation does not reduce the spatial heterogeneity and hence biodiversity of hay meadows.     

Do intestinal nematodes affect productivity in adulthood?

Intestinal nematode infections have been associated with many physical and mental developmental insults. These include anaemia, wasting, stunting, cognitive impairment and lowered educational achievement, all of which have in turn been shown to interfere with productivity and wage-earning capacity in adults. Although there is no direct evidence for an effect of intestinal nematodes on productivity, circumstantial evidence suggests such an effect. Here, Helen Guyatt reviews the indirect evidence for an effect of intestinal nematodes on productivity in adults through current infection and associated morbidity, and on early ill-health in children, which might affect productivity later in life.     

Do gravidity and age affect pregnancy outcome?

Abstract

Fetal loss has generally been found to vary with gravidity, previous experience of fetal loss, and maternal age, but the literature is divided on the reasons for these associations. In this paper we examine pregnancy histories obtained retrospectively from a nationally representative one‐in‐one‐thousand sample of women in Australia aged 20 to 59 years. The relations of fetal loss ratios with both gravidity and previous outcome are consistent with heterogeneity of risk over the study population and a stopping rule, whereby high‐risk women undertake more pregnancies than low‐risk women to achieve the same number of live births. Evidence is presented that elevated loss ratios in the teens indicate not higher risk but a selection for short gestation intervals, while loss ratios beyond the mid‐thirties do not point unequivocally to a substantial increase in risk at the older reproductive ages.     

Do changes in floral odor cause speciation in sexually deceptive orchids?

 We investigated differences in floral odor between two sympatric, closely related sexually deceptive orchid species, Ophrys fusca and O. bilunulata, which are specifically pollinated by Andrena nigroaenea and A. flavipes, respectively. We identified biologically active compounds by gas chromatography with electroantennographic detection using antennae of the pollinator bees. Alkanes, alkenes, aldehydes, and farnesyl hexanoate released electroantennographic reactions. The relative amounts of alkanes were mostly the same between the two orchid species, whereas the relative amounts of most alkenes were significantly different. On the grounds of these findings and behavioral experiments conducted in earlier studies, we suggest that the difference in relative amounts of alkenes is responsible for the selective attraction of pollinators in the two orchids. Speciation in this group of Ophrys orchids may be brought about by changes in pattern of alkenes, which lead to attraction of a different pollinator species and therefore reproductive isolation. Received November 22, 2001; accepted February 21, 2002 Published online: November 7, 2002 Addresses of the authors: Florian P. Schiestl* and Manfred Ayasse, Department of Evolutionary Biology, Institute of Zoology, University of Vienna, Althanstrasse 14, A-1090 Vienna. *Present address: Geobotanical Institute ETH, Zollikerstrasse 107, CH-8008 Zürich. (e-mail: schiestl@geobot.umnw.ethz.ch)     

Perception of volatiles produced by UVC-irradiated plants alters the response to viral infection in na?ve neighboring plants

Interplant communication of stress via volatile signals is a well-known phenomenon. It has been shown that plants undergoing stress caused by pathogenic bacteria or insects generate volatile signals that elicit defense response in neighboring naïve plants.¹ Similarly, we have recently shown that naïve plants sharing the same gaseous environment with UVC-exposed plants exhibit similar changes in genome instability as UVC-exposed plants.² We found that methyl salicylate (MeSA) and methyl jasmonate (MeJA) serve as volatile signals communicating genome instability (as measured by an increase in the homologous recombination frequency). UVC-exposed plants produce high levels of MeSA and MeJA, a response that is missing in an npr1 mutant. Concomitantly, npr1 mutants are impaired in communicating the signal leading to genome instability, presumably because this mutant does not develop new necrotic lesion after UVC irradiation as observed in wt plants.² To analyze the potential biological significance of such plant-plant communication, we have now determined whether bystander plants that receive volatile signals from UVC-irradiated plants, become more resistant to UVC irradiation or infection with oilseed rape mosaic virus (ORMV). Specifically, we analyzed the number of UVC-elicited necrotic lesions, the level of anthocyanin pigments, and the mRNA levels corresponding to ORMV coat protein and the NPR1-regulated pathogenesis-related protein PR1 in the irradiated or virus-infected bystander plants that have been previously exposed to volatiles produced by UVC-irradiated plants. These experiments showed that the bystander plants responded similarly to control plants following UVC irradiation. Interestingly, however, the bystander plants appeared to be more susceptible to ORMV infection, even though PR1 mRNA levels in systemic tissue were significantly higher than in the control plants, which indicates that bystander plants could be primed to strongly respond to bacterial infection.     

How do soil resources affect herbivory in tropical plants along environmental gradients? A test using contrasting congeneric species

Plant Ecology - Plants adapted to different habitats exhibit differences in functional traits and these characteristics are influenced by soil properties. We tested the hypothesis that soil...     

Do tadpoles affect leaf decomposition in neotropical streams?

1. Of the relatively few studies that have examined consequences of amphibian declines on stream ecosystems, virtually all have focused on changes in algae (or algal‐based food webs) and little is known about the potential effects of tadpoles on leaf decomposition. We compared leaf litter decomposition dynamics in two neotropical streams: one with an intact community of tadpoles (with frogs) and one where tadpoles were absent (frogless) as a result of a fungal pathogen that had driven amphibians locally extinct. The stream with tadpoles contained a diverse assemblage (23 species) of larval anurans, and we identified five species of glass frog (Centrolenidae) tadpoles that were patchily distributed but commonly associated with leaf detritus and organic sediments in pools. The latter reached total densities of 0–318 tadpoles m^?2. 2. We experimentally excluded tadpoles from single‐species leaf packs incubated over a 40‐day period in streams with and without frogs. We predicted that decomposition rates would be higher in control (allowing access of tadpoles) treatments in the study stream with frogs than in the frogless stream and, in the stream with frogs, in the control than in the tadpole exclusion treatment. 3. In the stream with frogs, Centrolene prosoblepon and Cochranella albomaculata tadpoles were patchily distributed in leaf packs (0.0–33.3 m^?2). In contrast to our predictions, leaf mass loss and temperature‐corrected leaf decomposition rates in control treatments were almost identical in our stream with frogs (41.01% AFDM lost, k_{degree day} = ?0.028 day^?1) and in the frogless stream (41.81% AFDM lost, k_{degree day} = ?0.027 day^?1) and between control and tadpole exclusion treatments within each stream. Similarly, there were no significant differences in leaf pack bacterial biomass, microbial respiration rates or macroinvertebrate abundance between treatments or streams. Invertebrate assemblages on leaf packs were similar between treatments (SIMI = 0.97) and streams (SIMI = 0.95) and were dominated by larval Chironomidae, Simuliidae (Diptera) and larval Anchytarsus spp. (Coleoptera). 4. In contrast to dramatic effects of grazing tadpoles on algal communities observed previously, tadpoles had no major effects on decomposition. While centrolenid tadpoles were common in the stream with frogs, their patchy distribution in both experimental and natural leaf packs suggests that their effects on detrital dynamics and microbes are probably more localised than those of grazing tadpoles on algae.     

Do partially buried dune plants grow in optimal trajectories?

Plant adaptations minimising costs of burial responses are vital in mobile dune ecosystems. Conventionally, the burial responses of dune plants have been measured as vertical growth. However, a model developed here shows that growth normal to accumulating non-horizontal dune surfaces requires up to 18% less stem production than vertical growth. To determine whether dune plants grow with this optimal geometry a field survey of growth trajectories was made for three coastal plants, and a greenhouse experiment tested whether plants could actively change growth trajectories away from vertical. In the field and greenhouse partial burial resulted in shifts towards vertical growth, indicating that negative gravitropism is the major response to burial, and reduces the amount of stem needed to respond to burial relative to unburied growth trajectories. However, for two species in the field many buried stems grew closer to optimal (shorter) than vertical, mostly on northward, sun-facing dunes. Thus phototropism is the major stimulus for non-vertical growth, and coincides with optimal trajectories on north-facing dunes. Arctotheca populifolia also displayed non-vertical growth after burial on steep south-facing dunes, but responded to burial in the greenhouse with vertical growth. Measurements of the pressure of sand avalanches occurring on dune slipfaces and stem elasticity indicated that deep avalanches were sufficient to orient the flexible shoots of A. populifolia towards optimal trajectories. Thus, dune plants respond to burial by actively modulating growth towards vertical via negative gravitropism, and passively towards non-vertical—more optimal—trajectories via phototropic growth and the influence of sand avalanches.     

Does richness of emergent plants affect CO2 and CH4 emissions in experimental wetlands?

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Do method and species lifestyle affect measures of maximum metabolic rate in fishes?

The rate at which active animals can expend energy is limited by their maximum aerobic metabolic rate (MMR). Two methods are commonly used to estimate MMR as oxygen uptake in fishes, namely during prolonged swimming or immediately following brief exhaustive exercise, but it is unclear whether they return different estimates of MMR or whether their effectiveness for estimating MMR varies among species with different lifestyles. A broad comparative analysis of MMR data from 121 fish species revealed little evidence of different results between the two methods, either for fishes in general or for species of benthic, benthopelagic or pelagic lifestyles.     

Do mast cells affect villous architecture? Facts and conjectures

In adult life, the architecture of the intestinal villus is maintained by a complex series of epithelial-stromal interactions that involve different types of fixed and mobile cells located in the intestinal mucosa. Mast cells (MC) are normal constituents of the small bowel mucosa where they reside in the villous and pericryptal lamina propria as well as within the columnar epithelial cell layer. Besides being involved in numerous immune and inflammatory reactions in the context of both innate and acquired host defence, MC are known to exert important non-immunological functions like wound repair, extracellular matrix remodelling, angiogenesis and neurotrophism as well as modulation of fibroblast, epithelial cell and smooth muscle cell activity. These pleiotropic functions put MC in a central, strategic position to organize tissue defence, restore tissue damage and maintain tissue homeostasis. This review summarizes the most recent advances concerning the functional anatomy of the crypt-villus unit and discusses the way intestinal MC might become part of the instructive circuits that ultimately lead to the maintenance of a proper villous shape.