How far do experimentally elevated CO2 levels reach into the surrounding? – An example using the 13C label of soil organic matter as an archive

During the last two decades, free air CO₂ enrichment (FACE) studies have been conducted to study the effects of rising atmospheric CO₂ concentrations on ecosystems. The distances between fumigated and control plots differ widely among those projects, but no experimental data are available how far into the surrounding area an effect of CO₂ fumigation can be detected. As the CO₂ gas added to the fumigated plots has a different ¹³C label than ambient atmospheric CO₂, its carbon can be traced into plants and soil organic matter (SOM). The Swiss FACE in Eschikon had been conducted for 10 years on a grassland site. After it had ended, we analysed soil samples from three transects extending from the plots to the surrounding area for their organic carbon (C_org) content and carbon isotopic signature. We determined the maximum spatial extension to which carbon originating from the fumigation was incorporated into SOM. A budget of the fumigation gas‐derived C_org in the upper 10 cm of the soil showed that approximately 50 kg C were stored within the plots, and an additional 31 kg C were stored in their immediate surroundings up to a distance of 9 m from the gas pipes. The presented approach provides us with a method to determine a posteriori the extension to which the CO₂ fumigation treatment contaminated its immediate surroundings during a FACE experiment. In the presented example, this showed that the distances between plots could have been reduced significantly. Although not generalizable to other experimental settings, the finding indicates that optimizing the spatial layout, e.g. by modelling gas dispersion, will be useful when planning future large‐scale FACE infrastructures. Our approach provides a solid basis to test such gas‐dispersion models on existing FACE sites before planning new sites.     

The impact of anaesthetic technique on survival and fertility in Drosophila

Abstract The consequences of ice and carbon dioxide anaesthetics on the survival and reproductive success of Drosophila simulans and Drosophila melanogaster were investigated after observations of high levels of mortality in D. simulans, possibly associated with brief chill coma. The association between brief chill coma and death is confirmed in female D. simulans but there is no mortality in male D. simulans or D. melanogaster of either sex. Mortality is unlikely to be associated with a strain specific cold intolerance because two geographically distinct populations of D. simulans were examined. In addition to the effect of ice anaesthesia, anaesthetizing newly‐eclosed male D. simulans with CO₂ causes a reduction in fertility, which is evident 9–13 days after anaesthesia. This finding is important given that CO₂ anaesthesia is a standard technique used in Drosophila and other insect cultures, and may have important consequences for studies of male fertility and sperm competition.     

Elevation effects on the carbon budget of tropical mountain forests (S Ecuador): the role of the belowground compartment

Carbon storage and sequestration in tropical mountain forests and their dependence on elevation and temperature are not well understood. In an altitudinal transect study in the South Ecuadorian Andes, we tested the hypotheses that (i) aboveground net primary production (ANPP) decreases continuously with elevation due to decreasing temperatures, whereas (ii) belowground productivity (BNPP) remains constant or even increases with elevation due to a shift from light to nutrient limitation of tree growth. In five tropical mountain forests between 1050 and 3060 m a.s.l., we investigated all major above‐ and belowground biomass and productivity components, and the stocks of soil organic carbon (SOC). Leaf biomass, stemwood mass and total aboveground biomass (AGB) decreased by 50% to 70%, ANPP by about 70% between 1050 and 3060 m, while stem wood production decreased 20‐fold. Coarse and large root biomass increased slightly, fine root biomass fourfold, while fine root production (minirhizotron study) roughly doubled between 1050 and 3060 m. The total tree biomass (above‐ and belowground) decreased from about 320 to 175 Mg dry mass ha^?1, total NPP from ca. 13.0 to 8.2 Mg ha^?1 yr^?1. The belowground/aboveground ratio of biomass and productivity increased with elevation indicating a shift from light to nutrient limitation of tree growth. We propose that, with increasing elevation, an increasing nitrogen limitation combined with decreasing temperatures causes a large reduction in stand leaf area resulting in a substantial reduction of canopy carbon gain toward the alpine tree line. We conclude that the marked decrease in tree height, AGB and ANPP with elevation in these mountain forests is caused by both a belowground shift of C allocation and a reduction in C source strength, while a temperature‐induced reduction in C sink strength (lowered meristematic activity) seems to be of secondary importance.     

Soil heterogeneity buffers community response to climate change in species‐rich grassland

Climate change impacts on vegetation are mediated by soil processes that regulate rhizosphere water balance, nutrient dynamics, and ground‐level temperatures. For ecosystems characterized by high fine‐scale substrate heterogeneity such as grasslands on poorly developed soils, effects of climate change on plant communities may depend on substrate properties that vary at the scale of individuals (<m²), leading to fine‐scale shifts in community structure that may go undetected at larger scales. Here, we show in a long‐running climate experiment in species‐rich limestone grassland in Buxton, England (UK), that the resistance of the community to 15‐year manipulations of temperature and rainfall at the plot scale (9 m²) belies considerable community reorganization at the microsite (100 cm²) scale. In individual models of the abundance of the 25 most common species with respect to climate treatment and microsite soil depth, 13 species exhibited significant soil depth affinities, and nine of these have shifted their position along the depth gradient in response to one or more climate treatments. Estimates of species turnover across the depth gradient reviewed in relation to measurements of water potential, nitrogen supply, pH, and community biomass suggest that communities of shallow microsites are responding directly to microenvironmental changes induced by climate manipulation, while those of the deepest microsites are shifting in response to changes in competitive interference from more nutrient‐demanding species. Moreover, for several species in summer drought and winter heated treatments, climate response in deep microsites was opposite that of shallow microsites, suggesting microsite variation is contributing to community stability at the whole‐plot level. Our study thus demonstrates a strong link between community dynamics and substrate properties, and suggests ecosystems typified by fine‐scale substrate heterogeneity may possess a natural buffering capacity in the face of climate change.     

Carbon sequestration potential of tropical pasture compared with afforestation in Panama

Tropical forest ecosystems play an important role in regulating the global climate, yet deforestation and land‐use change mean that the tropical carbon sink is increasingly influenced by agroecosystems and pastures. Despite this, it is not yet fully understood how carbon cycling in the tropics responds to land‐use change, particularly for pasture and afforestation. Thus, the objectives of our study were: (1) to elucidate the environmental controls and the impact of management on gross primary production (GPP), total ecosystem respiration (TER) and net ecosystem CO₂ exchange (NEE); (2) to estimate the carbon sequestration potential of tropical pasture compared with afforestation; and (3) to compare eddy covariance‐derived carbon budgets with biomass and soil inventory data. We performed comparative measurements of NEE in a tropical C₄ pasture and an adjacent afforestation with native tree species in Sardinilla (Panama) from 2007 to 2009. Pronounced seasonal variation in GPP, TER and NEE were closely related to radiation, soil moisture, and C₃ vs. C₄ plant physiology. The shallow rooting depth of grasses compared with trees resulted in a higher sensitivity of the pasture ecosystem to water limitation and seasonal drought. During 2008, substantial amounts of carbon were sequestered by the afforestation (–442 g C m^–2, negative values denote ecosystem carbon uptake), which was in agreement with biometric observations (–450 g C m^–2). In contrast, the pasture ecosystem was a strong carbon source in 2008 and 2009 (261 g C m^–2), associated with seasonal drought and overgrazing. In addition, soil carbon isotope data indicated rapid carbon turnover after conversion from C₄ pasture to C₃ afforestation. Our results clearly show the potential for considerable carbon sequestration of tropical afforestation and highlight the risk of carbon losses from pasture ecosystems in a seasonal tropical climate.     

Maize Transposable Elements in Development and Evolution

Transposable elements were first discovered in maize by BarbaraMcClintock more than 40 years ago. Today it is apparent thattransposable elements are a common component of the geneticmaterial in virtually all organisms. The best studied maizetransposable elements belong to the Activator-Dissociation andSuppressor-mutator families. They are short DNA sequences thatconsist of genes required for mobility and regulation. Boththe expression and the mobility of transposable elements areregulated in development by a mechanism that relies on the methylationof element sequences critical for expression. Elements can bestably inactivated by the same mechanism, persisting in thegenome in a cryptic form for long periods. The ability of thehost organism to regulate the highly mutagenic transposableelements may be critical to their survival, as well as theirutility as agents of genomic change.     

Karyolysus sp. (Haemogregarinidae, Adeleida, Apicomplexa): Host-Parasite Relationships of Persisting Stages

ABSTRACT. Two persisting stages in the life cycle of a hemogregarine Karyolysus sp. are described from the liver and blood cells of its intermediate host, the lizard Lacerta raddei nairensis. The tissue cell merozoites lie in a parasitophorous vacuole. Despite the protective role of the vacuolar membrane, the intracellular parasites are progressively destroyed and eliminated during the autumn and winter. Some of the merozoites that normally survive within the host cell even in cold seasons appear to be surrounded by another type of parasitophorous vacuole which is connected to the intercellular space by narrow channels. The intraerythrocytic gamonts that persist in the circulating blood are encapsulated and undergo progressive, obvious structural changes. The two persisting stages are compared with hypnozoites of other Sporozoa.     

Increased Vascular Resistance by Prostaglandins B<Subscript>1</Subscript> and B<Subscript>2</Subscript> in the Isolated Rat Pancreas

IN view of the possibility that prostaglandins (PG) regulate local blood flow¹, we are investigating this activity in the pancreas. We have already found that PGE₂ reduces vascular resistance in the perfused rat pancreas whereas PGF_2α has the opposite effect². These effects were seen at low doses (0.1 µg/ml.) and with good reproducibility.     

Plant‐mediated effects of butterfly egg deposition on subsequent caterpillar and pupal development,across different species of wild Brassicaceae

1. Herbivory can change plant quality, which may have consequences for interactions between the inducing herbivore and other insect community members. 2. Studies investigating the effects of plant quality on herbivore performance often have neglected the egg stage, and instead introduced larvae onto the plant. Recently, we reported that herbivore oviposition by Pieris brassicae (Linnaeus) (Large Cabbage White Butterfly) reduced the plant quality of Brassica nigra L. (black mustard) for subsequent herbivores. 3. It remains unclear how persistent and common these plant‐mediated effects of oviposition are. Here, five species of wild Brassicaceae were used (B. nigra L., Brassica oleracea L., Sinapis arvensis L., Moricandia arvensis L., and Moricandia moricandioides Boiss). The response to oviposition by the specialist P. brassicae was determined by following the natural sequence of events: oviposition, egg, larval, and pupal development. All tested plant species are known to interact with P. brassicae in nature. Caterpillar, pupal mass, and development time on plants exposed to butterfly eggs were assessed compared with egg‐free plants. 4. It was shown that the plant‐mediated effects of oviposition are not specific for B. nigra but occur in most of the tested plant species except for M. arvensis. However, the strength of the plant‐mediated effect on caterpillar growth depended on plant species. Thus, across different members of the Brassicaceae family, oviposition can influence plant quality and has negative consequences on P. brassicae growth. Further studies are needed to assess to what extent this trait might be phylogenetically conserved.