Earth's Changing Land

Entre el 14 i el 18 de març de 1998 es va celebrar a Barcelona la conferència Earth’s Changing Land sota la tutela dels programes internacionals Global Change in Terrestrial Ecosystems (GCTE) i Land Use and Land Cover Change (LUCC). L’objectiu principal de la trobada era presentar les darreres aportacions científiques sobre els efectes presents i previsibles del canvi global sobre els ecosistemes terrestres i la societat. Al mateix temps, es volia afavorir l’establiment de ponts de diàleg entre els professionals implicats en el canvi global

Impact of coronal mass ejections, interchange reconnection, and disconnection on heliospheric magnetic field strength

An update of Owens et al. (2008) shows that the relationship between the coronal mass ejection (CME) rate and the heliospheric magnetic field strength predicts a field floor of less than 4 nT at 1 AU. This implies that the record low values measured during this solar minimum do not necessarily contradict the idea that open flux is conserved. The results are consistent with the hypothesis that CMEs add flux to the heliosphere and interchange reconnection between open flux and closed CME loops subtracts flux. An existing model embracing this hypothesis, however, overestimates flux during the current minimum, even though the CME rate has been low. The discrepancy calls for reasonable changes in model assumptions.

Effect of biotic factors on the isolation of Lupinus albus protoplasts

Several tissue types of Lupinus albus L. were investigated as sources for the isolation of protoplasts. Cotyledons from in vitro seedlings were found to yield the highest number of protoplasts compared with leaves, hypocotyls and roots. A combination of the protoplast isolation enzymes, cellulase and Pectolyase Y23, was capable of releasing the highest number of protoplasts compared with a combination of cellulase and Macerase. Protoplast yield increased with increasing cotyledon age but was accompanied by a progressive decline in protoplast viability. The optimal combination of protoplast yield and viability occurred when the protoplasts were isolated from 14- to 18-day-old cotyledons. The ratio between the volume of enzyme solution and the tissue biomass did not affect the protoplast production significantly. This is the first report of the isolation of protoplasts from a lupin cotyledon and, following the procedure described in this paper, an average yield of 1.2 x 10(6) protoplasts per gram of fresh tissue was obtainable.

The role of biotic and abiotic factors in evolution of ant dispersal in the milkwort family (Polygalaceae)

A phylogenetic approach was taken to investigate the evolutionary history of seed appendages in the plant family Polygalaceae (Fabales) and determine which factors might be associated with evolution of elaiosomes through comparisons to abiotic (climate) and biotic (ant species number and abundance) timelines. Molecular datasets from three plastid regions representing 160 species were used to reconstruct a phylogenetic tree of the order Fabales, focusing on Polygalaceae. Bayesian dating methods were used to estimate the age of the appearance of ant-dispersed elaiosomes in Polygalaceae, shown by likelihood optimizations to have a single origin in the family. Topology-based tests indicated a diversification rate shift associated with appearance of caruncular elaiosomes. We show that evolution of the caruncular elaiosome type currently associated with ant dispersal occurred 54.0-50.5 million year ago. This is long after an estimated increase in ant lineages in the Late Cretaceous based on molecular studies, but broadly concomitant with increasing global temperatures culminating in the Late Paleocene-Early Eocene thermal maxima. These results suggest that although most major ant clades were present when elaiosomes appeared, the environmental significance of elaiosomes may have been an important factor in success of elaiosome-bearing lineages. Ecological abundance of ants is perhaps more important than lineage numbers in determining significance of ant dispersal. Thus, our observation that elaiosomes predate increased ecological abundance of ants inferred from amber deposits could be indicative of an initial abiotic environmental function.

Effect of biotic factors on the isolation of Lupinus albus L. protoplasts

Several tissue types of Lupinus albus L. were investigated as sources for the isolation of protoplasts. Cotyledons from in vitro seedlings were found to yield the highest number of protoplasts compared with leaves, hypocotyls and roots. A combination of the protoplast isolation enzymes, cellulase and Pectolyase Y23, was capable of releasing the highest number of protoplasts compared with a combination of cellulase and Macerase. Protoplast yield increased with increasing cotyledon age but was accompanied by a progressive decline in protoplast viability. The optimal combination of protoplast yield and viability occurred when the protoplasts were isolated from 14- to 18-day-old cotyledons. The ratio between the volume of enzyme solution and the tissue biomass did not affect the protoplast production significantly. This is the first report of the isolation of protoplasts from a lupin cotyledon and, following the procedure described in this paper, an average yield of 1.2 × 106 protoplasts per gram of fresh tissue was obtainable.

Multiple stressors on biotic interactions: how climate change and alien species interact to affect pollination

Global change may substantially affect biodiversity and ecosystem functioning but little is known about its effects on essential biotic interactions. Since different environmental drivers rarely act in isolation it is important to consider interactive effects. Here, we focus on how two key drivers of anthropogenic environmental change, climate change and the introduction of alien species, affect plant–pollinator interactions. Based on a literature survey we identify climatically sensitive aspects of species interactions, assess potential effects of climate change on these mechanisms, and derive hypotheses that may form the basis of future research. We find that both climate change and alien species will ultimately lead to the creation of novel communities. In these communities certain interactions may no longer occur while there will also be potential for the emergence of new relationships. Alien species can both partly compensate for the often negative effects of climate change but also amplify them in some cases. Since potential positive effects are often restricted to generalist interactions among species, climate change and alien species in combination can result in significant threats to more specialist interactions involving native species.

In situ signatures of interchange reconnection between magnetic clouds and open magnetic fields: a mechanism for the erosion of polar coronal holes?

We outline a method to determine the direction of solar open flux transport that results from the opening of magnetic clouds (MCs) by interchange reconnection at the Sun based solely on in-situ observations. This method uses established findings about i) the locations and magnetic polarities of emerging MC footpoints, ii) the hemispheric dependence of the helicity of MCs, and iii) the occurrence of interchange reconnection at the Sun being signaled by uni-directional suprathermal electrons inside MCs. Combining those observational facts in a statistical analysis of MCs during solar cycle 23 (period 1995 – 2007), we show that the time of disappearance of the northern polar coronal hole (1998 – 1999), permeated by an outward-pointing magnetic field, is associated with a peak in the number of MCs originating from the northern hemisphere and connected to the Sun by outward-pointing magnetic field lines. A similar peak is observed in the number of MCs originating from the southern hemisphere and connected to the Sun by inward-pointing magnetic field lines. This pattern is interpreted as the result of interchange reconnection occurring between MCs and the open field lines of nearby polar coronal holes. This reconnection process closes down polar coronal hole open field lines and transports these open field lines equatorward, thus contributing to the global coronal magnetic field reversal process. These results will be further constrainable with the rising phase of solar cycle 24.

Interchange reconnection: remote sensing of solar signature and role in heliospheric magnetic flux budget

Interchange reconnection at the Sun, that is, reconnection between a doubly-connected field loop and singly-connected or open field line that extends to infinity, has important implications for the heliospheric magnetic flux budget. Recent work on the topic is reviewed, with emphasis on two aspects. The first is a possible heliospheric signature of interchange reconnection at the coronal hole boundary, where open fields meet closed loops. The second aspect concerns the means by which the heliospheric magnetic field strength reached record-lows during the recent solar minimum period. A new implication of this work is that interchange reconnection may be responsible for the puzzling, occasional coincidence of the heliospheric current sheet and the interface between fast and slow flow in the solar wind.

Biotic carbon feedbacks in a materially-closed soil-vegetation-atmosphere system

The magnitude and direction of the coupled feedbacks between the biotic and abiotic components of the terrestrial carbon cycle is a major source of uncertainty in coupled climate–carbon-cycle models1, 2, 3. Materially closed, energetically open biological systems continuously and simultaneously allow the two-way feedback loop between the biotic and abiotic components to take place4, 5, 6, 7, but so far have not been used to their full potential in ecological research, owing to the challenge of achieving sustainable model systems6, 7. We show that using materially closed soil–vegetation–atmosphere systems with pro rata carbon amounts for the main terrestrial carbon pools enables the establishment of conditions that balance plant carbon assimilation, and autotrophic and heterotrophic respiration fluxes over periods suitable to investigate short-term biotic carbon feedbacks. Using this approach, we tested an alternative way of assessing the impact of increased CO2 and temperature on biotic carbon feedbacks. The results show that without nutrient and water limitations, the short-term biotic responses could potentially buffer a temperature increase of 2.3 °C without significant positive feedbacks to atmospheric CO2. We argue that such closed-system research represents an important test-bed platform for model validation and parameterization of plant and soil biotic responses to environmental changes.

Flavor-protein binding: disulfide interchange reactions between ovalbumin and volatile disulfides

The irreversible binding of selected sulfur-containing flavor compounds to proteins was investigated in aqueous solutions containing ovalbumin and a mixture of disulfides (diethyl, dipropyl, dibutyl, diallyl, and 2-furfuryl methyl) using solid-phase micro-extraction (SPME). In systems which had not been heated, the recovery of disulfides from the headspace above the protein at the native pH (6.7) was similar to that from an aqueous blank. However, significant losses were observed when the pH of the solution was increased to 8.0. When the protein was denatured by heating, much greater losses were observed and some free thiols were produced. In similar heat-denatured systems at pH 2.0, no losses of disulfides were observed. Disulfides containing allyl or furfuryl groups were more reactive than saturated alkyl disulfides. Interchange reactions between protein sulfhydryl groups and the disulfides are believed to be responsible for the loss of the disulfides.

Species richness declines and biotic homogenization have slowed down for NW-European pollinators and plants

Concern about biodiversity loss has led to increased public investment in conservation. Whereas there is a widespread perception that such initiatives have been unsuccessful, there are few quantitative tests of this perception. Here, we evaluate whether rates of biodiversity change have altered in recent decades in three European countries (Great Britain, Netherlands and Belgium) for plants and flower visiting insects. We compared four 20-year periods, comparing periods of rapid land-use intensification and natural habitat loss (1930–1990) with a period of increased conservation investment (post-1990). We found that extensive species richness loss and biotic homogenisation occurred before 1990, whereas these negative trends became substantially less accentuated during recent decades, being partially reversed for certain taxa (e.g. bees in Great Britain and Netherlands). These results highlight the potential to maintain or even restore current species assemblages (which despite past extinctions are still of great conservation value), at least in regions where large-scale land-use intensification and natural habitat loss has ceased.

Sugarcane response to two biotic stressors: Diatraea saccharalis and Mahanarva fimbriolata

In a field experiment in 2007/08 in São Paulo state, Brazil cane was exposed to sugarcane borer (Diatraea saccharalis) and spittlebug (Mahanarva fimbriolata) alone or in combination. Plots comprised 2 m(2) caged and uncaged sugarcane stalks. Compared with the caged (un-infested) control, spittlebug nymphs decreased cane yield by 17.6%, whereas infestation from spittlebug nymphs + sugarcane borer combined and sugarcane borer alone, decreased cane yields by 15.5% and 6.9%, respectively. There was no significant difference among the treatments in levels of soluble solids and cane sucrose content.