Creation and preservation of vegetation patterns by grazing

Structural patterns of tall stands (“tussock”) and short stands (“lawn”) are observed in grazed vegetation throughout the world. Such structural vegetation diversity influences plant and animal diversity. A possible mechanism for the creation and preservation of such patterns is a positive feedback between grazing and plant palatability. Although some theoretical studies have addressed this point in a non-spatial setting, the spatial consequences of this feedback mechanism on the stability and spatial characteristics of vegetation structure patterns have not been studied.We addressed this issue by analyzing a spatially explicit individual-based plant-grazer simulation model, based on published empirical relations and the assumption of optimal foraging.In the model, the selection by the grazer of short stands (that have a higher energy content and are more palatable) is affected by traveling costs and the spatial organization of swards. Nevertheless, the most selected biomass in this type of short stands was the optimal biomass predicted by cropping and digestion constraints. As a result of the optimal foraging strategy, the grazers displayed Lévy-flight traveling behavior during the simulations with characteristic exponent μ ≈ 2.Patterns of short and tall stands created by grazing were preserved for at least a decade. Even in seasonal habitat, the spatial organization of the patterns remained relatively constant, despite fluctuations in the area of short stands. Heterogeneity of initial vegetation increased heterogeneity of the grazing-induced pattern, but did not affect its stability.The area of short stands that was preserved by grazing scaled with the herbivore mass to the power 0.4 and with the carrying capacity of the vegetation to the power −0.75.Patterns of tall and short stands can be created and perpetuated by optimally grazing ruminants, irrespective of possible underlying soil patterns. The simulations generate predictions for the stability and spatial characteristics of such structural vegetation patterns.     

Ubiquitous eight-carbon volatiles of fungi are infochemicals for a specialist fungivore

An enormous variety of volatile substances are released in distinctive blends by fungal substrates that should be recognisable for fungivores. Certain compounds dominate in most of the fungal species. Fungal oxylipins as the eight-carbon volatiles are the most prominent. This raises the question whether such are specific enough to qualify as appropriate host cues for a fungivore. We could demonstrate differentiated responses of the fungivorous beetle Bolitophagus reticulatus to eight-carbon volatiles: Nine eight-carbon volatiles were identified with GC–MS from its host fungus Fomes fomentarius. 1-Octen-3-ol, 3-octanone and 3-octanol induced contrasting behaviour of beetles in olfactometer bioassays. Electroantennographic experiments investigating the beetle olfactory sense revealed distinguishable antennal responses. Moreover, their individual release from F. fomentarius fruiting bodies changes not only considerably, but also independently over successive stages of beetle colonisation. Concentrations of attractive and repellent eight-carbon volatiles correlate to frequency of beetles in the field and further substantiate their relevance as host cues. Our results show that a specialist fungivore is able to differentiate the most common eight-carbon volatiles of fungi to assess host quality. Key roles and marked similarities of fungal to plant oxylipins suggest a comparable importance of eight-carbon volatiles to fungivores as green leaf volatiles have to herbivores.     

Calibration of the Chemcatcher passive sampler for monitoring selected polar and semi-polar pesticides in surface water

Passive sampling is a powerful method for continuous pollution monitoring, but calibration experiments are still needed to generate sampling rates in order to estimate water concentrations for polar compounds. We calibrated the Chemcatcher device with an uncovered SDB-XC Empore disk as receiving phase for 12 polar and semi-polar pesticides in aquatic environments in flow-through tank experiments at two water flow velocities (0.135 m/s and 0.4 m/s). In the 14-day period of exposure the uptake of test substances in the sampler remained linear, and all derived sampling rates R(s) were in the range of 0.1 to 0.5 L/day. By additionally monitoring the release of two preloaded polar pesticides from the SDB-XC disks over time, very high variation in release kinetics was found, which calls into question the applicability of performance reference compounds. Our study expands the applicability of the Chemcatcher for monitoring trace concentrations of pesticides with frequent occurrence in water.     

Modeling Ethylene Bisdithiocarbamate Efficacy Potential in the Presence of a Zoospore Attractant

A common class of fungicides are the ethylene bisdithiocarbamates (EBDCs) which decompose into ethylene bis-isothiocyanate sulfide (EBIS). EBIS is the primary fungitoxic component which is effective on various life stages of oomycete fungi, including zoospores (primary infection agents of oomycete fungal diseases). It is hypothesized that increased fungicide effectiveness can occur if zoospores are attracted to the toxicant (site of fungicide deposition) through chemotaxis using zoospore attractants (ZAs). Several probe studies proved this hypothesis when a ZA was formulated with EBDC products. A highly effective zoospore attractant is isovaleraldehyde (IVA), but IVA is volatile and dissipates rapidly in the environment. Therefore, various precursors for IVA and EBIS were studied to characterize the transient production and decline of EBIS and IVA from precursor material. First-order kinetic material balances and a stochastic modeling tool are created to fully exploit the conditions when the overlap of EBIS and IVA is maximized. A metric is proposed (measure of the overlap of fungicide and ZA residue) as an indirect measure of the potential for preventative fungicide efficacy when ZAs are included within the formulation. Therefore, fungicide formulations containing a ZA can be designed through model deployment that considers the production and decline patterns of both the fungicide and ZA, and the daily environmental dew cycle responsible for achieving the maximum concentration overlap when zoospores are the most infectious (e.g., mobile in the presence of dew) for enhanced crop disease control. It is found that the poly-IVA produrg investigated provides the maximum overlap of EBIS and IVA residues for many different EBDC formulations investigated. This modeling approach, and the examples provided for EBIS and IVA material balances, can be expanded for different fungicides and ZAs allowing for cause/effect to be inferred from multiple interacting factors, and formulations can be designed for optimal release characteristics that maximize the overlap of fungitoxic material and zoospore attractant.     

Sorption of chlorimuron-ethyl on montmorillonite clays: effects of exchangeable cations,pH, and ionic strength

Sorption interaction of chlorimuron-ethyl with montmorillonite clays was investigated under varied types of exchangeable cation, pH, and ionic strength conditions. Chlorimuron-ethyl sorption on bentonites exhibited pronounced cation dependency, and the sorption ability increased as the sequence Ca²⁺- < Na⁺- < Al³⁺- < Fe³⁺-bentonite, due to different sorption mechanisms, whereas the cation dependency was influenced by the clay type and much weaker for montmorillonites. The decrease of pH at the range of 4.0–6.0 prominently increased sorption of chlorimuron-ethyl on all cation-exchanged montmorillonite clays, and nearly a neglected sorption (about 2 %) can be observed at pH over 7.0. In the presence of CaCl₂, sorption of chlorimuron-ethyl on Fe³⁺-bentonite was promoted because of complexion of Ca²⁺ and the surface of Fe³⁺-bentonite. However, as the concentration of CaCl₂ increased, chlorimuron-ethyl sorption on Ca²⁺- and Fe³⁺-exchanged bentonite decreased, suggesting that Ca bridging was not the prevailing mechanism for sorption of chlorimuron-ethyl on these clays. Furthermore, chlorimuron-ethyl sorption was relatively sensitive to pH, and the change of pH may obscure effect of other factors on the sorption, so it was quite necessary to control pH at a constant value when the effect of other factor was being studied.     

Linking local impacts to changes in climate: a guide to attribution

Assessing past impacts of observed climate change on natural, human and managed systems requires detailed knowledge about the effects of both climatic and other drivers of change, and their respective interaction. Resulting requirements with regard to system understanding and long-term observational data can be prohibitive for quantitative detection and attribution methods, especially in the case of human systems and in regions with poor monitoring records. To enable a structured examination of past impacts in such cases, we follow the logic of quantitative attribution assessments, however, allowing for qualitative methods and different types of evidence. We demonstrate how multiple lines of evidence can be integrated in support of attribution exercises for human and managed systems. Results show that careful analysis can allow for attribution statements without explicit end-to-end modeling of the whole climate-impact system. However, care must be taken not to overstate or generalize the results and to avoid bias when the analysis is motivated by and limited to observations considered consistent with climate change impacts.     

Effects of SO2 and/or NO2 on Native Plants of the Mojave Desert and Eastern Mojave-Colorado Desert

Ten species of plants, five perennials and five annuals, native to the Mojave desert were grown in pots and fumigated in open top plastic greenhouses, 25 hours/week, with SO₂ and/or NO₂. Three levels of SO₂: 2.0, 0.67, and 0.22 parts per million (ppm); three levels of NO₂: 1.0, 0.33, and 0.11 ppm; three treatments with 2.0 ppm SO₂ + 1.0 ppm NO₂, 0.67 ppm SO₂ + 0.33 ppm NO₂ and 0.22 ppm SO₂ + 0.11 ppm NO₂ plus untreated control plants were used in the fumigations. The perennials were fumigated for 16 weeks in 1977 and 32 weeks in 1978. Three species of annuals were grown and fumigated for 17 weeks, a fourth for 16 weeks, and a fifth for 12 weeks. A second crop of the first three annuals were grown; one for 12 weeks, a second for 8, and a third for 9 weeks.

Individual species differed widely in their particular responses to the fumigants. The fumigations of perennials with 2.0 ppm of SO₂ or NO₂ at 1.0 ppm caused extensive leaf injury, and reduced growth or dry weight of Larrea divaricate Cav., Chilopsls linearis Cav., and Ambrosia dumosa (Gray) Payne. The combined fumigants had additive effects. No suggestion of synergism was noted. These fumigants at lower concentrations stimulated lateral growth of Encelia farinosa Gray ex Torr. and Erodium cicutarium (L.) L’Her., dry weight of Atriplex canescens (Pursh) Nutt. and Plantago insularis Eastw. and increased flowering of Balleya pleniradiata Harv. and Gray, thus indicating beneficial effects.

Annual species were more severely affected by 2.0 ppm SO₂ than the perennials and extensive injury or death of plants occurred in all annuals. At the 0.67 ppm level severe leaf injury occurred. NO₂ at 1.0 ppm was less injurious than SO₂ and addition of NO₂ to SO₂ suggested an antagonistic effect. Plant survival and flowering was increased by adding NO₂ to plants being treated with SO₂

Comparison of perennial species showed Larrea sensitive, Chilopsis, Encella and Ambrosia intermediate, and Atriplex resistant. The annual species showed Erodium cicutarium and Plantago Insularis to be extremely sensitive, Phacelia crenulata Torr very sensitive and Baileya pleniradiata sensitive. Chaenactis carphoclinia Gray grew poorly and no valid rating was possible.     

III. Ökotoxikologische Charakterisierung der Schwermetall-Immissionsmuster

The spatial variation of the immission patterns of Cr, Fe, Pb and V in the region Leipzig-Halle is dicussed in terms of similarities as well as dissimilarities. The representation by isopleths enables the identification of areas with high and low air pollution. The immission patterns can be used as criteria to select areas suitable for in-field testing so that possible effects on fauna und flora and xenobiotic fluxes can be studied at representative sites. The comparison with literature data yields a first characterization of the ecotoxic potential of the heavy-metal immission for the region. By the principal component analysis a comparative evaluation of the spatial structure of all element contents is performed, which leads to conclusions about emission sources and the physicochemical behaviour of the elements.     

Polychlorinated naphthalenes in sediments from the industrial region of Bitterfeld

Bitterfeld (Germany) was a major site of chemical production in the former German Democratic Republic with chloralkali electrolysis as the basic process. Effluents were dumped via the creek Spittelwasser into the rivers Mulde and Elbe. Despite the fact that the chloralkali industry is known as a possible source of polychlorinated naphthalenes (PCNs), to date no data about PCN pollution in the region of Bitterfeld and downstream regions are available. Therefore, sediments of the creek Spittelwasser were isomer-specifically analysed for penta-, hexa- and heptachlorinated naphthalenes using GC/MS. Concentrations of 880, 543 and 1120 ng/g dry weight were found, respectively. The isomer pattern suggests chloralkali industry as the major source of PCN contamination. Because of their toxicological relevance we suggest to include PCNs into monitoring and risk assessment programs of the rivers Mulde and Elbe downstream of Bitterfeld.