Paleozoic Atmospheric CO2: Importance of Solar Radiation and Plant Evolution

Changes in solar radiation, as it affects the rate of weathering of silicates on the continents, and other changes involving weathering and the degassing of carbon dioxide (CO(2)) have been included in a long-term carbon-cycle model. These additions to the model show that the major controls on CO(2) concentrations during the Paleozoic era were solar and biological, and not tectonic, in origin. The model predictions agree with independent estimates of a large mid-Paleozoic (400 to 320 million years ago) drop in CO(2) concentrations, which led to large-scale glaciation. This agreement indicates that variations in the atmospheric greenhouse effect were important in global climate change during the distant geologic past.     

Die biologische Bekämpfung des Eukalyptusblattsaugers Ctenarytaina eucalypti (Maskell) (Hemiptera, Psyllidae) durch die Erzwespe Psyllaephagus pilosus Noyes (Hymenoptera, Encyrtidae) – eine Erfolgsgeschichte in Kalifornien und Westeuropa, aber auch in Sachsen

The Australian psyllid Ctenarytaina eucalypti has been accidentally introduced into many parts of the world. In America as well as in Europe it caused severe damage on Eucalyptus cut-foliage plantations. Insecticide treatments have proven to be expensive and not-sustainable. Therefore a biocontrol project was carried out in the Center for Biological Control at Berkely, California. The search for a monophagous parasitoid of the blue gum psyllid in the natural habitat in Australia and New Zealand was successful. After quarantine for elimination of hyperparasitoids the natural enemy Psyllaephagus pilosus has been released in Californian Eucalyptus plantations since 1993. It established itself rapidly, resulting in a decrease of the pest below the economic threshold. Following this impressive effect the parasitoid has also been released in some West European countries. The rapid spread over great territories was similar. The parasitization rates reached 100 percent, providing a sustainable control of the psyllid. In the last years several accidental introductions of C. eucalypti into Germany occurred. The first record in Saxony was in 2000 in the botanical garden of the Dresden University of Technology on Eucalyptus globulus. However, the spontaneous attack of the blue gum psyllid by P. pilosus during the next two years eradicated the infestation. To avoid a possible threat to natural ecosystems, the well-directed future use of exotic biological control agents against unintentionally introduced pests is in urgent need of a legal regulation at the EU or national level in Germany. The FAO and EPPO standards on this topic should be considered as a basis for this.     

Direct and indirect effects of nitrogen deposition on litter decomposition

Elevated nitrogen (N) deposition can affect litter decomposition directly, by raising soil N availability and the quantity and quality of litter inputs, and indirectly by altering plant community composition. We investigated the importance of these controls on litter decomposition using litter bags placed in annual herb based microcosm ecosystems that had been subject to two rates of N deposition (which raised soil inorganic N availability and stimulated litter inputs) and two planting regimes, namely the plant species compositions of low and high N deposition environments. In each microcosm, we harvested litter bags of 10 annual plant species, over an 8-week period, to determine mass loss from decomposition. Our data showed that species differed greatly in their decomposability, but that these differences were unlikely to affect decomposition at the ecosystem level because there was no correlation between a species’ decomposability and its response to N deposition (measured as population seed production under high N, relative to low N, deposition). Litter mass loss was ～2% greater in high N deposition microcosms. Using a comprehensive set of measurements of the microcosm soil environments, we found that the most statistically likely explanation for this effect was increased soil enzyme activity (cellobiosidase, β-glucosidase and β-xylosidase), which appears to have occurred in response to a combination of raised soil inorganic N availability and stimulated litter inputs. Our data indicate that direct effects of N deposition on litter input and soil N availability significantly affected decomposition but indirect effects did not. We argue that indirect effects of changes to plant species composition could be stronger in natural ecosystems, which often contain a greater diversity of plant functional types than those considered here.     

Crop yield and soil fertility response to reduced tillage under organic management

Conservation tillage (no-till and reduced tillage) brings many benefits with respect to soil fertility and energy use, but it also has drawbacks regarding the need for synthetic fertilizers and herbicides. Our objective was to adapt reduced tillage to organic farming by quantifying effects of tillage (plough versus chisel), fertilization (slurry versus manure compost) and biodynamic preparations (with versus without) on soil fertility indicators and crop yield. The experiment was initiated in 2002 on a Stagnic Eutric Cambisol (45% clay content) near Frick (Switzerland) where the average annual precipitation is 1000 mm. This report focuses on the conversion period and examines changes as tillage intensity was reduced. Soil samples were taken from the 0–10 and 10–20 cm depths and analysed for soil organic carbon (C_org), microbial biomass (C_mic), dehydrogenase activity (DHA) and earthworm density and biomass. Among the components tested, only tillage had any influence on these soil fertility indicators. C_org in the 0–10 cm soil layer increased by 7.4% (1.5 g C_org kg⁻¹ soil, p < 0.001) with reduced tillage between 2002 and 2005, but remained constant with conventional tillage. Similarly, C_mic was 28% higher and DHA 27% (p < 0.001) higher with reduced than with conventional tillage in the soil layer 0–10 cm. In the 10–20 cm layer, there were no significant differences for these soil parameters between the tillage treatments. Tillage had no significant effect on total earthworm density and biomass. The abundance of endogeic, horizontally burrowing adult earthworms was 70% higher under reduced than conventional tillage but their biomass was 53% lower with reduced tillage. Wheat (Triticum aestivum L.) and spelt (Triticum spelta L.) yield decreased by 14% (p < 0.001) and 8% (p < 0.05), respectively, with reduced tillage, but sunflower (Helianthus annuus L.) yield was slightly higher with reduced tillage. Slurry fertilization enhanced wheat yield by 5% (p < 0.001) compared to compost fertilization. Overall, C_org, C_mic, and DHA improved and yields showed only a small reduction with reduced tillage under organic management, but long-term effects such as weed competition remain unknown.     

Effects of temperature and humidity on the survival of urediniospores of gladiolus rust (<Emphasis Type="Italic">Uromyces transversalis</Emphasis>)

Uromyces transversalis is an autoecious microcyclic rust mainly infecting Gladiolus spp. The pathogen is considered of plant quarantine importance in Europe and the USA. In 2006, the pathogen was found for the first time in the USA in several commercial nurseries in Florida and California. The US Department of Agriculture (USDA) initiated an eradication programme that recommended the immediate removal and destruction of infected plants followed by a host-free period, use of a fungicide treatment schedule, and equipment decontamination. In support of this plan, a study was conducted to determine how long urediniospores of U. transversalis would continue to germinate at temperatures of 2.8, 15.0, 18.8 and 25.0°C under controlled relative humidities (RH) of 11, 23, 43, 75, 93 and 100%. Choice of temperature and humidity parameters were mostly based on historical multi-year climate data from areas where the disease was detected in California and Florida. Analysis of variance (ANOVA) indicated no significant effect of RH on urediniospore germination but a highly significant effect of temperature. No germinating urediniospores were detected after 79 days for any treatment, but the 15°C treatment was more likely to be the result of germination independent of any low or high temperature-induced spore quiescence. Thus, lack of germination after 79 days was probably a good indicator of the lack of viable spores after this time for the 15°C treatment.     

Differences in grain/straw ratio,protein content and yield in landraces and modern varieties of different wheat species under organic farming

Hulled wheat species (einkorn, emmer, spelt) are presumed to be an alternative to bread wheat in organic agriculture since the yield penalty is less pronounced under organic farming and generally higher prices can be achieved for specialty grains. The present study analyzed differences between wheat species with respect to biomass production, harvest index, grain yield and protein content. Spring hulled wheat genetic resources and bread wheat check cultivars were grown in organic field trials in the Czech Republic and Austria between 2010 and 2012. Generally, hulled wheat species were inferior in grain yield and distribution of assimilates to the grain compared to modern bread wheat. Biomass production of some emmer and spelt landraces was similar to bread wheat. A higher protein content (+3–6 %) was observed for spelt, however, considering protein yield the differences between spelt and bread wheat became less pronounced. With respect to the recent high market demand for spelt and the absence of available spring grown varieties some of the landraces were identified as valuable resources for the development of spring spelt varieties suitable for organic farming.     

Retinoid signaling determines germ cell fate in mice

Germ cells in the mouse embryo can develop as oocytes or spermatogonia, depending on molecular cues that have not been identified. We found that retinoic acid, produced by mesonephroi of both sexes, causes germ cells in the ovary to enter meiosis and initiate oogenesis. Meiosis is retarded in the fetal testis by the action of the retinoid-degrading enzyme CYP26B1, ultimately leading to spermatogenesis. In testes of Cyp26b1-knockout mouse embryos, germ cells enter meiosis precociously, as if in a normal ovary. Thus, precise regulation of retinoid levels during fetal gonad development provides the molecular control mechanism that specifies germ cell fate.     

The effect of ozone and drought on the photosynthetic performance of canola

Canola plants were fumigated in open-top chambers with ozone(O_3)(120 ppb)under well-watered(WW)and water-stressed(WS)conditions for 4 weeks.Non-fumigated plants were also studied to facilitate comparison between treatments for the same week and over time.Therefore,the treatments were:WW,WW-O_3,WS and WS-O_3.The fast chlorophyll a fluorescence transients OJIP for the four treatments emitted upon illumination of dark-adapted leaves were measured after week 1,2,3,4 and analysed by the JIP-test to evaluate the resulting changes in photosynthetic performance.Ozone fumigation led to a decline of total performance index(PI_(total))in well-watered plants.The effect of O_3 was minor under drought conditions,as revealed by a decrease of PI_(total) by 3%.The PI_(total) decreased as the treatment was prolonged,due to leaf ageing for all cases and the decline was more pronounced under WW-O_3.Taking the average of all weeks,WW had the highest PI_(total )and the lowest WW-O_3(decrease by 27%),while in WS and WS-O_3,it was lower than WW(14 and 17%,respectively).We found that the absorption(ABS)/reaction centre(RC)increases,while the maximum quantum yield of primary photochemistry(φ_(Po))undergoes slight changes,and trapping(TR_0)/RC closely followed the increase in ABS/RC.This indicates that O_3and drought caused an increase in the functional antenna size.The maximum quantum yield of primary photochemistry showed slight differences for all treatments and over time,suggesting that this parameter is less sensitive to drought and O_3 stress.Therefore,the more sensitive components of the photosynthetic electron transport chain appeared to be the probability that an electron from the intersystem electron carriers is transferred to reduce end electron acceptors at the PSI acceptor side(δ_(Ro))and the RC density on a chlorophyll basis(RC/ABS).     

Effects of temperature on urediniospore germination, germ tube growth, and initiation of infection in soybean by phakopsora isolates

ABSTRACT Temperature is a critical factor in plant disease development. As part of a research program to determine how specific environmental variables affect soybean rust, we determined temperature effects on urediniospore germination and germ tube growth of four isolates of Phakopsora pachyrhizi, one each from Brazil, Hawaii, Taiwan, and Zimbabwe, and an isolate of P. meibomiae from Puerto Rico, collected over a 25-year period. Also compared were the effects of temperature during a night dew period on initiation of disease by the P. pachyrhizi isolates. All variables were fit to a nonlinear beta function with temperature as the independent variable. Minimum, maximum, and optimum temperatures, along with shape parameters of the beta function for each variable, were statistically analyzed. All Phakopsora isolates behaved similarly as to how temperature affected urediniospore germination, germ tube growth, and initiation of disease. The results suggest that P. pachyrhizi has changed little in the past few decades with respect to how it responds to temperature and that previously collected research data continues to be valid, simplifying the development of soybean rust disease models.