Water inputs across a tropical montane landscape in Veracruz,Mexico: synergistic effects of land cover,rain and fog seasonality,and interannual precipitation variability

Land‐cover change can alter the spatiotemporal distribution of water inputs to mountain ecosystems, an important control on land‐surface and land‐atmosphere hydrologic fluxes. In eastern Mexico, we examined the influence of three widespread land‐cover types, montane cloud forest, coffee agroforestry, and cleared areas, on total and net water inputs to soil. Stand structural characteristics, as well as rain, fog, stemflow, and throughfall (water that falls through the canopy) water fluxes were measured across 11 sites during wet and dry seasons from 2005 to 2008. Land‐cover type had a significant effect on annual and seasonal net throughfall (NTF <0=canopy water retention plus canopy evaporation; NTF >0=fog water deposition). Forest canopies retained and/or lost to evaporation (i.e. NTF<0) five‐ to 11‐fold more water than coffee agroforests. Moreover, stemflow was fourfold higher under coffee shade than forest trees. Precipitation seasonality and phenological patterns determined the magnitude of these land‐cover differences, as well as their implications for the hydrologic cycle. Significant negative relationships were found between NTF and tree leaf area index (R²=0.38, P<0.002), NTF and stand basal area (R²=0.664, P<0.002), and stemflow and epiphyte loading (R²=0.414, P<0.001). These findings indicate that leaf and epiphyte surface area reductions associated with forest conversion decrease canopy water retention/evaporation, thereby increasing throughfall and stemflow inputs to soil. Interannual precipitation variability also altered patterns of water redistribution across this landscape. Storms and hurricanes resulted in little difference in forest‐coffee wet season NTF, while El Niño Southern Oscillation was associated with a twofold increase in dry season rain and fog throughfall water deposition. In montane headwater regions, changes in water delivery to canopies and soils may affect infiltration, runoff, and evapotranspiration, with implications for provisioning (e.g. water supply) and regulating (e.g. flood mitigation) ecosystem services.     

Growth of ectomycorrhizal fungi stimulated by lipids from a pine root exudate

Summary The content of fatty acids was analysed in an exudate from roots of pine seedlings grown axenically in vermiculite with a synthetic nutrient medium. The dominating fatty acdis were fewer in the exudate than in the roots. Unsaturated fatty acids were predominant. The total lipid fraction of the exudate promoted mycelial growth in two of the three ectomycorrhizal fungi tested.     

Choline transport in Fusarium graminearum A 3 5

Fusarium graminearum A 3/5 possesses a high affinity system (Km = 32 +/- 8 microM; mean +/- SE) for uptake of choline, which was shown to be energy-dependent and constitutive. The maximum rate of choline uptake by this system was repressed by ammonia and glucose, showing a three-fold increase in maximum activity after nitrogen (2 h) or carbon (4 h) starvation. The system was highly specific for choline with only dimethylethanolamine (Ki = 198 +/- 29 microM), betaine aldehyde (Ki = 95 +/- 14 microM) and chlorocholine (Ki = 352 +/- 40 microM) acting as competitive inhibitors. Hemicholinium-3 acted as a mixed (non-competitive) inhibitor (KIES = 1.9 +/- 0.6 microM; KIE = 3.6 +/- 1.9 microM).     

Extracellular peptidases of insect-associated fungi and their possible use in biological control programs and as pathogenicity markers

This review deals with characteristics of peptidases of fungi whose life cycles are associated with insects to varying degrees. The review examines the characteristic features of the extracellular peptidases of entomopathogenic fungi, the dependence of the specificity of these peptidases on the ecological characteristics of the fungi, and the role of peptidases in the development of the pathogenesis. Data on the properties and physiological role of hydrolytic enzymes of symbiotic fungi in “fungal gardens” are also considered in detail. For the development of representations about mechanisms of control over populations of insect pests, special attention is given to analysis of possibilities of genetic engineering for the creation of entomopathogens with enhanced virulence. Clarification of the role of fungi and their secreted enzymes and careful environmental studies are still required to explain their significance in the composition of the biota and to ensure widespread adoption of these organisms as effective biological control agents. The systematization and comparative analysis of the existing data on extracellular peptidases of insect-associated fungi will help in the planning of further work and the search for markers of pathogenesis and symbiosis.     

Anwendung der automatisierten Festphasenextraktion bei der Bestimmung von Ochratoxin A

For some foodstuffs, determination of the mycotoxin ochratoxin A (OTA) requires time consuming clean up by means of solid phase extraction (SPE). Therefore a system for automated SPE was tested for cleaning up roasted coffee as a possible way of shortening preparation time. Validation of the method in accordance to the so called “Concept '98” led to a LOD of 0.2 μg/kg and a recovery rate of 92%. By using the described procedure with samples of roasted coffee the OTA contents varied between the LOD and 3.4 μg/kg. This method was also used to determine ochratoxin A in liquorice roots, ginger and valerian.

Presented at the 26^th Mykotoxin Workshop in Herrsching, Germany, May 17–19, 2004     

Effect of roasting on ochratoxin A level in green coffee beans inoculated with Aspergillus ochraceus

The heat stability of ochratoxin A in green coffee beans inoculated with Aspergillus ochraceus was studied. Heat treatment (roasting) at 200 °C for 10 or 20 min reduced the levels of ochratoxin A by only 0–12% in the dried whole beans. Almost all of the ochratoxin A was infused into the coffee decoction when the roasted samples were ground and extracted with boiling water. Therefore, the reduction of ochratoxin A concentration of contaminated coffee beans by roasting under these conditions is ineffective.     

Ion currents associated with root tips, emerging laterals and induced wound sites in Nicotians tabacum: spatial relationship proposed between resulting electrical fields and phytophthoran zoospore infection

Abstract Growing roots of Nicotiana tabacum var. Havana generate transcellular ion currents which traverse developing and wounded tissues. Positive current of around 10 mA m^?2 enters meristematic and elongating cells at the tip of primary roots. The growing tips of first order laterals are also traversed by a similar positive current with a density of around 2.0 mA m^?2, as are immature laterals emerging at the primary root surface. These self-generated ion currents flow basipetally through developing tissues and leave from mature non-elongating tissue. A large positive current of around 70 mA m^?2 also enters induced wound sites on the primary root surface. Motile zoospores of the fungal pathogen Phytophthora parasitica var. nicotianae have been reported to associate preferentially with these regions of the root. This might suggest that electrotaxis may be part of the mechanism by which zoospores locate root regions susceptable to fungal infection.     

High-level expression of a tobacco chitinase gene in Nicotiana sylvestris. Susceptibility of transgenic plants to Cercospora nicotianae infection

Endochitinases (E.C. 3.2.14, chitinase) are believed to be important in the biochemical defense of plants against chitin-containing fungal pathogens. We introduced a gene for class I (basic) tobacco chitinase regulated by Cauliflower Mosaic Virus 35S-RNA expression signals into Nicotiana sylvestris. The gene was expressed to give mature, enzymatically active chitinase targeted to the intracellular compartment of leaves. Most transformants accumulated extremely high levels of chitinase-up to 120-fold that of non-transformed plants in comparable tissues. Unexpectedly, some transformants exhibited chitinase levels lower than in non-transformed plants suggesting that the transgene inhibited expression of the homologous host gene. Progeny tests indicate this effect is not permanent. High levels of chitinase in transformants did not substantially increase resistance to the chitin-containing fungus Cercospora nicotiana, which causes Frog Eye disease. Therefore class I chitinase does not appear to be the limiting factor in the defense reaction to this pathogen.     

Biodiversity amongst filamentous fungi

Diversities in fungi are manifold. Fungi themselves are heterogeneous and constitute at least three unrelated major taxa. Structural diversity reflects, in most cases, adaptive and functional strategies. Diversity in nucleic acids and chemical compounds is very high in several fungal taxa. Fungi play an essential role in the function of ecosystems. The diversity of plant parasites is extremely high and species-dependent associations exist. Saprobic fungi are most important in wood and litter decay and diverse taxa comprise the main decomposers in specific successional niches. Two dominating symbiotic systems have evolved convergently in various fungal groups, notably lichens and mycorrhizas, both remarkably diverse in their heterotrophic partners.