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Moist Conditions (moist + condition)
Selected AbstractsEmissions of N2O from soils during cycles of freezing and thawing and the effects of soil water, texture and duration of freezingEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2004R. Teepe Summary Freezing and thawing influence many physical, chemical and biological processes in soils, including the production of trace gases. We studied the effects of freezing and thawing on three soils, one sandy, one silty and one loamy, on the emissions of N2O and CO2. We also studied the effect of varying the water content, expressed as the percentage of the water-filled pore space (WFPS). Emissions of N2O during thawing decreased in the order 64% > 55% > 42% WFPS, which suggests that the retardation of the denitrification was more pronounced than the acceleration of the nitrification with increasing oxygen concentration in the soil. However, emissions of N2O at 76% WFPS were less than at 55% WFPS, which might be caused by an increased ratio of N2/N2O in the very moist conditions. The emission of CO2 was related to the soil water, with the smallest emissions at 76% WFPS and largest at 42% WFPS. The emissions of CO2 during thawing exceeded the initial CO2 emissions before the soils were frozen, which suggests that the supply of nutrients was increased by freezing. Differences in soil texture had no marked effect on the N2O emissions during thawing. The duration of freezing, however, did affect the emissions from all three soils. Freezing the soil for less than 1 day had negligible effects, but freezing for longer caused concomitant increases in emissions. Evidently the duration of freezing and soil water content have important effects on the emission of N2O, whereas the effects of texture in the range we studied were small. [source] Fire in the American South: Vegetation Impacts, History, and Climatic RelationsGEOGRAPHY COMPASS (ELECTRONIC), Issue 8 2010Charles W. Lafon Fire plays a key role in many ecosystems of the southeastern U.S. Longleaf pine (Pinus palustris) and Table Mountain pine-pitch pine (P. pungens,P. rigida) forests along with other ecosystems , including oak (Quercus) forests, grasslands, and spruce-fir (Picea-Abies) forests , illustrate the range of fire effects and plant persistence strategies in the American South. Fire history research reveals that fires and fire-associated vegetation were common before the fire exclusion of the past century. Both lightning and anthropogenic ignitions (caused by American Indians or European settlers) contributed to burning, but their relative importance is debated. The humid climate constrains burning, especially by lightning-ignited fires, which often occur during moist conditions. Studies of fire climatology indicate the importance of dry conditions (e.g. drought years and relatively dry areas) for widespread burning in this humid region. Landscape fragmentation also influences burning. In the past some fires also likely grew much larger than today because they were unimpeded by roads, farms, and other barriers. [source] Body size,climate relationships of European spidersJOURNAL OF BIOGEOGRAPHY, Issue 3 2010Wiebke Entling Abstract Aim, Geographic body size patterns of mammals and birds can be partly understood under the framework of Bergmann's rule. Climatic influences on body size of invertebrates, however, appear highly variable and lack a comparable, generally applicable theoretical framework. We derived predictions for body size,climate relationships for spiders from the literature and tested them using three datasets of variable spatial extent and grain. Location, Europe. Methods, To distinguish climate from space, we compared clines in body size within three datasets with different degrees of co-variation between latitude and climate. These datasets were: (1) regional spider faunas from 40 European countries and large islands; (2) local spider assemblages from standardized samples in 32 habitats across Europe; and (3) local spider assemblages from Central European habitats. In the latter dataset climatic conditions were determined more by habitat type than by geographic position, and therefore this dataset provided a non-spatial gradient of various microclimates. Spider body size was studied in relation to latitude, temperature and water availability. Results, In all three datasets the mean body size of spider assemblages increased from cool/moist to warm/dry environments. This increase could be accounted for by turnover from small-bodied to large-bodied spider families. Body size,climate relationships within families were inconsistent. Main conclusions, Starvation resistance and accelerated maturation can be ruled out as explanations for the body size clines recorded, because they predict the inverse of the observed relationship between spider body size and temperature. The relationship between body size and climate was partly independent of geographic position. Thus, the restriction of large-bodied spiders to their glacial refugia owing to dispersal limitations can be excluded. Our results are consistent with mechanisms invoking metabolic rate, desiccation resistance and community interactions to predict a decrease in body size from warm and dry to cool and moist conditions. [source] High hybrid fitness at seed and seedling life history stages in Louisiana irisesJOURNAL OF ECOLOGY, Issue 3 2003Jill A. Johnston Summary 1,Relative fitness of hybrid genotypes will determine the role that hybrids can play in the evolution of a plant species complex. To realistically evaluate hybrid fitness and how environmental variation affects fitness in a long-lived species, all life stages must be considered. 2,We evaluated germination, seedling survival and growth of two Louisiana iris species and their early generation hybrids in several experimental environments created by manipulating light and water levels. 3,Species and hybrids all required similar moist conditions for germination. The proportion of germinated seeds was highest in shade and seedling survival highest in sun. 4,Iris brevicaulis exhibited the lowest germination and seedling survival overall, yet those individuals that survived grew vigorously. Iris fulva had high levels of germination and seedling survival, but yielded the smallest plants at the end of one season of growth. 5,Germination rates, seedling survival and seedling growth of hybrids equalled or exceeded one or both parent species, indicating that hybrids in this system have high relative fitness at seed and seedling stages in several environmental conditions. 6,We conclude that Iris fulva and I. brevicaulis share a common regeneration niche and similar early stage relative fitness with their hybrids. Thus, environment-dependent fitness in this system is due primarily to selection at adult stages. [source] Ground-level changes after wildfire and ploughing in eucalyptus and pine forests, Portugal: implications for soil microtopographical development and soil longevityLAND DEGRADATION AND DEVELOPMENT, Issue 2 2002R. A. Shakesby Abstract Soil level changes over four years at 50 sites in three types of post-fire eucalyptus and pine forest management practices (natural pine seedling regeneration; eucalyptus regrowth from coppiced stumps; and deep-(rip-) ploughed areas planted with eucalyptus seedlings) in the Águeda Basin, Portugal are reported. Average ground lowering at regrowth sites was high during the first year after fire (up to an estimated 18,mm), declining sharply by the third year with vegetation growth and litter cover development. In the first year after rip-ploughing, there was greater surface lowering (up to 27,mm recorded), with recovery within three,four years. This sharp post-ploughing reduction in soil loss is attributed to stone lag development through erosion of fines. Soil erosion resulting from a wildfire,rip-ploughing cycle is estimated to be up to 174,t,ha,1, which would lead to ultimate physical degradation for typically thin soils within 50,100 years. Soil surface roughness decreased slightly or remained virtually stable for the moist Águeda Basin stony soil compared with a model of increased roughness for dry Mediterranean stony soils. This difference is attributed to moist conditions encouraging vegetation growth and rapid fermentation of organic matter together with transported sediment infilling surface indentations. The value of a ground-level change approach, and of the soil erosion bridge in particular, in soil erosion studies is discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Tobacco blue mould disease caused by Peronospora hyoscyami f. sp. tabacinaMOLECULAR PLANT PATHOLOGY, Issue 1 2010ORLANDO BORRÁS-HIDALGO SUMMARY Blue mould [Peronospora hyoscyami f. sp. tabacina (Adam) Skalicky 1964] is one of the most important foliar diseases of tobacco that causes significant losses in the Americas, south-eastern Europe and the Middle East. This review summarizes the current knowledge of the mechanisms employed by this oomycete pathogen to colonize its host, with emphasis on molecular aspects of pathogenicity. In addition, key biochemical and molecular mechanisms involved in tobacco resistance to blue mould are discussed. Taxonomy: Kingdom: Chromista (Straminipila); Phylum: Heterokontophyta; Class: Oomycete; Order: Peronosporales; Family: Peronosporaceae; Genus: Peronospora; Species: Peronospora hyoscyami f. sp. tabacina. Disease symptoms: The pathogen typically causes localized lesions on tobacco leaves that appear as single, or groups of, yellow spots that often coalesce to form light-brown necrotic areas. Some of the leaves exhibit grey to bluish downy mould on their lower surfaces. Diseased leaves can become twisted, such that the lower surfaces turn upwards. In such cases, the bluish colour of the diseased plants becomes quite conspicuous, especially under moist conditions when sporulation is abundant. Hence the name of the disease: tobacco blue mould. Infection process: The pathogen develops haustoria within plant cells that are thought to establish the transfer of nutrients from the host cell, and may also act in the delivery of effector proteins during infection. Resistance: Several defence responses have been reported to occur in the Nicotiana tabacum,P. hyoscyami f. sp. tabacina interaction. These include the induction of pathogenesis-related genes, and a correlated increase in the activities of typical pathogenesis-related proteins, such as peroxidases, chitinases, ,-1,3-glucanases and lipoxygenases. Systemic acquired resistance is one of the best characterized tobacco defence responses activated on pathogen infection. [source] Effects of bryophytes and lichens on seedling emergence of alvar plants: evidence from greenhouse experimentsOIKOS, Issue 3 2000Manuela Zamfir Emergence of seedlings of four alvar grassland species (Arenaria serpyllifolia, Festuca ovina, Filipendula vulgaris and Veronica spicata) in bryophyte and lichen carpets was analysed in a series of greenhouse experiments. The aspects investigated were: the influence of thickness of moss mats, both in dry and moist conditions, the effects of thick Cladonia spp. clumps, and of living vs dead moss shoots and lichen podetia. Overall, Festuca seedlings emerged best whereas the small-seeded species, Arenaria and Veronica , had the lowest emergence. Moisture had a significant effect only on the emergence of Festuca seedlings, which emerged better in the dry treatment than in the moist. A thick moss cover negatively affected seedling emergence of Arenaria and Veronica but did not affect the emergence of Festuca. Filipendula showed lower seedling emergence in both thick and thin moss than on bare soil only in the dry treatment, whereas in the moist treatment emergence did not differ among the three substrates. Arenaria seedlings emerged less in thick and thin moss than on bare soil in the dry treatment, whereas in the moist treatment emergence in the thin moss was not different from bare soil. Thus, in relatively dry environments even a thin moss cover may inhibit rather than facilitate seedling emergence. The lichen clumps inhibited only the emergence of the forbs. Both living moss shoots and lichen podetia inhibited emergence of Veronica seedlings but did not affect Festuca. In contrast, emergence in the presence of dead mosses and lichens did not differ from emergence in their absence for both species. Hence, inhibition of seedling emergence by bryophytes and lichens of at least some vascular plant species may be mediated by some biotic factor. However, the effect of differences in substrate properties on germination cannot be excluded [source] Short-term fitness benefits of physiological integration in the clonal herb Hydrocotyle peduncularisAUSTRAL ECOLOGY, Issue 6 2002Andrew G. Peterson Abstract We test whether physiological integration enhances the short-term fitness of the clonal herb Hydrocotyle peduncularis (Apiaceae, R. Brown ex A. Richards) subjected to spatial variation in water availability. Our measures of fitness and costs and benefits are based on the relative growth rate of fragmented genets. Physiological integration over a gradient in soil moisture resulted in a highly significant net benefit to genet growth of 0.015 g g,1 day,1. This net benefit represents a significant enhancement of the average fitness of fragmented genets spanning the moisture gradient relative to the average of those growing in homogeneous moist or dry conditions. Sections of genet fragments growing in dry conditions in spatially heterogeneous treatments had significantly higher growth than the sections they were connected to that were growing in moist conditions. Within fragments, older (parent) sections growing in moist conditions experienced significant costs from connection to younger (offspring) sections growing in dry conditions. In contrast, offspring sections with ample water did not experience any costs when connected to parent sections growing in dry conditions. However, the net benefit of physiological integration was similar for parent and offspring sections, suggesting that parent and offspring sections contributed equally to the net benefit of physiological integration to genet growth and short-term fitness. [source] Effects of nest temperature and moisture on phenotypic traits of hatchling snakes (Tropidonophis mairii, Colubridae) from tropical AustraliaBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2006GREGORY P. BROWN Previous research on developmentally plastic responses by reptile embryos has paid relatively little attention to tropical species, or to possible interactions between the effects of thermal and hydric regimes. In the present study, eggs of keelback snakes (Tropidonophis mairii), from a tropical area with strong temporal and spatial variation in soil temperatures and moisture levels, were incubated. The phenotypic traits of hatchling snakes (body size, shape, muscular strength) were affected by moisture content of the incubation medium (vermiculite plus 100% vs. 50% water by mass), by mean incubation temperatures (25.7 vs. 27.9 °C) and by diel thermal variation (diel range 6.0 vs. 8.4 °C). Interactions between these factors were negligible. Cooler, more thermostable, moister conditions resulted in larger offspring, a trait under strong selection in this population. Thermal and hydric conditions covary in potential nest-sites (e.g. deeper nests are more thermostable as well as moister). This covariation may influence the evolution of reaction norms for embryogenesis. For example, if moister nests enhance offspring fitness and are cooler, then selection will favour the ability to develop in cool as well as moist conditions. Thus, the evolution of optimal incubation conditions with respect to one variable (e.g. temperature) may be driven by patterns of association with another variable (e.g. soil moisture) among natural nest-sites. Perhaps for this reason, the thermal optimum for incubation is surprisingly low in this tropical species. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 89, 159,168. [source] | ||||||||||||||||