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Ecotypic variation in summer dormancy of blackbrush shrubs (Coleogyne ramosissima Torr.) was investigated through a field irrigation experiment in Cold Creek Canyon of the Spring Mountains in southern Nevada. Blackbrush were irrigated in lower and upper elevational boundaries (ecotones) compared with adjacent unirrigated (control) individuals to determine to what extent summer dormancy has a genetic (obligatory) or environmental (facultative) basis. Significantly more blackbrush became dormant under dry than moist soil conditions at both upper and lower ecotones. Under dry soil conditions, the proportion of dormancy was similar in both upper and lower ecotones. However, under moist soil conditions, significantly more blackbrush became dormant at the lower than upper ecotone. The elevation * month interaction was significant for air temperature. The elevation * irrigation interaction was significant for duration of dormancy and water potential of blackbrush. All blackbrush survived dormancy and resumed growth in the fall after a summer monsoonal season. This study suggested that an obligatory dormant ecotype occurred primarily at the lower ecotone, whereas a facultative dormant ecotype was more abundant at the upper ecotone in Cold Creek Canyon of southern Nevada.
This study examines the impacts of slash pile size and burning on various soil chemical characteristics and nutrient concentrations. Changes in soil characteristics following slash pile burns associated with forest thinning treatments may affect native and non-native floral species establishment and have broad implications for ecosystem functions, processes, and management. We sampled soils from plots under various slash pile burning treatments at The Arboretum at Flagstaff, Arizona, to determine their chemical characteristics.The characteristics consist of concentrations of macro- and micro-nutrients (N, P, K, Ca, Mg, Na, Mn, Fe, Zn, Cu, B) and pH. We compared the amounts of nutrients in burned plots with those in unburned plots where slash was removed by chipping. The treatments were tested on large and small piles. Burned slash pile plots had higher soil nutrient levels overall. The levels of N, Ca, K, Zn, and Na best illustrate this fertilizing effect. Significantly different values of N and P existed between treatments; however, the results show no distinct patterns related to the burning of slash. Nevertheless, there is enough evidence for a forest management decision involving burning any part of the forest to consider the effect of fires on soil chemistry.
Extensive research has been conducted on the structure, function, and management of biological soil crusts (BSCs) (cf. Belnap and Lange 2003). Little research, however, has been conducted on spatial aspects of BSCs, such as (micro)climate, biogeomorphology, and model-building for large area assessment and management. This preliminary experiment explores the micrometeorology of both a dry and a wet stand of BSC on a pediment in the Sonoran Desert. A researcher-induced precipitation event was used to simulate an actual precipitation event on a 0.5-m2 plot; another, adjacent plot was left “dry.” Using a thermister, connected to a datalogger, temperature above, in, and below the BSC was recorded in 5-min intervals over a 24-hr period. Simultaneously, using a solarimeter, incoming and outgoing radiation measurements were recorded at the same temporal scale and intervals. The data show a significant difference between the dry and wet BSC plots in both temperature and outgoing radiation over the temporal scale tested. Perhaps due in part to the activation of microorganisms and color changing of surface organisms when a precipitation event happens, the wet BSC plot experienced less extreme temperatures and a consistently positive outgoing radiation flux. The study also demonstrates the need for further research in the area of BSC spatiality and microclimate, and advocates for the use of research methods that may have been overlooked in present BSC research endeavors.
The purpose of this study was to determine the spatial and temporal aspects of the urban heat island in the small, arid city of Casa Grande, Arizona. Temperature and dewpoint were collected through a combination of fixed stations and two mobile transect routes on four separate clear and calm nights during the period of 15–18 March 2004. A mobile transect on 18 March revealed a maximum heat difference of 4.7°C along an east-to-west route across the city, with a spatially interpolated temperature map illustrating warmest areas in the far eastern commercial corridor and cooler areas in the far southern and western regions of the city, consisting of rural agricultural fields. Wind speed at the Casa Grande Airport during transect times was seen to be a significant factor in determining intensity of heat differences. However, due to very light wind conditions encountered on all three nights (<2.5 m s−1), surface thermal properties and land cover may have played the largest role in determining heat island intensity. Thermal imagery taken of the area at a time similar to transect times (2125 LST) confirms the idea that surface thermal material properties may play a large role in determining heat island characteristics near the ground with the absence of strong winds.
Neurofilament (NF) proteins play key structural and functional roles in healthy neuronal tissues. However, in neuro-degenerative diseases aggregates of NF proteins form and this aggregation process appears to play a mechanistic role in the disease process. Because neurofilaments are obligate heteropolymers, the ability of neurofilament proteins to form filaments may depend on their domain structure. Therefore, a series of chimeric neurofilament proteins were constructed and the ability of these chimeric proteins to form filaments was tested. All were expected to form filaments with vimentin. Surprisingly, several chimeric NF constructs were unable to form filaments with vimentin. Expression of these chimeric proteins not only disassembled the existing vimentin meshwork but formed aggregates instead. The composition of these aggregates was investigated by immunofluorescence microscopy. Based on the resulting colocalization data, we conclude that these aggregates are similar to those seen in neurodegenerative diseases. Therefore, we conclude that these cell lines are a valid model system for the study of the aggregation of NF proteins and the role of these aggregates in neurodegenerative disease processes.
Sky Harbor International Airport (SKA) is the first-order weather station in the Phoenix metropolitan area. Meteorological variables from the weather station, including precipitation, are reported by the media to the general public as the official weather results for the Phoenix metropolitan area, which measures more than 15,000 square miles. While temperature is a continuous meteorological parameter that does not vary much spatially across Phoenix, precipitation is a discrete and more variable weather phenomenon, even during winter, when mid-latitude storms bring wide swaths of precipitation to Arizona. Does the precipitation measured at Sky Harbor International Airport spatially characterize precipitation in the rest of the Phoenix area during winter? Have correlations between Sky Harbor winter precipitation and the rest of the Phoenix area changed over time? Precipitation data for the months of December to March were compiled for 28 Phoenix area weather stations for the time period 1990–2004 and for 8 stations from 1954–2004. Five definitions of precipitation, including total, frequency, intensity, duration, and true intensity were developed to define precipitation. Regression equations using Sky Harbor precipitation as the independent variable were run to determine correlations and variance explained with surrounding stations. Additional regressions were run on subsets of the 1954–2004 data to determine if correlations have changed over time. Overall, Sky Harbor explains between 71 to 99% of total seasonal precipitation and between 85 to 98% of the seasonal frequency, although these numbers are significantly reduced for daily data. Locations closer to Sky Harbor are more highly correlated for all variables than those farther away. Correlation coefficients show significant changes due to the urban heat island as well from climate teleconnections.
Valleys and basins across the western United States experience frequent episodes of radiation fog during the winter season. Freezing fog (FZFG) however is more rare. The high desert basins of northern Nevada are more likely to experience FZFG than lower elevation valleys as October–March minimum temperatures regularly fall below 0°C. During a period in mid-January 2005, northern Nevada, from Reno to Winnemucca experienced an unprecedented freezing fog episode. In Reno there were 14 daily reports of FZFG during January 2005, and nine of these days occurred consecutively from 16 through 24 January. Meteorological conditions for the nine day run of FZFG events in Reno were not extreme compared to single day episodes from 1997–2005. The height of the inversion base, inversion depth, surface temperature, wind speed, and surface pressure were found to be consistently above the mean but well below the maximum values for prior FZFG events. Regional scale surface conditions and synoptic scale upper atmospheric conditions were important factors in FZFG formation and persistence during the period 16–24 January.