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Warren-Rhodes K.A.,NASA | Warren-Rhodes K.A.,Search for Extraterrestrial Intelligence Institute | McKay C.P.,NASA | Boyle L.N.,University of Washington | And 13 more authors.
Journal of Geophysical Research: Biogeosciences | Year: 2013

Hypolithic microbial communities are productive niches in deserts worldwide, but many facets of their basic ecology remain unknown. The Namib Desert is an important site for hypolith study because it has abundant quartz rocks suitable for colonization and extends west to east across a transition from fog- to rain-dominated moisture sources. We show that fog sustains and impacts hypolithic ecology in several ways, as follows: (1) fog effectively replaces rainfall in the western zone of the central Namib to enable high (≥95%) hypolithic abundance at landscape (1-10 km) and larger scales; and (2) high water availability, through fog (western zone) and/or rainfall (eastern zone), results in smaller size-class rocks being colonized (mean 6.3 ± 1.2 cm) at higher proportions (e.g., 98% versus approximately 3%) than in previously studied hyperarid deserts. We measured 0.1% of incident sunlight as the lower limit for hypolithic growth on quartz rocks in the Namib and found that uncolonized ventral rock surfaces were limited by light rather than moisture. In situ monitoring showed that although rainfall supplied more liquid water (36 h) per event than fog (mean 4 h), on an equivalent annual basis, fog provided nearly twice as much liquid water as rainfall to the hypolithic zone. Hypolithic abundance reaches 100% at a mean annual precipitation (MAP) of approximately 40-60 mm, but at a much lower MAP (approximately 25 mm) when moisture from fog is available. Key Points Fog effectively replaces rainfall to enable high hypolithic abundance in Namib Hypolithic colonization is light, not moisture, limited at 1% incident sunlight Fog supplied nearly twice the liquid water to the hypolithic zone as rainfall ©2013. American Geophysical Union. All Rights Reserved. Source


Wing M.R.,Sir Francis Drake High School | Knowles A.J.,Sir Francis Drake High School | Melbostad S.R.,Sir Francis Drake High School | Jones A.K.,Sir Francis Drake High School
Trees - Structure and Function | Year: 2014

Six hundred and eleven Great Basin bristlecone pines (Pinus longaeva) were surveyed in two separate groves in California's White Mountains. The presence and direction of spiral grain were recorded for each tree as well as elevation above sea level, horizon angles, latitude and longitude, trunk diameter, whether the tree was dead, and whether the trunk was broken. The proportions of left-handed, right-handed and straight trees were similar in every part of both groves, although the groves lie at different elevations. No significant correlation was found between the direction of spiral grain and any environmental factor. The hypothesis that spiral grain is an adaptation to distribute sap evenly between the roots and the crown in Pinus longaeva is not strongly supported, since spiral grain is not correlated with asymmetric environments and most trees exhibit <90° rotation through the main stem. The data also do not support the idea that spiral grain makes the tree more resistant to breaking in strong winds. Right-handed spiral grain is predicted by this hypothesis, but most bristlecone pines are either left-handed or exhibit no spiral grain. Bristlecone pines are often uprooted from thin soils by strong winds, but rarely are the main stems broken by this mechanism. Spiral grain in Pinus longaeva growing in California's White Mountains does not appear to be under environmental control. © 2013 Springer-Verlag Berlin Heidelberg. Source

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