University of Utah

About: University of Utah is a education organization based out in Salt Lake City, Utah, United States. It is known for research contribution in the topics: Population & Medicine. The organization has 52894 authors who have published 124076 publications receiving 5265834 citations. The organization is also known as: The U & The University of Utah.

Stomatal conductance and photosynthesis vary linearly with plant hydraulic conductance in ponderosa pine

Abstract: Recent work has shown that stomatal conductance (gs) and assimilation (A) are responsive to changes in the hydraulic conductance of the soil to leaf pathway (KL), but no study has quantitatively described this relationship under controlled conditions where steady-state flow is promoted. Under steady-state conditions, the relationship between gs, water potential (Y ) and KL can be assumed to follow the Ohm’s law analogy for fluid flow. When boundary layer conductance is large relative to gs, the Ohm’s law analogy leads to gs = KL (Ysoil - Yleaf)/D, where D is the vapour pressure deficit. Consequently, if stomata regulate Yleaf and limit A, a reduction in KL will cause gs and A to decline. We evaluated the regulation of Yleaf and A in response to changes in KL in well-watered ponderosa pine seedlings (Pinus ponderosa). To vary KL, we systematically reduced stem hydraulic conductivity (k) using an air injection technique to induce cavitation while simultaneously measuring Yleaf and canopy gas exchange in the laboratory under constant light and D. Short-statured seedlings ( 0·90), indicating that changes in KL may affect plant carbon gain.

Xylem Embolism in Ring-Porous, Diffuse-Porous, and Coniferous Trees of Northern Utah and Interior Alaska

Abstract: Xylem embolism was measured in nine tree species for one or more years. Species were ring-porous (Quercus sp.), diffuse-porous (Alnus, Betula, Populus spp.) or coniferous (Picea, Larix, Abies spp.). Intraspecific (Populus tremuloides) and intrageneric (Betula, Alnus) comparisons were made between sites in northern Utah and interior Alaska. Most embolism, >90% in some dicot species, occurred in winter. Within sites, dicot trees embolized more than conifers. Between sites, Alaskan dicot trees embolized less than their Utah counterparts. Differences were explained by vulnerability to embolism caused by freeze-thaw cycles. Most conifers were entirely resistant, whereas dicot trees were vulner- able. Less embolism in Alaskan dicot trees was associated with fewer freeze-thaw events in Alaska vs. Utah. Vulnerability was positively correlated with conduit volume and hy- draulic conductance per unit xylem area (ks). Tracheids were superior to vessels in avoiding freeze-thaw-induced embolism, and had lower k,. At the other extreme, ring-porous xylem had the highest k, but lost > 90% of hydraulic conductance after a single freeze-thaw event. Vulnerability to water-stress-induced cavitation was not correlated with conduit volume or k,. Dicot species either reversed winter embolism by refilling vessels with positive root pressures during spring (Betula, Alnus spp.), or tolerated it and relied on new xylem pro- duction to restore hydraulic conductance (Quercus sp.). Conifers reversed embolism by refilling tracheids in the absence of positive pressure. Populus species behaved inconsis- tently, showing some reversal one year but none the next. Even without embolism reversal, Populus species had hydraulic conductances per unit leaf area equal to other diffuse-porous species.

Are plutons assembled over millions of years by amalgamation from small magma chambers

Abstract: APRIL/MAY 2004, GSA TODAY ABSTRACT Field and geochronologic evidence indicate that large and broadly homogeneous plutons can accumulate incrementally over millions of years. This contradicts the common assumption that plutons form from large, mobile bodies of magma. Incremental assembly is consistent with seismic results from active volcanic areas which rarely locate masses that contain more than 10% melt. At such a low melt fraction, a material is incapable of bulk flow as a liquid and perhaps should not even be termed magma. Volumes with higher melt fractions may be present in these areas if they are small, and this is consistent with geologic evidence for plutons growing in small increments. The large melt volumes required for eruption of large ignimbrites are rare and ephemeral, and links between these and emplacement of most plutons are open to doubt. We suggest that plutons may commonly form incrementally without ever existing as a large magma body. If so, then many widely accepted magma ascent and emplacement processes (e.g., diapirism and stoping) may be uncommon in nature, and many aspects of the petrochemical evolution of magmatic systems (e.g., in situ crystal fractionation and magma mixing) need to be reconsidered.

Multidimensional transfer functions for interactive volume rendering

Abstract: Most direct volume renderings produced today employ 1D transfer functions which assign color and opacity to the volume based solely on the single scalar quantity which comprises the data set. Though they have not received widespread attention, multi-dimensional transfer functions are a very effective way to extract materials and their boundaries for both scalar and multivariate data. However, identifying good transfer functions is difficult enough in 1D, let alone 2D or 3D. This paper demonstrates an important class of 3D transfer functions for scalar data, and describes the application of multi-dimensional transfer functions to multivariate data. We present a set of direct manipulation widgets that make specifying such transfer functions intuitive and convenient. We also describe how to use modern graphics hardware to both interactively render with multidimensional transfer functions and to provide interactive shadows for volumes. The transfer functions, widgets and hardware combine to form a powerful system for interactive volume exploration.