Plant physiology and competition in a Mojave Desert riparian ecosystem: Proximate solutions to ultimate questions

The distribution and abundance patterns of species are of primary interest in ecology, and the interactions between an organism and its abiotic and biotic environment provide a basis for a better understanding of the mechanisms by which distribution and abundance patterns are governed. Physiological ecology provides an ideal platform for integrating the effects of both biotic and abiotic influences upon species performance, thus conferring a process-oriented insight into ecological patterns. This dissertation considers the physiological characteristics that may be related to Mojave Desert floodplain domination by Tamarix ramosissima, an exotic invasive riparian plant; Four woody riparian species---Tamarix ramosissima, Salix exigua, Prosopis pubescens and Pluchea sericea---were studied along the Virgin River in southern Nevada. Through field observation and manipulative experiments in the field and glasshouse, the relationships between plant water relations, competition, facilitation, and abiotic stress and environment were investigated at both proximate (i.e., process) and ultimate (i.e., pattern) levels; Tamarix dominated the Virgin River floodplain at a previously burned site (Half-Way Wash) within 50 years following fire. Physiological mechanisms for the success of Tamarix include its water use (on both leaf- and whole branch-levels), starch storage, early investment in additional ramets, and slow radial growth. Pluchea, a native, summer-active halophyte, dominates early seres through tolerance to extreme abiotic stresses, as indicated by the general unresponsiveness of physiological characteristics to the imposition of stress. Salix, which is also native, demonstrated radial growth patterns consistent with sensitivity to drought stress, demonstrated sensitivity to heat and drought stresses in many key physiological traits, and was relatively insensitive to the presence of other species; Studies of plant responses to stress yield a great deal of information concerning the relationships, both inhibitive and facilitative, between species. Furthermore, the relationships between abiotic stress, inhibition, facilitation, and chance environmental events (e.g., aseasonal flooding) contributes to further understanding the short- and long-term mechanisms involved in the successful invasion of the Virgin River floodplain by Tamarix ramosissima

Crafting Audience Encounters

This paper documents a research project demonstrating the potential to engage audiences, promote practitioners and add value to craft work, through the use of relatively low-cost and accessible digital communications technologies in the context of a public exhibition. The project involves: filming, photographing and editing together audio-visual material; the creation of a website from which to access films and leave feedback; and a number of options for viewing web-based film footage including Quick Response (QR) codes and smartphone technology, iPads and a desktop computer to deliver internet-hosted content. ‘In the Frame’ is an interdisciplinary research project involving a team of researchers, film-makers and technologists, and Level 3 Contemporary Craft students at Falmouth University. It is a pilot study within Supercrafted, * a two year research project at Falmouth University, exploring and developing online digital interaction of benefit to craft practitioners and stakeholders in the craft value chain, including audiences, customers, makers and suppliers

Bowen ratio estimates of evapotranspiration for stands on the Virgin River in Southern Nevada

A Bowen ratio energy balance was conducted over a Tamarix ramosissima (saltcedar) stand growing in a riparian corridor along the Virgin River in southern Nevada. Measurements in two separate years were compared and contrasted on the basis of changes in growing conditions. In 1994, a drought year, record high temperatures, dry winds, and a falling water table caused partial wilt of outer smaller twigs in the canopy of many trees in the stand around the Bowen tower. Subsequently, evapotranspiration (ET) estimates declined dramatically over a 60‐day period (11 mm d−1 tod−1). In 1995, the Virgin River at the Bowen tower area changed its course, hydrologically isolating the Tamarix stand in the vicinity of the tower. In 1996, a 25% canopy loss was visually estimated for the Tamarix growing in the area of the tower. Higher soil temperatures relative to air temperatures were recorded in 1996 in response to this loss in canopy. With a more open canopy, thermally induced turbulence was observed in 1996. On day 160 of 1996, a 28°C rise over a 9‐hour period was correlated with increased wind speeds of greater than 4 m s−1. Subsequently, higher ET estimates were made in 1996 compared to 1994 (145 cm versus 75 cm). However, the energy balance was dominated by advection in 1996, with latent energy flux exceeding net radiation 65% of the measurement days compared to only 11% in 1994. We believe this advection was on a scale of the floodplain (hundreds of meters) as opposed to regional advection, since the majority of wind (90%) was in a N–S direction along the course of the river, and that a more open canopy allowed the horizontal transfer of energy into the Tamarix stand at the Bowen tower. Our results suggest that Tamarix has the potential to be both a low water user and a high water user, depending on moisture availability, canopy development, and atmospheric demand, and that advection can dominate energy balances and ET in aridland riparian zones such as the Virgin River

Global change-type drought-induced tree mortality: Vapor pressure deficit is more important than temperature per se in causing decline in tree health

Drought-induced tree mortality is occurring across all forested continents and is expected to increase worldwide during the coming century. Regional-scale forest die-off influences terrestrial albedo, carbon and water budgets, and landsurface energy partitioning. Although increased temperatures during drought are widely identified as a critical contributor to exacerbated tree mortality associated with "global-change-type drought", corresponding changes in vapor pressure deficit (D) have rarely been considered explicitly and have not been disaggregated from that of temperature per se. Here, we apply a detailed mechanistic soil-plant-atmosphere model to examine the impacts of drought, increased air temperature (+2°C or +5°C), and increased vapor pressure deficit (D; +1 kPa or +2.5 kPa), singly and in combination, on net primary productivity (NPP) and transpiration and forest responses, especially soil moisture content, leaf water potential, and stomatal conductance. We show that increased D exerts a larger detrimental effect on transpiration and NPP, than increased temperaturealone, with or without the imposition of a 3-month drought. Combined with drought, the effect of increased D on NPP was substantially larger than that of drought plus increased temperature. Thus, the number of days when NPP was zero across the 2-year simulation was 13 or 14 days in the control and increased temperature scenarios, but increased to approximately 200 days when D was increased. Drought alone increased the number of days of zero NPP to 88, but drought plus increased temperature did not increase the number of days. In contrast, drought and increased D resulted in the number of days when NPP = 0 increasing to 235 (+1 kPa) or 304 days (+2.5 kPa). We conclude that correct identification of the causes of global change-type mortality events requires explicit consideration of the influence of D as well as its interaction with drought and temperature. © 2013 The Authors

Modelling Seasonal and Inter-annual Variations in Carbon and Water Fluxes in an Arid-Zone Acacia Savanna Woodland, 1981–2012

© 2016, Springer Science+Business Media New York. Changes in climatic characteristics such as seasonal and inter-annual variability may affect ecosystem structure and function, hence alter carbon and water budgets of ecosystems. Studies of modelling combined with field experiments can provide essential information to investigate interactions between carbon and water cycles and climate. Here we present a first attempt to investigate the long-term climate controls on seasonal patterns and inter-annual variations in water and carbon exchanges in an arid-zone savanna-woodland ecosystem using a detailed mechanistic soil–plant–atmosphere model (SPA), driven by leaf area index (LAI) simulated by an ecohydrological model (WAVES) and observed climate data during 1981–2012. The SPA was tested against almost 3 years of eddy covariance flux measurements in terms of gross primary productivity (GPP) and evapotranspiration (ET). The model was able to explain 80 and 71% of the variability of observed daily GPP and ET, respectively. Long-term simulations showed that carbon accumulation rates and ET ranged from 20.6 g C m−2 mon−1 in the late dry season to 45.8 g C m−2 mon−1 in the late wet season, respectively, primarily driven by seasonal variations in LAI and soil moisture. Large climate variations resulted in large seasonal variation in ecosystem water-use efficiency (eWUE). Simulated annual GPP varied between 146.4 and 604.7 g C m−2 y−1. Variations in annual ET coincided with that of GPP, ranging from 110.2 to 625.8 mm y−1. Annual variations in GPP and ET were driven by the annual variations in precipitation and vapour pressure deficit (VPD) but not temperature. The linear coupling of simulated annual GPP and ET resulted in eWUE having relatively small year-to-year variation

Human milk bile-salt stimulated lipase Sequence similarity with rat lysophospholipase and homology with the active site region of cholinesterases

AbstractTo determine the active site residue, human milk bile-salt stimulated lipase (BSSL) was labelled with [3H]diisopropyl fluorophosphate (DFP). Partial sequence analysis or cyanogen bromide fragments (a total of 146 residues from 6 peptides) revealed 84% sequence identity with a putative rat lysophospholipase. Sequence analysis of a [3H]DFP-labelled peptide indicated that the active site serine was contained in the sequence Gly-Glu-Scr-Ala-Gly. In addition to similarity with rat lysophospholipase, this sequence showed homology with regions of human butyrylcholinesterase and electric ray acetylcholinesterase (68% identity). It is concluded that these proteins are members of a new supergene family