Time filter

Source Type

CA, United States

Pieruschka R.,Julich Research Center | Pieruschka R.,Carnegie Institution of Washington | Albrecht H.,Julich Research Center | Muller O.,Julich Research Center | And 5 more authors.
Tree Physiology | Year: 2014

The photosynthesis of various species or even a single plant varies dramatically in time and space, creating great spatial heterogeneity within a plant canopy. Continuous and spatially explicit monitoring is, therefore, required to assess the dynamic response of plant photosynthesis to the changing environment. This is a very challenging task when using the existing portable field instrumentation. This paper reports on the application of a technique, laser-induced fluorescence transient (LIFT), developed for ground remote measurement of photosynthetic efficiency at a distance of up to 50m. The LIFT technique was used to monitor the seasonal dynamics of selected leaf groups within inaccessible canopies of deciduous and evergreen tree species. Electron transport rates computed from LIFT measurements varied over the growth period between the different species studied. The LIFT canopy data and light-use efficiency measured under field conditions correlated reasonably well with the single-leaf pulse amplitude-modulated measurements of broadleaf species, but differed significantly in the case of conifer tree species. The LIFT method has proven to be applicable for a remote sensing assessment of photosynthetic parameters on a diurnal and seasonal scale; further investigation is, however, needed to evaluate the influence of complex heterogeneous canopy structures on LIFT-measured chlorophyll fluorescence parameters. © 2014 The Author.

Lin B.B.,CSIRO | Philpott S.M.,156 High Street | Jha S.,University of Texas at Austin
Basic and Applied Ecology | Year: 2015

Urban landscapes are spatially constrained, and vegetative land uses that provide beneficial ecosystem services are difficult to maintain. Urban agricultural (UA) systems appear in many forms - from community farms and rooftop gardens to edible landscaping and urban orchards - and can be productive features of cities and provide important environmental services. As highly managed plant communities, UA can exhibit high levels of biodiversity, often exceeding that of other green space areas within the city. Additionally, it is likely that variation in vegetation cover, diversity, and structure influence not only the biodiversity in UA, but also the quantity and quality of ecosystem services supported by such systems. The biodiversity and ecosystem services (B&ES) of UA can have potentially large societal and environmental benefits for cities, such as enhanced food security, air quality, and water regulation. Yet few studies have synthesized knowledge regarding UA vegetation management impacts on the quantity, quality, and stability of B&ES provided. This article presents the first survey of the existing research on the characteristics of UA management and their potential to support ecosystem service delivery. Specifically, we examine: (1) biodiversity patterns in UA, (2) ecosystem services provided by UA, and (3) the challenges of promoting UA systems that support B&ES. Overall, our review reveals that varied vegetative structure, increased native plant diversity, and reduction of urban impervious surface are key features of UA systems that contribute significantly to urban biodiversity and provide important ecosystem services such as pollination, pest control, and climate resilience. We conclude with a discussion of critical gaps in current research and strategies to better understand and support UA and ecosystem services. © 2015 Gesellschaft für Ökologie.

Alaeddini A.,University of Washington | Erzberger H.,156 High Street | Dunbar W.,156 High Street
AIAA Guidance, Navigation, and Control Conference 2011 | Year: 2011

In this paper, the problem of designing conflict-free maneuvers for planar multipleaircraft encounters in en-route flight is studied. An algorithm for automated and distributed conflict resolution for two or more aircraft is developed. The algorithm is intended for use in the future air traffic system, which may be implemented in a distributed way that permits free flight. The proposed algorithm searches several different scenarios for conflict resolutions between multiple aircraft while preventing secondary conflicts where possible. The multiple aircraft resolution algorithm generalizes the ground-based centrally coordinated pair-wise conflict resolution algorithm that was developed previously at NASA Ames Research Center. The proposed algorithm can in principle resolve a conflict involving any number of aircraft. Simulations are done for up to 5 times the current air traffic density. In these simulations conflicts between 2, 3, 4 and 5 aircraft are observed and resolved by the algorithm. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Reyes C.,156 High Street | Murphy J.N.,156 High Street | Saltikov C.W.,156 High Street
Environmental Microbiology | Year: 2010

Arsenate respiration and Fe(III) reduction are important processes that influence the fate and transport of arsenic in the environment. The goal of this study was to investigate the impact of arsenate on Fe(III) reduction using arsenate and Fe(III) reduction deficient mutants of Shewanella sp. strain ANA-3. Ferrihydrite reduction in the absence of arsenate was similar for an arsenate reduction mutant (arrA and arsC deletion strain of ANA-3) compared with wild-type ANA-3. However, the presence of arsenate adsorbed onto ferrihydrite impeded Fe(III) reduction for the arsenate reduction mutant but not in the wild-type. In an Fe(III) reduction mutant (mtrDEF, omcA, mtrCAB null mutant of ANA-3), arsenate was reduced similarly to wildtype ANA-3 indicating the Fe(III) reduction pathway is not required for ferrihydrite-associated arsenate reduction. Expression analysis of the mtr/omc gene cluster of ANA-3 showed that omcA and mtrCAB were expressed under soluble Fe(III), ferrihydrite and arsenate growth conditions and not in aerobically grown cells. Expression of arrA was greater with ferrihydrite pre-adsorbed with arsenate relative to ferrihydrite only. Lastly, arrA and mtrA were simultaneously induced in cells shifted to anaerobic conditions and exposed to soluble Fe(III) and arsenate. These observations suggest that, unlike Fe(III), arsenate can co-induce operons (arr and mtr) implicated in arsenic mobilization. © 2010 Society for Applied Microbiology and Blackwell Publishing Ltd.

Discover hidden collaborations