| 1. |
- Mattsson, Marie, et al.
(författare)
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Temporal variability in bioassays of the stomatal ammonia compensation point in relation to plant and soil nitrogen parameters in intensively managed grassland
- 2009
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Ingår i: Biogeosciences. - Kaltenburg-Lindau : Copernicus Publications (on behalf of the European Geosciences Union). - 1726-4170 .- 1726-4189. ; 6:2, s. 171-179
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Tidskriftsartikel (refereegranskat)abstract
- The exchange of ammonia between crop canopies and the atmosphere depends on a range of plant parameters and climatic conditions. However, little is known about effects of management factors. We have here investigated the stomatal ammonia compensation point in response to cutting and fertilization of a grass sward dominated by Lolium perenne. Tall grass had a very low NH3 compensation point (around 1 nmol mol−1), reflecting the fact that leaf nitrogen (N) concentration was very low. During re-growth after cutting, leaf tissue concentrations of NO3−, NH4+, soluble N and total N increased along with apoplastic NH4+ concentrations. In contrast, apoplastic pH decreased resulting in largely unaltered NH3 compensation points. Nitrogen fertilization one week after cutting caused the apoplastic NH4+ concentration of the newly emerging leaves to increase dramatically. The NH3 compensation point peaked between 15 and 25 nmol mol−1 the day after the fertiliser was applied and thereafter decreased over the following 10 days until reaching the same level as before fertilisation. Ammonium concentrations in leaf apoplast, bulk tissue and litter were positively correlated (P=0.001) throughout the experimental period. Bulk tissue NH4+ concentrations, total plant N and soil NH4+ concentrations also showed a positive correlation. A very high potential for NH3 emission was shown by the plant litter.
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| 2. |
- Sutton, M. A., et al.
(författare)
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Dynamics of ammonia exchange with cut grassland : Strategy and implementation of the GRAMINAE Integrated Experiment
- 2009
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Ingår i: Biogeosciences. - : Copernicus Publications (on behalf of the European Geosciences Union). - 1726-4170 .- 1726-4189. ; 6:3, s. 309-331
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Tidskriftsartikel (refereegranskat)abstract
- A major international experiment on ammonia (NH3) biosphere-atmosphere exchange was conducted over intensively managed grassland at Braunschweig, Germany. The experimental strategy was developed to allow an integrated analysis of different features of NH3 exchange including: a) quantification of nearby emissions and advection effects, b) estimation of net NH3 fluxes with the canopy by a range of micrometeorological measurements, c) analysis of the sources and sinks of NH3 within the plant canopy, including soils and bioassay measurements, d) comparison of the effects of grassland management options on NH3 fluxes and e) assessment of the interactions of NH3 fluxes with aerosol exchange processes. Additional technical objectives included the inter-comparison of different estimates of sensible and latent heat fluxes, as well as continuous-gradient and Relaxed Eddy Accumulation (REA) systems for NH3 fluxes. The prior analysis established the spatial and temporal design of the experiment, allowing significant synergy between these objectives. The measurements were made at 7 measurement locations, thereby quantifying horizontal and vertical profiles, and covered three phases: a) tall grass canopy prior to cutting (7 days), b) short grass after cutting (7 days) and c) re-growing sward following fertilization with ammonium nitrate (10 days). The sequential management treatments allowed comparison of sources-sinks, advection and aerosol interactions under a wide range of NH3 fluxes. This paper describes the experimental strategy and reports the grassland management history, soils, environmental conditions and air chemistry during the experiment, finally summarizing how the results are coordinated in the accompanying series of papers.
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| 3. |
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| 4. |
- Coates, Melissa M., et al.
(författare)
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The spectral sensitivity of the lens eyes of a box jellyfish, Tripedalia cystophora (Conant)
- 2006
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 209:19, s. 3758-3765
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Tidskriftsartikel (refereegranskat)abstract
- Box jellyfish, or cubomedusae (class Cubozoa), are unique among the Cnidaria in possessing lens eyes similar in morphology to those of vertebrates and cephalopods. Although these eyes were described over 100 years ago, there has been no work done on their electrophysiological responses to light. We used an electroretinogram ( ERG) technique to measure spectral sensitivity of the lens eyes of the Caribbean species Tripedalia cystophora. The cubomedusae have two kinds of lens eyes, the lower and upper lens eyes. We found that both lens eye types have similar spectral sensitivities, which likely result from the presence of a single receptor type containing a single opsin. The peak sensitivity is to blue-green light. Visual pigment template fits indicate a vitamin A-1 based opsin with peak sensitivity near 500 nm for both eye types.
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| 5. |
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| 6. |
- Kelber, Almut, et al.
(författare)
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Light intensity limits the foraging activity in nocturnal and crepuscular bees.
- 2006
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Ingår i: Behavioral Ecology. - : Oxford University Press (OUP). - 1045-2249 .- 1465-7279. ; 17:1, s. 63-72
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Tidskriftsartikel (refereegranskat)abstract
- A crepuscular or nocturnal lifestyle has evolved in bees several times independently, probably to explore rewarding pollen sources without competition and to minimize predation and nest parasites. Despite these obvious advantages, only few bee species are nocturnal. Here we show that the sensitivity of the bee apposition eye is a major factor limiting the ability to forage in dim light. We present data on eye size, foraging times, and light levels for Megalopta genalis (Augochlorini, Halictidae) in Panama, and Lasioglossum (Sphecodogastra) sp. (Halictini, Halictidae) in Utah, USA. M. genalis females forage exclusively during twilight, but as a result of dim light levels in the rain forest, they are adapted to extremely low intensities. The likely factor limiting their foraging activity is finding their nest entrance on return from a foraging trip. The lowest light intensity at which they can do this, both in the morning and the evening, is 0.0001 cd m–2. Therefore, they leave the nest at dimmer light levels in the morning than in the evening. Lasioglossum (Sphecodogastra) foraging is limited by light intensity in the evening, but probably by temperature in the morning in the temperate climate of Utah. We propose that the evolution of nocturnality in bees was favored by the large variance in the size of females.
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| 7. |
- Ladenheim, D, et al.
(författare)
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Potential health risks of complementary alternative medicines in HIV patients.
- 2008
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Ingår i: HIV Medicine. - : Wiley. - 1464-2662 .- 1468-1293. ; 9:8, s. 653-9
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Tidskriftsartikel (refereegranskat)abstract
- There are potentially significant health risks posed by the concomitant use of CAMs in patients taking ARV therapy. Medical practitioners need to be able to identify CAM use in HIV-positive patients and recognize potential health risks. Patients should be encouraged to disclose CAM use to their clinicians and other healthcare professionals.
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| 8. |
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