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Oxidation of atmospheric methane in Northern European soils, comparison with other ecosystems, and uncertainties in the global terrestrial sink (2000)

Smith, K. A. ; Dobbie, K. E. ; Ball, B. C. ; [et al.]

Oxford, UK : Blackwell Science Ltd

Global change biology 6 (2000), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: This paper reports the range and statistical distribution of oxidation rates of atmospheric CH4 in soils found in Northern Europe in an international study, and compares them with published data for various other ecosystems. It reassesses the size, and the uncertainty in, the global terrestrial CH4 sink, and examines the effect of land-use change and other factors on the oxidation rate.Only soils with a very high water table were sources of CH4; all others were sinks. Oxidation rates varied from 1 to nearly 200 μg CH4 m−2 h−1; annual rates for sites measured for ≥1 y were 0.1–9.1 kg CH4 ha−1 y−1, with a log-normal distribution (log-mean ≈ 1.6 kg CH4 ha−1 y−1). Conversion of natural soils to agriculture reduced oxidation rates by two-thirds –- closely similar to results reported for other regions. N inputs also decreased oxidation rates. Full recovery of rates after these disturbances takes 〉 100 y. Soil bulk density, water content and gas diffusivity had major impacts on oxidation rates. Trends were similar to those derived from other published work. Increasing acidity reduced oxidation, partially but not wholly explained by poor diffusion through litter layers which did not themselves contribute to the oxidation. The effect of temperature was small, attributed to substrate limitation and low atmospheric concentration.Analysis of all available data for CH4 oxidation rates in situ showed similar log-normal distributions to those obtained for our results, with generally little difference between different natural ecosystems, or between short-and longer-term studies. The overall global terrestrial sink was estimated at 29 Tg CH4 y−1, close to the current IPCC assessment, but with a much wider uncertainty range (7 to 〉 100 Tg CH4 y−1). Little or no information is available for many major ecosystems; these should receive high priority in future research.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2486.2000.00356.x

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Sugarbeet yield response to competition from Sinapis arvensis or Lolium perenne growing at three different distances from the beet and removed at various times during early growth (2002)

Heisel, T ; Andreasen, C ; Christensen, S

Oxford, UK : Blackwell Science Ltd

Weed research 42 (2002), S. 0

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ISSN: 1365-3180

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: A sugarbeet field experiment was conducted in 1999 and 2000 to measure beet yield where Sinapis arvensis or Lolium perenne were growing in the crop row at 2, 4 or 8 cm from the beet plants. The weeds were removed by cutting once in the growing season in either late May, mid-June or early July. The number of neighbouring beet plants to every target beet plant was recorded. Projected leaf cover of a subset of the data with non-cut weeds was analysed by using image analysis to investigate whether this could be used to predict beet yield loss early in the growing season. Increasing the distance between beet and weed from 2 to 8 cm increased the beet yield significantly by an average of 20%, regardless of weed species. The dry weight of non-cut and re-growing weeds at harvest time decreased when cutting was postponed to the period between mid-June and early July. The number of neighbours described a sigmoidal yield decline of the single beet plants. Results from image analysis showed that approximately 33 g of beet yield was lost in October/November for each per cent relative projected leaf cover of the weeds in May, despite variation in growing conditions. The results are discussed in relation to potentials for robotic in-row weed control.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-3180.2002.00301.x

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3

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Cutting weeds with a CO2 laser (2001)

Heisel, T ; Schou, J ; Christensen, S ; [et al.]

Oxford UK : Blackwell Science Ltd

Weed research 41 (2001), S. 0

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ISSN: 1365-3180

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Stems of Chenopodium album. and Sinapis arvensis. and leaves of Lolium perenne. were cut with a CO2 laser or with a pair of scissors. Treatments were carried out on greenhouse-grown pot plants at three different growth stages and at two heights. Plant dry matter was measured 2 to 5 weeks after treatment. The relationship between dry weight and laser energy was analysed using a non-linear dose–response regression model. The regression parameters differed significantly between the weed species. At all growth stages and heights S. arvensis was more difficult to cut with a CO2 laser than C. album. When stems were cut below the meristems, 0.9 and 2.3 J mm−1 of CO2 laser energy dose was sufficient to reduce by 90% the biomass of C. album and S. arvensis respectively. Regrowth appeared when dicotyledonous plant stems were cut above meristems, indicating that it is important to cut close to the soil surface to obtain a significant effect. When cutting L. perenne plants with 2-true leaves at a height of 2 cm from the soil surface with a laser, the biomass decreased significantly compared with plants cut by scissors, indicating a delay in regrowth. This delay was not observed for the dicotyledonous plants nor for the other growth stages of L. perenne.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-3180.2001.00212.x

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4

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Using laser to measure stem thickness and cut weed stems (2002)

Heisel, T ; Schou, J ; Andreasen, C ; [et al.]

Oxford, UK : Blackwell Science Ltd

Weed research 42 (2002), S. 0

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ISSN: 1365-3180

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary Stem thickness of the weed Solanum nigrum and the crop sugarbeet was determined with a He–Ne laser using a novel non-destructive technique measuring stem shadow. Thereafter, the stems were cut close to the soil surface with a CO2 laser. Treatments were carried out on pot plants, grown in the greenhouse, at two different growth stages, and plant dry matter was measured 2–5 weeks after treatment. The relationship between plant dry weight and laser energy was analysed using two different non-linear dose–response regression models; one model included stem thickness as a variable, the other did not. A binary model was also tested. The non-linear model incorporating stem thickness described the data best, indicating that it would be possible to optimize laser cutting by measuring stem thickness before cutting. The general tendency was that more energy was needed the thicker the stem. Energy uses on a field scale are discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-3180.2002.00282.x

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5

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Real-time weed detection, decision making and patch spraying in maize, sugarbeet, winter wheat and winter barley (2003)

Gerhards, R ; Christensen, S

Oxford, UK : Blackwell Science Ltd

Weed research 43 (2003), S. 0

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ISSN: 1365-3180

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Information on temporal and spatial variation in weed seedling populations within agricultural fields is very important for weed population assessment and management. Most of all, it allows a potential reduction in herbicide use, when post-emergence herbicides are only applied to field sections with weed infestation levels higher than the economic weed threshold; a review of such work is provided. This paper presents a system for site-specific weed control in sugarbeet (Beta vulgaris L.), maize (Zea mays L.), winter wheat (Triticum aestivum L.) and winter barley (Hordeum vulgare L.), including online weed detection using digital image analysis, computer-based decision making and global positioning systems (GPS)-controlled patch spraying. In a 4-year study, herbicide use with this map-based approach was reduced in winter cereals by 60% for herbicides against broad-leaved weeds and 90% for grass weed herbicides. In sugarbeet and maize, average savings for grass weed herbicides were 78% in maize and 36% in sugarbeet. For herbicides against broad-leaved weeds, 11% were saved in maize and 41% in sugarbeet.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-3180.2003.00349.x

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6

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A decision algorithm for patch spraying (2003)

Christensen, S ; Heisel, T ; Walter, A M ; [et al.]

Oxford, UK : Blackwell Science Ltd

Weed research 43 (2003), S. 0

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ISSN: 1365-3180

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: It has been established that weeds are spatially aggregated with a spatially varying composition of weed species within agricultural fields. Site-specific spraying therefore requires a decision method that includes the spatial variation of the weed composition and density. A computerized decision method that estimates an economic optimal herbicide dose according to site-specific weed composition and density is presented in this paper. The method was termed a ‘decision algorithm for patch spraying’ (DAPS) and was evaluated in a 5-year experiment, in Denmark. DAPS consists of a competition model, a herbicide dose–response model and an algorithm that estimates the economically optimal doses. The experiment was designed to compare herbicide treatments with DAPS recommendations and the Danish decision support system PC-Plant Protection. The results did not show any significant grain yield difference between DAPS and PC-Plant Protection; however, the recommended herbicide doses were significantly lower when using DAPS than PC-Plant Protection in all years. The main difference between the two decision models is that DAPS integrates crop–weed competition and estimates the net return as a continuous function of herbicide dose. The hypothesis tested is that the benefit of using lower herbicide doses recommended by DAPS would disappear after a few years because weed density will increase and thus require higher doses. However, the results of weed counting every year did not confirm this hypothesis.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-3180.2003.00344.x

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Evaluation of the utility of xanthophyll cycle pigment dynamics for assessing upper ocean mixing processes at Station ALOHA (2014)

Bidigare, R. R., Buttler, F. R., Christensen, S. J., Barone, B., Karl, D. M., Wilson, S. T.

Oxford University Press

In: Journal of Plankton Research

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Publication Date: 2014-11-11

Description: We had the opportunity to evaluate the utility of the chromophyte xanthophyll cycle pigments (XCP), diadinoxanthin (DDX) and diatoxanthin (DTX), for assessing upper ocean mixing processes at Station ALOHA (22.75°N, 158°W) during August–September 2012. De-epoxidation state (DES, [DTX]/[DDX + DTX]) kinetic rate experiments were performed that quantified the conversion of DDX to DTX in the light. DES values ranged from 0.13 to 0.51 (weight:weight), and yielded a first-order rate constant of 0.16 ± 0.02 min –1 . In addition, a time-series of chromophyte pigments was collected from the sea-surface in order to quantify the time-dependent rate of change in the ratio of XCP to chlorophyll a (XCP/CHLA). In situ XCP/CHLA values were measured by rapid collection of cells in the mixed layer using a diaphragm pumping system and the xanthophyll cycle activity inhibitor dithiothreitol. Turbulent transfer velocity (TTV) was estimated as the quotient of the XCP/CHLA photoadaptation rate and the XCP/CHLA gradient in the mixed layer. TTVs ranged from 0.3 to 0.5 cm s –1 , and agreed to within a factor of ~2 of the Lagrangian float-derived estimate of vertical mixing at a comparable friction velocity. Coincident measurements of dissolved gases suggest that XCP dynamics may be useful for the interpretation of trace gases species distributions, such as hydrogen and carbon monoxide, in the upper ocean.

Print ISSN: 0142-7873

Electronic ISSN: 1464-3774

Topics: Biology

Published by Oxford University Press

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Endonuclease domain of non-LTR retrotransposons: loss-of-function mutants and modeling of the R2Bm endonuclease (2016)

Govindaraju, A., Cortez, J. D., Reveal, B., Christensen, S. M.

Oxford University Press

In: Nucleic Acids Research

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Publication Date: 2016-04-21

Description: Non-LTR retrotransposons are an important class of mobile elements that insert into host DNA by target-primed reverse transcription (TPRT). Non-LTR retrotransposons must bind to their mRNA, recognize and cleave their target DNA, and perform TPRT at the site of DNA cleavage. As DNA binding and cleavage are such central parts of the integration reaction, a better understanding of the endonuclease encoded by non-LTR retrotransposons is needed. This paper explores the R2 endonuclease domain from Bombyx mori using in vitro studies and in silico modeling. Mutations in conserved sequences located across the putative PD-(D/E)XK endonuclease domain reduced DNA cleavage, DNA binding and TPRT. A mutation at the beginning of the first α-helix of the modeled endonuclease obliterated DNA cleavage and greatly reduced DNA binding. It also reduced TPRT when tested on pre-cleaved DNA substrates. The catalytic K was located to a non-canonical position within the second α-helix. A mutation located after the fourth β-strand reduced DNA binding and cleavage. The motifs that showed impaired activity form an extensive basic region. The R2 biochemical and structural data are compared and contrasted with that of two other well characterized PD-(D/E)XK endonucleases, restriction endonucleases and archaeal Holliday junction resolvases.

Print ISSN: 0305-1048

Electronic ISSN: 1362-4962

Topics: Biology