Structural field margin characteristics affect the functional traits of herbaceous vegetation

Background: Field margins are ecologically important to an agroecosystem as they are a source of biodiversity. They can be composed of a diverse flora which may offer resources to a wide range of insects and birds. The vegetation composition of field margins is determined by soil characteristics, management, and landscape structures. However, little is known about the effect of individual field margin components such as ditches, grass strips, shrubs and trees, and the overall margin's complexity, on the vegetation composition and its functional effect and response traits. Methods: This paper reports on the effects of field margin component typology (ditches, grass strips, shrubs, trees, and vehicle tracks) and complexity (the number of components), on the herbaceous vegetation of field margins. Forty field margins were sampled in 2016 in a 200 ha. organic mixed arable livestock farm. Results: The factor which was identified as having the most effect on vegetation composition was adjacent land-use type, which reflected the margins' management regime. However, field margin components were found to affect vegetation response and effect traits. Tree components had less grassweeds than vehicle tracks while more complex field margins also had less grassweeds than simple field margins near cropped fields, most likely due to the lower availability in light and less disturbance from vehicles. Simple grassy margins produced a high proportion of hymenoptera flowers. Discussion: These results highlight the importance of field margin components in maintaining a high diversity of vegetation typologies differing in effect traits that are relevant for the provisioning of ecosystem services, such as supporting pollen and nectar requirements of beneficial insects, as well as their importance in determining the presence of weed species that could potentially invade the cropped fields

The influence of field margin characteristics on syrphid abundance

Field margins have an important ecological role in agroecosystems including hosting beneficial insect such as syrphids. However, little is known of syrphid preferences for different types of field margins. Syrphids were sampled in field margins in an organic agroecosystem to test the hypothesis that syrphid abundance in field margins depends not only on the floral resource abundance but also on field margin component type, field margin complexity, and adjacent land-use type. Floral resource abundance had the greatest influence on the number of syrphids surveyed. Field margin characteristics were deemed to effect syrphid abundance both independently of their effect on floral resources and by altering floral resource abundance. Syrphids were more abundant in field margins adjacent to cropped fields than those adjacent to grazed fields or roads. More syrphids were found in ditch components than in tree or grass strip components. The influence of floral resources on syrphid abundance varied depending on their botanical families, although no significant differences were observed for the effect of botanical family floral resource index on syrphid abundance. These findings demonstrate that field margin characteristics play an important role in facilitating plant–syrphid interactions and offer an insight in agroecosystem management for the promotion of beneficial insects. The influence of field margin characteristics on other beneficial insect groups should also be investigated

Minimal Necessary Weed Control Does Not Increase Weed-Mediated Biological Pest Control in Romaine Lettuce (Lactuca sativa L., var. Romana)

Lettuce is one of the most consumed leafy greens. Depending on the variety, it is ready for harvesting 40–80 days after sowing, and therefore several growth cycles can be concluded within a growing season. Due to its high market standards, lettuce may require intensive management. This study implemented a critical period of weed interference (CPWI) trial to understand at which moment of the cropping cycle weeds can be tolerated without impacting crop yield to decrease the time needed for weeding and assess the potential support weeds can give to biological pest control in lettuce. Treatments represented two gradients of weed intensity: (1) increasingly weed-free, and (2) increasingly weedy. Dose–response curves were produced to find the CPWI based on lettuce relative yield. RLQ analysis was used to explore the relationships between weeding regime and weed functional traits for biological pest control. Yield was above the 5% acceptable yield loss threshold in all plots kept weed-free for 20 days or more, indicating a necessary weed-free period of 20 days from transplanting. However, the support of beneficial insects was not guaranteed at the end of the necessary weed-free period. We suggest that it is possible to limit intense weed management to the beginning of the growing season, reducing the cost of plastic mulches and increasing on-farm biodiversity, but field margins could be better suited to deliver conservation biological control in short-term crops where this service is of primary interest

On some differential-geometric aspects of the Torelli map

In this note we survey recent results on the extrinsic geometry of the Jacobian locus inside $\mathsf{A}_g$. We describe the second fundamental form of the Torelli map as a multiplication map, recall the relation between totally geodesic subvarieties and Hodge loci and survey various results related to totally geodesic subvarieties and the Jacobian locus.Comment: To appear on Boll. UMI, special volume in memory of Paolo de Bartolomei

Efficient Hardware Acceleration of Robust Volumetric Light Transport Simulation

Efficiently simulating the full range of light effects in arbitrary input scenes that contain participating media is a difficult task. Unified points, beams and paths (UPBP) is an algorithm capable of capturing a wide range of media effects, by combining bidirectional path tracing (BPT) and photon density estimation (PDE) with multiple importance sampling (MIS). A computationally expensive task of UPBP is the MIS weight computation, performed each time a light path is formed. We derive an efficient algorithm to compute the MIS weights for UPBP, which improves over previous work by eliminating the need to iterate over the path vertices. We achieve this by maintaining recursive quantities as subpaths are generated, from which the subpath weights can be computed. In this way, the full path weight can be computed by only using the data cached at the two vertices at the ends of the subpaths. Furthermore, a costly part of PDE is the search for nearby photon points and beams. Previous work has shown that a spatial data structure for photon mapping can be implemented using the hardware-accelerated bounding volume hierarchy of NVIDIA's RTX GPUs. We show that the same technique can be applied to different types of volumetric PDE and compare the performance of these data structures with the state of the art. Finally, using our new algorithm and data structures we fully implement UPBP on the GPU which we, to the best of our knowledge, are the first to do so

Dealing with Post-Kogeko

Inter-organizational systems are only used to some extend within the domain of transportation and logistics. Distributed agent technologies show a large potential to build a new generation of inter-organizational systems that overcome the hurdles earlier technologies were not able to take [2, 4]. In this paper we present an ongoing research project in which we try to establish a WebServices based agent platform to be used by a logistics service provider (LSP) in an inter-organizational context – which will connect the LSP’s internal processes, with processes that span organizational boundaries and therefore is likely to result in interesting process improvements; cost savings and improved competitive advantage are expected outcomes. This paper describes the process we followed, and gives a glimp of our preliminary findings. We conclude the paper with a short discussion and our research agenda

The regulation of the structure and function of flavin (vitamin B2) on binding to apoflavoproteins and its biological implications

1H, 13C, 15N and 31P NMR was applied to a study of free and protein-bound flavins in order to obtain a better insight into the mechanism by which the function of the flavin coenzyme is "tuned" upon binding to apoflavoproteins. A thorough 13C and 15N investigation of free flavins provided a detailed view on the effects of sterical hindrance and polarization on the structure of oxidized and reduced flavins. Moreover, this study resulted in a semi-empirical basis for the interpretation of NMR data obtained on protein-bound flavins. Remarkable results of the study of free flavins are the fact, that oxidized isoalloxazine is not fully planar in an apolar medium, and that fully reduced isoalloxazine is more planar than believed up till now. Unsubstituted reduced isoalloxazine in water has an almost fully sp 2hybridized N(10) and an N(5) atom which is approximately 70% sp 2hybridized. Upon modification the hybridization of N(5) and N(10) can be modulated rather independently due to steric hindrance. The so-called "butterfly" motion has a low activation barrier, which is probably an important feature for the mentioned tuning mechanism.Flavodoxin from Megasphaeraelsdenii is the protein which is most extensively studied in this thesis. By a 13C relaxation study it was shown that the isoalloxazine ring is strongly immobilized upon binding to apoflavodoxin. Also the phosphate group of FMN is strongly immobilized in the interior of the protein. Moreover, the phosphate group is dianionic in the complex, regardless of the redox state of bound FMN. Based on the NMR data, it was shown that the redox potential for the transition semiquinone/hydroquinone is mainly governed by charge interactions. For the first time a quantification of the redox potential modification by the apoprotein could be established, thereby showing that, contrary to literature reports, the redox potential modulation is not governed by steric effects exerted on the isoalloxazine moiety. Both by 31P NMR and 1H NMR it was shown that M.elsdenii flavodoxin acts as a one-electron transferring protein shuttling between the semiquinone and hydroquinone state, because the oxidized state is ruled out as a biologically relevant redox state in this protein due to the introduction of a high activation barrier between the oxidized and semiquinone state. Moreover, the electron transfer mechanism is of an outer sphere type. Based on the NMR data some arguments are presented that a specific complex formation between M.elsdenii flavodoxin and the electron donor or acceptor is not needed for an effective electron transfer. An important part of the active center of M.elsdenii flavodoxin was elucidated using time resolved photochemically induced dynamic nuclear polarization (CIDNP) and modern two-dimensional NMR techniques. The use of the paramagnetic semiquinone state in combination with 2D NMR techniques allowed the generation of NMR spectra of only the active center. Complete assignments were given in both the oxidized and the hydroquinone state for Trp-91, Ala-56 and Tyr-89, which are all very close to the isoalloxazine ring. It was shown that the relative position of Trp-91 with respect to the prosthetic group is slightly different in the two redox states. The active center of flavodoxin from M.elsdenii and Clostridium MP appear to be similar. The only small difference between results of the crystallographic study on Clostridium MP flavodoxin and 1H NMR results on M.elsdenii flavodoxin was observed for the relative position of Ala-56 and Tyr-89.A detailed 13C and 15N NMR study was performed on the complex of riboflavin and Riboflavin Binding Protein from the egg yolk and egg white. Subtle information on hydrogen bonding, conformation of the isoalloxazine ring and solvent accessibility were obtained in oxidized and reduced state. As far as the results could be compared with reported binding studies of riboflavin analogues, the results appear to be in excellent agreement. The pyrimidine ring is exposed to solvent, except for 0(4α) in both redox states. N(10) is forced into the molecular plane, which in turn probably causes N(1) to be somewhat out of the plane. The NMR results are consistent with a partial opening of the protein at pH 6 and a more stable conformation at pH 9. Based on the NMR results a possible function for the complex in the embryonic development is suggested.As an example of the class of dehydrogenases, lipoamide dehydrogenase from Azotobacter vinelandii was studied by 13C NMR. In the oxidized state hydrogen bonds exist to 0(2α) and 0(4α), but the polarization of the isoalloxazine ring probably does not extend to the N(10) atom. The 4 electron reduced protein (both the essential disulfide and the flavin are reduced) contains an essentially planar N(10) atom, and again hydrogen bonds to 0(2α) and 0(4α). The 2 electron reduced protein (EH 2 ) appeared to be particularly interesting. It consists of an equal mixture of protein in which the disulfide is reduced and the flavin oxidized, and protein in which the disulfide is oxidized and the flavin reduced. The results allowed a detailed description of the electronic structure of the two-electron reduced protein. From the NMR results it is concluded that the redox potential of both centers is roughly the same. The results show that if the disulfide is reduced one thiol group is present as an anionic thiol group and extremely close to the C(4a) atom of the flavin. The exchange of reduction equivalents between the two redox centers in EH 2 is slow (<5 s -1). In combination with reported kinetic data, it became evident that NAD +accelerates considerably the exchange of reduction equivalents between the disulfide and the flavin. The results show that this transfer must be implemented in the reaction cycle and offer a nice explanation of some "anomalous" kinetic data.As an example of the class of hydroxylases, p-hydroxybenzoate hydroxylase from Pseudomonas fluorescens was studied by 1C NMR. Without substrate the isoalloxazine ring is probably exposed to solvent. Upon substrate binding a drastic change of the polarization of C(2) occurs, which is in accord with the published enzyme-substrate complex as revealed by crystallographic methods. It is suggested, that the active center without substrate is rather mobile in order to facilitate the binding of substrate. A conformational change accompanies the binding of substrate. The active center, as present in the oxidized enzyme-substrate complex, is probably already essentially formed upon reduction of the enzyme in the absence of substrate, which explains the drastically decreased binding rate of substrate after reduction. Upon complex formation' with substrate in the reduced state the N(5) is forced into the molecular plane of flavin. Some arguments are presented suggesting that the sp 2hybridization degree of N(5) and N(10) are the main factors which govern the reactivity (or "activation") of oxygen, but not the πelectron density at the C(4a) center of flavin. An electron transfer from the hydroquinone state towards oxygen probably precedes the formation of a C(4a) peroxyflavin by radical pair combination

An Integrated Weed Management framework: A pan-European perspective

Initiatives to reduce the reliance of agriculture on pesticides, including the European Union (EU) Directive 2009/ 128/EC on the sustainable use of pesticides (SUD), have yet to lead to widespread implementation of Integrated Pest Management (IPM) principles. Developments in weed management have strongly focused on increasing the efficiency of herbicides or substituting herbicides with other single tactics such as mechanical control. To in- crease sustainability of agricultural systems in practice, a paradigm shift in weed management is needed: from a single tactic and single growing season approach towards holistic integrated weed management (IWM) consid- ering more than a single cropping season and focusing on management of weed communities, rather than on control of single species. To support this transition, an IWM framework for implementing a system level approach is presented. The framework consists of five pillars: diverse cropping systems, cultivar choice and establishment, field and soil management, direct control and the cross-cutting pillar monitoring and evaluation. IWM is an integral part of integrated pest management (IPM) and adopting IWM will serve as a driver for the development of sustainable agricultural systems of the futur