Crop-specific differences in the concentrations of lipids in leachates from the root zone

Although lipids are involved in diverse soil processes and affect various soil properties, the contribution of rhizodeposits and the root zone to lipid concentrations and distributions in soils is unknown. For the first time, we determined the concentrations of alkanoic acids, n-alkanes and n-alkenes in root zone leachates and roots of maize and potato using gas chromatography/mass spectrometry (GC/MS). In total, the lipid concentrations of leachates were 100 μg g^?1 (maize) and 17 μg g^?1 (potato). The saturated n-alkanoic acids, ranging from n-C₁₄ to n-C₂₈ and having the maximum at n-C₂₂ (maize) and at n-C₁₆ (potato), were more abundant than the other compounds. Maize leachates had more alkanes (20 μg g^?1) than potato leachates (3.1 μg g^?1), but the members of the homologues were nearly the same. Comparison of these distributions with data for roots, microorganisms and soil indicated that the lipids in the leachates from the root zone mainly originated from abrasion of fine roots, rhizodeposits and rhizosphere microorganisms.     

Evaluation of agro-industrial by-products as nutrient source for plant growth

Nutrient leaching from dry (COD) and wet (COW) coffee, sisal (SIS), brewery barley malt (BEB) and sugar cane (FIC) by-products, and linseed (LIC) and niger seed cakes (NIC), and uptake by maize were studied in a pot experiment with tropical Alfisol. After three months, soils were leached to recover labile plant nutrients, and root and shoot biomass was harvested. The leachate from FIC-amended soil had the highest concentration of inorganic P (0.90 μmol L^?1), whereas the highest concentrations of potassium (K) (48,088 μmol L^?1) and calcium (2566 μmol L^?1) were determined in leachates from COD and BEB treatments, respectively. The amendments significantly increased K uptake by maize proportional to the amount of K applied, but the effects for other plant nutrients were small. The results indicated that pre-decomposition of agro-industrial by-products may increase the nutrient release in tropical soils.     

Impact of human interventions on the spread of bluetongue virus serotype 8 during the 2006 epidemic in north-western Europe

Bluetongue virus (BTV) can be spread by movement or migration of infected ruminants. Infected midges (Culicoides sp.) can be dispersed with livestock or on the wind. Transmissions of infection from host to host by semen and trans-placental infection of the embryo from the dam have been found. As for any infectious animal disease, the spread of BTV can be heavily influenced by human interventions preventing or facilitating the transmission pathways. This paper describes the results of investigations that were conducted on the potential role of the above-mentioned human interventions on the spread of BTV-8 during the 2006 epidemic in north-western Europe. Data on surveillance and control measures implemented in the affected European Union (EU) Member States (MS) were extracted from the legislation and procedures adopted by the national authorities in Belgium, France, Germany, and The Netherlands. The impact of the control measures on the BTV-incidence in time and space was explored. Data on ruminant transports leaving the area of first infection (AFI) to other areas within and beyond the affected MS were obtained from the national identification and registration systems of the three initially affected MS (Belgium, Germany, The Netherlands) and from the Trade Control and Expert System (TRACES) of the European Commission. The association between the cumulative number of cases that occurred in a municipality outside the AFI and the number of movements or the number of animals moved from the AFI to that municipality was assessed using a linear negative binomial regression model. The results of this study indicated that the control measures which were implemented in the affected MS (in accordance with EU directives) were not able to fully stop further spread of BTV and to control the epidemic. This finding is not surprising because BT is a vector-borne disease and it is difficult to limit vector movements. We could not assess the consequences of not taking control measures at all but it is possible, if not most likely, that this would have resulted in even wider spread. The study also showed an indication of the possible involvement of animal movements in the spread of BTV during the epidemic. Therefore, the prevention of animal movements remains an important tool to control BTV outbreaks. The extension of the epidemic to the east cannot be explained by the movement of animals, which mainly occurred in a north-western direction. This indicates that it is important to consider other influential factors such as dispersal of infected vectors depending on wind direction, or local spread.     

Detailed genetic analysis of feeding behaviour in Romane lambs and links with residual feed intake

Breeding strategies based on feed efficiency are now implemented in most animal species using residual feed intake (RFI) criteria. Although relevant, the correlated responses of feeding behaviour traits resulting from such selection on RFI are poorly documented. We report the estimated feeding behaviour at three time levels (visit, meal and day) and genetic parameters between the feeding behaviour traits and their links with RFI and its components. Feed intake, feeding duration at three time levels (per visit, meal and day), feeding rate, number of visits and time‐between‐visits were estimated for 951 Romane lambs fed via automatic concentrate feeders. Heritability estimates of feeding behaviour traits ranged from 0.19 to 0.54 with higher estimates for the day level than the visit level. Daily feed intake was not genetically linked to feed intake at the visit level, whereas feeding duration between visit and day levels was moderately correlated (R_g = +0.41 ± 0.12). RFI was not significantly correlated with feeding rate, but was positively linked to feed intake and feeding duration at the day level (+0.73 ± 0.09 and +0.41 ± 0.13, respectively) and negatively at the visit level (?0.33 ± 0.14 and ?0.22 ± 0.17, respectively). Selecting animals with lower RFI values might modify their feeding behaviour by increasing feed intake and feeding duration at the visit level but decrease the number of visits per day (+0.51 ± 0.14).     

Effect of triple superphosphate and biowaste compost on mycorrhizal colonization and enzymatic P mobilization under maize in a long‐term field experiment

Phosphorus (P) fertilizers and mycorrhiza formation can both significantly improve the P supply of plants, but P fertilizers might inhibit mycorrhiza formation and change the microbial P cycling. To test the dimension and consequences of P fertilizer impacts under maize (Zea mays L.), three fertilizer treatments (1) triple superphosphate (TSP, 21–30 kg P ha^?1 annually), biowaste compost (ORG, 30 Mg ha^?1 wet weight every third year) and a combination of both (OMI) were compared to a non‐P‐fertilized control (C) in 2015 and 2016. The test site was a long‐term field experiment on a Stagnic Cambisol in Rostock (NE Germany). Soil microbial biomass P (P_mic) and soil enzyme activities involved in P mobilization (phosphatases and ß‐glucosidase), plant‐available P content (double lactate‐extract; P_DL), mycorrhizal colonization, shoot biomass, and shoot P concentrations were determined. P deficiency led to decreased P immobilization in microbial biomass, but the maize growth was not affected. TSP application alone promoted the P uptake by the microbial biomass but reduced the mycorrhizal colonization of maize compared to the control by more than one third. Biowaste compost increased soil enzyme activities in the P cycling, increased P_mic and slightly decreased the mycorrhizal colonization of maize. Addition of TSP to biowaste compost increased the content of P_DL in soil to the level of optimal plant supply. Single TSP supply decreased the ratio of P_DL:P_mic to 1:1 from about 4:1 in the control. Decreased plant‐benefits from mycorrhizal symbiosis were assumed from decreased mycorrhizal colonization of maize with TSP supply. The undesirable side effects of TSP supply on the microbial P cycling can be alleviated by the use of compost. Thus, it can be concluded that the plant‐availability of P from soil amendments is controlled by the amendment‐specific microbial P cycling and, likely, P transfer to plants.     

Assessing the phenotypic and genotypic diversity of <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis> in France

White mould caused by the ascomycete Sclerotinia sclerotiorum affects the production of many economically important crops. The incidence of this disease has recently increased in France, especially in melon crops, which were not affected much in the past. One possible explanation for this situation is the emergence of strains with particular characteristics, including increased aggressiveness to melon. To test this hypothesis, 200 isolates of S. sclerotiorum were collected from six host crops (bean, brassica oilseed rape, carrot, lettuce, melon, witloof chicory) in different regions. They were genotyped with 16 microsatellites markers. A subsample of 96 isolates were assessed for their aggressiveness on melon leaves. Overall, the isolates from melon did not show higher aggressiveness on melon leaves than those which originated from other host plants. Moreover, the melon isolates did not present distinctive genetic characteristics in comparison with those from other crops and shared several of the 128 identified multilocus haplotypes with isolates collected from carrot, witloof chicory and oilseed rape. Furthermore the Bayesian analysis of the genetic structure indicated that the host plant is not a structuring factor of the three genetic clusters identified, and it suggested instead the occurrence of an isolation-by-distance process. Possible consequences of these results for the management of white mould and alternative hypotheses to explain the recent changes in disease incidence are presented.     

Effects of nitrogen and phosphorus fertilization on mycorrhizal formation of two poplar clones (Populus trichocarpa and P. tremula x tremuloides)

Mineral fertilization is a common management practice in short rotation forestry. The mycorrhizal formation of trees can be affected by fertilizer applications, however, very little is known on such effects in arable soils. The effects of a nitrogen (N) and phosphorus (P) fertilization on mycorrhizal formation of two poplar clones (Populus trichocarpa and P. tremula x tremuloides) were investigated at the plantation Abbachhof (South Germany). We determined the ectomycorrhizal colonization and the abundance of VAM spores in the soil during three years, and the species richness of sporocarps during one growing season. Approximately 26 to 73% of the fine roots of P. trichocarpa and 41 to 82% of the fine roots of P. tremula x tremuloides were colonized with ectomycorrhizal fungi. The percentage of ectomycorrizal colonization on P. tremula x tremuloides was significantly reduced after both fertilization treatments. On P. trichocarpa only the P‐fertilization reduced the ectomycorrhizal colonization. The composition of ectomycorrhizal morphotypes was significantly affected by the N and P fertilization on P. tremula x tremuloides, but not on P. trichocarpa. Sporocarps of 12 ectomycorrhizal fungi species were found at the plantation. Cortinarius uliginosus, Lactarius controversus and Krombholziella aurantiaca produced sporocarps only on control plots, whereas Cortinarius croceocaeruleus, Inocybe umbrina, Laccaria tortilis, Paxillus involutus and Rhizopogon roseolus produced sporocarps only on fertilized plots. Inocybe geophylla, I. glabripes, Laccaria laccata and Tuber borchii produced sporocarps on both control and fertilized plots. The density of VAM spores was lower in the rooting zone of Populus trichocarpa than under P. tremula x tremuloides. In an efficient management of these short rotation plantations mineral fertilizer applications must be low enough to avoid undesired suppressions of mycorrhizal formation.     

Surfing and marine conservation: Exploring surf‐break protection as IUCN protected area categories and other effective area‐based conservation measures

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Weed suppressiveness of paving joint filling materials under diverging water regimes

Since 2015, chemical weed control on public pavements in Flanders has been banned. This necessitates alternative weed control strategies. In this study, growth chamber experiments evaluated the weed suppressive ability of different joint filling materials under various water regimes. The tested materials comprised five unbound standard fillers (white quartz sand, sea sand, limestone 0/2 mm, limestone 2/6.3 mm and porphyry 2/6.3 mm) and two innovative materials (Dansand^® and Eco Fugensand^®). Their weed suppressiveness was tested in pure and organically polluted states. Germination and biomass accumulation of two weed species that are abundantly found on public pavements (Lolium perenne and Taraxacum officinale) were investigated. Germination and biomass accumulation were lowest in both innovative materials, irrespective of organic contamination level, plant species and water regime. Weed growth in the standard materials was affected by plant species and water regime. Monthly biomass accumulation increased with increasing monthly water supply and number of irrigation days. Furthermore, the materials best capable of reducing weed growth, under all water regimes, even when organically polluted, were the innovative materials and sea sand. The results of this study show that the implemented water regime can influence weed suppressiveness (absolute as well as relative) of a joint filler. Hence, to fully assess weed suppressive ability, commercially launched joint fillers should be tested under diverging water regimes.     

Clonal and seasonal shifts in communities of saprotrophic microfungi and soil enzyme activities in the mycorrhizosphere of Salix spp.

The species‐specific microbial root and rhizosphere colonization contributes essentially to the plant nutrient supply. The species number and colonization densities of cultivable saprotrophic microfungi and the activities of nutrient‐releasing soil enzymes (protease, acid and alkaline phosphatase, arylsulfatase) were investigated in the rhizosphere of one low mycorrhizal (Salix viminalis) and one higher mycorrhizal (S. × dasyclados) willow clone at a Eutric Cambisol in N Germany. After soil washing, in total 32 and 28 saprotrophic microfungal species were isolated and identified microscopically from the rhizosphere of S. viminalis and S. × dasyclados, respectively. The fungal species composition changed within the growing season but the species number was always lower under S. × dasyclados than under S. viminalis. Under both willow clones, the fungal colonization density was largest in spring, and the species number was largest in autumn. Acid‐phosphatase activity (p < 0.001) and protease activity (p < 0.003) were significantly affected by the Salix clone, whereas arylsulfatase and alkaline‐phosphatase activities did not show clone‐specific differences. All enzyme activities reached their maxima in the summer sampling. Rhizosphere colonization with Acremonium butyri, Cladosporium herbarum, and Penicillium janthinellum contributed significantly to explain the activities of acid phosphatase. Rhizosphere colonization with Cylindrocarpon destructans, Penicillium spinulosum, Plectosphaerella cucumerina, and Trichoderma polysporum contributed significantly to explain the arylsulfatase activities. Effects of the saprotrophic fungal colonization densities on the protease activities in the rhizosphere were low. Acid‐ and alkaline‐phosphatase and arylsulfatase activities in the rhizosphere soil were stronger affected by the composition of the saprotrophic fungal communities than by the Salix clone itself. In conclusion, the colonization density of some saprotrophic microfungi in the rhizosphere contributed to explain shifts in soil‐enzyme activities of the P and S cycles under different willow clones.