Soil fumigation with the methyl isothiocyanate (MITC) generators metam-sodium, metam-potassium and dazomet gives rise to residual gasses that need to be checked prior to sowing or planting. Different ...factors determine the residual amount: dose rate, soil type, soil organic matter content, soil humidity, soil temperature, soil porosity and tarping. Under practical conditions this safety check is made after soil tarp removal or, if not covered by plastic film, prior or after soil aeration e.g. by rotovation. Forced aeration is often standard practice and will speed up the removal of potential phytotoxic gasses. MITC monitoring will help to decide on the necessity of forced aeration or even repetition of it. Classic test for phytotoxic risk evaluation only is the cress seed germination test. Alternative seeds, such as lettuce, are also in use. This is the slowest method, needing at least 2 days. Another possibility of monitoring is the use of specific gas detection tubes giving sensitive response within 3 minutes and especially of interest in the fumigated environment, e.g. operator and bystander exposure or risk for neighbouring residents. A hand held pump is needed and the tubes are consumables. A specific measuring principle is by quartz micro balance (QMB). This is also known as the ‘electronic nose’ and was beyond other applications also developed for MITC. The instrument can become operated in the field with a car power adaptor. The whole procedure takes 45 min. Photo ionization detection is possible with hand held instruments. It is not very specific but among MITC and other volatile and active degradation compounds majority of the instrument response is for MITC with a 10.6 eV lamp. It is also very useful for environmental monitoring. Measuring and response time is a few seconds. Other possibilities need to become explored or are under consideration, e.g. infrared analyzer allowing specific detection.
Basamid micro-granule is used worldwide as a broad spectrum soil fumigant generator and has replaced methyl bromide for many applications. A lot is known for decades regarding the factors determining ...the success of the application from soil preparation and conditions to the application and soil sealing or soil tarping, as well as the operations and hygienic measures after the fumigant contact time. This paper explains last 6 years studies regarding the improvement of application methods, both from the viewpoint of homogenous incorporation of the granule over the soil profile to become treated as well as from possible premature loss of the gaseous active methyl isothiocyanate (MITC) by using improved tarping materials. Both result in lower environmental exposure and better biological performance of the application. In that respect, product incorporation in soil was studied in France and in Italy with more recent commercially available Basamid application machinery, and 29 plastic films have been compared for their MITC barrier properties with an 'in house' developed method. Film testing allowed clear categorizing in standard (monolayer) films, V.I.F. (Virtually Impermeable Film) and T.I.F. (Totally Impermeable Film). The paper presents the methodology for granule incorporation study and results from trials with two specific Basamid application machines compared with a classic rotovator, the methodology and comparison of plastic film barrier properties testing, and directives to minimize exposure and to maximize performance.
The deep chlorophyll maximum (DCM) is a ubiquitous feature of phytoplankton vertical distribution in stratified waters that is relevant to our understanding of the mechanisms that underpin the ...variability in photoautotroph ecophysiology across environmental gradients and has implications for remote sensing of aquatic productivity. During the PEACETIME (Process studies at the air-sea interface after dust deposition in the Mediterranean Sea) cruise, carried out from 10 May to 11 June 2017, we obtained 23 concurrent vertical profiles of phytoplankton chlorophyll a, carbon biomass and primary production, as well as heterotrophic prokaryotic production, in the western and central Mediterranean basins. Our main aims were to quantify the relative role of
photoacclimation and enhanced growth as underlying mechanisms of the DCM and to assess the trophic coupling between phytoplankton and heterotrophic prokaryotic production. We found that the DCM coincided with a maximum in both the biomass and primary production but not in the growth rate of phytoplankton, which averaged 0.3 d−1 and was relatively constant across the euphotic layer. Photoacclimation explained most of the increased chlorophyll a at the DCM, as the ratio of carbon to chlorophyll a (C:Chl a) decreased from ca. 90–100 (g:g) at the surface to 20–30 at the base of the euphotic layer, while phytoplankton carbon biomass increased from ca. 6 mg C m−3 at the surface to 10–15 mg C m−3 at the DCM. As a result of photoacclimation, there was an uncoupling between chlorophyll a-specific and carbon-specific productivity across the euphotic layer. The ratio of fucoxanthin to total chlorophyll a increased markedly with depth, suggesting an increased contribution of diatoms at the DCM. The increased biomass and carbon fixation at the base of the euphotic zone was associated with enhanced rates of heterotrophic prokaryotic activity, which also showed a surface peak linked with warmer temperatures. Considering the phytoplankton biomass and turnover rates measured at the DCM, nutrient diffusive fluxes across the nutricline were able to supply only a minor fraction of the
photoautotroph nitrogen and phosphorus requirements. Thus the deep maxima in biomass and primary production were not fuelled by new nutrients but likely resulted from cell sinking from the upper layers in combination with the high photosynthetic efficiency of a diatom-rich, low-light acclimated community largely sustained by regenerated nutrients. Further studies with increased temporal and spatial resolution will be required to ascertain if the peaks of deep primary production associated with the DCM persist across the western and central Mediterranean Sea throughout the stratification season.
In Belgium the production of lettuce is economically very important. The major problems in lettuce production are the plant pathogenic fungi Sclerotinia sclerotiorum (causing lettuce drop) and ...Rhizoctonia solani (causing bottom rot). These fungi can survive for different years in the soil as sclerotia and can cause serious crop losses. Until January 2006, methyl bromide played a key role in the production of lettuce. However, methyl bromide is phased out as it is an ozone-depleting chemical and alternatives are needed. The chemical alternative should be effective against fungi, weeds and nematodes. Therefore, the efficacy of different fumigants and combinations was tested in a field experiment against fungi, nematodes and weeds. The tested fumigants were methyl bromide (MB), methyl iodide (MI), MI with chloropicrin (CP), metam sodium (MS), metam potassium (MP), 1,3-dichloropropene (DD), dimethyldisulfide (DMDS), dazomet (Daz), DD with Daz, DMDS with Daz, CP and CP with DD. Lettuce was planted 4 weeks (autumn crop) and 27 weeks (spring crop) after disinfestation. In both cultures lettuce weighted more than the control for each treatment, however less significant differences were found during the second one. Almost no significant differences were observed regarding infestation degree of Sclerotinia and Rhizoctonia (only tested in the second culture). This resulted in no significant differences in lettuce drop caused by Sclerotinia. Concerning the efficacy of the different fumigants against fungi in general, only in the first crop significant differences were found, indicating that the efficacy of the fumigants is reduced after 27 weeks. This could also be observed for the efficacy of the fumigants against weeds, where the efficacy of the fumigants was significantly higher during the first cultivation. During the second one less significant differences were found.
Hydrolysis of dissolved organic phosphorus by marine planktonic microorganisms is a key process in the P cycle, particularly in P-depleted, oligotrophic environments. The present study assessed ...spatiotemporal variations in phosphomonoesterase (PME) and phosphodiesterase (PDE) activities using concentration kinetics in the eastern Mediterranean Sea in two contrasting situations: the end of winter (including a small bloom period) and autumn. The distribution and regulation of the maximum hydrolysis rate (Vm) and half-saturation constant (Km) of both ectoenzymes were assessed in relation to the vertical structure of the epipelagic layers. PME reached its maximum activities (Vm) after the addition of 1 µM MUF-P (4-methylumbelliferyl phosphate), whereas, for PDE, it was necessary to add up to 50 µM bis(4-methylumbelliferyl)phosphate (bis-MUF-P) to reach saturation state. On average, the Km of PDE was 33 ± 25 times higher than that of PME. The Vm of PME and Vm of PDE were linearly correlated. Conversely to the Km values, Vm values were on the same order of magnitude for both ectoenzymes, with their ratio (Vm PME : Vm PDE) ranging between 0.2 and 6.3. Dissolved organic phosphorus (DOP) and the phosphomonoesterase hydrolysable fraction of DOP explained most of the lack of variability in Vm PME and Vm PDE. On the contrary, Vm of both phosphohydrolase enzymes was inversely correlated to the concentration of dissolved inorganic phosphorus. The particular characteristics of concentration kinetics obtained for PDE (saturation at 50 µM, high Km, high turnover times) are discussed with respect to the possible unequal distribution of PDE and PME among the size continuum of organic material and accessibility of phosphodiesters.
The surface mixed layer (ML) in the Mediterranean Sea is a well-stratified
domain characterized by low macronutrients and low chlorophyll content for almost 6 months of the year. In this study we ...characterize the
biogeochemical cycling of nitrogen (N) in the ML by analyzing simultaneous in situ measurements of atmospheric deposition, nutrients in seawater, hydrological conditions, primary production, heterotrophic prokaryotic production, N2 fixation and leucine aminopeptidase activity. Dry deposition was continuously measured across the central and western open Mediterranean Sea, and two wet deposition events were sampled, one in the Ionian Sea and one in the Algerian Basin. Along the transect, N budgets were computed to compare the sources and sinks of N in the mixed layer. In situ leucine aminopeptidase
activity made up 14 % to 66 % of the heterotrophic prokaryotic N demand, and the N2 fixation rate represented 1 % to 4.5 % of the phytoplankton N demand. Dry atmospheric deposition of inorganic nitrogen, estimated from dry deposition of nitrate and ammonium in aerosols, was higher than the N2 fixation rates in the ML (on average 4.8-fold). The dry atmospheric input of inorganic N represented a highly variable proportion of biological N demand in the ML among the stations, 10 %–82 % for heterotrophic
prokaryotes and 1 %–30 % for phytoplankton. As some sites were visited on several days, the evolution of biogeochemical properties in the ML and within the nutrient-depleted layers could be followed. At the Algerian Basin site, the biogeochemical consequences of a wet dust deposition event were monitored through high-frequency sampling. Notably, just after the rain, nitrate was higher in the ML than in the nutrient-depleted layer below. Estimates of nutrient transfer from the ML into the nutrient-depleted layer could explain up to a third of the nitrate loss from the ML. Phytoplankton did not benefit directly from the atmospheric inputs into the ML, probably due to high competition with heterotrophic prokaryotes, also limited by N and phosphorus (P) availability at the time of this study.
Primary producers decreased their production after the rain but recovered
their initial state of activity after a 2 d lag in the vicinity of the
deep chlorophyll maximum layer.
In the marine environment, transparent exopolymeric particles (TEP) produced from abiotic and biotic sources link the particulate and dissolved carbon pools and are essential vectors enhancing ...vertical carbon flux. We characterized spatial and temporal dynamics of TEP during the VAHINE experiment that investigated the fate of diazotroph-derived nitrogen and carbon in three replicate dissolved inorganic phosphorus (DIP)-fertilized 50 m3 enclosures in the oligotrophic New Caledonian lagoon. During the 23 days of the experiment, we did not observe any depth-dependent changes in TEP concentrations in the three sampled depths (1, 6, 12 m). TEP carbon (TEP-C) content averaged 28.9 ± 9.3 and 27.0 ± 7.2 % of total organic carbon (TOC) in the mesocosms and surrounding lagoon respectively and was strongly and positively coupled with TOC during P2 (i.e., days 15–23). TEP concentrations in the mesocosms declined for the first 9 days after DIP fertilization (P1 = days 5–14) and then gradually increased during the second phase. Temporal changes in TEP concentrations paralleled the growth and mortality rates of the diatom–diazotroph association of Rhizosolenia and Richelia that predominated the diazotroph community during P1. By P2, increasing total primary and heterotrophic bacterial production consumed the supplemented P and reduced availability of DIP. For this period, TEP concentrations were negatively correlated with DIP availability and turnover time of DIP (TDIP), while positively associated with enhanced alkaline phosphatase activity (APA) that occurs when the microbial populations are P stressed. During P2, increasing bacterial production (BP) was positively correlated with higher TEP concentrations, which were also coupled with the increased growth rates and aggregation of the unicellular cyanobacterial Group C (UCYN-C) diazotrophs that bloomed during this period. We conclude that the composite processes responsible for the formation and breakdown of TEP yielded a relatively stable TEP pool available as both a carbon source and facilitating aggregation and flux throughout the experiment. TEP were probably mostly influenced by abiotic physical processes during P1, while biological activity (BP, diazotrophic growth and aggregation, export production) mainly impacted TEP concentrations during P2 when DIP availability was limited.
For the first time, the effect of pulsed electric field (PEF) and mild thermal processing on the texture of cortex and vascular carrot tissue during subsequent thermal processing (i.e. cooking ...behaviour) was compared and the degree of methylesterification (DM) of pectin from the pretreated tissues was investigated. The PEF and mild thermal pretreatment slowed down the cooking behaviour of the carrot tissues, especially when the pretreatments were combined. The DM of pectin from vascular tissue was lowered after both types of pretreatments, the effect being most pronounced in the case of the combination of the PEF and mild thermal pretreatment. In contrast, the DM of cortex pectin only decreased after the mild thermal pretreatment and after the combination pretreatment. This study demonstrates that besides mild thermal pretreatments also PEF pretreatments can be considered in the context of texture preservation of thermally processed fruits and vegetables.
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•Pulsed electric field (PEF) pretreatment alters cooking behaviour of carrot tissue•PEF treatment facilitates carrot pectin demethylesterification•Effect of PEF on pectin structure and on texture after cooking is tissue dependent•PEF technology can be considered for texture preservation during thermal processing
Although atmospheric dust fluxes from arid as well as human-impacted areas represent a significant source of nutrients to surface waters of the Mediterranean Sea, studies focusing on the evolution of ...the metabolic balance of the plankton community following a dust deposition event are scarce, and none were conducted in the context of projected future levels of temperature and pH. Moreover, most of the experiments took place in coastal areas. In the framework of the PEACETIME project, three dust-addition perturbation experiments were conducted in 300 L tanks filled with surface seawater collected in the Tyrrhenian Sea (TYR), Ionian Sea (ION) and Algerian basin (FAST) on board the R/V Pourquoi Pas? in late spring 2017. For each experiment, six tanks were used to follow the evolution of chemical and biological stocks, biological activity and particle export. The impacts of a dust deposition event simulated at their surface were followed under present environmental conditions and under a realistic climate change scenario for 2100 (ca. +3 ∘C and −0.3 pH units). The tested waters were all typical of stratified oligotrophic conditions encountered in the open Mediterranean Sea at this period of the year, with low rates of primary production and a metabolic balance towards net heterotrophy. The release of nutrients after dust seeding had very contrasting impacts on the metabolism of the communities, depending on the station investigated. At TYR, the release of new nutrients was followed by a negative impact on both particulate and dissolved 14C-based production rates, while heterotrophic bacterial production strongly increased, driving the community to an even more heterotrophic state. At ION and FAST, the efficiency of organic matter export due to mineral/organic aggregation processes was lower than at TYR and likely related to a lower quantity/age of dissolved organic matter present at the time of the seeding and a smaller production of DOM following dust addition. This was also reflected by lower initial concentrations in transparent exopolymer particles (TEPs) and a lower increase in TEP concentrations following the dust addition, as compared to TYR. At ION and FAST, both the autotrophic and heterotrophic community benefited from dust addition, with a stronger relative increase in autotrophic processes observed at FAST. Our study showed that the potential positive impact of dust deposition on primary production depends on the initial composition and metabolic state of the investigated community. This impact is constrained by the quantity of nutrients added in order to sustain both the fast response of heterotrophic prokaryotes and the delayed one of primary producers. Finally, under future environmental conditions, heterotrophic metabolism was overall more impacted than primary production, with the consequence that all integrated net community production rates decreased with no detectable impact on carbon export, therefore reducing the capacity of surface waters to sequester anthropogenic CO2.
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