Allelopatiska egenskaper av tomatidin och andra alkaloider från potatisväxter

Alkaloids are a heterogeneous group of secondary metabolites in plants with toxic attributes. These substances often have toxic effects on different organisms and are found in many species of the nightshade family (Solanaceae). This study shows that the alkaloid tomatidine from tomato (Solanum lycopersicum) are allelopathic to arabidopsis (Arabidopsis thaliana, cv. Col), cornflower (Cyanus segetum) and tobacco (Nicotiana tabacum, cv. SRI) but not to tomato itself. The allelopathic effect were shown to be specific for tomatidine, the other 8 structurally similar alkaloids from nightshades that were tested did not yield the same effect. The plant material was grown in MS-medium containing tomatidine and its root growth were inhibited due to impaired cell elongation. The roots were deformed and shorter in the presence of 1 - 5 μM tomatidine compared to untreated control plants. The addition of sterols or plant hormones to arabidopsis grown in tomatidine did not stimulate the root growth. Germination of seeds from different agricultural plants were not affected by tomatidine, however, the growth was retarded which resulted in significantly less germinating seeds of flax (Linum usitatissimum)

Effekter av kvävekvalitet och kvantitet på konkurrens mellan ogräs och gröda : ett växthusexperiment med Avena sativa och Avena fatua

The intensification of agricultural activities has provided unprecedented increases in crop production. In the light of this development concerns have been raised about its negative environmental impact. High-input farm management has further reduced the weed diversity and shaped weed communities to consist of a few highly competitive weed species. Ecological theory and soil microbial processes presents another perspective focusing on managing weeds with the use of different nutrient sources and crop diversity. The establishment of distinct resource pools in soil allow nutrients to be segregated between species and reduce weed-crop competition. The aim of this study was to investigate the influence of different nutrient sources in different quantities on competitive interactions between the weed species Avena fatua (wild oat) and Matricaria perforata (scentless chamomille) and the crop Avena sativa (oat) intercropped with the cover crop Trifolium resupinatum (Persian clover). The model plants were grown in a greenhouse in pots prepared with three soil substrates containing different nitrogen sources and quantities. A. fatua and A. sativa biomass and shoot height were statistically analysed in order to investigate the species responses to changes in nitrogen quality and quantity. A. sativa yield loss due to A. fatua competition were studied at four different A. fatua densities. The response to changes in soil nitrogen quality, nitrogen quantity and plant density were greater for A. sativa compared to A. fatua. Higher resource pool diversity increased the interspecific competition between A. fatua and A. sativa. The unresponsiveness of A. fatua to changing nutrient regimes and competition suggests that reinforced competition from the crop could be used to exhaust the weed’s energy reserves. Growth of T. resupinatum and M. perforata was insufficient to influence A. sativa in the experiment.Intensifieringen av jordbrukets aktiviteter har bidragit till en produktionsökning utan motstycke. Samtidigt har en oro kring dess negativa miljöpåverkan ökat i ljuset av denna utveckling. Det moderna lantbrukets stora tillförsel av insatsvaror har lett till en minskad mångfald av ogräsarter och format ett ogrässamhälle bestående av några få starkt konkurrenskraftiga ogräs. Ekologisk teori och mikrobiella markprocesser bidrar med ett annat perspektiv med fokus på ogräskontroll, utifrån val av näringskällor och ökad mångfald av grödor i växtföljden. Genom att etablera åtskilda pooler av resurser i marken möjliggörs en uppdelning av näringen mellan arter med en minskad konkurrens mellan ogräs och gröda som följd. Målet med denna studie var att utforska vilket inflytande olika näringskällor, med varierande näringsmängd, har på konkurrensen mellan ogräsarterna Avena fatua (flyghavre) och Matricaria perforata (baldersbrå) och grödan Avena sativa (havre) samodlad med mellangrödan Trifolium resupinatum (persisk klöver). Modellväxterna odlades i växthus i krukor med tre jordsubstrat innehållande olika kvävekällor samt olika mängd kväve. Biomassa och planthöjd från A. fatua och A. sativa registrerades och analyserades i olika modeller för att utreda arternas respektive känslighet för förändrad kvalitet av kväve och kvävemängd. Skördebortfall av A. sativa till följd av konkurrens från A. fatua studerades vid fyra olika planttätheter av A. fatua. Responsen av förändrad kvävekvalitet och kvävemängd samt planttäthet var större för A. sativa i jämförelse med A. fatua. En större diversitet av näringskällor ökade mellanartskonkurrensen mellan A. fatua och A. sativa. A. fatuas okänslighet gentemot förändrade näringsbetingelser och konkurrens antyder att en förstärkt konkurrens från grödan kan användas till att uttömma ogräsets energireserver. Tillväxt av T. resupinatum och M. perforata var otillräcklig för att påverka A. sativa i försöket

Catchment controls of denitrification and nitrous oxide production rates in headwater remediated agricultural streams

Heavily modified headwater streams and open ditches carry high nitrogen loads from agricultural soils that sustain eutrophication and poor water quality in downstream aquatic ecosystems. To remediate agricultural streams and reduce the export of nitrate (NO3-), phosphorus and suspended sediments, two-stage ditches with constructed floodplains can be implemented as countermeasures. By extending hydrological connectivity between the stream channel and riparian corridor within constructed floodplains, these remediated ditches enhance the removal of NO3- via the microbial denitrification process. Ten remediated ditches were paired with upstream trapezoidal ditches in Sweden across different soils and land uses to measure the capacity for denitrification and nitrous oxide (N2O) production and yields under denitrifying conditions in stream and floodplain sediments. To examine the controls for denitrification, water quality was monitored monthly and flow discharge continuously along reaches. Floodplain sediments accounted for 33% of total denitrification capacity of remediated ditches, primarily controlled by inundation and stream NO3- concentrations. Despite reductions in flow-weighted NO3- concentrations along reaches, NW removal in remediated ditches via denitrification can be masked by inputs of NW-rich groundwaters, typical of intensively managed agricultural landscapes. Although N2O production rates were 50 % lower in floodplains compared to the stream, remediated ditches emitted more N2O than conventional trapezoidal ditches. Higher denitrification rates and reductions of N2O proportions were predicted by catchments with loamy soils, higher proportions of agricultural land use and lower floodplain elevations. For realizing enhanced NO3- removal from floodplains and avoiding increased N2O emissions, soil type, land use and the design of floodplains need to be considered when implementing remediated streams. Further, we stress the need for assessing the impact of stream remediation in the context of broader catchment processes, to determine the overall potential for improving water quality

Advances in Catchment Science, Hydrochemistry, and Aquatic Ecology Enabled by High-Frequency Water Quality Measurements

High-frequency water quality measurements in streams and rivers have expanded in scope and sophistication during the last two decades. Existing technology allows in situ automated measurements of water quality constituents, including both solutes and particulates, at unprecedented frequencies from seconds to subdaily sampling intervals. This detailed chemical information can be combined with measurements of hydrological and biogeochemical processes, bringing new insights into the sources, transport pathways, and transformation processes of solutes and particulates in complex catchments and along the aquatic continuum. Here, we summarize established and emerging high-frequency water quality technologies, outline key high-frequency hydrochemical data sets, and review scientific advances in key focus areas enabled by the rapid development of high-frequency water quality measurements in streams and rivers. Finally, we discuss future directions and challenges for using high-frequency water quality measurements to bridge scientific and management gaps by promoting a holistic understanding of freshwater systems and catchment status, health, and function

Biogeochemical role of subsurface coherent eddies in the ocean: Tracer cannonballs, hypoxic storms, and microbial stewpots?

Subsurface coherent eddies are well-known features of ocean circulation, but the sparsity of observations prevents an assessment of their importance for biogeochemistry. Here, we use a global eddying (0.1° ) ocean-biogeochemical model to carry out a census of subsurface coherent eddies originating from eastern boundary upwelling systems (EBUS), and quantify their biogeochemical effects as they propagate westward into the subtropical gyres. While most eddies exist for a few months, moving over distances of 100s of km, a small fraction (< 5%) of long-lived eddies propagates over distances greater than 1000km, carrying the oxygen-poor and nutrient-rich signature of EBUS into the gyre interiors. In the Pacific, transport by subsurface coherent eddies accounts for roughly 10% of the offshore transport of oxygen and nutrients in pycnocline waters. This "leakage" of subsurface waters can be a significant fraction of the transport by nutrient-rich poleward undercurrents, and may contribute to the well-known reduction of productivity by eddies in EBUS. Furthermore, at the density layer of their cores, eddies decrease climatological oxygen locally by close to 10%, thereby expanding oxygen minimum zones. Finally, eddies represent low-oxygen extreme events in otherwise oxygenated waters, increasing the area of hypoxic waters by several percent and producing dramatic short-term changes that may play an important ecological role. Capturing these non-local effects in global climate models, which typically include non-eddying oceans, would require dedicated parameterizations

Advances in Catchment Science, Hydrochemistry, and Aquatic Ecology Enabled by High-Frequency Water Quality Measurements

High-frequency water quality measurements in streams and rivers have expanded in scope and sophistication during the last two decades. Existing technology allows in situ automated measurements of water quality constituents, including both solutes and particulates, at unprecedented frequencies from seconds to subdaily sampling intervals. This detailed chemical information can be combined with measurements of hydrological and biogeochemical processes, bringing new insights into the sources, transport pathways, and transformation processes of solutes and particulates in complex catchments and along the aquatic continuum. Here, we summarize established and emerging high-frequency water quality technologies, outline key high-frequency hydrochemical data sets, and review scientific advances in key focus areas enabled by the rapid development of high-frequency water quality measurements in streams and rivers. Finally, we discuss future directions and challenges for using high-frequency water quality measurements to bridge scientific and management gaps by promoting a holistic understanding of freshwater systems and catchment status, health, and function