Effects of crop rotation and field management methods on weed density and species composition in the southeastern part of Latvia

Integrated weed management (IWM) is a complex approach to weed control that is based on use of several different methods complementing each other, instead of relying on one single method, like chemical weed control. Weed control methods that can be used as parts of IWM strategy include mechanical weed control, application of herbicides, low tillage, changes in the rate and application time of fertilizers, use of undersown crops and crop rotation. Weed surveys were carried out in 2013 and 2014 in the southeastern part of Latvia. The aim of this study was to assess the effect of crop rotation and other field management practices on weed density and weed species composition using the data collected in the surveys. Survey was carried out in the arable fields of conventional farms within four different size categories. One of the significant factors that explained the variation of weed composition within a field was a proportion of cereals in crop rotation within a four year period. Further surveys are required to estimate the effects of climatic variables. Density-dependence can also be important for practical management decisions for particular weed species and should be investigated

Ultraviolet radiation accelerates photodegradation under controlled conditions but slows the decomposition of senescent leaves from forest stands in southern Finland

Depending on the environment, sunlight can positively or negatively affect litter decomposition, through the ensemble of direct and indirect processes constituting photodegradation. Which of these processes predominate depends on the ecosystem studied and on the spectral composition of sunlight received. To examine the relevance of photodegradation for litter decomposition in forest understoreys, we filtered ultraviolet radiation (UV) and blue light from leaves of Fagus sylvatica and Bettda pendula at two different stages of senescence in both a controlled-environment experiment and outdoors in four different forest stands (Picea abies, Pagus sylvatica, Acer platanoides, Betula pendula). Controlling for leaf orientation and initial differences in leaf chlorophyll and flavonol concentrations; we measured mass loss at the end of each experiment and characterised the phenolic profile of the leaf litter following photodegradation. In most forest stands, less mass was lost from decomposing leaves that received solar UV radiation compared with those under UV-attenuating filters, while in the controlled environment UV-A radiation either slightly accelerated or had no significant effect on photodegradation, according to species identity. Only a few individual phenolic compounds were affected by our different filter treatments, but photodegradation did affect the phenolic profile. We can conclude that photodegradation has a small stand- and species-specific effect on the decomposition of surface leaf litter in forest understoreys during the winter following leaf fall in southern Finland. Photodegradation was wavelength-dependent and modulated by the canopy species filtering sunlight and likely creating different combinations of spectral composition, moisture, temperature and snowpack characteristics.Peer reviewe

Germination ecophysiology of coastal plants: seed dormancy and the effect of environmental factors

Darba mērķis ir raksturot dažādu piekrastes biotopu augu sēklu miera periodu un dažādu vides faktoru ietekmi uz to dīgšanu. Augu sēklas ievāca Baltijas jūras piekrastē (Kurzeme) un Rīgas jūras līča piekrastē. Vienā no diedzēšanas eksperimentiem izmantoja sēklas no Millenium Seed Bank (RBG Kew, Lielbritānija) kolekcijas. Diedzēšanas eksperimentus veica LU Bioloģijas fakultātē no 2005. līdz 2009. gadam un MSB laboratorijā 2009. gadā. Ir noteikts un raksturots sēklu organiskā miera perioda (OMP) veids vairākām piejūras mitrāju un kāpu augu sugām, kā arī raksturota NaCl ietekme uz šo sugu sēklu dīgšanu. Juncus balticus un Triglochin maritima sēklām ir salīdzināta NaCl un polietilēnglikola (PEG) ietekme uz sēklu dīgšanu un dīgtspējas atjaunošanos. T. maritima sēklām noteica aukstās stratifikācijas ietekmi uz sēklu dīgtspēju dažādās NaCl un PEG koncentrācijās. Linaria loeselii un L. Vulgaris piemērā ir izpētītas minimālās dīgšanas temperatūras izmaiņas aukstās stratifikācijas procesā, kā arī vairāku Linaria ģints sugu sēklām ir noteikta NaCl ietekme uz minimālo un maksimālo dīgšanas temperatūru. Eryngium maritimum sēklām, kurām ir noteikts morfofizioloģiskais sēklu OMP izpētīja aukstās stratifikācijas un giberelskābes ietekmi uz dīgšanu, kā arī sēklu embriju attīstības dinamiku stratifikācijas laikā. Aukstā stratifikācija un NaCl ietekmē vairāku Linaria ģints sugu sēklu populāciju dīgšanu. Minimālās (Tb) un maksimālās (Tc) dīgšanas temperatūras noteikšana ļauj kvantitatīvi un kvalitatīvi novērtēt OMP izpausmes izmaiņas un NaCl izraisīto ietekmi uz dīgšanu sēklu populācijā. Salīdzinot L. Loeselii un L. Vulgaris piekrastes populāciju sēklas, ir noteiktas atšķirības to OMP izpausmē. Šīs atšķirības ilustrē abu sugu pielāgošanos noteikta veida biotopiem un dažādu ģeneratīvās vairošanās stratēģiju. L. Vulgaris sēklu populācijai ir raksturīga vājāka OMP izpausme un lielāka heterogenitāte, kas pieļauj dīgšanu dažādos apstākļos un var būt viens no faktoriem, kuri sekmē sugas plašāku ģeogrāfisko izplatību. Nosakot sāļuma ietekmi uz dažādu dzimtu sugu sēklu dīgšanu ir izveidots pamats turpmākiem detalizētākiem pētījumiem par osmotiskā potenciāla ietekmi uz piekrastes augu ekoloģiju. Parādīta sēklu OMP saistība ar sāļuma ietekmi, kā arī, pētīto sugu gadījumā, sakarība starp sēklu spēju dīgt NaCl ietekmē un attiecīgai sugai raksturīgo piekrastes biotopu.Germination ecophysiology of coastal plants: seed dormancy and the effect of environmental factors The aim of this study was to characterize seed dormancy and the effect of various environmental factors on seed germination in several coastal plant species. Dormancy types were characterized in dune and coastal marsh species: Juncus balticus, Triglochin maritimum, T. palustre, Eryngium maritimum, Anthyllis maritima, Linaria loeselii. The effect of NaCl on germination was determined in several plant species. The effect of NaCl and PEG on seed germination was compared in J. balticus and T. maritima. The results showed a relationship between the species‘ habitat and salinity tolerance of the seeds. In E. maritimum the effect of cold stratification on the development of seed embryos was measured. The effect of cold stratification and NaCl on changes in minimum and maximum germination temperature was measured. Dormancy levels were compared in L. loeselii and L. vulgaris. The results allow to quantify changes in dormancy level and help to describe different germination strategies. Keywords: seed germination, dormancy, coastal habitat

Variability of Seed Germination and Dormancy Characteristics and Genetic Analysis of Latvian Avena fatua Populations

Avena fatua is an economically detrimental weed found in cereal growing areas worldwide. Knowledge about the variation of dormancy and germination characteristics, as well as of the genetic diversity and structure can provide additional information about different populations within a region. Identification and development of potential indicators or markers of seed germination behavior, would be useful for modelling emergence and seed bank dynamics. This study aimed to describe the initial germination, dormancy, and morphological characteristics of seeds from different Latvian populations of A. fatua and to investigate the genetic structure of local populations. Seed samples from 26 to 41 locations in different regions of Latvia were collected over three years. Seed morphology, initial germination, and the effect of dormancy-breaking treatments were determined. Seeds from 18 Latvian populations with contrasting seed dormancy characteristics were genotyped. Although morphological differences between seeds from different regions were revealed, genetic analysis of the selected populations indicated that the population structure was not related to geographical location, which probably reflects the impact of anthropogenic dispersal of A. fatua seeds. The effect of dormancy-breaking treatments varied between years, between climatic zones and between populations, indicating environmental influences as well as inherited dormancy

Epiphytic and Endophytic Fungi Colonizing Seeds of Two <i>Poaceae</i> Weed Species and <i>Fusarium</i> spp. Seed Degradation Potential In Vitro

Fungi colonizing the surface and endosphere of two widespread Poaceae weed species, Avena fatua and Echinochloa crus-galli, were isolated to compare the taxonomic composition between the plant species, location, and year of the seed collection. The seed-degrading potential of Fusarium isolated from the seeds was tested by inoculating seeds of E. crus-galli with spore suspension. Molecular identification of epiphytic and endophytic fungal genera was performed by sequencing the ITS region of rDNA. Endophytes comprised of significantly lower fungal richness compared to epiphytes. A significant taxonomic overlap was observed between the endosphere and seed surface. The most abundant genera were Alternaria, Fusarium, Cladosporium, and Sarocladium. Analysis of similarities and hierarchical clustering showed that microbial communities were more dissimilar between the two plant species than between the years. Fusarium isolates with a high potential to infect and degrade E. crus-galli seeds in laboratory conditions belong to F. sporotrichioides and F. culmorum

Arable Weeds and Management in Europe

“Arable Weeds and Management in Europe” is a collection of weed vegetation records from arable fields in Europe, initiated within the Working Group Weeds and Biodiversity of the European Weed Research Society (EWRS). Vegetation-plot data from this scientific community was not previously contributed to databases. We aim to prove the usefulness of collection for large scale studies through some first analyses. We hope to assure other weed scientists who have signalled willingness to share data, and plan to construct a full data base, making the data available for easy sharing. Presently, the collection has over 60,000 records, taken between 1996 and 2015. Many more studies for potential inclusion exist. Data originate mostly from studies exploring the effect of agricultural management on weed vegetation. The database is accompanied with extensive meta-data on crop and weed management on the surveyed fields. The criteria for inclusion were a minimum amount of information on the cultivated crop, and a georeference. Most fields were surveyed repeatedly, i.e. transects, multiple random plots, or repeated visits. All surveys aimed to record the complete vegetation on the plots. Sometimes, taxa were identified only to genus level, due to survey dates very early in the vegetation period. Plant taxonomy is standardized to the Euro+Med PlantBase.B. was funded by Deutsche Forschungsgemeinschaft under the grant number BU 3097/1-1

Two sides of one medal: Arable weed vegetation of Europe in phytosociological data compared to agronomical weed surveys

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