Browsing by Subject "typensidonta"

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  • Haarala, Jaakko (Helsingin yliopisto, 2020)
    Ilmastonmuutos tuo mukanaan Suomeen äärioloja, jotka lisäävät typen huuhtoutumista, mutta myös mahdollisuuksia pidempinä ja lämpimimpinä kasvukausina. Viimeisen kahdenkymmenen vuoden aikana lajikejalostus ei ole kuitenkaan lisännyt käytännön satotasoja, vaan sadot ovat jopa taantuneet. Laskeneet satotasot eivät selity pelkästään laskeneilla typpilannoitustasoilla, ja satokuilua onkin lähdetty ratkaisemaan monimuotoisemmalla viljelykierrolla, joihin sisältyy esimerkiksi härkäpapua. Tutkimuksen tavoitteena oli selvittää esikasvina toimineen härkäpavun (Vicia faba L.) vaikutusta maaperän liukoisiin typpivaroihin ja seuraavien viljelykasvustojen typpidynamiikkaan. Tutkimus toteutettiin Haltialan pellolla satunnaistettuna täydellisten lohkojen kerrannekokeena, jossa käsittelynä oli yhteensä kuusi kasvia ja neljä lannoitustasoa. Kasvustoista mitattiin lehtivihreäpitoisuus, lehtialaindeksi (LAI) sekä määritettiin kuiva-aineen kehittyminen ja koeruuduista otettiin maanäytteet vähintään viidesti kasvukauden aikana. Biomassamääritysten pohjalta analysoitiin kasvinosien typpipitoisuudet ja laskettiin typpisadot. Maanäytteet uutettiin (2M KCl) NH4+- ja NO3--N-pitoisuuksien määrittämiseksi. Kasvustojen typpidynamiikkaa (NUE, UPE, UTE, NHI), typpisatoja ja koeruutujen mineralisaatiota sekä mineraalityppipitoisuuksia vertailtiin lannoitus ja esikasvi taustatekijöinä. Lämmin ja kuiva kasvukausi viivästytti kasvustojen sulkeutumista ja epätasaisuus vaikutti tuloksiin enemmän kuin esikasvi tai lannoitus. Lannoittamattomat kasvustot eivät eronneet tilastollisesti biomassaltaan tai typenotoltaan lannoitetuista. Kasvien typenotto vaikutti enemmän maaperän NO3--N kuin NH4+-N-pitoisuuksiin. Härkäpapuesikasvi lisäsi kauran lehtialan kestoa (LAD). Laskennallinen mineralisaatio oli suurin nollalannoitusruuduissa, keskimäärin 127 N kg ha-1. Kasvustojen UPE, UTE ja NUE jäivät pieniksi maan pintahorisontin ollessa lakastumisrajalla koko kesän. Härkäpavulla on hyvin todennäköisesti vaikutusta maan typpivaroihin, mutta tarkemmat arviot vaativat syvemmälle maahan ulottuvia mittauksia ja edullisemman kasvukauden.
  • Orasmaa, Saila (Helsingfors universitet, 2012)
    This study was conducted to find suitable methods for the quality control of commercial plant growth-promoting (PGP) microbial products. A commercial bacterial product called TwinN was evaluated for its microbiological quality, physiological features of its bacterial strains, and its ability to promote plant growth. Other bacterial strains which had shown PGP features in earlier studies, were used as reference strains. The microbiological composition of the TwinN bacterial lyophilisate corresponded to the manufacturer's description, as it was composed of bacteria belonging to the genera Azoarcus, Azorhizobium, and Azospirillum. However, the concentrations of some of the bacterial species were lower than reported. If the product was used according to the manufacturer's instructions, the bacterial counts in the plants wouldn't necessarily reach a sufficient level. With the TwinN product, a powdery growth medium was also supplied, which appeared to be highly contaminated with bacteria and moulds. The nature and source of these microbes remained unknown. The bacteria in the TwinN product were isolated as pure cultures, and identified based on the partial sequences of their 16S rRNA genes. Specific plate and broth culturing techniques were used to uncover the potential PGP physiological features of the pure cultures. The bacterial strains were able to produce indole-3-acetic acid, ACC deaminase and siderophore, which suggests that they might also have PGP activity. The ability of the bacteria to promote plant growth was tested in a plant experiment using hydroponic growth pouches. An Azospirillum brasilense strain isolated from the TwinN product was able to increase the dry weight of the shoots of chinese gabbage almost 41 % compared with the uninoculated control plants. Of the five bacterial treatments used, the A. brasilense strain was the only one able to promote plant growth. Chinese cabbage was the only plant species out of six that gave a positive response to the A. brasilense treatment. For some reason, the TwinN product itself didn't show any PGP activity. The plants showed signs of nitrogen deficiency, which indicates that no bacterial nitrogen fixation had taken place. The method used to determine the microbial composition of the TwinN product, was Amplicon sequencing. Combined with the results of traditional culturing techniques, Amplicon sequencing proved to be a useful method for the assessment of the microbiological quality of the product. The physiological tests that could be of use in the quality control of PGP products, are siderophore production test, phosphate solubilization test and the test that measures indole-3-acetic acid production.
  • Palmgren, Kristina; Saarsalmi, Anna; Weber, Assi (Suomen metsätieteellinen seura, 1985)
  • Rinne, Ilkka; Melvasalo, Terttu; Niemi, Åke; Niemistö, Lauri (Vesihallitus. National Board of Waters, 1979)
    Vesientutkimuslaitoksen julkaisuja 34, 88-107
    Sinilevien typensidonta Itämeressä 1975 ja 1977.
  • Ritala, Kaisa (Helsingin yliopisto, 2015)
    Nitrogen is an important nutrient for forest growth. The sources of nitrogen in boreal forests are underground processes, biological nitrogen fixations and depositions. The availability of nitrogen in boreal forests is limited, which is why biological nitrogen fixation is a crucial thing. In natural forests, nitrogen is fixed in bottom layer vegetation and in the bacteria that live on the ground, especially in cyanobacteria. The fixing activity of bacteria depends on many environmental factors, of which the temperature, moisture and species of the bottom layer are the most important. It’s been predicted that forest fires will increase in the boreal zone, due to climate change. This will increase the number of different successional stages. Forest fires are the most important disturbance in boreal forests, since they can initiate the succession from the beginning and affect the circulation of nutrients. Fires also affect the activity of biological nitrogen fixation by releasing nutrients and, partly or completely, destroying the bottom layer vegetation. The results of fires at different successional stages are poorly known and there’s no research concerning the whole bottom layer. The purpose of the study was to find out the effects to biological nitrogen fixation when a forest fire has started succession at the beginning. The material was collected at Värriö nature reserve in Northern Finland (67?46´ N, 29?35´ E). Four forests were chosen for the research. In these areas, fires had occurred 5, 45, 62 and 156 years ago. The forest type was sub-xeric heath forest, dominated by Scots pine (Pinus sylvestris L.). To measure the nitrogen fixation, a sample plot was built in each forest. Ten samples of the ground vegetation and humus layer were collected four times during the summer from each plot. The biological nitrogen fixation was defined with acetylene reduction assay. The samples were analyzed for both the field moisture and saturation humidity at the different moisture stages. The inventory of the vegetation was performed with a 1 m2 area during the summer. In this study, it was discovered that the successional stage, growing season, vegetation and moisture affect the nitrogen fixation. Along with the succession process, the amount of bottom layer mosses increases, which enables a larger growing area for bacteria. The diversity of mosses can be linked to the moisture status, which is an essential thing for nitrogen fixation. From the results, it can be concluded that biological nitrogen fixation becomes important when mosses are recovered during the late succession stages. Climate change is supposed to increase the temperature and precipitation, which can slightly raise the level of the biological nitrogen fixation. In this study, the nitrogen fixation of free living bacteria was found, which might be of interest for future research.