Browsing by Subject "nutrient cycling"

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  • Bernard, Guillaume; Kauppi, Laura; Lavesque, Nicolas; Ciutat, Aurelie; Gremare, Antoine; Masse, Cecile; Maire, Olivier (2020)
    The invasive mussel Arcuatula senhousia has successfully colonized shallow soft sediments worldwide. This filter feeding mussel modifies sedimentary habitats while forming dense populations and efficiently contributes to nutrient cycling. In the present study, the density of A. senhousia was manipulated in intact sediment cores taken within an intertidal Zostera noltei seagrass meadow in Arcachon Bay (French Atlantic coast), where the species currently occurs at levels corresponding to an early invasion stage. It aimed at testing the effects of a future invasion on (1) bioturbation (bioirrigation and sediment mixing) as well as on (2) total benthic solute fluxes across the sediment-water interface. Results showed that increasing densities of A. senhousia clearly enhanced phosphate and ammonium effluxes, but conversely did not significantly affect community bioturbation rates, highlighting the ability of A. senhousia to control nutrient cycling through strong excretion rates with potential important consequences for nutrient cycling and benthic-pelagic coupling at a broader scale. However, it appears that the variability in the different measured solute fluxes were underpinned by different interactions between the manipulated density of A. senhousia and several faunal and/or environmental drivers, therefore underlining the complexity of anticipating the effects of an invasion process on ecosystem functioning within a realistic context.
  • Fagerholm, Freja (Helsingin yliopisto, 2021)
    In the process of decomposition soil carbon is transformed into CO2 by microbial respiration, which makes decomposition a key process for understanding carbon cycling an releases of CO2. Since the northern permafrost regions contain half of all belowground carbon and the tundra regions are expected to be markedly affected by climate warming, it is of particular interest to understand how warming will affect decomposition in the tundra. Decomposition is however influenced by many factors, from climatic factors such as temperature and precipitation to the belowground organisms inhabiting the soils and the aboveground system dictating the litter that falls to the ground and is decomposed. Further, grazing has been shown to oppose some of the effects of warming on tundra. In this thesis I analyzed data collected from two long-term field experiments, one in Kilpisjärvi (NW Finland) and the other close to Kangerlussuaq Fjord (SW Greenland), both using fencing for manipulation of grazing regime and open-top chambers for artificial warming. My aim was to not only investigate how warming and grazing affect decomposition, but also to understand whether the magnitude of changes in decomposition can be explained by changes in plant community traits and soil characteristics. I found that in contrast to my hypothesis, warming decreased decomposition in Kangerlussuaq, where the soil was drier and contained less carbon than in Kilpisjärvi. I found no effects of grazing on decomposition, plant community traits nor soil characteristics in neither of the study locations. Neither did I find any consistent associations between changes in decomposition and changes in plant community traits, indicating that the effect of litter quality on decomposition is minor in these areas likely rather limited by climate. I found an association for increased decomposition when plant community C:N ratio and C:P ratio increased as a response to warming, but only in Kilpisjärvi, and since increased plant community C:N and C:P ratios are linked to resistant litter this positive effect is unlikely driven by enhanced litter quality. However, I did find a positive relationship between increased root biomass and increased decomposition as a response to warming that was consistent across areas and grazing regimes, indicating that warming can boost decomposition in different tundra habitats by promoting root growth.
  • Westerling, Kim (Helsingfors universitet, 2011)
    In Finland most of the accumulated phosphorus in the agricultural soils is underutilized and at the same time excess phosphorus in soil is susceptible to leaching. Arbuscular mycorrhiza (AM) has the potential to promote plant phosphorus nutrition and growth, and reduce nutrient leaching. The aim of this study was to investigate the effect of mycorrhizal symbiosis on plant growth and phosphorus nutrition with three different fertilization management practices. The influence of fertilization management history on field AMF population was also studied. To relate the impact on AM to impacts on other soil quality aspects, the effect of the fertilization rates on crop growth and indicators of soil functioning was evaluated. Long term field experiments established in 1965-66 on three sites in Northern Sweden were utilized. Six years’ rotation either with five grass years and a barley year or barley monoculture was treated with recommended (NPK) and double the recommended (2NPK) rate of mineral fertilisation or with farmyard manure (FYM) with a nutrient amount corresponding to the NPK –treatment for 32 years. The effect of three long term practices on the potential AM contribution to crop phosphorus nutrition and growth was studied in a bioassay. To study the impact of longterm management practices on functional properties of AMF, the sterilised soil from the field plots of NPK and FYM treatments was re- and cross-inoculated (5 v-%) with untreated field soil from each of the same treatments. Crop yields were measured in the field and field soil quality was assessed. Benefit from AM in terms of crop phosphorus nutrition and growth was greatest when manure was applied while there were no differences among the mineral fertiliser treatments. There were no statistically significant differences in the bioassay with re- and cross-inoculations. Grass and barley yields were highest when mineral NPK fertiliser was applied at double the recommended rate. Crop performed equally well or better in terms of yield with manure compared to a corresponding nutrient amount in mineral fertilizers. Manure applications seemed to increase soil carbon and nitrogen contents relative to the recommended amount of NPK, yet keeping the plant-available phosphorus concentration liable for leaching at a similarly low level. Thus, enhanced recycling of nutrients through use of farmyard manure to replace mineral NPK fertilisation favoured reliance on AM in phosphorus nutrition of crops with no trade-off in yields, simultaneously enhancing soil quality.
  • Kinnunen, Ossi (Helsingin yliopisto, 2019)
    Current food system produces significant share of global greenhouse gas emissions, in addition to causing other negative environmental impacts. One option for reducing these negative impacts is to use recycled fertilizers: however, the vastly varying properties of different recycled fertilizers affect the utilization of nutrients by plants, as well as the nutrients’ behaviour in soil. The proper use of recycled fertilizers requires understanding about the functioning of nutrients - especially nitrogen - in soil, in addition to knowledge about the properties of the fertilizer. The aim of this thesis was to study how different kinds of recycled fertilizers affect the flows of ni- trogen and nitrogen field balance in oat cultivation. The data was collected from HYKERRYS- project’s (2016-2019) field experiment in growing season 2017. Fertilizer treatments included in the study were ammonium sulphate (AS), meat and bone meal pellet (MB), vermicompost (VC) and biogas digestate (BD), while unfertilized (NF) and chemically fertilized (CF) treatments served as controls. Nitrogen contents of the grain yield and straw were determined from samples collected from the field experiment. Other nitrogen flows were estimated based on literature and existing models. Based on the results, nitrogen flow models and field balances were developed for each treatment. The oat grain yield contained between 78 and 143 kg N/ha. The nitrogen yield in the CF treatment was significantly greater than in NF or VC treatment, but other treatments did not differ significantly from the CF treatment. The nitrogen content of the whole oat crop (including straw and roots) was between 121 and 361 kg N/ha: the N contents of NF and VC treatments were significantly smaller than in the CF treatment. The nitrogen field balance was -73 for NF, 7 for AS, -59 for MB, -48 for VC, -30 for BD and -18 kg N/ha/a for CF treatment. The field balance of the NF treatment was sig- nificantly lower than in CF treatment, but the field balances of the recycled fertilizer treatments did not differ significantly from the CF treatment. The nitrogen flows in soil-plant system do not only depend on the amount of nitrogen fertilization, but also differ depending on the type and properties of the fertilizer. There are differences between the chemical and recycled fertilizers, but also amongst the recycled fertilizers. In this study, the use of recycled fertilizers did not increase the nitrogen field balance.