Browsing by Subject "NITROGEN DYNAMICS"

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  • Riikonen, Anu; Pumpanen, Jukka; Mäki, Mari Jasmiina; Nikinmaa, Eero (2017)
    We assessed the net carbon (C) sequestration dynamics of street tree plantings based on 10 years of measurements at two case study sites each with different tree species in Helsinki, Finland. We assessed C loss from tree soils and tree C accumulation, tested the applicability of pre-existing growth and biomass equations against observations, and estimated the time point for the beginning of net C sequestration for the studied street tree plantings. The tree woody biomass C accumulation in the first 10 years after planting was 18-32 kg per tree. At the same time the C loss from the growth media was at least 170 kg per growth media volume (25 m(3)) per tree. If this soil C loss was accounted for, the net C sequestration would begin, at best, approximately 30 years after planting. Biomass equations developed for traditional forests predicted more stem biomass and less leaf and branch biomass than measured for the species examined, but total aboveground biomass was generally well predicted.
  • Adamczyk, Bartosz; Adamczyk, Sylwia; Smolander, Aino; Kitunen, Veikko; Simon, Judy (2018)
    Processes underlying soil organic matter (SOM) transformations are meeting growing interest as SOM contains more carbon (C) than global vegetation and the atmosphere combined. Therefore, SOM is a crucial element of the C cycle, especially in ecosystems rich in organic matter, such as boreal forests. However, climate change may shift the fate of this SOM from C sink into C source, accelerating global warming. These processes require a better understanding of the involved mechanisms driving both the C cycle and the interlinked nitrogen (N) cycle. SOM transformations are balanced by a network of interactions between biological, chemical and physical factors. In this review, we discuss the findings of the most recent studies to the current state of knowledge about the main drivers in SOM transformations. We focus on plant-derived secondary metabolites, as their biochemical traits, especially interactions with soil microbial communities, organic N compounds and enzymes make them potential regulators of SOM decomposition. However, these regulatory abilities of plant-derived compounds are not fully explored.
  • Karhu, Kristiina; Kalu, Subin; Seppänen, Aino; Kitzler, Barbara; Virtanen, Eetu (2021)
    Addition of biochar to soil has been shown to reduce nitrogen (N) leaching in pot experiments, but direct field measurements are scarce, and data is lacking especially from colder, boreal conditions. We studied the effect of soil organic amendments on nitrate (NO3-) and ammonium (NH4+) leaching using the resin bag method, by placing the bags containing ion-exchange resins under the plough layer. We compared N leaching under five different treatments at the Päästösäästö project site (Soilfood Oy) in Parainen, south-western Finland: non-fertilized control, fertilized control, and three different organic amendments: spruce biochar, willow biochar and nutrient fiber. During the 2017 growing season, resin bags were changed monthly between the end of May and beginning of September, extracted with 1 M NaCl, and analyzed for inorganic N. The daily leaching rate of NO3- was greatest at the beginning of the growing season, right after fertilization. Ammonium leaching was generally lower, and independent of the time since fertilization. The spruce biochar reduced cumulative NO3- leaching by 68% compared to the fertilized control. The NH4+leaching in the organic amendment treatments did not statistically significantly differ from the fertilized control in pairwise comparisons. In October 2017, after harvesting, the resin bags were placed under soil columns again, and left in the soil over winter to accumulate N leached during the plant-free period. Cumulative NO3- leaching during winter was consistent with the corresponding summer results, and average leaching decreased in the order: willow biochar >fertilized control >nutrient fiber >non-fertilized control >spruce biochar. Thus, we show here, for the first time in a field study from boreal conditions that spruce biochar soil application decreased nitrate leaching, while increasing its retention in the surface layer of the biochar-amended soil.
  • Tao, Fulu; Palosuo, Taru; Rötter, Reimund P.; Díaz-Ambrona, Carlos Gregorio Hernández; Inés Mínguez, M.; Semenov, Mikhail A.; Kersebaum, Kurt Christian; Cammarano, Davide; Specka, Xenia; Nendel, Claas; Srivastava, Amit Kumar; Ewert, Frank; Padovan, Gloria; Ferrise, Roberto; Martre, Pierre; Rodríguez, Lucía; Ruiz-Ramos, Margarita; Gaiser, Thomas; Höhn, Jukka G.; Salo, Tapio; Dibari, Camilla; Schulman, Alan H. (2020)
    Robust projections of climate impact on crop growth and productivity by crop models are key to designing effective adaptations to cope with future climate risk. However, current crop models diverge strongly in their climate impact projections. Previous studies tried to compare or improve crop models regarding the impact of one single climate variable. However, this approach is insufficient, considering that crop growth and yield are affected by the interactive impacts of multiple climate change factors and multiple interrelated biophysical processes. Here, a new comprehensive analysis was conducted to look holistically at the reasons why crop models diverge substantially in climate impact projections and to investigate which biophysical processes and knowledge gaps are key factors affecting this uncertainty and should be given the highest priorities for improvement. First, eight barley models and eight climate projections for the 2050s were applied to investigate the uncertainty from crop model structure in climate impact projections for barley growth and yield at two sites: Jokioinen, Finland (Boreal) and Lleida, Spain (Mediterranean). Sensitivity analyses were then conducted on the responses of major crop processes to major climatic variables including temperature, precipitation, irradiation, and CO2, as well as their interactions, for each of the eight crop models. The results showed that the temperature and CO2 relationships in the models were the major sources of the large discrepancies among the models in climate impact projections. In particular, the impacts of increases in temperature and CO2 on leaf area development were identified as the major causes for the large uncertainty in simulating changes in evapotranspiration, above-ground biomass, and grain yield. Our findings highlight that advancements in understanding the basic processes and thresholds by which climate warming and CO2 increases will affect leaf area development, crop evapotranspiration, photosynthesis, and grain formation in contrasting environments are needed for modeling their impacts.