Peat Biogeochemistry and Greenhouse Gas Emissions during Peat Use in Horticulture

Peatlands cover only 3% of the world's land cover, but in the northern hemisphere they store up to a third of organic carbon (C). The organic matter stored in peat bogs, known as peat, is highly sought-after as a growing medium for horticulture and agriculture in controlled environments. Peat extraction involves draining the natural peat bog and extracting the peat over several decades. The peat extracted is generally acidic and low in nutrients, so nutrients, limestone to raise the pH and other horticultural additives are added to enhance plant growth. Peat to which horticultural additives are added is called growing medium. Peat decomposition rates are relatively well known. However, data on the biogeochemical properties and decomposition rates of peat-based growing substrates are scarce but necessary to facilitate ongoing debates on the carbon footprint of peat use in horticulture. The aims of this thesis are i) to characterize growing substrates and compare how they differ from raw peat ii) to measure the decomposition rate of growing substrates iii) to explore the role of horticultural additives in increasing the decomposition rate of growing iv) analyze the decomposition rate of growing substrates on a Canadian scale and report the emission factor (EF) of peat use in horticulture and v) quantify the role of horticultural plants in increasing the decomposition rate of growing substrates. My work combines a variety of measurements ranging from Greenhouse Gas (GHG) flux measurements, δ13C, radiocarbon measurements, microbial analysis, soil biogeochemistry and modeling to arrive at the set objectives. I measured that the biogeochemistry and decomposition rates of growing substrates vary considerably from those of peat. To understand the causes of this increased decomposition rate in growing substrates, I show, using factorial experiments, that limestone added to increase pH increases the decomposition rate of growing substrates. Extrapolation of the values to a national scale shows that current IPCC Tier 1 emissions overestimate emissions from peat used in horticulture, and I suggest a revision to Intergovernmental Panel on Climate Change (IPCC) Tier 2 values. Growing lettuces and petunias in peat-based growing substrates in a controlled environment, I report on the different components of plant and soil respiration. Using radiocarbon measurements, I show that plant roots increase peat decomposition, but this could be species dependent. The results of this thesis help to revise the EFs related to the use of peat in horticulture in Canada and to improve the understanding of horticultural peat

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.