BEGIN:VCALENDAR VERSION:2.0 PRODID:-//132.216.98.100//NONSGML kigkonsult.se iCalcreator 2.20.4// BEGIN:VEVENT UID:20251105T074553EST-40973JN3FV@132.216.98.100 DTSTAMP:20251105T124553Z DESCRIPTION:Abstract The nature and intensity of environmental changes pro jected by climate models for Eastern Canada could significantly affect the functioning of boreal forest ecosystems. In this thesis\, I tested experi mentally the effects of some of these changes (increased soil temperature and atmospheric N deposition\, and summer droughts) in a mature boreal bal sam fir stand (Abies balsamea (L.) Mill.) in the Réserve faunique des Laur entides (Quebec). The general objective of the thesis was to evaluate the adaptation of the soil/plant system to these changes. In the first experi ment\, using heat-resistance cables buried in the ground and water nozzles set up above the trees\, soil temperatures were increased (+4°C)\, spring snowmelt hastened (2-3 weeks)\, and higher levels of atmospheric N were d eposited on the canopy (3x the natural NH4NO3 concentration in the rain) f or three years. In the second experiment\, a summer drought (starting in J uly) was simulated in two consecutive years by means of throughfall exclus ion using polyethylene sheets maintained 1.3-2 m aboveground and redirecti ng the water outside the plots. In the soil warming – N deposition experim ent\, volumetric soil water content was assessed weekly\, soil chemistry w as monitored with ion-exchange membranes (PRS-probesTM) and soil extractio ns\, while soil respiration was measured in a laboratory incubation experi ment. Tree nutrition was assessed through leaf sampling and nutrient analy ses\, radial growth was monitored using dendrometers and seasonal xylogene sis was assessed using microscopic analyses of wood microcores extracted w eekly from April to October each year. In the second experiment\, the anal ysis of wood microcores was also used to assess the effects of throughfall exclusion on balsam fir xylogenesis\, while the volumetric soil water con tent was monitored weekly.             Three years of warmer soils decrea sed the soil mineralizable C pool by 11-15% with limited effects on the av ailability of inorganic N (NH4 and NO3). The availability of K\, Mg and SO 4 increased by 43\, 44 and 79% in the forest floor of heated plots\, respe ctively\, while Mg\, SO4 and Al increased by 29\, 66 and 23% in the minera l horizon\, respectively. Increased nitrogen deposition did not affect soi l nutrient availability. The treatments had no effects on the amount of wo od produced or the foliar nitrogen concentration of balsam fir. The experi mentally induced earlier snowmelt did not hasten resumption of xylogenesis \, although an eight-day earlier peak in diameter growth was observed in h eated plots in the second year. Finally\, two consecutive years of summer drought reduced by 16.1% the diameter of tracheids and increased the thick ness of their cell wall by 14.1% during both years. In addition\, the trea tment delayed by more than a week the tracheid differentiation process in the second year\, with a concomitant decrease of 26% in the number of trac heids produced.             If the short-term responses of balsam fir obs erved in our studies persist over time\, it should be considered relativel y resilient to warmer soils and higher N deposition but responsive to drou ght episodes. Thus\, a higher frequency and/or intensity of droughts could have major consequences on the productivity of the balsam fir ecosystem. However\, other environmental factors that are expected to change in the f uture were not included in this thesis (e.g. increasing air temperature an d atmospheric CO2) and could affect the response of the ecosystem to incre ased soil temperature\, N deposition and water stress. DTSTART:20130627T130000Z DTEND:20130627T160000Z LOCATION:R3-038\, Raymond Building\, CA\, QC\, St Anne de Bellevue\, H9X 3V 9\, 21111 Lakeshore Road SUMMARY:Loïc D'Orangeville PhD Oral Defense: Global changes and the balsam fir ecosystem: Effects of increased soil temperature\, nitrogen deposition and water stress on soil chemistry and xylogenesis URL:/nrs/channels/event/lo%C3%AFc-dorangeville-phd-ora l-defense-global-changes-and-balsam-fir-ecosystem-effects-in END:VEVENT END:VCALENDAR