Browsing by Author "Munir, Tariq"

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    Mineral nitrogen and phosphorus pools affected by water table lowering and warming in a boreal forested peatland
    (2017-09-14) Munir, Tariq; Khadka, Bhupesh; Xu, Bin; Strack, Maria; Munir, Tariq
    Changes in atmospheric temperature and lowering in water-table (WT) are expected to affect peatland nutrient dynamics. To understand the response of peatland nitrogen (N) and phosphorus (P) dynamics to warming and drainage in a continental wooded-bog of hummock – hollow microtopography, we compared three sites: 1) control, 2) recently drained (2-3 years; experimental), and 3) older drained (12-13 years; drained), during 2013. The WT was lowered at experimental and drained sites to 74 cm and 120 cm, respectively, while a warming of ~1 °C was created at one-half of the microforms using open-top chambers. Responses of peat total-inorganic- nitrogen [TIN = nitrate nitrogen (NO3--N) + ammonium nitrogen (NH4+-N)] and phosphate-P [PO43--P] pools and, vegetation C:N ratio, δ13C, and δ15N to the experimental treatments were investigated across sites/microforms and over time. Peat TIN available and extractable pools increased with deepening of WT and over time, and were greater at hummocks relative to hollows. In contrast, the PO4 pools increased with short-term drainage but reverted to very close to their original (control) nutrient values in the longer-term. The WT and warming driven change in the peat TIN pool was strongly reflected in the vascular vegetation C:N ratio and, shrub δ13C and δ15N, while moss nutrient dynamics did not vary between sites. Therefore, we suggest that atmospheric warming combined with WT deepening can increase the availability of mineral N and P, which then can be reflected in vascular vegetation and hence modify the productivity and ecosystem functioning of the northern mid-latitude continental forested bogs in the long-term.
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    Partitioning Forest-Floor Respiration into Source Based Emissions in a Boreal Forested Bog: Responses to Experimental Drought
    (MDPI, 2017-03-10) Munir, Tariq; Khadka, Bhupesh; Xu, Bin; Strack, Maria
    Northern peatlands store globally significant amounts of soil carbon that could be released to the atmosphere under drier conditions induced by climate change. We measured forest floor respiration (RFF) at hummocks and hollows in a treed boreal bog in Alberta, Canada and partitioned the flux into aboveground forest floor autotrophic, belowground forest floor autotrophic, belowground tree respiration, and heterotrophic respiration using a series of clipping and trenching experiments. These fluxes were compared to those measured at sites within the same bog where water‐table (WT) was drawn down for 2 and 12 years. Experimental WT drawdown significantly increased RFF with greater increases at hummocks than hollows. Greater RFF was largely driven by increased autotrophic respiration driven by increased growth of trees and shrubs in response to drier conditions; heterotrophic respiration accounted for a declining proportion of RFF with time since drainage. Heterotrophic respiration was increased at hollows, suggesting that soil carbon may be lost from these sites in response to climate change induced drying. Overall, although WT drawdown increased RFF, the substantial contribution of autotrophic respiration to RFF suggests that peat carbon stocks are unlikely to be rapidly destabilized by drying conditions
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    Peatland Biogeochemistry and Plant Productivity Responses to Field-based Hydrological and Temperature Simulations of Climate Change
    (2015-01-09) Munir, Tariq; Strack, Maria
    Northern peatlands have accumulated approximately one third of all soil carbon (C) and therefore play an important role in the global C cycle. Besides the C sink function, peatlands are one of the largest biological sources of atmospheric methane (CH4) and represent approximately 10% of global soil nitrogen (N) stocks. These ecosystems are present at latitudes that are predicted to be highly sensitive to climate change that will likely result in deeper water table positions. The reduction in soil moisture may increase peat decomposition rates and consequently affect nutrient dynamics. While attempts have been made to assess the impact of climate change on peatland C gas exchange and nutrient dynamics, controlled field experimentation remains limited. Therefore, the objectives of this thesis were to estimate the responses of peatland carbon dioxide (CO2) and CH4 flux, nutrient dynamics, and plant productivity to a recent- and a ten-year old drainage, and a warming treatment induced by open-top chambers, across the peatland’s hummock-hollow microtopography. The study was carried out at a dry continental treed bog in boreal Alberta during 2011-2013. Water level drawdown in the longer-term resulted in shifts in biomass coverage and plant community composition between the microforms. The moss biomass was replaced by vascular plant biomass (mostly woody shrubs) at hummocks, and by lichen biomass at hollows. The shift in dominant vegetation was reflected in CO2 fluxes; the longer-term drained hummocks were the largest sink of CO2 while hollows at the same site were the largest sources. While the short- and longer-term drained sites were net sources of CO2, the warming treatment converted the longer-term drained site to a sink of CO2-C. Water table drawdown greatly reduced CH4 flux at both hummocks and hollows, and the reduction increased with time. The warming treatment increased emissions of CH4 at hollows and increased consumption of CH4 at hummocks. The extractable and available nutrient pools in the peat soil increased with deepening of water level, and over time. The water level driven dynamics of peat nutrient pools were reflected in the vegetation C:N ratio. The warming treatment increased nutrient pools more at hummocks than at hollows and the impact increased with time. Based on these results, I suggest that, models of peatland development need to include C and nutrient cycling links to moisture and temperature parameters to better predict plant productivity and C exchange under changing climatic conditions.