Examining Mechanisms of Methane Transport in Populus trichocarpa
Abstract
Although the dynamics of methane (CH4 ) emission from croplands and wetlands have been fairly well investigated, the contribution of trees to global CH4 emission and the mechanisms of tree transport are relatively unknown. CH4 emissions from the common wetland tree species Populus trichocarpa (black cottonwood) native to the Pacific Northwest were measured under hydroponic conditions in order to separate plant transport mechanisms from the influence of soil processes. Roots were exposed to CH4 enriched water and whole-canopy emissions of CH4 were measured. The average flux for 34 trials (at temperatures ranging from 17 to 25 C) was 2.8 ± 2.2 μg CH4 min-1(whole canopy). Overall intra-tree CH4 flux increased with temperature. Compared to the isotopic composition of root water CH4 , δ13 C values were depleted for canopy CH4 where the warmest temperatures (24.4-28.7 C) resulted in an epsilon of 2.8 ± 4.7‰; midrange temperatures (20.4- 22.1 C) produced an epsilon of 7.5 ±3.1 ‰; and the coolest temperatures examined (16.0-19.1 C) produced an epsilon of 10.2 ± 3.2 ‰. From these results it is concluded that there msy br multiple transport processes at work in CH4 transport through trees and the dominance of these processes clearly changes with temperature. Overall, the intra-tree transport mechanisms that dominates at lower temperatures and during lower fluxes results in a larger overall fractionation, while the transport mechanisms that prevail at higher temperatures and higher and higher overall fluxes produces a smaller isotopic fractionation. These findings, as well as additional lab and field-based measures will be presented. Finally, the implications of possibly distinct forms of CH4 gas transport within trees, and it's impact on understanding of biogeochemical processes, will be discussed.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.B21N..08R
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCESDE: 0486 Soils/pedology;
- BIOGEOSCIENCESDE: 0490 Trace gases;
- BIOGEOSCIENCES