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TitleResponse strategies of boreal spruce trees to anthropogenic changes in air quality and rising pCO2
AuthorSavard, M MORCID logo; Bégin, C; Marion, J
SourceEnvironmental Pollution vol. 261, 114209, 2020 p. 1-10, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20190296
Mediapaper; on-line; digital
File formatpdf; html
ProvinceBritish Columbia; Alberta; Saskatchewan; Manitoba; Ontario; Quebec; New Brunswick; Nova Scotia; Prince Edward Island; Newfoundland and Labrador; Northwest Territories; Yukon; Nunavut; Canada
NTS1; 2; 3; 10; 11; 12; 13; 14; 15; 16; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 52; 53; 54; 55; 56; 57; 58; 59; 62; 63; 64; 65; 66; 67; 68; 69; 72; 73; 74; 75; 76; 77; 78; 79; 82; 83; 84; 85; 86; 87; 88; 89; 92; 93; 94; 95; 96; 97; 98; 99; 102; 103; 104; 105; 106; 107; 114O; 114P; 115; 116; 117; 120; 340; 560
Lat/Long WENS-141.0000 -50.0000 90.0000 41.7500
Subjectsenvironmental geology; geochemistry; Nature and Environment; Science and Technology; water utilization; nitrogen; oxides; carbon dioxide; isotopes; climate; climate effects; Trees
Illustrationsplots; graphs; tables
ProgramEnvironmental Geoscience Sources
Released2020 02 20
AbstractLittle is known about how forests adjust their gas-exchange mode while atmospheric CO2 rises globally and air quality changes regionally. The present study aims at addressing this research gap for boreal spruce trees growing in three different regions of Canada, submitted to distinct levels of atmospheric emissions, by examining the amount of carbon gained per unit of water lost in trees, i.e., the intrinsic water use efficiency (iWUE).
Under pristine air quality conditions, middle-to long-term trends passed from no-reaction mode to passive strategies due to atmospheric CO2, and short-term iWUE variations mostly ensue from year-to-year climatic conditions. In contrast, in trees exposed to pollutants from a copper smelter and an oil-sands mining region, air quality deterioration generated swift, long-term iWUE rises immediately at the onset of operations. In this case, the very active foliar strategy sharply reduced the intra-foliar CO2 (Ci) pressure. Statistical modeling allowed identifying emissions as the main trigger for the iWUE swift shifts; subsequent combined effects of emissions and rising CO2 led to passive foliar modes in the recent decades, and short-term variations due to climatic conditions appeared all along the series.
Overall, boreal trees under different regional conditions modified their foliar strategies mostly without changing their stem growth. These findings underline the potential of acidifying emissions for prompting major iWUE increases due to lowering the stomatal apertures in leaves, and the combined influence of rising CO2 in modulating other foliar responses. A fallout of this research is that degrading air quality may create true divergences in the relationship between tree-ring isotopes and climatic conditions, an impact to consider prior to using isotopic series for paleo-climatic modeling.
Summary(Plain Language Summary, not published)
Trees play a key role in the carbon planetary cycle because they consume atmospheric CO2 to produce their tissues. Important questions arise from this fonction because the current rise of CO2 may increase their growth rate as suggested by previous studies. However, studies never investigated together the combined effects of rising pCO2, climate change and degradation of air quality. Here we have examined the efficiency in fixing carbon per amount of water lost (water use efficiency - WUE) of boreal spruce trees exposed to various levels of acidifying emissions, from acute exposition to practically pristine air. We find that trees swiftly increase their WUE under acute exposition to acidifying emissions, but adopt passive foliar strategies when only exposed to rising pCO2 and climate change, without enhancing their growth. These findings imply that reconstructing climate using isotopic tree-ring series should avoid periods of climate-isotope divergence caused by pollution.

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