Whole Ecosystem Warming Induces Physiological Stress and Tree Mortality in a Boreal Bog Ecosystem
Abstract
As annual atmospheric CO2 concentration increases, the resulting changes in climate are on track to increase global temperature by > 2 °C by 2100. Temperature increases are expected to be substantially greater in the boreal and arctic biomes, which could have significant impacts on net ecosystem carbon uptake and atmospheric feedbacks. At the southern edge of the boreal forest large, open-topped enclosures are exposing a natural peatland to whole-ecosystem warming × CO2enrichment (https://mnspruce.ornl.gov/). After three years of warming (+0, +2.25, +4.5, +6.75, +9 °C) and CO2 (+0, +500ppm) treatments, the plant community in this bog ecosystem is showing signs of stress. We have witnessed crown damage, branch tip dieback and mortality in the dominant tree and shrub species: the deciduous Larix laricina, evergreen Picea mariana and the semi-evergreen Rhododendron groenlandicum and Chamaedaphne calyculata shrubs. We examined the mechanisms of this damage, hypothesizing that there would be differential hydraulic and carbon stress due to differential plant functional strategies and degree of physiological plasticity.
Damage and mortality were observed in both tree species in the +9 °C, ambient CO2 plot, but not in the +9 °C, elevated CO2 plot. Damaged trees in general displayed lower stored stem NSC and increased water stress. However, contrasting hydraulic strategies emerged with the warming treatments inducing substantially lower water potentials for L. laricina and C. calyculata compared to controls but with little effect on P. mariana or R. groenlandicum. L. laricina displayed excessive hydraulic stress where midday water potentials dropped below -2.5 MPa. In contrast, P. mariana maintained hydraulic safety. The cost of this strategy was evident in the reduction of the fluorescence parameter Fv/Fm indicated reduced quantum efficiency of PSII compared to L. laricina, and a reduction in total NSC in the warmest treatments indicating carbon stress. C. calyculata also had lower Fv/Fm than it's shrub counterpart. Excessive hydraulic and carbon stress in C. calyculata as compared with R. groenlandicum, and alternate hydraulic (L. laricina) or carbon (P. mariana) stress in the trees may lead to a shift in community composition and net C uptake in this ecosystem under future warming.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B53N2595P
- Keywords:
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- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES;
- 1807 Climate impacts;
- HYDROLOGY;
- 1813 Eco-hydrology;
- HYDROLOGY;
- 1851 Plant ecology;
- HYDROLOGY