Scaling ozone responses of forest trees to the ecosystem level in a changing climate

Abstract

Many uncertainties remain regarding how climate change will alter the structure and function of forest ecosystems. At the Aspen FACE experiment in northern Wisconsin, we are attempting to understand how an aspen/birch/maple forest ecosystem responds to long-term exposure to elevated carbon dioxide (CO 2 ) and ozone (O 3 ), alone and in combination, from establishment onward. We examine how O 3 affects the flow of carbon through the ecosystem from the leaf level through to the roots and into the soil microorganisms in present and future atmospheric CO 2 conditions. We provide evidence of adverse effects of O 3 , with or without co-occurring elevated CO 2 , that cascade through the entire ecosystem impacting complex trophic interactions and food webs on all three species in the study: trembling aspen ( Populus tremuloides Michx . ), paper birch ( Betula papyrifera Marsh), and sugar maple ( Acer saccharum Marsh). Interestingly, the negative effect of O 3 on the growth of sugar maple did not become evident until 3 years into the study. The negative effect of O 3 effect was most noticeable on paper birch trees growing under elevated CO 2 . Our results demonstrate the importance of long-term studies to detect subtle effects of atmospheric change and of the need for studies of interacting stresses whose responses could not be predicted by studies of single factors. In biologically complex forest ecosystems, effects at one scale can be very different from those at another scale. For scaling purposes, then, linking process with canopy level models is essential if O 3 impacts are to be accurately predicted. Finally, we describe how outputs from our longterm multispecies Aspen FACE experiment are being used to develop simple, coupled models to estimate productivity gain/loss from changing O 3 .

New exposure-based metric approach for evaluating O3 risk to North American aspen forests

“…The experiment comprises three randomized blocks containing 12, 30-m diameter FACE rings, assigned to factorial treatments of CO 2 and O 3 . Design and performance characteristics of Aspen FACE have been published and are available elsewhere (Dickson et al, 2000;Karnosky et al, 2003bKarnosky et al, , 2005Kubiske et al, 2006). Growth, O 3 , and meteorology data from a 5-year period (1999e2003) were used in this study.…”

“…This approach also has great potential for determining contribution of O 3 to changes measured in tree growth, and for scaling hourly effects of O 3 to cumulative impact over the growing season (McLaughlin et al, 2003). However, preliminary regression analysis of the efficacy of a modified (growing season) version of the USeCanadian O 3 air quality standard metric form by Karnosky et al (2005) has indicated that the growing season 4th highest daily maximum average O 3 concentration was potentially a good indicator of trembling aspen (Populus tremuloides Michx.) diameter growth.…”

Forest response to elevated CO2is conserved across a broad range of productivity

“…These CO 2 treatments were chosen on the basis of current projections of atmospheric [CO 2 ] anticipated for 2050 (14). Detailed descriptions of the exposure systems and the CO 2 concentration dynamics are provided for DukeFACE (10), ORNL-FACE (15), AspenFACE (16,17), and POP-EUROFACE (11).…”

The physiological, transcriptional and genetic responses of an ozone- sensitive and an ozone tolerant poplar and selected extremes of their F 2 progeny

“…For agricultural and forest ecosystems, tropospheric ozone is considered the most widespread and damaging pollutant (Lindroth, 2010;Wittig et al, 2009). Karnosky et al (2005) reported the long-term effects of ozone pollution on several tree species, and demonstrated a negative impact throughout the whole ecosystem, not only on the trees themselves but also on associated pests and soil microorganisms.…”