Scaling ozone effects from seedlings to forest trees

Abstract

Biospheric ozone has become a widely distributed air pollutant, and a growing body of research indicates that ozone impacts forest health and productivity. Ozone effects are mediated by the ozone concentration present in the external environment and the movement of ozone into the leaf via the stoma. The cumulative dose received by the plant is, in the simplest terms, a function of ambient ozone concentration and stomatal conductance to water vapor. This relationship is important in understanding ozone flux into the leaf and subsequent ozone response in plants. Here, current progress in understanding ozone uptake in juvenile and mature trees is examined. Through an analysis of two long‐term case studies, the significant uncertainty in assessing ozone effects on forests is pinpointed to be the scaling of ozone sensitivity from controlled seedling studies to large forest trees. A rigorous statistical and monitoring approach, which includes ozone uptake as a cause variable, may provide the missing information on processes that are known to be important to risk assessment of ozone impacts on forest trees.

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

“…This presents large challenges when scaling impacts beyond the tree level (Samuelson and Kelly, 2001). Earlier, Grünhage and Jäger (1994) suggested that O 3 flux into the plant could be used as an underlying mechanism for establishing standards to protect vegetation.…”

“…Building on their approach, we used indicator and response data recently available from a long-term, ecosystem-scale free-air manipulative experiment in which air quality and meteorological measurements were coupled in time and space against a backdrop of inter-annual variability in climate (Kubiske et al, 2006). To partly address some of the scaling challenges enunciated by Samuelson and Kelly (2001) and to advance forest O 3 risk analysis within the North American ambient air quality context, our initial exposureeresponse regression analysis was completed using models comprising key meteorological indicators (GDD, WS, PAR, RH, precip.) of O 3 concentration and one important O 3 flux regulator (SMC) that would have been expected to yield a first-order approximation of atmospheric O 3 flux and stomatal uptake, as originally proposed by Krupa et al (2003).…”

“…Interestingly, simulations by Tingey et al (2004) were among the first to demonstrate a link between improved emission control strategies and improved tree growth. However, there remain questions as to whether process models can be accurately parameterized to predict mature tree response (Samuelson and Kelly, 2001).…”

European aspen and hybrid aspen under changing environment – Leaf traits, growth and litter decomposition

“…Previously, the results from studies on frost hardening of conifer seedlings using a similar freeze-test technique to study II, have correlated fairly well with survival test results from field experiments on mature trees (Andersson 1992). In the case of exposure to O 3 , the response of mature trees to O 3 stress may differ from that of seedlings (Samuelson and Kelly 2001).…”

Avaliação da sensibilidade de plantas jovens de quiabo (Abelmoschus esculentus (L.) Moench. - Malvaceae) ao ozônio

“…O O 3 entra nas folhas por meio dos estômatos e, no espaço intercelular, reage com a água formando espécies ativas de oxigênio (EAO), que têm um alto potencial oxidativo (Samuelson & Kelly 2001, Fuhrer & Booker 2003, Baier et al 2005. Entre estas espécies, encontram-se o radical superóxido (O 2˙-), o peróxido de hidrogênio (H 2 O 2 ), o radical hidroxila (OH˙) (Scandalios 1993) e o radical peridroxila (O 2 H˙) (Bray et al 2000).…”