Ozone effects on seedling sugar maple (Acer saccharum) and yellow-poplar (Liriodendron tulipifera): gas exchange

Abstract

The effects of one to two seasons of ozone (O 3 ) exposure ranging from subambient to 1.7 times ambient on the gas exchange of sugar maple (Acer saccharum Marsh.) and yellow-poplar (Liriodendron tulipifera L.) were studied in standard 3 m diameter open-top chambers. Cumulative O 3 exposures based on SUM00 index ranged from 16 to 107 ppm⋅h in 1990 and 31 to 197 ppm⋅h in 1991. During the 120-day exposure in 1990, rates of net photosynthesis and stomatal conductance of sugar maple foliage were not affected by O 3 . Based on estimates from light-response curves, net photosynthesis at saturating light, dark respiration, compensation irradiance, and quantum efficiency were not affected in sugar maple leaves exposed to elevated O 3 . Gas exchange rates of leaves of yellow-poplar grown in elevated O 3 were significantly reduced in 1990 and 1991, when compared with foliage of seedlings grown in charcoal-filtered air (CF air). In 1990, seasonal monthly net photosynthesis of yellow-poplar leaves was reduced 11.7% in 1.5 times ambient O 3 air compared with leaves of seedlings grown in CF air. The light response of yellow-poplar foliage generally was not affected by exposure to O 3 during either growing season; with the exception in 1991 of net photosynthesis at saturating light being reduced 13 to 42% in leaves of seedlings exposed to 1.7 times ambient O 3 air compared with leaves of seedlings grown in CF air. Stomatal conductance rates were generally not affected by exposure to O 3 during either exposure season. In 1991, the response of newly mature (node 3 to 5 from apex) and older leaves (node 8 to 12 from apex) of ozone-exposed yellow-poplar were compared and responded similarly to elevated O 3 . Ozone effects on seasonal diurnal photosynthetic response of newly mature and older yellow-poplar foliage were observed in 1991. Reductions (21-42%) in net photosynthetic rates of leaves of yellow-poplar exposed to elevated O 3 were first observed after 42 days of treatment (113 ppm⋅h exposure). Predawn and post-sunset respiration and stomatal conductance were not affected by exposure to elevated O 3 . Despite significant reductions of net photosynthesis of O 3 -exposed yellow-poplar during both seasons, significant negative growth effects were not observed until the final harvest in June 1992. Root/shoot ratios of yellow-poplar seedlings exposed to 1.7 times ambient O 3 were reduced 30% compared with those seedlings exposed to CF air.

Response of Acer saccharum seedlings to elevated O3 and CO2 concentrations

“…These seedlings were harvested at the same dates and biomass accumulation at the end of the second season of exposure did not decrease compared with the control seedlings (data not shown). Similar results were reported for sugar maple seedlings by Rebbeck and Loats (1997) and Scherzer (1991) after exposure to 304 ppm h O3 and 199 ppm h O3 respectively over two growing seasons.…”

“…However, increasing O3 levels may impose more frequent oxidative stress periods, which may counteract this advantage (Rebbeck and Scherzer 2002;Rebbeck et al 2004;Riikonen et al 2005). Sugar maple has been reported as a tolerant species to O3 (Laurence et al 1996;Rebbeck and Loats 1997). However, other studies have shown that this species can be affected by O3 (Kress and Skelly 1982;Tjoelker et al 1995).…”

Long-Term Leaf Production Response to Elevated Atmospheric Carbon Dioxide and Tropospheric Ozone

“…In fact, the +O 3 treatment has had little effect relative to ambient on the L mass of either species in the aspen-maple community (Figure 4). Although maple (Acer saccharum) is relatively insensitive to elevated O 3 (Noble and others 1992;Rebbeck and Loats 1997), we are not able to explain why there has been no reduction in aspen leaf mass in this community. For the aspen-only community, Kubiske and others (2007) found using measurements of tree survival and stem volume during the first 8 years of the experiment that the +O 3 treatment had diminished the relative importance of O 3 -sensitive clones and increased the importance of O 3 -tolerant clones.…”

Foliar physiology of yellow-poplar ( Liriodendron tulipifera L.) exposed to O 3 and elevated CO 2 over five seasons.

“…Measurements were taken over 3 days with one treatment replicate completed per day. Since yellowpoplar photosynthetic rates were determined to be saturated at 800 mmol m 2 s 1 PAR (photosynthetically active radiation) (Loats and Rebbeck 1999;Rebbeck and Loats 1997), leaves were illuminated with an artificial light (GE Cool-Beam PAR Lamp Model 300PAR 56/2WFL) when ambient light dropped below saturating conditions. Leaves were measured at the CO 2 concentration at which they were grown.…”